Cellulose nanofibers (CNFs) have been attracting attention as engineering materials because CNFs have high tensile properties in addition to the biodegradability and reproducibility. Many research works have been conducted to produce high performance composite materials using CNFs. Alignment of CNFs in composite materials is critical for achieving higher mechanical performance, but it is challenging because CNFs have high flexibility. Wet spinning of CNFs is a technique to obtain a pure CNF yarn by injecting CNF hydrogel into a liquid like acetone, followed by drying. The high shear rate in the injection nozzle gives orientation of CNFs along with the flow direction, resulting in almost unidirectional alignment of CNFs in the yarn. In this study, the effect of the inner diameter of the injection nozzle and the CNF concentration of hydrogel on the feasibility of pro-duction of CNF yarns was experimentally investigated. The results showed that a limited range of the inner diameter of the injection nozzle enabled us to produce CNF yarns, but it was possible to produce CNF yarns within a certain range of CNF concentrations.

In recent years, there has been a significant increase in the widespread utilization of carbon fiber reinforced plastic (CFRP) due to its remarkable specific strength and rigidity. This material finds extensive application in various mechanical products, particularly in components that experience minimal or static loads, such as outer panels and structural elements. Moreover, researchers have been investigating the impact response of CFRP and have discovered its potential for exceptional shock absorption properties. By altering the orientation of carbon fibers and adjusting the number of layers, the structural strength of CFRP can be customized according to specific requirements. Based on these characteristics, the researchers conducted a drop weight test on test specimens with varying layer configurations to elucidate the shock absorption performance of the material.

Tensile tests were conducted on injection-molded short-glass-fiber reinforced plastics (SGFRP) plates, with specimens cut from the center and near the edge of the plate. The results showed that both Young's modulus and tensile strength were higher in the edge specimens than in the center specimens. Fiber orientation was measured using X-ray CT, and it was found that the ratio of fibers oriented in the injection direction increased towards the edge. In this study, the elastic constants were estimated through micromechanics, utilizing the fiber orientation measurement results obtained from X-ray CT, and the tensile strength of SGFRP was predicted based on the matrix stress.

The objective of this study was to develop thermoplastic transparent glass fiber reinforced plastics (transparent GFRTP). The technology of dispersing the metal oxide nanoparticles to the matrix resin makes the refractive index of matrix close to that of glass fiber. In this study, acrylic monomer added zirconia nanoparticle dispersion was used as a matrix of GFRTP molded by hand layup method. The molded GFRTP showed that transparency was improved at a zirconia nanoparticle content of approximately 45%. In addition, the results of flexural and dynamic viscoelasticity tests showed that the elastic modulus increased by approximately 60% and flexural strength decreased by about 3%. On the other hand, the glass transition temperature was about 80°C, a decrease of about 20°C.

The effect of fabrication methods on tribological properties, such as friction coefficient and specific wear rate, was investigated using several Al, its alloys and Al-based composites. Tribological properties of these materials were evaluated under dry conditions at room temperature using a ball-on-disk wear tester. The friction coefficient in the casting process decreased gradually, while the friction coefficient in the powder solidification extrusion decreased suddenly. This is due to that the reinforcing particles in the powder solidification extrusion are deposited on the sliding traces and the base metal portion is ejected to the edge. The presence of deposited reinforcing material is also assumed to suppress of specific wear rate. The wettability of pure Al and the reinforced material showed that samples with a large surface free energy difference showed a sudden decrease in the friction coefficient due to early delamination of the reinforced materials. It is concluded that (1) the preparation of samples by powder solidification extrusion and (2) the wettability of the material is effective in improving tribological properties.

The purpose of this study is to elucidate the effect of the number of cells in the cell structure by structural analysis using the finite element method. Numerical experiments were conducted using the FEM solver RADIOSS (Explicit method). The analytical model consists of upper and lower rigid walls, cell structure. The cell structure was meshed using shell elements. Compression simulations were performed by applying a constant velocity of 20 m/s (1000/s) to the upper rigid wall. The cell structure model used in this study has a total of 25 patterns (5 cell number types). With an increase in the cell number, an averaging of compressive properties and a decrease in the sudden increase or decrease in stress due to changes in the microcellular structure were observed. In the plateau region, there was almost no effect of increasing the number of cells. On the other hand, the slope of the elastic response increased with increasing cell number, and the amount of strain that initiates densification tended to decrease slightly with increasing cell number.

