This study investigates how incorporating a twisted wall structure into a lattice structure improves sound absorption performance based on the numerical and experimental investigation. The twisted wall structure is expected to lengthen the flow path of sound waves inside the sound-absorbing structure. In this study, FEM simulations have been conducted to compare the sound absorption characteristics at twisted angles of 0 deg, 180 deg and 360 deg. Note that the direct and homogenization methods are also applied in the simulations, and sound absorption measurements were also performed to confirm the same trends as the numerical and experimental results. As a result, an increase in the peak sound absorption coefficient and an improvement in the sound absorption coefficient at low frequencies were confirmed as the torsional angle increases. Furthermore, by calculating the flow length passing inside the sound-absorbing structure, the frequency at the peak sound absorption coefficient can be predicted.

Porous media heat sinks have attracted much attention because of their large surface area, light weight, which are expected to improve heat transfer characteristics. In this study, the heat transfer characteristics of lattice structures under impinging flow conditions were investigated both by using FE simulation and experiment. In our investigation, the BCC lattice and PIN structures with different heights were manufactured by using the metal 3D printer, and their heat transfer coefficient were compared. From our FE simulation as well the measurement of the temperature, it was confirmed that the BCC lattice has superior heat transferring response than the PIN structure for a shorter one. In addition, we attempt to maximize the performance of the lattice heat sink by applying the density method which is commonly used in topology optimization, and optimize the relative density distribution of lattice units based on grayscale optimization.

Micro bell structure metal is a novel vibration damping metal material with high rigidity and high heat resistance that surpasses rubber materials, and the bell structure design inside the material makes it possible to "super" absorb vibrations in any frequency band. This paper explains the general vibration characteristic measurement methods and introduces the in-house bell structure-specific vibration characteristic measurement system.

It is well known that plastic deformation of thermoplastic induces anisotropic mechanical characteristics. The present study develops a constitutive model consisted of an anisotropic elasticity and anisotropic plasticity in order to simulate the mechanical behavior in the necking part of polycarbonate, PC. The anisotropic plasticity is based on Hill’s orthogonal anisotropic plastic model with considering anisotropic hardening plasticity. The identified mechanical parameters indicate that Hill’s anisotropic plastic parameters depend on Hill’s equivalent plastic strain, i.e., anisotropic hardening plasticity. To verify the developed constitutive model, the constitutive model is implemented in an Abaqus user subroutine and analyzed using the identified mechanical parameters. It is confirmed that the analysis results are in good agreement with the stress-strain relationship obtained by uniaxial tensile tests for the necking part of PC. Therefore, the developed constitutive model can reproduce the anisotropy mechanical behavior in in the necking part of PC.

Resin materials are widely used in industrial fields as adhesives, coatings, etc. When used as adhesives or coatings, it is necessary to evaluate the bonding strength quantitatively to ensure their reliability. Several test methods to evaluate adhesion have been proposed and used. However, they have some problems in that the evaluation results are affected by experimental conditions, such as the adhesion thickness, the edge geometry of the interface, etc. In this study, the test method to evaluate the bonding strength using a small column resin formed on the surface of the adherend was proposed, and the validity of the bonding strength assessed by this method was discussed after considering the sample size effect. The main conclusions are summarized as follows. (1) The bonding strength decreased as the column diameter increased due to increasing the deformation of the resin column. (2) The proposed test method could provide a valid bonding strength equivalent to the conventional lap shear test when the optimum column diameter was selected to prevent large deformation in the column.

In this study, the thermal buckling temperatures of square-plate sandwich panels with Pyramid cores were determined by the finite element method. In particular, we focused on the boundary conditions and compared six patterns of CCCC, CCSC, CSSC, CSCS, CSSS, and SSSS, in which S means simply supported edges and C means clamped edges. The buckling modes observed are classified into two types: global buckling and local buckling. Global buckling occurs when the core height tc/a, which is the distance tc between face plates per side length a, is small, while local buckling occurs when the core height tc/a is large. The results showed that the buckling temperatures of CCCC, CCSC, CSCS, CSSC, CSSS, and SSSS were higher in the order of total buckling, and the behavior was similar to that of the theoretical solution. On the other hand, in partial buckling, the buckling temperatures of all plates converged to a constant value for each number of cores.

The authors have proposed a stochastic lattice biomimetically designed based on cancellous bone, which has isotropic interconnection and orientation of the struts with stochastically determined beam lengths and bifurcation counts, without any repeated units. This study aims to investigate the effect of build direction of PBF-LB/M and compressive loading direction on mechanical properties in this lattice. A cubic model (25×25×25 mm³) with volume fraction about 40% was generated. The diameter and mean length of struts and the mean bifurcation count in the model were analyzed. The model was manufactured in each three principal axes of the model respectively, via laser beam-powder bed fusion (PBF-LB) using stainless steel (SUS316L). The samples were shaped into a cube of 20×20×20 mm³, ensuring that the center corresponded to the center of the model. The compressive tests were conducted in same or different direction of PBF-LB/M building and mechanical properties, which were elastic modulus, offset stress, plateau stress, and energy absorption from zero to 45% strain, were calculated. As a result of compression tests, the elastic modulus, offset stress, plateau stress, and energy absorption showed isotropic without dependence of build directions, which suggests tha t the lattice may reduce the effects of anisotropy by the PBF-LB/M building direction.

