In recent years, elastic-plastic analysis has been increasingly used in the seismic design of nuclear piping. However, in the case of using elastic-plastic analysis to actual piping design, it is necessary to take into consideration the need to limit residual strain in the welded joints and pipe fittings to be evaluated as much as possible. On the other hand, it is known that the in-production strain of pipe fittings (elbows, tees, reducers) used in nuclear piping is large, exceeding 50% in the case of elbows. Although large residual strain (pre-strain) is likely to be a factor in reducing the low cycle fatigue life of pipe fittings, few studies have investigated the relationship between residual strain in pipe fittings and low cycle fatigue life of pipe fittings. In this paper, the fabrication method of pipe fittings and the mechanical properties and true fracture strain of elbows before and after forming were investigated by monotonic tensile strength testing and low cycle fatigue test. In conclusion, we reported that the mechanical properties of elbows before and after forming are almost the same, and that the true fracture strain does not decrease significantly.

Currently, retreading for extending the life of tires has been discussed to reduce the environmental impact. Therefore, obtaining very high cycle fatigue properties of steel wires used to reinforce radial tires are required. In this study, the very high cycle fatigue properties of solid fine wires of eutectoid steels were obtained for the fundamental understanding of the fatigue mechanism. Solid fine wires of 0.3 mm in diameter produced by the blast furnace and the electric arc furnace were prepared with the same Young's modulus and tensile strength. A method to prepare dumbbell-shaped specimens from solid fine wires was developed by using electropolishing to prevent fatigue failure at an edge of the grips. In the method, the cathode was formed into a circle shape, and an anode, i.e. a specimen, was placed so that it passed through the center of the cathode circle. Then, fatigue tests under axial loading were conducted using an electromagnetic fatigue testing machine. The stress ratio was set to 0.1 and the cyclic frequency was set to 200 Hz. The results showed that the fatigue limits were about 600 MPa for both materials and the influence of steel production process on the fatigue limit was not found.

The objective of this study was to clarify the effects of creep and oxygen-related damage induced by tensile dwell at high temperature on fatigue crack propagation in a polycrystalline Ni-base superalloy, Alloy 718. Crack propagation tests with single tensile dwell applied during fatigue loading were performed at 650 °C. Five tests were conducted, involving various stress intensity levels and different dwell times of the tensile dwell, to observe the creep and oxygen effects on the fatigue crack propagation behavior. When the stress intensity level is high, acceleration of the fatigue crack propagation occurred after the tensile dwell. On the other hand, when the stress intensity level is low, retardation of the fatigue crack propagation occurred following temporary acceleration after the tensile dwell. Parallelly, the same experiments, but interrupted right after the tensile dwell, were conducted to observe the damage zone ahead of crack tips using a scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). By comparing the damage zone observed by the SEM and EDS and the crack propagation rates affected by tensile dwell, it was revealed that the acceleration of the fatigue crack was caused by the oxygen-related damage along grain boundaries induced by the tensile dwell. Also, a transition from the retardation to the acceleration depending on the stress intensity levels was rationalized based on a size comparison between the damage zone and stress relaxation zone ahead of the crack tip caused by the tensile dwell.

Nickel-based superalloys used in gas turbine disks are required to operate under frequent and random fluctuations in power output at elevated temperatures. Under such high-temperature creep-fatigue loading conditions, the crystallinity near grain boundaries deteriorates rapidly, and intergranular cracking occurs, significantly reducing material life. It is also known that the accumulation of fine voids at the interface between the precipitates and the matrix phase accelerates damage. In this study, the acceleration mechanism of intergranular cracking observed in GH4169, which is one of the representative nickel-based alloys for jet engines, was investigated using molecular dynamics. At temperatures above 650°C, the γ" (Ni₃Nb) phase of the dispersion strengthened precipitation structure coarsens, and the more stable δ (Ni₃Nb) phase precipitates mainly in needle-like form near the grain boundary. In the experiments, fine voids accumulated near the interface between the δ-phase precipitated near grain boundaries and the matrix phase, and intergranular cracking was accelerated. In MD simulations modeling the δ-phase precipitated near the grain boundary of the nickel matrix, the formation of a local stress concentration field near the interface between the δ-phase precipitates and the nickel matrix under creep loading induced the generation of dislocations between the precipitates and the unstable grain boundary. A large lattice mismatch at the interface between the δ-phase and the nickel matrix causes the formation of this stress concentration field. The stress concentration field at the interface between the δ-phase adjacent to a grain boundary and the matrix phase increased the instability of the grain boundary, accelerating the degradation of crystallinity near the grain boundary and deteriorating the grain boundary strength. It was also found that the rate and magnitude of grain boundary strength degradation is non-uniform, depending on the crystallographic orientation of the grain boundary where the δ-phase precipitates.

Nuclear power plants promise to play an essential role in achieving carbon neutrality. Under such circumstances, the Generation IV reactor currently under development uses liquid sodium as the coolant, and the operating temperature is 550°C, surpassing that of conventional reactors. Stainless steel SUS316LN, known for its high corrosion resistance to liquid sodium, is a potential material for the pressure vessel and piping in this reactor. However, the accelerated formation and accumulation of voids and dislocations near grain boundaries in high-temperature creep-loading conditions lead to significant deterioration of fracture life due to intergranular cracking. In this study, high-temperature creep tests of stainless steel SUS316LN were conducted to investigate the grain boundary damage process. The loading stress was set at 120 MPa, and creep tests were conducted at 675°C, 700°C, and 725°C for a certain period. The degradation process around grain boundaries was then evaluated using KAM (Kernel Average Misorientation) values obtained from EBSD analysis. The KAM values near the grain boundary increased monotonically with increasing loading time and test temperature, confirming the damage accumulation process near grain boundaries. The activation energy of the increase in KAM values caused by creep loading was evaluated using an Arrhenius plot, and the increase in KAM values was quantitatively explained by a modified Arrhenius equation that considers the stress-induced change in the activation energy of Fe atom diffusion. Therefore, the formation and accumulation processes of voids near grain boundaries under creep loading can be evaluated based on the atomic diffusion accelerated by the local strain field near grain boundaries caused by the superposition of a loading stress and lattice mismatch between grains.

In this paper, a strain-based damage evaluation method based on elastic-plastic analysis was examined for carbon steel piping elbows. In order to simulate the results of the fatigue tests on piping elbows reported in the ‘NUPEC Piping System Ultimate Strength Test Program Report’, we carried out the strain-based damage evaluation by using elastic-plastic analysis. In the elastic-plastic analysis of the elbows, a hybrid model consisting of beam elements and shell elements was used, and the Chaboche model was used to accurately simulate the cyclic hardening behavior of the material. The fatigue curve used for fatigue damage evaluation was the fatigue curve by ‘modified Manson universal slope method’. As a result, it was confirmed that the fatigue test results of piping elbows reported in previous studies could be simulated using elastic-plastic analysis by using elastic-plastic analysis and the ‘correction method for fatigue life based on the ductile consumption law’. In addition, we also report on our investigation into the ‘cumulative strain estimation method’ used in the ‘cumulative plastic damage evaluation for combination load of reversing dynamic load and non-reversing dynamic load’ in the ASME code case (CC N-900).