Nowadays, an aluminum alloy carbody structure is prevalent in railway vehicles by their lighter weight compared with a steel carbody structure. However, in the event of a collision with a truck at a level crossing, the carbody of a railway vehicle made of aluminum alloy may undergo significant deformation, and a relatively long time is needed to repair because more processes are needed comparing to carbody structure made of steel, so that the method to shorten time to repair railway vehicle is required. In this paper, we propose a carbody structure that incorporates replaceable crash-energy absorbing structures at the front. In the event of a collision, the replaceable crash-energy absorbing structure is primarily deformed, resulting in reducing the collision energy transferred to the main frame of the carbody and mitigating deformation. Finite Element Method (FEM) analysis demonstrates that car body structure adopting the replaceable crash-energy absorbing structure mitigates deformation in the main frame of the carbody structure in railway vehicle.

Explains that wave dynamic resonance characteristics can be obtained from the impedance between electrodes. A large current flows at the resonance point, and a drive device using the generated magnetic field is proposed. A magnetic field is generated in a circumferential shape with respect to the current according to Ampère's law. And the magnetic field generates electromagnetic force in the vicinity of the electric wire. The position of the wire so that the magnetic field generated in the circumferential shape can be combined to obtain a sustained electromagnetic force in a straight line in a constant direction and the driving force can be maintained in the moving part. We propose an example of setting the direction of the current. We propose the electrode arrangement of a drive device that moves in a linear or circular shape. Also, the speed at which the moving part moves is calculated from the electrode spacing and frequency.

The lightweight yet high specific strength of carbon fiber reinforced plastic (CFRP) is widely used in space development. However, there are concerns about the potential degradation of the material's mechanical properties due to various factors present in the space environment, such as gamma rays, electron beams, ultraviolet rays, temperature thermal cycles, and atomic oxygen. In this study, electron beam and atomic oxygen irradiation were applied to polyimide CFRP, and hyper velocity impact experiments were conducted by a two-stage light gas gun to simulate space debris impact. By analyzing the perforation holes after the impact experiments and the cumulative number distribution of forward ejecta, the effect of electron beams and atomic oxygen irradiation to the CFRP’s facture behavior was evaluated.

In recent years, damage by improvised explosive devices, known as IEDs, has occurred in conflict zones. Therefore, research and development of Blast Mitigating Seats for use by the occupants is needed as one of the measures to prevent IED damage. In previous studies, impacts were applied to the lower part of a reduced model of the vehicle body to accommodate the seat, and the behaviour of the vehicle body model, which displaces only vertically upwards, was considered. However, the vehicle body may be subjected to an explosive impact accompanied by vehicle body rotation, for which countermeasures are required. Therefore, the purpose of this study is to develop a seating mechanism that protects the occupants from explosive impact with vehicle body rotation.

Protective structures as rope nets and sheets/plates have been used against tornado debris in nuclear power plants. However, energy absorption of such flexible structures has not been exhaustively studied. To compare the energy absorption of different flexible protective structures, a comprehensive study of both rope nets and sheets/plates subjected to drop weight impacts has been carried out. An aramid fiber rope net has been modeled with beam finite elements and a cable material. A steel plate has been modeled with shell finite elements and an elastic-plastic material. And, an aramid fiber sheet has been modeled with membrane finite elements and a fabric material. The simulation results showed that the aramid fiber rope net and sheet absorb energy locally in the impact zone, while the steel plate absorbs energy also by plastic deformations outside the impact zone. However, both materials have the same level of energy absorption.

The purpose of this study is to estimate the surface condition of road material, such as dry, wet, ice and snow, by using the ultrasonic system on the moving vehicle. As a first step, five kinds of road material were used as the specimen for examination and verification of the possibility of estimation by the ultrasonic measurement with moving system. The airborne ultrasonic wave (the central frequency of 40 kHz) which reflects at the interface of air and material surface by the difference of surface condition is received by the ultrasonic transducer and recorded to the oscilloscope. The roughness of road material is also measured as surface profile by laser displacement sensor. The maximum amplitude of reflected ultrasonic wave from each specimen were evaluated quantitatively by the roughness of road surface. The ultrasonic method is effective for the estimation of the road material with different surface condition.

Effective stress-true plastic strain curves of aluminum alloy 5005-O were obtained by an optimization method using the experiment analysis of digital image correlation method and the simulation of finite element method. Notched plate specimens with a radius of 30 mm were used for tensile tests. The effects of strain rate on flow stress after stress correction were examined. The flow stresses at a true strain of 0.40 corrected about 5%. Strain-rate sensitivity exponents m before and after stress correction were almost the same.