When a railway carbody is damaged significantly in the event of a level crossing accident, the train may not be available for an extended period of time due to the restoration of it. Aiming to achieve early restoration of a carbody following such an accident, the authors performed level crossing accident simulations regarding a replaceable crash-energy absorbing structure to be installed in front of the leading car made of aluminum alloy for use on conventional lines, and determined the specifications (e.g., load-displacement characteristics) of the crash-energy absorbing structure. Several types of prototype energy absorbing elements by ribbed circular tube were created and we performed the drop weight impact tests for the prototype ribbed elements to evaluate their performance. In this paper, finite element analyses corresponding to the drop weight tests were performed to compare the test and analysis results.

Three-layer aluminum composite with 10vol.%SiC-Al composite+3vol.%SiC-Al composite+3col.%CF/Al composite was fabricated by stacking and sintering mixed Al powder containing SiC particles, CF and Al powders. The composites were also hot-rolled, and the CF was oriented in the rolling direction. The three-layer composites after rolling have high strength and high ductility. The thermal conductivity was also high in the rolling direction. The three-layer composites were slightly inferior to the CF/Al composites but were comparable to a single Al block. It shows that the three-layer composites allows the production of a material with high strength and ductility while maintaining thermal conductivity.

Diffuse reflection of thermal radiation transfer by Mie scattering can provide a thermal barrier without conversion leading to conduction heat transfer. Applying such a system to internal thermal insulating materials of a stand-off thermal protection systems (TPS) provides an efficient means of preventing thermal radiation transfer. Porous MgAl₂O₄ ceramics have high thermal resistance and low emissivity. For this study, the heat transfer between the porous MgAl₂O₄ ceramics and the fibrous insulator was evaluated using the Lambert-Beer rule and the Fourie rule in a vacuum infrared lamp system for the radiation heating layer (Layer-1) and the back layer (Layer-2) to investigate the effect of the decrease in apparent heat transfer coefficient. The effect of using a low-emissivity material for the radiation heating surface and a low thermal conductivity layer for the second layer was confirmed to be more effective in reducing the apparent thermal conductivity than when a single material was used. It is suggested that the low emissivity layer on the radiation heating surface not only suppresses the heat input of the radiation but also suppresses the heat transfer in the thickness direction.

This study investigates the strength degradation of SiC fibers (Hi-Nicalon® Type S) and SiC/SiC composites produced by the PIP method (using Hi-Nicalon® Type S fibers) in high-temperature steam environments. SiC is known to oxidize in high-temperature steam, leading to strength degradation. SiC fibers and SiC/SiC composites with and without BN surface coating were exposed to dry and steam environments at 1000°C. Cross-sections of the exposed fibers were observed to measure fiber diameter and SiO₂ thickness. Tensile tests of SiC fibers and SiC/SiC composites were conducted before and after exposure to evaluate changes in tensile strength. The tensile strength of the SiC fibers degraded due to oxidation, with the most significant degradation occurring in the steam environment and without BN surface coating. BN surface coating decelerated the oxidation of SiC fibers and reduced strength degradation. Based on the obtained results, a method is proposed to predict the strength degradation of SiC/SiC composites.

This paper reports on vertical twin roll casting of aluminum alloy A7075. Aluminum alloy A7075 belongs to the highest strength alloys, and sheet is produced by rolling and extrusion. It is used in the aerospace industry and for special applications, but sheet is not readily available due to its high susceptibility to solidification cracking. Since twin roll casting can produce thin sheets directly from molten metal, it is possible to produce plate materials other than conventional alloys for sheet. In this study, thin sheets were produced using copper rolls, which have higher thermal conductivity than the iron rolls used in the previous study. The objective of this study was to use copper rolls with higher thermal conductivity to solidify the material faster and produce good thin sheets. The effects of roll peripheral speed and roll material on plate continuity, surface properties, and thickness were investigated. Experiments were conducted using iron rolls under five conditions of roll peripheral speeds of 1, 3, 5, 7, and 10 m/min and copper rolls under three conditions of roll peripheral speeds of 5, 7, and 10 m/min. In this experiment, thinning was possible under all conditions except 1 m/min with iron rolls, and thinning of aluminum alloy A7075 by vertical twin roll casting was possible.