A non-standard circumferentially cracked round bar (CRB) specimen has been examined as a replacement for the standard fracture toughness compact tension (CT) specimen since 1981. The thickness of CT specimens corresponds to the circumferential direction without a free surface in CRB specimens. This allows the strain constraint around a crack tip in a CT specimen to be replicated by a small CRB specimen. Fracture toughness testing using small specimens is especially important for materials intended for fusion reactors. Several studies have been conducted on fracture toughness tests using CRB specimens for materials with low fracture toughness, and it has been shown that CRB specimens can substitute for CT specimens. However, data on materials with medium and high fracture toughness are scarce, preventing detailed validation. There are several issues to address, including the required specimen size, achieving strain constraint equivalent to plane strain, measuring crack length, and obtaining the J-R curve. In the author’s previous study, it was found that, if an adequately sized CRB specimen is used, materials with medium fracture toughness (100 - 200 kJ/m²) can also be evaluated. However, there are specific considerations in the experimental procedure, and applying the procedure to high fracture toughness materials is expected to be more challenging. In particular, necking of the round bar surface in materials with high toughness alters the stress concentration field around the circumferential crack tip. When a CRB specimen with an outer diameter of 10 mm is used, evaluating materials with fracture toughness greater than 200 kJ/m² becomes difficult. This report discusses the possibilities and limitations of fracture toughness testing for materials with medium and high toughness using CRB specimens.

Lithium-ion batteries are used in a variety of products. However, during long-term use, incidents such as overheating and ignition often occur due to fatigue failure of the electrode materials. In this study, mechanical fatigue tests were conducted on these materials to investigate their fatigue mechanisms and to establish a method for predicting fatigue life. Conducting fatigue tests on the electrode materials alone is challenging because they are brittle thin films. Therefore, this study validated a plane bending fatigue tester equipped with strain sensors to measure the fatigue life of the electrode materials coated on metal foil. The electrode material consists of an active material and a binder, with the binder elongating to failure at a microscopic level. To evaluate the strain amplitude of the specimens, it is essential to consider not only the strain on the substrate from the plane bending fatigue tests but also the permanent strain obtained from the tensile fatigue tests. The specimens used for the tensile fatigue tests were thin films with a binder concentration of 30wt%. The test conditions were set with maximum strains ranging from 0.003 to 0.007 and a minimum load of 0.1 N, based on the results of the plane bending fatigue tests. The number of cycles was limited to 1,000 to investigate the relationship between permanent strain and number of cycles. The results indicated that the data trends closely followed the prediction lines derived from the relationship between total dissipated strain energy to fracture, the number of fracture cycles, and both the dissipated strain energy and strain amplitude, focusing on the dissipated energy observed in the tensile fatigue tests.

The Evaluation of fatigue limit by measuring temperature change using infrared thermography has attracted significant interest owing to its potential for rapid assessment. However, physical background and validity of this technique are not yet fully understood. The utilization of infrared thermography is not limited to the study of the fatigue limit; research on the relationship between crack propagation and temperature dissipation has also been carried out as part of the study of fatigue damage in metallic materials. In this study, temperature change during cyclic loading is measured by infrared camera using four types of single crystal notched specimens with different crystallographic orientations. Local slip deformation is quantified using crystal plasticity finite element analyses. First, the effect of crystallographic orientation on fatigue crack initiation and the temperature field was investigated. It is found from the experimental and numerical results that the distribution and magnitude of second harmonic temperature and the local slip deformation (a plastic shear strain on the most active slip system) are affected by the crystallographic orientation. However, the correlation between plastic shear strain and second harmonic amplitude when crack initiates, as well as threshold values of these parameters for crack initiation, is independent of the crystallographic orientation. Second, the effect of crystallographic orientation on fatigue crack propagation and temperature field was investigated. It is found that the magnitude of second harmonic amplitude differ corresponding to the fatigue crack propagation rate and the fatigue crack growth threshold in each orientation. However, the correlation between the plastic shear strain and the second harmonic amplitude when crack propagates, as well as the threshold values of these parameters for crack growth threshold, is independent of the crystallographic orientation.

The effect of crystal anisotropy on the threshold of the stress intensity factor range ΔKth was investigated in a single crystal Ni-based superalloy. First, fatigue crack propagation tests were conducted in air at room temperature using four types of test specimen with different crystal orientations in the loading direction and crack propagation direction. In the four types of test specimen, three types had fatigue cracks that propagated along the slip plane, whereas the other type showed an opening mode cracking without following the slip plane. ΔKth calculated from the projected crack length differed for the four types of test specimen affected by crystal anisotropy. In order to investigate the effect of crystal anisotropy, a 3D finite element models were created to reproduce the crystal orientation and crack propagation path, and the slip deformation near the crack tip was calculated according to the crystal plasticity theory. It was found that the damage parameter based on the plastic shear strain on the slip surface can evaluate ΔK_th for the three types of test specimens in which the crack propagated along the slip plane.

Since thin plate and foil have been widely used as mechanical component, improvements of mechanical property and long reliability are demanded. However, general surface treatments (surface peening and coating) may make a plate/foil deflect due to unbalance in internal residual stress. The thickness of surface hardening layer is critical for such a thin plate and foil. This study developed a surface treatment based on Laser Induced Particle Impact Test (LIPIT) to improve fatigue damage resistance. Using pulsed laser ablation, LIPIT enables us to conduct hypervelocity microparticle projectile which impacts on material surface. With LIPIT, microparticles (15 μm in diameter or smaller) impact on the material surface with the velocity of about 900 m/s. As a result, large plastic strain is introduced, and nano crystalline structure are developed in a target surface. This method can utilize small particles with micrometer and sub-micrometer. This appeared to locally introduce hardening layer at the surface, since the particle size is small and flying velocity is fast. On the specimen surface, particle impact induces a crater with large strain and large strain rate. This hardening layer is expected to improve mechanical properties and fatigue damage resistance of material. At first, LIPIT was conducted repeatedly as surface treatment for wide area of thin metallic plate. It is confirmed that the target plate does not deflect, even if surface hardening layer develops. To evaluate the mechanical properties, uniaxial tensile test was carried out to obtain stress-strain curves. It is found that LIPIT treatment improved the yield strength and flow stress. To investigate fatigue strength, we conducted cyclic fatigue testing. It is found that LIPIT treatment increased the fatigue strength. The developed surface work hardening layer is investigated from observations of SEM and SIM as well as computational method with FEM to discuss the mechanism.

Ultra-high tensile steels are increasingly utilized to produce thinner automotive bodies to reduce vehicle weight. However, its application in suspension systems has been delayed due to concerns regarding reduced fatigue strength at stress concentration sites in complex shapes. Additionally, recent reports have highlighted cases of ultra-high tensile steel cracking under compressive loads during press forming. It is critical to address these cracking issues to ensure the reliable use of ultra-high tensile steel in suspension components. Prior studies have attributed such cracking to surface depressions due to local buckling, though the influence of depression geometry on crack formation remains unclear. This study conducted compression tests on ultra-high tensile steel specimens with artificially induced defects of varying shapes and sizes, followed by microstructural evaluations of the areas surrounding the cracks. The relationship between surface defect geometry and crack initiation mechanisms was investigated by analyzing the microstructure before and after testing. The results demonstrated that the crack length at the bottom of the artificial defect in the ultra-high tensile steel was shorter than in the high tensile steel. Furthermore, the Electron Backscatter Diffraction (EBSD) analysis revealed that the grain refinement at the bottom of the artificial defect was refined in an ultra-high-strength steel sheet. These results suggest that grain refinement increases the crack propagation resistance.