This paper concerns the λ-type enforcement breaking device (EBD), which aims the traffic accident prevention. The device is supposed to be installed in a road construction region, according to the actual traffic-lane regulations. We contend, the forced halting of an automobile by means of EBD, would result in the significant increase of drivers’, pedestrians’ as well as road construction workers’ safety. The ongoing improvement of EBD mechanisms concerns their performance, structural optimization as well as continuing efforts to reduce the breaking distance. In this report, we discuss the effect of the mast angle for breaking performance. Simple model collision tests and theoretical calculations based on the principle of energy conservation were utilized in our study. The collision tests concerned three selected velocities of a vehicle and models that has four selected mast angles of EBD with long-arm. We demonstrate that changes in the mast angle in the λ-type EBD, substantially affect the braking characteristics.

Penetration evaluation is an important indicator for protecting buildings and structures from serious accidents, such as impacts from tornado-borne objects and aircraft collisions. Conventionally, the evaluation of penetration has been carried out using a penetration evaluation formula to calculate the penetration limit thickness. However, the conventional penetration evaluation formula does not consider important characteristics of penetration phenomena, such as the deformation and strain rate dependence of the penetrated material. Therefore, this study aims to improve the accuracy of the penetration evaluation formula and focuses on the formulation of steel plate penetration phenomena considering the strain rate dependence of the deformation and fracture characteristics of the penetrated material. In this report, experiments were conducted by colliding cylindrical steel projectiles, assuming tornado-borne objects, with SM400 material to examine the factors influencing the penetration limit thickness. From the experimental results, it was clarified that the tip shape of the projectile greatly affects the ballistic limit velocity of the steel plate.

When using strain gauges, the time resolution limits the measurement to only a few hundred kHz. Unfortunately, this time resolution is insufficient for capturing high-speed phenomena above several MHz. In this study, our focus was on the gauge length and material constants that can effectively improve time resolution. We aimed to develop a MEMS strain gauge with enhanced temporal and spatial resolution by reducing the gauge length to approximately 1/10 of conventional gauges. Through numerical analysis, we confirmed that utilizing different material constants at the base can reduce the disparities in strain history by loosening the constraints on the elements near the base. Additionally, varying the thickness of the base can also decrease discrepancies in strain history by decreasing the constraints on the elements near the base. These results provide clarity on the influence of the base on both the gauge and the specimen.

In the safety evaluation of nuclear power plant structures, the penetration evaluation of structures assuming the impact of tornadic flying objects is an important indicator. In the penetration evaluation, empirical relationship equations between the projectile and the target plate's characteristic quantities (penetration evaluation formula) are widely used. The penetration evaluation formulas assume that there is no edge deformation of the target plate, and the applicable range is defined by the size ratio of the projectile to the target plate and other factors. However, the validity of the applicable range is not clear. In this study, the effect of edge deformation of the target plate on penetration was investigated by finite element analysis simulating a penetration test of a SUS304 steel plate. The results of the analysis, in which the diameter of the target plate (w) was fixed and the diameter of the projectile (d) was varied, showed that edge deformation affected the critical velocity for penetration at w/d ≈ 11 or less. The results of the analysis for different target plate diameters showed that as the target plate became larger and the effect of edge deformation became smaller, the increase in the critical velocity of penetration became slower.

We have developed a stress correction method from multiaxial to uniaxial stress state of flow stress in the stress-strain relationship required for numerical simulation. Using this, we calculated the true stress-true strain curves of ferrous metals and aluminum alloys over the entire strain range, and verified them by several methods. Since the devised correction method requires repeated tension simulations and data processing until convergence, an automated system using Alteryx was developed with the aim of improving efficiency and convenience. In this report, we used this system to re-verify ferrous metals and aluminum alloys, and also tried to apply it to polycarbonate.

When the projectile penetrates into the sand at high velocity, meandering of the projectile and crushing of particles have been observed experimentally. However, the details of how these phenomena occur have not been clarified. It is difficult to investigate the behaviors of the projectile and sand particles inside target material, on the other hand, it is possible to visualize above behaviors by numerical analysis. In the present study, we performed numerical analysis of high-velocity penetration of the projectile into sand to compare with experimental results. In numerical analysis, we have constructed a new equation of state (EOS) to assess the propagation velocity of pressure wave accurately during high-velocity impacts into sand. Our new EOS redefined the compressive process non-linearly, and simulated measurement results better than conventional compaction models described linearly. We compared the propagation velocities of pressure wave obtained by numerical analysis using the new model and the conventional model. As a result, numerical results using the new model described the propagation velocity of pressure wave more closely to measurement values.