The operating temperature of aircraft jet engines has been increased to improve thermal efficiency for addressing global warming by reducing greenhouse gas emissions. The Ni-based superalloy GH4169 (IN718) is used in aircraft components because of its high-temperature strength, fracture toughness, and oxidation resistance. In GH4169, which has a higher Nb content (about five mass%) than other nickel-base alloys, the γ"(Ni₃Nb) phase coarsens at temperatures above 650°C and precipitates as the more stable δ-phase in needle-like form near grain boundaries. Under high-temperature creep loading, fine voids accumulate near the interface between the δ-phase precipitated around grain boundaries and the matrix phase and accelerate intergranular cracking, indicating that the effect of δ-phase precipitates on creep damage evolution should be considered when this alloy is used in a high-temperature condition. To investigate the mechanism by which the δ-phase reduces grain boundary strength, intermittent creep tests were conducted at around 800°C on GH4169. Scanning electron microscopy (SEM) observations were performed on the interrupted creep specimens to quantitatively evaluate the δ-phase content and the temperature and stress dependence of the precipitation rate. The tensile strength decreased in specimens where the δ-phase precipitated compared to specimens without the δ-phase. After creep loading, an increase in the δ-phase content was observed, particularly at 825°C, where precipitation within the grains accelerates, leading to a significant increase in the δ-phase content. Additionally, the content of the δ-phase increased in the region of higher load at the same temperature, indicating that the synergistic effect of temperature and stress accelerates the precipitation of the δ-phase.

The application of AI to the maintenance of various types of machinery is expanding. In image-based diagnosis, convolutional neural networks (CNNs) are sometimes used, in which a digital filter is convolved with an input image to filter it, creating multiple images with different characteristics for analysis by the CNN. In this study, we investigate the possibility of improving the accuracy of NNs by using analog filters in addition to digital filters. Specifically, three types of analog filters were created by placing a cellophane film between polarizing plates at different angles. The filters were placed in front of a camera, and multiple images obtained through the filters were used as input images for the CNN. In this study, stickers imitating rust were placed on walls and pillars, and a CNN was created to determine the presence or absence of rust. We compared the accuracy of the NNs when the images were taken without filters and analyzed using only digital filters, and when the images taken through analog filters were also input and analyzed in conjunction with digital filters. As a result, we confirmed that accuracy was improved when an analog filter was used and the pooling layer was not placed immediately after the analog filter input.

Infrared thermography has emerged as a promising method for inspecting tiled building exteriors, leveraging temperature variations caused by solar radiation to detect detached tiles. Traditional methods require positioning an infrared camera at high altitudes to ensure that the angle between the camera's optical axis and the vertical axis of the tile surface does not exceed 45 degrees. While drones have been employed to address this challenge, stringent regulations in urban areas often restrict their use.

This study proposes an innovative approach to exterior wall inspections using a balloon-mounted infrared camera. This method offers several advantages over drone-based systems, including the elimination of requirements for aircraft certification, pilot licenses, and other permits. Additionally, balloons operate quietly and safely, reducing operational risks and costs. The balloon-mounted system provides stable and unrestricted operation, making it particularly suitable for densely populated urban environments where drone usage is heavily regulated.

Our results demonstrate that the balloon-mounted infrared camera system is capable of maintaining the necessary angle and resolution for effective thermographic inspections, achieving a pixel density significantly exceeding regulatory standards. This approach enhances the efficiency and reliability of detecting potential detachment areas on building exteriors, providing a viable alternative to traditional methods. The findings highlight the potential of this balloon-based technique to revolutionize the field of high-rise building inspections.

Predicting the long-term deformation behavior of CFRP laminates is important from the viewpoint of structural durability. In this paper, the behaviors of deformation and crack opening displacement (COD) of cracked CFRP laminates under creep loading or stress relaxation were investigated numerically and theoretically. Finite element analysis (FEA) was used for the numerical analysis, and the viscoelastic continuum damage mechanics (CDM) model predicting effective creep compliances was used for the theory. The maximum COD of a matrix crack in a CFRP cross-ply laminate increases with time both under creep (constant stress) and stress relaxation (constant displacement) conditions. The average longitudinal strain at the surface of the 0-degree layer increases under creep but remains constant under stress relaxation. In contrast, the average strain at the midplane of the 90-degree layer decreases under stress relaxation and increases under creep. However, the incremental creep strain in the 90-degree layer is smaller than decremental relaxation strain in the 90-degree layer and the incremental creep strain in the 0-degree layer. FEA revealed that this behavior is due to the fact that the time variation to longitudinal strain of each layer during creep or stress relaxation is different near the matrix crack and far from the matrix crack. Numerical analysis based on the CDM model supported the reasonability of this behavior.

The Load-Depth (L-D) curves obtained from indentation tests have scatters due to the measurement and material microstructure. However, previous research has primarily focused on estimating the elastic-plastic properties based on representative curves. It is essential to consider statistical estimation methods that take the scatters into account and the optimal material constitutive equations used for the estimation. At a first step, this study proposes using Bayesian inference with replica exchange Monte Carlo to statistically estimate material parameters from the averaged L-D curve obtained from indentation tests with a spherical indenter and to investigate the estimation accuracy. Type 316L stainless steel was used as the test specimen. The material was assumed to follow the Swift law, and four parameters in the equation were estimated. As a result, the most appropriate set of material parameters, i.e., the set that minimizes the mean square error between the experimental results and the finite element analysis results, was determined. However, a posterior distribution showed that there were parameters with insufficient estimation accuracy, and it was found that it was necessary to clarify the factors behind them to estimate the material properties from indentation results with the scatters.

Tensile tests at 650℃ and crystal plasticity finite element analysis on CMSX-4 bi-crystal were performed to investigate the effect of grain boundary misorientation angle (GBMA) on the tensile behavior and failure mode. The tensile tests showed that transgranular fracture occurred at the GBMAs of 6.3° and 10.3°, while intergranular fracture occurred at the GBMA of 20.5°. In addition, the stiffness increased and the 0.2% proof stress decreased as the GBMA increased. The result of crystal plasticity finite element analysis indicated that there is a stress singularity along the radial direction due to the differences in deformability of each grain. Furthermore, the element sizes in the radial and hoop directions were determined by examining different element sizes. It is considered that mode mixing loading led to intergranular fracture because the shear stress on the grain boundary increases with increasing GBMA.

As part of the fitness-for-service evaluation for Light Water Reactor structural components, evaluating crack growth due to the superposition of SCC (Stress Corrosion Cracking) and fatigue is sometimes required. However, it is difficult to predict the sequence in which the sustained loads that induce SCC crack growth and the cyclic loads that cause fatigue crack growth will be applied. This study investigates the influences of various loading sequences on crack growth using the SCC and fatigue crack growth evaluation equations specified in the JSME Codes for Nuclear Power Generation Facilities. Furthermore, it discusses how the loading sequence should be considered to ensure a conservative crack growth evaluation.