The effective stress intensity factor range for surface crack in A7075 aluminum alloy under tensile or bending load was determined based on the displacement distribution around the crack tip obtained from the digital image correlation method. Calculation of the opening stress at the crack tip from the effective stress intensity factor range indicated that crack closure occurred under all experimental conditions. The log-log plots of crack growth rate versus the effective stress intensity factor range showed that the data for tensile and bending loads collapsed into a factor of two scatter band. It was also clarified that the crack growth life can be predicted with an error of about ±20% when the modified Paris law is applied to calculate the crack growth life.

The objective of this study is to identify the crack tip location from the measured displacement of the bonded material surface around the crack tip obtained by Digital Image Correlation (DIC) method using the least-squares method with the theoretical displacement as a model function. The theoretical displacement around the crack tip position is considered as a subset. The residual sum of squares of the measured displacements obtained by DIC is calculated for each assumed crack tip position along the bonding interface. The coordinate with the smallest residual sum of squares is taken as the crack tip position. At the same time, the stress intensity factor is determined. In this study, to verify the proposed method, theoretical displacements were used as measured values to determine the residual sum of squares. As a result, the local minimum value of the residual sum of squares indicated the set crack tip position. At the same time, the stress intensity factor was obtained.

In the conventional deflectometry, since an observation target is a mirror image by an observed mirror, the sensitivity to measure the titling angle of the observed mirror is very high. On the other hand, it is hard to use this method to measure the displacement of the observed mirror because the sensitivity is too small to detect the component of out-of-plane displacement. Therefore, for using the deflectometry to measure out-of-plane displacement, we had proposed a new type of deflectometry method, in which the observation target is imaged near the surface of the observed mirror. We called it 'imaging-type deflectometry'. In this study, we propose a method that can separate out-of-plane displacement and rotation angle components and simultaneously measure them.

Thermoplastics are lightweight materials with excellent moldability and are used in a wide range of applications, from everyday life to the automotive industry. Among them, melt molding is a process in which thermoplastics are melted to form a desired shape, then cooled and solidified. Molded products produced by this molding process exhibit anisotropic (directional) mechanical properties due to molecular orientation. The anisotropy is particularly pronounced when several plastic materials, called polymer blends, are mixed together, and it is known that the morphology of the mixed phase has a significant effect on the mechanical properties. However, it is difficult to quantitatively evaluate the mechanical anisotropy of polymer blend molded products using conventional evaluation methods, and the development of new evaluation methods is required. Against this background, this study aims to quantitatively evaluate the mechanical anisotropy in injection molded polymer blend products using a test method called the short-beam test and to clarify its significance.The short beam shear test is a method of measuring mechanical properties by applying a bending load to a small specimen. The data obtained from this test is expected to be analyzed to elucidate the mechanism of anisotropy in polymer blend molded products. Specifically, the degree and direction of anisotropy in mechanical properties can be quantified, providing useful information for optimizing material design and manufacturing processes. This research is expected to improve our understanding of anisotropy in polymer blend molded products and contribute to the development of higher performance products and the promotion of sustainable use of plastics.

The propagation of localized deformations is often observed as a typical deformation behavior of polymeric materials. In such cases, it has been confirmed that the necking portion of a specimen should be hardened, otherwise the deformation progress in this portion leads to the fracture of the specimen. However, actually the necking portion is softened according to the results of hardness tests. The aim of this study is to elucidate the relationship between localized deformations and strength change of Polycarbonate and ABS, that enables us to consider the causes of the contradiction. The authors conducted tensile tests of thin strip specimens and measured the axial and lateral strains by DIC method, then the deformation behavior was evaluated numerically, and the true stress was calculated from the strain values. From this result, increase in true stress during plastic deformation including necking propagation was observed. The Micro-Vickers hardness measurement for a gauge length was also performed to clarify the strength distribution of a specimen, and the results showed that the entire deformed area was softened, and the necking part was further softened. Since there was concern that the specimen might be hardened in the cross-section perpendicular to the tensile axis, the hardness of the cross-section was measured, and it was confirmed that the specimen was softened in the cross-section as well. The authors consider causes of contradictions in specimen strength as deviation from linearity at low stress in stress curve at reloading. Vickers hardness for polymeric materials may reflect this point of deviation.

Present study examined the impact behavior of tennis rackets during swinging by players. First, the 3D motion of racket in swing was estimated from the 2D video by transforming it into match-stick motion picture using an AI method of Openpose. As a result, it looks like that players stop their wrist to accelerate the rotation of racket head during the impact. Next, a strain gauge was glued on rackets and the bending strain was measured when hitting a ball. It was found that the acceleration of racket have bent the racket significantly before the impact; the flexure was as large as the bending vibration induced by hitting a ball.