As important thermal-hydraulic factors influencing the structural integrity of plant components, recent studies on the fluid temperature fluctuation at a T-junction, the thermal stratification in a closed-end branch pipe, the flow-accelerated corrosion, and the liquid droplet impingement erosion are overviewed. The effect of the rapture hole shape on the behavior of the discharged liquid jet is also discussed.

High Temperature Gas-cooled Reactor (HTGR) components are characterized by dominant creep damage depending on primary stress and thermal stress. In the JSME M&M2023 conference, a simplified creep-fatigue damage evaluation method based on elastic analysis has been proposed, in which both an elastic follow-up coefficient and a post-relaxation stress are considered. In this paper, the influence of temperature, the elastic follow-up coefficient and the post-relaxation stress on the predicted creep damage is discussed. The simplified method was applied to heat-transfer helical tube with distribution of temperature, primary stress and thermal stress. Predicted creep damages along the tube were conservative within a factor of 3 compared with the results of detailed inelastic analysis. Difference of creep damage during relaxation were analyzed between Hastelloy XR and 316FR assuming HTGR and Fast Reactor (FR) respectively; rapid relaxation and high creep damage were found to be to the special characteristics of HTGR components. Influence of the elastic follow-up coefficient on creep damage was also studied.

Equipment in energy facilities often faces damages such as corrosion, which accounts for over 25% of US pipeline failures between 2002 to 2018 by the Pipeline Hazardous Material Safety Administration. Japan is also experiencing a shortage of skilled engineers due to an aging population, with a decline of 644,000 population in 2020-2021. In 2023, 89% of Japanese companies reported challenges in staffing issues, making it harder to manage damage modes in these facilities. Not limited to a specific industry, AI models trained on data from a variety of industries are being developed to predict damage mechanism, helping ensure safe operations despite workforce shortages for extensive application. This research compares AI models for classifying eleven damage mechanisms across literal field datasets with nineteen parameter component combinations, such as plant type, system processes, material specifications, and chemical environmental conditions. The study evaluates ten machine learning models, including Logistic Regression, Support Vector Machine, Naïve Bayes, K-Nearest Neighbor, Random Forest, Extreme Gradient Boosting, Light Gradient Boosting Machine, Gradient Boosting, Category Boosting, and Adaptive Boosting. These models are tested on damage mechanism results combinations of past field failures 691 datasets, with a One-vs-Rest approach for multiclass classification. Performance is measured using accuracy, precision, recall, F1-Score, and ROC-AUC. The study also uses Shapley additive explanations and feature importance to rank parameters influencing damage classification. Logistic Regression, SVM, KNN, and Naïve Bayes scored below 80% in ROC-AUC, while tree-based methods, such as XGBoost, CatBoost, and Gradient Boosting, scored above 85%. CatBoost demonstrated the best performance with an ROC-AUC score of 89.85%. Stress anomaly conditions had the highest SHAP value of 1.281, indicating that stress anomaly is the parameter that most influences damage mechanism classification. This research shows that machine learning is effective in accurately classifying damage mechanisms based on the condition of various components from past cases.

In recent years, the demand for higher temperature and higher efficiency in high-temperature equipment such as jet engines and gas turbines has led to the research and development of heat-resistant steels and Ni-based superalloys, which have greatly improved heat resistance. Ti-Al alloys have been attracting attention as advanced heat-resistant materials for further improvement of efficiency and weight reduction. The microstructure of this alloy can be controlled by heat treatment, and the strength properties change accordingly. In this study, we elucidated the creep properties of a forged Ti-Al alloy Ti-43Al-5V-4Nb with a triplex microstructure. Therefore, nondestructive evaluation of such Ti-Al alloys was conducted to evaluate the damage and to predict the remaining life of these alloys when used at high temperatures. We investigated the evolutions of two nonlinear acoustic characterizations: resonant frequency shift and high harmonic components, with electromagnetic acoustic resonance (EMAR) throughout the creep life in the advanced heat-resistant Ti-Al alloy, Ti-43Al-5V-4Nb. EMAR is a contactless resonant method with an electromagnetic acoustic transducer (EMAT). This method enables not only to measure exact ultrasonic attenuation of sample but also to eliminate nonlinear acoustic effect between the sample and transducer. We used the axial SH wave EMAT, which transmits and receives axially polarized shear wave along a cylindrical surface of a circular rod for non-ferromagnetic materials. Two nonlinear ultrasonic properties and attenuation coefficients gradually decreases as creep advance. These changes can capture microstructural changes during creep.

The interfacial fracture characteristic of SOFC electrode/electrolyte interfaces is one of the key factors for improving the reliability and durability of the cell. The fracture toughness at a porous/dense interface was evaluated using all-ceramic four-point bending specimens consisting of a thin porous NiO–8YSZ electrode layer sandwiched between two dense 3YSZ electrolyte beams. The Weibull plot of the interfacial fracture toughness data shows that the Weibull modulus was smaller than that of bending strength in a single material of 3YSZ or NiO–8YSZ, and the variation of the interfacial fracture toughness was large. In addition, when the specimens were reduced and the electrode was changed to Ni–8YSZ, the interfacial fracture toughness tended to decrease.

Electrode sheet of lithium-ion battery (LiB) has a layered structure consisting of an active material layer (composite of binder and active material) and a current-collecting layer (metallic foil). One of the problems against mechanical loading is cracking in binder due to a manufacturing process and charge-discharge cycle. This leads to shorten battery life and reduce electrical capacity. In addition, exfoliation from a current-collecting layer is also critical issue during charge-discharge cycle. This study first investigated that microcrack occurs around particle of active material due to the stress concentration. For the microstructural design of the active material layer, finite element method (FEM) was carried out. In this study, the damage criterion was employed to FEM in order to simulate crack propagation in binder with particles of active material. Due to non-linear plastic deformation of binder, this criterion is established based on accumulative strain increment. We simulated microcrack propagation in active material layer subjected to uni-axial tension. The validity of the crack simulation was conducted by comparison of actual experiment. This kind of mechanical integrity evaluation may be useful for electrode design for material and integrity of aged electrode after charge-discharge cycle.

The basic mechanical properties of different binder materials in the anode material of lithium-ion batteries were investigated based on the microstructure of the electrode material. Anode materials consisting of carbon powder, and polyvinylidene fluoride (PVDF) or styrene-butadiene rubber (SBR) binders were subjected to tensile tests and a single cycle fatigue test, loading and unloading tests. Stress-strain curve, tensile strength, permanent strain, and the dissipated strain energy were measured in these tests and estimated using a simple model proposed in a previous study. The proposed model approximates the arrangement of carbon particles as body-centered cubic (bcc) or face-centered cubic (fcc). External loads on the model were supported by the binders placed between the carbon particles. Test results showed that the mechanical properties of the SBR binder, as well as the PVDF binder, affect the macroscopic mechanical properties of the anode material. Tensile strengths were approximately between the upper and lower limits of the proposed model. Stress-strain diagrams, permanent strain, and the dissipated strain energy were in good agreement using the bcc<110> model, one of the proposed models.