The behavior of acoustic emission (AE) generation during the tensile test of the double cantilever beam (DCB) specimens with chevron joints, which aligned along the longitudinal direction of those, was examined from the viewpoint of the reference platform for the AE method. The specimens were fabricated by the material jetting type 3-dimensional printer to have triangular-thin-columns of different sizes between the upper and the lower half of DCB. The load-displacement diagram and the characteristics of AE count during the test demonstrate that independent crack growth inducing AE occurs intermittently, and the results of AE source location show that those occur at each chevron joint. These facts imply that we can obtain expected AE signals generated within the specific region of the specimen at different timing. It was also found that both stable and unstable fractures, with low amplitude successive AE signals and high amplitude sudden AE signals, occur so that one can check the specification of instruments and engineer’s skills to measure different kinds of waveforms using the specimens. As a consequence, the specimens have the potential to act as the platform for discussing the performance of AE measurement systems.

In recent years, the authors have succeeded in obtaining a strain gage dedicated to stress intensity factor analysis (hereinafter referred to as K-value gage) with a single element with an error rate of ± 5% from the theoretical value. In this study, an experimental analysis of the out-of-plane bending stress intensity factor of a strip crack was attempted using this single-element K-value gage. The stress intensity factor analytical formula for cracks subjected to out-of-plane bending was derived by M. L. Williams, and the bending of plate materials was further developed and reported by G. C. Sih et al.. The stress formula derived by M. L. Williams was used as the out-of-plane bending stress analysis formula for cracks at the starting point of this study. This stress equation was converted into a strain equation to derive the K-value gage equation.

Carbon nanotube (CNT), one of the representative nanocarbon materials, is expected as a structural material for space elevators because of its overwhelming strength-to-weight ratio. To use CNTs as engineering materials in the near future, it is necessary to increase the size of single-walled CNTs while maintaining their excellent mechanical characteristics. However, in practice, many defects are introduced during the enlargement process, causing a significant strength reduction. This paper discusses an effective method how to bundle and size up single-walled CNTs based on recent strength evaluation results to maintain their superior strength values.

Carbon nanotube (CNT) is an advanced material with excellent specific strength and specific stiffness, and is expected to be applied to composite materials, whose use is expanding in the aerospace field. Wet spinning and dry spinning are the two main methods of CNT yarn production. The direct spinning method, one of the dry spinning methods, uses Floating Catalyst-Chemical Vapor Deposition (FC-CVD) to continuously spin CNTs, and is considered to be capable of synthesizing high-purity CNTs. However, the strength of CNT yarns is significantly lower than that of CNTs as a single material, and there is an urgent need to increase the strength of CNT yarns by post-processing in order to expand their industrial use. In this study, we investigated the basic physical properties of CNT yarns produced by FC-CVD and evaluated the factors affecting strength. In addition, PAA/DMSO treatment was applied to increase the strength, and the fracture morphology was evaluated by observing the fractured area. From the test results, it was confirmed that CNT yarns of FC-CVD had low functional group content and high purity, and that the PAA/DMSO treatment was not effective enough. TEM observation of the fracture area showed that the CNT bundle was the smallest unit of the fracture, and it was confirmed that the CNT bundle was fractured due to slippage between CNTs, resulting in a pull-through fracture.

CNT yarns produced by dry spinning are expected to be used as a next-generation carbon material to replace carbon fibers already in practical use. However, the current strength of CNT spun yarn (~0.4 GPa) is lower than that of carbon fiber (6 GPa). In order to increase the strength of CNT spun yarn, a method of cross-linking CNT bundles with sulfur has been reported in recent years. In this study, we attempted to introduce a sulfur cross-linked structure by immersing CNT yarn in a sodium polysulfide solution for a long time to increase CNT yarn's strength. The sulfur cross-linked structure suppressed "slipping," which is the breaking mechanism of CNT spun yarn, and significantly increased the strength of the CNT spun yarn to a maximum tensile breaking stress of 4.93 GPa (untreated: 0.37 GPa).

Ultrasonic cavitation induced fragmentation is a simple way to cut carbon nanotubes (CNTs) 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 and diameter on the tensile strength of CNTs are evaluated by using the ultrasonic cavitation induced fragmentation, where annealing and reducing the diameter of CNTs are known as measures to improve the tensile strength of CNTs. Furthermore, the edges of CNTs after ultrasonic cavitation-induced fragmentation were observed by transmission electron microscopy.

The purpose of this study is to elucidate the mechanism of strength development of CNT untwisted yarn, which is an aggregate of CNTs, by molecular dynamics simulation. Two findings were obtained from the analysis. First, while the strength of single CNTs is superior in the armchair type when lattice defects are small, there is no significant difference in chirality as the amount of defects increases. Second, it is suggested that the failure mode may change from CNT interfacial slip to CNT single CNT failure depending on the amount of defects in the CNTs. The bundle strength of about 5 GPa obtained from the analysis and the strength of the untwisted CNT yarn is about 3 GPa, suggesting that the smallest unit of fracture may be the slip between the bundles.

The stepped lap joint has intermediate properties of butt joints and lap joints. By changing the step number Ns, it is possible to simulate the unevenness of the bonding interface to improve the adhesive strength. In this paper, the intensity of a singular stress field (ISSF) is focused, and the effect of Ns on the adhesive strength is investigated in terms of the ISSF. Two models are considered. One is the model to analyze the ISSF at the end of the stepped joint. The other is the model to investigate the ISSF at the first corner of the bonded interface when the first step is broken. The adhesive strength mechanism is studied in terms of those ISSFs values under the σ_x^∞ and σ_x^∞ = σ_c^Initial applied and also under the crack initiation load is applied.

The adhesive strength is usually expressed as an average stress σ_c = P/A but it is known that σ_c decrease with increasing the volume of the adhesives. Here, P is an ultimate tensile load and A is an adhesive area. In this study, three models are considered based on ISSF = const. The first model changes the adhesive thickness h under fixed the adhesive area A = W² based on JIS. The second model changes A = W² under fixed h. The third model changes the adhesive volume under fixed the adhesive layer’s geometry h/W. It is found that σ_c can be used to express the adhesive strength since σ_c is independent of the volume of adhesives under the same adhesive thickness h.

In this paper, the attempt is made to evaluate the intensity of singular stress field (ISSF) in the interface corner in the 3-dimensional (3D) scarf joint with two real stress singularities by the proportional method. The 3D scarf joint with fixed surfaces which reappears the 2D scarf joint under the plane strain condition is used as the reference model. The ISSF for the reference 3D scarf joint is approximated with that for the 2D scarf joint. The numerical simulations are performed on the 3D bonded model with the interface inclined by 45o which is composed of the steel and resin. It is shown that the asymptotic solution is in good agreement with the FEM stress distributions. Then, a significant difference between the stresses at the interface corner and along the interface edge is found. Although the compression stress occurs along the interface edge, the tensile stress occurs at the interface corner.

There are several tightening methods for the bolted jonts such as the torque control, the angle control, and etc.According to JISB 1083, the tightening coefficient Q (F_max/F_min) by the angle control method is smaller than the torque control method. It means that there are possibilities to adopt smaller size bolts. To determine tightening specifications of the angle control method, it is important to understand the relationships between the tightening angles θ[°] and the bolt axial forces F[kN]. In the tightening process, the relationships show closely liner characteristic after the snag points. It was previously shown that the values of inclinations dF/dθ[kN/°] obtained by the simplified calculation formulas or FEM analyses are larger than by physical tests. As the reasons, the approach of interfaces ζ[μm] caused by deformations of fine surface roughness on the each contact surface are considered. In this study, the tightening tests using steel(S45C), aluminum alloy(A6061-T6) and spheroidal graphite iron casting(FCD450) with different surface roughness as clamped prats are conducted. As a result, it is shown that the value of dF/dθ[kN/°] in case of the surface roughness 20μmRz is smaller than in case of 10μmRz, and that the value of dF/dθ[kN/°] in case of combination of A6061-T6 and S45C is smaller than in case of FCD450 and S45C, even if the surface roughness at the contact surface is same.

In this study, many experimental data were collected by changing the properties of the contact surface of the bolt/nut/washer in order to obtain information on the thread torque residual rate after tightening with M12 hexagon bolts. Furthermore, the behavior of thread torque and clamp force was discussed based on the obtained experimental data.

In this study, a strain generated in a molded part during metal additive manufacturing process was investigated by in- situ measurement using a digital image correlation method that utilizes the unevenness pattern on surface of a molded object. During the molding process, large strain was measured at the top of a molding part. This is thought to be related to the distance between a base plate and the top of a molding object. A base plate was fixed at the four corners with screws and had high stiffness. However, by progressing of the molding process, the lower part of a molding object supported distortion of the upper part instead of a base plate and resulted in increasing strain due to lower stiffness in the lower part. Strain generated in the molding object tended to decrease by increase in height of the molding object, which might be due to increase in cross-sectional secondary moment of the molding object.