Hydrogen-fueled gas turbines are being expected to contribute achieving carbon neutrality. The components used in the gas turbine are exposed to a hydrogen environment of several hundred degrees Celsius. Therefore, it is essential to evaluate the effect of hydrogen on damage processes. Creep tests were conducted using 304 stainless steel in a hydrogen environment at 500℃ and the surface damage morphologies were evaluated. In the hydrogen environment, cracks and slip lines were observed on the surface, and the surface slip density was higher in the hydrogen environment compared to that in the argon environment. It was considered that the higher surface slip density is induced due to the activation of dislocation motion by hydrogen.

This study focuses on hydrogen embrittlement of austenitic stainless steels. Among the many studies on hydrogen embrittlement of austenitic stainless steels, two phenomena, martensitic transformation and microcrack formation, are important to discuss the susceptibility to hydrogen embrittlement. This study focuses on eddy current testing, a non-destructive test used to evaluate the electromagnetic properties of materials, as a method to evaluate these phenomena. The objective of this study is to evaluate two phenomena, martensitic transformation and microcrack formation, using eddy current testing. Tensile tests were performed on AISI 304 specimens of metastable austenitic stainless steel, followed by hydrogen charging. Two types of hydrogen charging methods, electrolytic cathodic charging and high-pressure hydrogen gas exposure were used to prepare specimens with different hydrogen penetration depths. Several specimens were prepared with and without hydrogen charging and with different residual strain values. The impedance of each specimen was measured by eddy current testing. The relative permeability and equivalent conductivity of the specimens were estimated by comparing the measured results with an analytical solution for the coil impedance. The results showed that the relative permeability of the specimens increases, and the equivalent conductivity decreases with increasing strain for hydrogen-charged specimens. The increase in permeability is correlated with martensitic transformation. It is suggested that the phase transformation is caused by the application of hydrogen and strain. The decrease in conductivity was more significant for specimens with microcracks on the specimen surface. A correlation between the decrease in conductivity and microcracking was suggested.

The puncture resistance of Polyethylene (PE)-based mono-material films play a significant role in flexible packaging product’s performance. Due to its inherent thinness, obtaining the fracture properties directly through laboratory experiments is difficult. Therefore, in this paper, numerical analysis was employed to reproduce the force and displacement results from static puncture test. First, the analysis was conducted for single layer stretched PE films. Results were found in an excellent agreement when the Hosford-based orthotropic plasticity model was applied, in contrast to the conventional isotropic hardening model. This improved material model was then applied into multilayer film, which consists of LLDPE, HDPE, and stretched PE. Experimental results show good agreement when the previously reproduced single-layer stretched-PE simulation results were extracted and incorporated as biaxial stress and strain properties into the multilayer model. For failure prediction, layer-by-layer failure analysis was conducted. Through employing parametric optimization against maximum plastic strain failure criteria for stretched PE and HDPE, the experimental result can be reproduced up until the maximum load. This work brings out a novel approach of applying the orthotropic plasticity model and layer-by-layer failure modeling to obtain the biaxial failure strain of multilayer PE films, which is valuable for the development process of mono-material packaging.

Carbon fiber reinforced plastics (CFRPs) are widely used as structural materials for commercial aircrafts because of their properties, such as strength and stiffness. The elastic constants of carbon fiber significantly influence the mechanical properties of CFRPs. Therefore, correct estimation of elastic constants of carbon fibers is an important issue. However, there have been some difficulties in estimating them due to their small size and mechanical anisotropy. The method known as resonant ultrasound spectroscopy (RUS) enables the determination of elastic constants by performing iterative calculations to match the experimentally obtained resonance frequencies with the numerically calculated ones. In this work, we determined the elastic constants of carbon fiber in unidirectional CFRP specimen by a vibration-mode-pattern-matching-assisted RUS. To ensure the consistency of vibration modes, vibration patterns were matched by assessing the cosine similarity between contour plots, which depict the vibration patterns obtained from the experiment and numerical analysis. To incorporate the viscoelastic properties of the polymer matrix into the calculation of elastic constants, dynamic mechanical analysis (DMA) tests are conducted to obtain the polymer’s viscoelastic properties. To identify the composite’s transversely isotropic viscoelastic material behavior, homogenization using a representative volume element (RVE) is performed. Six load cases are considered to obtain the master curve of five independent components of homogenized complex stiffness in the frequency domain. These homogenized properties are depicted by a generalized Maxwell model (GMM) for parametrizing user-defined material models implemented in numerical analysis. Overall, the elastic constants of carbon fibers are determined by using RUS, considering viscoelastic properties of the polymer matrix of CFRPs. The proposed method can assist material designers in accuracy and efficiently determining the elastic constants of CFRPs and its carbon fibers with accurate analysis considering polymer’s viscoelastic properties.

The use of Carbon Fiber Reinforced Thermoplastic (CFRTP) is being explored in the field of transport applications, such as in aircraft, where there is a need for both short molding cycle times and recyclability. An essential part of implementing CFRTP as a structural component is the design for fatigue strength, which ensures long-term reliability. However, predicting the fatigue life of CFRTP is challenging due to the significant nonlinear deformation exhibited by thermoplastic resin used as the matrix. This study investigates the effectiveness of a fatigue life prediction method based on Interfacial Plastic Strain Energy (IPSE) for unidirectional CFRTP specimens with polyamide 6 (PA6) as the matrix. Given the high hydrostatic pressure experienced by the PA6 within the CFRTP, we applied the Drucker-Prager yield criterion. A two-scale analysis method was proposed, which accurately predicts macroscopic stress in CFRTP specimens and calculates IPSE from the local mechanical field at the microscale. By applying the internal friction angle obtained from uniaxial tensile and compression tests on PA6, we computed the plastic strain energy within the PA6 of the CFRTP. We then transformed stress-life diagrams from fatigue tests into plastic strain energy-life diagrams, and conclude that the fatigue life of CFRTP can be accurately predicted by applying the IPSE evaluation method, resulting fatigue diagrams both for pure PA6 and that in the CFRTP specimens matched well.

Carbon fiber (CF) reinforced polymers (CFRPs) have excellent specific strength and stiffness. In particular, CFRPs with thermoplastic resin as a matrix (CFRTPs) are widely used in fields such as aircrafts and automobiles. Recently, CFRTPs have attracted attention for its high toughness, low energy consumption during manufacturing, low material costs and recyclability. Polypropylene (PP) resin has been noted as the matrix of CFRTP due to its excellent processability and wide products range. Angle-ply CF/PP resin laminates with CF orientation angles ranging from ±15° to ±60° were investigated, and it was revealed that angle-ply CF/PP resin laminates with CF angles of ±30°, ±45°, and ±60° exhibit pseudo-ductile behavior with a significant increase in failure strain. However, the mechanism of pseudo-ductile behavior of angle-ply CF/PP resin laminates has not yet been clarified. In this study, tensile tests were conducted to investigate the effect of laminate configuration on the tensile properties of angle-ply CF/PP resin laminates with fiber orientation angles of ±45°. Finite element analysis (FEA) was also performed using a representative volume element (RVE) model of ±45° angle-ply CF/PP resin laminates to reproduce the experimental stress-strain curves, the internal stress distributions and damage growth behavior were examined, to clarify the mechanisms of pseudo-ductile behavior. The experimental results revealed that the tensile strength and failure strain varied greatly depending on the laminate configuration. The angle-ply CF/PP resin laminates with repeated +45° and -45° fiber orientation showed higher tensile strength and failure strain. The damage in the RVE model was observed at the interface between the CF bundles and the PP resin, them gradually propagated along the CF bundles, leading to the formation transverse cracks.

Recently, carbon fiber reinforced thermoplastics (CFRTP) have been attracting attention from the viewpoint of reducing the weight of transportation vehicles. To apply CFRTP as structural members, it is necessary to join a CFRTP member with another CFRTP member. Mechanical joining using bolts and nuts is widely used to join CFRTP members but there are problems such as increased weight, limited design freedom, and stress concentration at bolt holes. Adhesive bonding is another method, but it requires time to bond, and it is difficult to bond CFRTP with general adhesives because of the difficulty in obtaining strong chemical bond. In this study, we focus on resistance welding. Resistance welding is a joining method in which thermoplastic film s and a mesh-like resistance heating element are placed between the adherends and a voltage is applied to the resistance heating element to generate heat, resulting in melting and solidification of the films and matrix. In this study, CFRTP joints were fabricated by using a carbon nanotube sheet as a Joule heating element, and single-lap shear strengths and out-of-plane tensile strengths were evaluated. As a result, it was confirmed that the normalized shear strength averaged about 2.5 for the glass transition temperature +148°C or above, implying the shear strength was sufficient. The normalized out-of-plane tensile strengths averaged about 0.3. Since the out-of-plane tensile strength is generally a few tenths of the shear strength, the out-of-plane tensile strength seems to be reasonable.

CFRP laminates were subjected to impact loading with different impact energy by means of a falling weight impact testing machine. The impact loading caused internal damage within CFRP laminates such as delamination, transverse cracks and debonding. In addition to the internal damage, impact loading caused heat generation within CFRP laminates. Therefore, the heat generation was measured in realtime by an infrared thermography. On the other hand, the internal damage within CFRP laminates was evaluated quantitatively by means of cross-sectional observation by an optical microscopy. In the evaluation, length and number of cracks were measured on a micrograph of the cross-section of specimens after impact loading. Then, distribution of internal damage with regard to distance from impact point was clarified. After all, the relationship between heat generation and internal damage was discussed by comparing change in temperature with amount of internal damage. The mechanism of heat generation was considered finally.

Carbon Fiber Reinforced Plastic (CFRP) consists of carbon fibers and resin, and the presence of various damage modes—such as resin cracking, delamination, and fiber breakage—makes it challenging to predict the remaining service life of the structure. Under cyclic loading, damage initiates after a certain number of cycles and gradually accumulates. The timing of damage occurrence varies depending on the type of damage. In many structures, the final damage mode to occur is fiber breakage, which typically occurs near the end of the structure's lifespan. The objective of this study is to investigate the feasibility of a system that incorporates a material into the CFRP, which fractures slightly earlier than the fiber breakage. The fracture of this material is detected through Acoustic Emission (AE) testing, enabling recognition that the structure is nearing the end of its service life. The study also aims to determine whether the failure of the marker material could be detected through AE testing and to assess the impact of the marker on the mechanical properties of the structure. In this paper, tensile tests were performed on specimens containing the marker material to assess its performance and observe the AE generated during the marker's fracture. Fatigue tests were also conducted on these specimens. The results confirmed that incorporating the marker material does not significantly affect the strength of the base material. Furthermore, AE signals generated by the fracture of the marker material were successfully detected.

Carbon nanotubes (CNTs) have excellent mechanical properties and are expected to be used in various applications, especially in composite materials. Since CNTs are nanoscale dimensions and difficult to handle individually, composite materials using CNT yarns, in which multiple CNTs are twisted together, as a reinforcing element of plastics, are currently studied. However, the tensile strength and Young's modulus of CNT yarn composites are much lower and far from practical application. To enhance the mechanical properties of CNT yarn composites, it is crucial to understand the tensile fracture mechanism of CNT yarn in a matrix environment. Since CNT yarn/epoxy matrix composites and carbon fiber reinforced plastics (CFRPs) have similar structures, we hypothesized that the failure mechanism of unidirectional CNT yarn/epoxy matrix composites could be understood from the aspect of unidirectional CFRPs. In this research, double-fiber specimens with two CNT yarns embedded in parallel in an epoxy matrix were prepared and the interaction of the distance between the yarns was evaluated. We conducted synchrotron radiation X-ray computed tomography and double fiber fragmentation tests to examine the fracture behavior of an adjacent CNT yarn in the epoxy matrix. This study showed that the CNT yarn in the epoxy matrix fractured in a brittle manner and that adjacent fractures occurred due to stress concentration, similar to the fracture behavior observed in unidirectional CFRPs. Additionally, we observed that matrix cracks occurred in a helical shape, and internal cracks within the CNT yarn propagated longitudinally, differing from the fracture morphology of carbon fibers in a matrix environment. Clarification of the fracture mechanism of the unidirectional CNT yarn/epoxy matrix composites will lead to improvement of the tensile strength and development of strength prediction models of CNT yarn/epoxy matrix composites, which will lead to the practical application of CNT yarn composites.

Carbon nanotubes (CNTs) are thought to have higher tensile strengths than those of carbon fibers. However, it is difficult to measure the strength of CNTs because of their nano-scale dimensions. In addition, there is a large discrepancy between the ideal strength of CNT and the experimental results for CNTs alone. This is thought to be due to defects in the CNTs and residual catalyst in the CNTs, which degrade the mechanical properties of the CNTs. In this study, tensile strength was estimated using a method called ultrasonic cavitation induced fragmentation, which is different from conventional strength evaluation methods. Ultrasonic cavitation induced fragmentation is a simple way to cut carbon nanotubes in suspension. The lengths of fragmented carbon nanotubes are made shorter by iterating ultrasonication but approaches a critical aspect ratio. It is possible to evaluate the tensile strength of CNTs from the critical aspect ratio. In this study, the effects of annealing, which is known to improve the tensile strength crystallinity of CNTs by reducing defects and catalysts, and diameter, the reduction of which reduces defects and increases the ratio of load-bearing layers, on the tensile strength of CNTs are evaluated by using the ultrasonic cavitation induced fragmentation. The results showed that thinner CNTs were stronger, and annealing decreased the tensile strength of MWNTs. The latter implies that the increase in crystallinity does not always increase the tensile strength of MWNTs.

Corrugated cardboard, known for its high cushioning properties and strength, is widely used in transportation. In the present study, we focused on the cross-sectional structure of cardboard with voids. Aiming to produce a lightweight, high-strength corrugated cup, we formed the drawn cup with a void structure and evaluated its strength. In the experiment, test material used was the mild carbon steel sheet SPCC, and pure titanium sheet TP270. The disk blank had a thickness of 0.3 mm and a diameter of 80 to 90 mm. The special die used was the roller ball die (RBD) with steel balls tightly packed into the shoulder of the die. It was used in combination with a normal die. The diameter of the steel balls ranged from 7.0 to 7.5 mm. The punch had a corner radius of 4 mm and a diameter of 39 mm. Both the punch and die underwent conventional heat treatment. The formability of the clad cup was investigated, including the adhesion between the constituent cups, residual stress of the cups, compressive strength, and sheet thickness distribution. The drawn cup did not break, and a corrugated layer was formed uniformly on the cross section of the cup. Furthermore, the maximum sheet thickness reduction rate was approximately 10 % or less. It was also found that it was possible to form the drawn cup with a void structure that exhibits high adhesion and high compressive strength.