Toward developing next generation rolls such as super-cermet rolls, the fatigue strength of the sleeve roll is considered in this paper. Considering the circumferential slippage appearing at the shrink-fit interface, the load shifting method is applied on the fixed roll to clarify the stress variation during roll rotation. Based on this simulation results, the fatigue strength of standard rolling rolls is estimated considering the slip defect. The defect dimension is characterized by the root area parameter √area. It may be concluded that if there is no slip damage, the fatigue strength of the sleeve roll is not very smaller compared to the fatigue strength of the solid roll with no shrink-fitting.

This study focuses on two advanced techniques applied to evaluate the thermal cycle durability of TBC, which were developed in joint research with NIMS. The first technique utilizes a new AE Method with Continuous Waveform Recording, which can detect AE events more precisely than conventional AE systems. The second technique is a non-contact strain measurement method using laser speckles, which can measure the strain on the TBC surface at high temperature. These techniques were combined with a laser thermal cycle test to establish the “∈_H-N diagram”, which shows the relationships between the hot shock strain ∈_H in the laser thermal cycle test and the cycle number N to failure for different TBC thicknesses. The obtained ∈_H-N diagram revealed the durability of TBC for various thicknesses and was transformed to an evaluation map to predict the TBC thickness limitation. MHI will apply the map to utilize the optimum thickness of TBC.

To investigate the evaporation factor in the laser ablation process, we controlled the laser power and ambient pressure in a nitrogen atmosphere, ablated AgPd, and attempted to observe the ablation plume. 5 minutes of laser irradiation was applied to AgPd, and the evaporation rate was calculated by dividing the evaporation amount by the irradiation time. The evaluation was made. The laser beam was scanned over the target at an angle of 45 degrees by moving the eccentric rotating mirror type galvanometer scanner and the X-Y table on which the target was installed. At the irradiation point, a luminescence called a plume was generated by the plasma of evaporated atoms of the target and ambient gas. The evaporation rate increased with increasing laser power and ambient pressure. In laser power control, the size of the plume was proportional to the evaporation rate, while in pressure control, the evaporation rate decreased with decreasing ambient pressure, but the plume increased. These results indicate that increasing laser power and ambient pressure are effective in increasing evaporation rate, but there is no correlation between plume size and evaporation rate.

In cold spray technology, the design of nozzle shape is important to generate the supersonic gas flow for sufficiently accelerates the particle and deposits as a coating. Among them, the spray pattern of coating was found to be affected by the design of nozzle shape especially length and ratio of divergent and parallel section, and copper coating was flattened by optimized rectangular cross section nozzle at previous study. However, in a recent study, thicker copper coating pattern with a view to molding in cold spray additive manufacturing was not flattened with the optimized nozzle, and it was necessary to review the nozzle dimensions for flatter copper coating and molding. In this study, in addition to review the nozzle ratio of length with particle size, CFD simulation conditions was improved due to mismatch of CFD and Experimental results. As a result, the spray pattern of copper coating is more flattened by the new optimized nozzle with a shorter divergent section, and moreover the pattern is possible to be estimated by the CFD.

In the current JSME S NF1-2009, "Environmental Fatigue Evaluation Method for Nuclear Power Plants", the Ke-factor could not be applied to the strain rate calculation for environmental fatigue evaluation because the conservative result is required. Although the conservatism is slightly reduced by adopting a strain rate that takes the Ke-factor into consideration, it is possible to optimize the excessive conservatism of the environmental fatigue evaluation and proceed with the evaluation rationally.

“Environmental Fatigue Evaluation Method for Nuclear Power Plants” (JSME S NF1) is utilized in Plant Life Management (PLM) evaluation for operating LWR plants. The first publication of JSMS S NF1 was 2006 Edition, and it was revised as 2009 Edition. After that, Subgroup on Fatigue Evaluation in the JSME Committee on Power Generation Facility Codes has developed three technical items for the JSME Environmental Fatigue Evaluation, and those have been approved by the Main Committee. Those revisions will be incorporated into 2022 Edition. The three technical items that are design fatigue curves, environmental fatigue life correction factor for PWR components, and Flaw Tolerance Approach for environmental fatigue evaluation are introduced.