The stress state at the interface in bonded materials can be expressed by material composite parameters. For isotropic dissimilar materials, it is known as the Dundurs parameters. The composite parameters have been derived for orthotropic dissimilar materials, but the relation between the composite parameters and the stress intensity factor of interface crack has not been clarified. In this study, the interface crack problems in orthotropic bonded materials are analyzed by the proportional method. The stress intensity factors of interface crack in orthotropic materials are compared with those of the interface crack in isotropic dissimilar materials, based on the material composite parameters. From the numerical results, the stress intensity factors and the singular stress field of interface crack in orthotropic dissimilar material can be roughly evaluated from that of interface cracks in isotropic dissimilar material when the material combination parameters are the same.

In the maintenance of machines and structures, nondestructive testing (NDT) plays a critical role in detecting discontinuities and measuring their dimensions. Specifically, when the height of a discontinuity projected onto the principal stress plane exceeds a certain threshold, it is classified as a defect, and NDT is required to detect such defects and measure their heights. Among NDT methods, the Time of Flight Diffraction (TOFD) technique is widely used in industrial applications due to its ability to simultaneously detect internal defects and measure their heights. Currently, experienced technicians manually inspect the data obtained through the TOFD method to detect and measure defects, which increases inspection time and costs. This study aims to develop a method that utilizes Artificial Intelligence (AI) to assist in the detection and measurement processes. In the conventional TOFD method, one transmitter and one receiver are used; however, this approach struggles to accurately detect and measure defects when discontinuities are not perpendicular to the inspection surface, even with AI assistance. To address this issue, the study proposes a new method using two transmitters and two receivers, increasing the amount of data by expanding the paths of ultrasonic waves. This additional data is then processed by AI to improve detection accuracy. The study employs the Finite-Difference Time-Domain (FDTD) method to simulate TOFD waveforms and applies AI to the data obtained from both the conventional and proposed methods. The results show that the proposed method achieves greater accuracy, with the Area Under the Curve (AUC) of the Receiver Operating Characteristic (ROC) curve improving from 0.93 to 0.97. Future work will focus on validating this approach with experimental field data rather than simulations.

The Japanese Industrial Standards (JIS) specify the adhesive strength σ_C^JIS as an average ultimate tensile stress by using a small specimen with adhesive area. For the adhesive specimen, singular stress field appears at the bonded interface end, and the uneven stress concentration in the adhesive area must be considered. Therefore, the bond strength σ_C^JIS varies depending on the adhesive geometory. As the authors have recently pointed out, if the intensity of the singular stress field (ISSF) at the interface end is taken into account, the adhesive strength can be expressed as ISSF = constant. However, this average adhesive strength σ_C^JIS is straightforward, easier to understand than the ISSF, and is widely recognized as adhesive strength. Therefore, this study discusses the validity of obtaining the adhesive strength σ_C^W from σ_C^JIS specified in JIS when the geometric dimensions of the bonded area are changed, such as when the bonded area is larger than the JIS bonded area. The bond strength decreases when the bond area is increased in a similar shape specimen. This can be explained in terms of ISSF. In the case of butt joints, σ_C^JIS is applicable when h in the JIS specimen is equal to h in the actual product, and in the case of lap joints, it is shown to vary depending on the adherend thickness and bond length.

For stepped lap joint, the joint area is larger than that of an ordinary straight joint, and thus the joint strength can be expected to be improved. Examples of the practical importance of stepped joints can be found in aircraft repair. This is because adhesively bonded repair patches are mechanically efficient, and they can be quickly applied depending on the size of the repair and the proficiency of the repair technician. In this way, since the importance of the stepped joint is well-known, several studies are available including stress analyses and experimental study. However, those previous studies have not considered yet the ISSFs (Intensity of Singular Stress Field) at corner points and interface ends. To clarify the improvement mechanism in stepped joints, this study focused on the singular stress fields as well as the ISSFs, which control the adhesive strength. The initial debonding stress evaluated from the fully bonded stepped joint with a constant ISSF agrees well with the initial debonding stress σ_{C EXP}^Initial. Furthermore, the variation of the second debonding stress σ_C^2nd evaluated from the partially delaminated stepped joint agrees well with the variation of the final fracture stress σ_C^Final. The reason why the final fracture strength σ_{C EXP}^final is much larger than the initial debonding strength as σ_{C EXP}^Initial ≪ σ_{C EXP}^final when N_S ≥ 6 can be explained as follows. The dimensionless ISSF F_σ^B under a constant load in the partially delaminated stepped joint decreases largely with increasing N_S although F_σ^A under a constant load in the fully bonded stepped joint does not change very much.

Adhesive bonding is a joining method for CFRP structures, but it may cause kissing bonds that are difficult to detect by nondestructive testing. Therefore, it is difficult to use adhesive bonding alone in joints where reliability is required, and adhesive bonding and fasteners are used together. However, the use of fasteners increases the weight of the joint structure, and the advantages of adhesive bonding cannot be fully utilized. On the other hand, even if a crack occurs or propagates at the adhesive joint, there is no problem with structural integrity if there is enough time before the unstable crack propagation starts and if it can be detected by nondestructive inspection before the unstable crack starts. For example, a crack arrester could be installed in the crack propagation path before the critical crack length where unstable crack propagation occurs, and a crack detection function could be added to the crack arrester itself or its surrounding area to guarantee the integrity of the joint. In this study, we investigated a method to detect crack propagation around the crack arrester by adding crack arrester performance to the adhesive layer by adding a convex shape to a part of the surface of the adhesive layer. As a result, it was confirmed that the method was effective in suppressing crack growth sufficiently, and a health monitoring method using the convex shape was devised without installing a sensor.

This study has clarified mechanical and dynamic characteristics of multi-material structures based on bolted joints including magnesium alloy and established an analysis method. Magnesium alloy specimen bolted in multiple combinations with other materials, and finite element method (FEM) were used to see natural frequency, vibration modes, clamping force, and interfacial stiffness of the jointed parts. A series of hammering tests and numerical simulations were performed to clarify the relationship between the natural frequency and the clamping force, and the effect of the magnesium alloy was investigated. The numerical simulations were executed by the FEM based on a mechanical model to simulate the mechanics of the real contact area between bolted joints interfaces. The natural frequency of the bolted joints asymptotically increases to a constant value as the increments of the clamping force. This is due by the real contact area of the interfaces between the bolted plates increases as the increments of the clamping force. Compared to the other materials, the natural frequency of the magnesium alloy joint tends to increase quickly to the constant value at a lower clamping force. It considers that the low Young’s modulus of the magnesium alloy creates the real contact area increase at a higher rate even at low clamping force, because the interfacial stiffness is saturated when the real contact area becomes large enough. In addition, the natural frequency of the multi-material bolted joints is affected by the constituent materials in the case of each materials characteristics affecting the deformation shape in different vibration modes of the bolted joints. The real contact area and the material constants show strong influences on the dynamic stiffness of magnesium alloy bolted joints. The rigidity of the constituent materials has more influence on the deformation shape with many nodes and antinodes through vibration modes.