A fatigue crack growth test was performed on a cracked SUS304 test specimen. Fracture surface observation was performed by SEM to clarify whether the fracture surface was due to fatigue crack growth or plastic collapse. The results revealed the following. To investigate the relationship between the crack coalescence behavior and the crack face distance, H, under fatigue conditions, the crack tip distance, S, was fixed, and the effect of H was investigated by fatigue tests. As a result, the cracks did not coalesce in any of the specimens. As a result of fracture surface observation, clear striations were observed from near the front to near the center of the crack tip, crack propagation occurred in the horizontal direction over a relatively long distance due to fatigue, and then gradually plastic collapse appeared on the fracture. However, it was found that the crack propagates horizontally and leads to plastic collapse. Comparing with the results of the previous study under creep conditions, in the high H region, crack coalescence was not observed under both fatigue and creep conditions, showing similar behavior. In the low H region, crack coalescence was observed under creep conditions, but not under fatigue conditions.

The effect of tension hold on high temperature fatigue crack propagation in Inconel 718 was investigated. Fatigue crack propagation tests were conducted at 650 °C in air, and single tension hold at maximum load was applied during cyclic loading with various conditions of stress intensity factor K and hold time. When the K value at the tension hold was high, fatigue crack acceleration occurred after the tension hold. When the K value was low, fatigue crack retardation occurred after the tension hold. Based on results of fracture surface analyses using scanning electron microscopy and energy dispersive X-ray spectroscopy, the acceleration was attributed to grain boundary embrittlement due to oxygen diffusion from the crack tip. On the other hand, the retardation was attributed to stress relaxation induced by creep deformation. The transition from the retardation to the acceleration depending on the K value was discussed based on a size comparison between the stress relaxation field calculated by finite element analysis and the grain boundary embrittlement area around of the crack tip.

Ribs are used to increase the stiffness of support structures such as skirts and lugs. The ribs are usually welded on two sides to the skirt and base plate or to the vessel and lugs, and often free on the other two sides. The skirts and lugs, which are the support structures of the vessel, generate a large moment mainly due to the response to earthquakes, and the ribs provided on the skirts and lugs are subjected to compressive loads due to the moment. The rules on design and construction for nuclear power plants of the Japan Society of Mechanical Engineers have restrictions on the width-thickness ratio and the effective slenderness ratio in consideration of the buckling of members subjected to compressive loads. These are shape restrictions considering the buckling of the plate under compressive load, and do not correspond to the loading conditions and support conditions of the two-side fixed ribs under the moment mentioned above. In order to clarify the buckling behavior of the ribs, buckling eigenvalue analysis was performed to obtain the buckling moment and the elastic buckling modulus for the ribs constrained on two sides.

A piping system subjected to earthquake possibly deforms plastically in design analysis because design seismic ground motions have been increased recent years. Though simplified elastic plastic analysis using elastic follow-up factor is standardized in design code to evaluate elastic plastic strain based on elastic analysis results for fatigue evaluation, elastic follow-up factor is conservative for piping systems. In this research, static elastic and elastic plastic analyses for elbow pipe connected to two straight pipes were performed with a view of streamlining the elastic follow-up factor. Forced displacements were applied to the analysis models so that four times stress of yield stress was generated at elbow pipe. In these analyses, outer diameter, thickness, curvature radius of elbow, and length of straight pipe were changed to verify the effect of pipe size on elastic follow-up factor. From the analysis results, it was clarified that elastic follow-up factors are varied depending on pipe size. Therefore, coefficient factor h’ was defined newly to represent pipe size, and it was indicated that elastic follow-up factor can be expressed as a function of coefficient h’. Mean line and upper envelope line were proposed to predict elastic follow-up factor as a function of coefficient h’.

In this study, we present defect topology identification analysis in a structure using hammering response data based on the inverse analysis methods. As for the inverse analysis method, the topology optimization method and the machine learning are applied to identify defect topologies. In numerical experiments using the topology optimization theory, the artificial response data, i.e., numerical simulation result, are employed for the identification analysis, and the practical hammering response data are used for the identification analysis based on the machine learning. In the presentation, the characteristic of each method is introduced, and some considerations based on numerical experiments are shown.

In thermal power generation, cavitation damage in the impeller of circulation pumps is a serious problem. In the past, such damaged part was replaced by brand new. Recently, advanced repairing process is required on site to reduce maintenance cost. The purpose of this study is to assess the reliability of the impeller material repaired by the laser metal deposition (LMD) method. For achieving this, a stainless cast steel material (SCS14), which is the same material as the actual impeller, is grooved to simulate cavitation damage, and this groove is then repaired by the LMD. The specimens were cut from the repaired part, and tensile and fatigue tests were conducted. As a result, it was confirmed that the tensile strength of the LMD repaired material was superior to that of the original material, and the fatigue strength was almost the same.