This study has investigated the vibration characteristics such as natural frequency and damping ratio of ABS resin plates with bolted joints by hammering tests. The natural frequency of the specimen was measured from the peak of the power spectrum obtained by the Fourier transform of the acceleration response, and the damping ratio was measured from the acceleration envelope obtained by the Hilbert transform. Then, the ratio of the effects of frictional damping and viscous damping in the damping capacity of the resin material with bolted joints was investigated using the vibration simulation by the finite element method (FEM). The same approach was also applied to S50C plates with bolted joints for comparison with the vibration characteristics of ABS resin. A contact model, which simulates the interfacial stiffness of nominally flat surfaces between the plates by the contact of spherical asperities, was introduced and computed using the FEM. The elastic modulus of the interface and the damping coefficient by friction were then derived and applied to both ABS and S50C plates. The viscosity coefficient was applied to ABS resin plates only. The hammering test results show that the natural frequency increased and the damping ratio decreased with the increase of clamping force of the ABS resin plates with bolted joints. The FEM results agreed with the hammering test results. The viscous damping was 10–30% of the damping ratio of the ABS resin plates with bolted joints. The stiffness and the natural frequency of ABS resin plates with bolted joints were lower, but the damping ratio was higher than that of the S50C plates with bolted joints.

In the field of transportation equipment such as automobiles and aircraft, the use of light metals instead of steel materials is progressing. In particular, magnesium alloys are lightweight and have high specific strength. Furthermore, they have excellent vibration absorption, machinability, and electromagnetic wave shielding properties, so their use as electronic device housings is expanding. However, their corrosion resistance is lower than that of steel materials. Therefore, research is being actively conducted on coating magnesium alloys with highly corrosion-resistant and wear-resistant materials using many surface treatment techniques such as plating and deposition. In the present study, shot lining, a joining method that applies shot peening, was performed to improve the corrosion resistance of magnesium alloys. The experimental materials used were commercially available flame-retardant magnesium alloy extruded round bars. The corrosion-resistant metal foil was pure titanium foil with a thickness of 0.02 to 0.04 mm. Pure titanium foil was joined to magnesium alloy by shot lining, and the joining property was investigated by bending tests. The main results are as follows. Pure titanium foil with a thickness of 0.04 mm could be joined at a processing temperature of 350 °C. It was found that the use of a pure aluminum foil insert material was effective in improving the bondability. In the workpiece bonded with a 0.04 mm thick titanium foil, it was found that the bondability was improved by heat treatment at 450 °C or higher.

Repair of piping damaged by corrosion or age-related deterioration in power plants and other infrastructure facilities is essential. In general, welding is used to repair cracks and holes in piping, however it involves long repair times and presents a fire risk due to sparks. To address these issues, this study explored the use of cold spray technique as an alternative repair technology. A previous study achieved successful hole repair with a mixed powder of Sn and Zn, however this coating poses a corrosion concern, highlighting the need for more durable solutions. In this study, the feasibility of repairing holes with corrosion-resistant stainless steel using a low-pressure cold spray technique was investigated. Initial repair tests using a mixture of stainless steel/WC powder at various spray angles revealed difficulties in successfully repairing the holes. Subsequently, stainless steel powder was mixed with soft materials such as Zn or Al powder to assist stainless steel particles deposition, leading to successful repairs. In addition, corrosion resistance tests on stainless steel/Zn and Zn deposits were conducted to evaluate the effect of stainless steel addition on corrosion resistance.

Diamond films have excellent properties such as high hardness, low friction, and high wear resistance; therefore, it is used in sliding parts such as mechanical seals. However, due to the rough surface, polishing after deposition incurs significant costs. In recent years, by increasing the CH4 concentration during diamond film synthesis, smooth surfaced nanocrystalline diamond (NCD) films have been obtained. However, due to their lower hardness, their wear resistance decreases. we developed a method to synthesize diamond films while modulating the carbon gas concentration. Moreover, the effects of concentration modulation on the friction and wear properties of diamond films synthesized via microwave plasma chemical vapor deposition (CVD) when using SiC, a material actually used in mechanical seals, as the counterpart material. CH4-H2 gas was used as the source gas. A concentration-modulated diamond (CMD) film was synthesized by modulating the methane concentration from 1% to 10%, which exhibited a surface roughness (Sa) of 20 nm and a hardness of 65 GPa. In friction testing with SiC as the counterpart material under dry conditions, the friction coefficient of the CMD film was below 0.5. The specific wear rate of the SiC ball was 0.8 mm³/Nm, which indicates a reduction in the wear of the counterpart material compared to conventional MCD films. Furthermore, the specific wear rate of the CMD film was 3.8 μm³/Nm, showing a decrease in the film's wear compared to conventional NCD films.

Carbon nitride has excellent mechanical properties. If the β-C₃N₄ structure can be obtained, hardness levels approaching those of diamond could be achieved. Numerous studies on the synthesis of carbon nitride films have been conducted using various deposition methods. In this study, we focused on the Microwave-Sheath Voltage Combination Plasma (MVP) method as the plasma source for synthesizing carbon nitride. The MVP method can achieve both high-density plasma and nitrogen ion impact at low pressure. This study investigated the effect of the source gas on the mechanical properties of carbon nitride films synthesized using the MVP method. A Si wafer was used as the substrate. A mixture gas of CH₄-N₂, CH₄-NH₃, and C₂H₂-N₂ was used as the reaction gas. The films were evaluated by Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction (XRD), scanning electron microscopy, nanoindentation test. The highest deposition rate was about 29.7 μm/h with the C₂H₂-N₂ gas system. Raman spectra of all samples exhibited characteristics of amorphous carbon. The XRD patterns showed no peaks, indicating that the films had an amorphous structure. The nitrogen content of the films ranged from 2 to 27 at.%, with the highest nitrogen content obtained using the C₂H₂-N₂ gas system. The hardness of the films synthesized using CH₄-N₂, CH₄-NH₃, and C₂H₂-N₂ was 16.3, 11.5, and 0.2 GPa, respectively.

Magnesium alloys with the long period stacking ordered (LPSO) structure, known as LPSO-type Mg alloys, show the superior strength and have been attracting attention as helping to solve energy problems. In the LPSO-type Mg alloys, kink deformation is an important deformation mechanism as well as slip deformation in the crystalline scale and may be the origin of the material strengthening. The bending kink band microstructure in the alloys is expected to bring the new material strengthening called the kink strengthening. The inhomogeneous deformation due to kink band causes the strain gradient around the band, and it can be considered as one of the origins of kink strengthening. The higher-order gradient crystal plasticity is the theory that takes into account the effect of geometrically necessary (GN) dislocation density caused by strain gradients. In this model, an additional governing equation expressing the dislocation density field is introduced, and both the displacement and dislocation density fields can be solved simultaneously. The previous studies have suggested that misorientation on the kink boundaries may significantly affects kink strengthening. However, the detailed relationship between the kink shape and the kink strengthening is still unclear. In this study, the numerical analysis is conducted by the mesh-free method using the higher-order gradient crystal plasticity model focusing on the number of kink bands. The deformation behavior around the multiple adjacent kink bands is evaluated to reveal the kink strengthening mechanism of the LPSO-type Mg alloys.