This paper reports on the vertical twin roll casting of aluminum alloy A6061. Generally, thin aluminum sheet fabrication involves multiple processes and is expensive. In this paper, we investigate the conditions under which thin aluminum alloy A6061 sheets can be fabricated by the twin roll casting method, which can directly fabricate thin sheets from molten metal. The effects of roll speed on sheet continuity, surface properties, and thickness were investigated, and the characteristics of twin-roll casting were evaluated by observing the microstructure of the sheets and conducting Vickers hardness tests. The experimental apparatus was newly designed and fabricated to study continuous casting of thin sheets under low-speed and high-pressure conditions. The roll material is CCM-A, a copper alloy. Experiments were conducted under three conditions of roll peripheral speeds of 3, 5, 7, 10, and 12 m/min, and thin sheets could be produced under all conditions. The surface of the fabricated sheets consisted of metallic luster and cloudy areas, and fine solidification cracks were observed in some places.

Aluminum alloy-based composites are characterized by high strength, high rigidity, and high wear resistance, but they are difficult to machine using conventional methods. Here, we propose semi-solid forging as a new machining method for aluminum alloy matrix composites. Semi-solid forging has the advantage that near-net-shape products can be fabricated more cheaply and quickly than with existing processing methods, because the material is melted once and is formed into the product shape during the period between cooling and solidification. In this study, we investigated the feasibility of semi-solid forging of aluminum alloy-based composites. Experimental conditions were set as follows: solidus ratio of approximately 20 %, experimental temperature of 585 °C, load of 40 t, holding time of 10 s, die temperature of 20 °C, and stroke of 225 mm. The press speed was increased to 5 spm, 10 spm, and 30 spm, and the effects of the increase in press speed were evaluated from the results of appearance and microstructure observations. As a result of visual observation, when the press speed was increased to 5 spm and 10 spm, the semi-solidified slurry was observed to fill up to the edge of the specimen. However, when the press speed was set to 30 spm, the specimens became thinner than the other specimens. The microstructural observation showed that SiC tended to collect in the center of the specimen and decreased in the periphery at all pressing speeds, and no effect of pressing speed was observed.

SiC/SiC composites are attracting attention as high-temperature structual materials. However, SiC/SiC composites has low corrosion resistance due to vapor oxidation in high-temperature combustion atmospheres. To prevent steam oxidation thinning, protective coatings to protect SiC/SiC composites from the corrosion attacks are essential and critical technology. The influence of residual stress on the adhesion of protective coatings is essential. It is known well that pre-heating the SiC/SiC composite substrate before the thermal spray process affects the residual stress. In this study, the effect of the substrate pre-heating temperature on the adheasion strength in a protective alumin acoating sprayed on the SiC substrate was investigated by indentation tests.

In the field of diffusion bonding of steel materials, there is a need to develop processes for bonding at low temperatures and in air. In this study, low temperature joining of steel materials was performed using electrodeposited Ni as an intermediate material, which exhibits superplasticity. At first, we examined the adhesion of electrodeposited Ni to steel substrates. The adhesion shear strength of 452 MPa was achieved by subjecting the steel substrate to an alkaline bath prior to electrodeposition of Ni. Subsequently, the bonding was carried out at 450 °C in air and at a strain rate of 1.0×10−4 s−1. The bond strength was measured by shear test and achieved 102 MPa. The specimens fractured not at the bonding interface, but within the electrodeposited Ni. This finding suggests that the bonding process employed in this study effectively mitigated the detrimental effects on bondability resulting from the presence of an oxide film on the bonding surfaces. It is postulated that by appropriately polishing the bonding surfaces and augmenting the compressive strain, the amount of microplastic deformation at the bonding surfaces is increased, resulting in sufficient oxide film rupture at the bonding surfaces and enhanced bondability. This novel bonding process enables the bonding of steel materials at temperatures below the conventional diffusion bonding threshold.

In this study, we investigated the displacement of the coefficient of friction between the material and the mold in order to improve the current poor analysis accuracy of the forming process in which the material flows into the mold. First, a new testing machine was fabricated to measure the coefficient of friction under high-speed and high-pressure conditions that simulate actual press forming. The test specimens were coated with press oil on both sides, attached to the chuck of the testing machine, and the surface pressure was adjusted to an appropriate level by tightening a bolt. The specimen was then pulled out by the servo press at an appropriate speed after confirming that the load cell signal was displayed on the monitor. The friction coefficient was derived using the holding load and the pull-out load obtained here. As a result, a surface pressure dependence was observed under all conditions of this experiment. This is thought to be due to the fact that the lubricant is trapped in the uneven surface of the material, resulting in a smaller coefficient of friction. In addition, velocity dependence was observed in some conditions. This is considered to be due to a change in the ease of lubricant flow caused by the difference in test time.

In recent years, sintered compacts have been attracting attention in the field of automotive parts manufacturing. However, it has been reported that the mechanical properties of sintered compacts are inferior due to internal microporous and surface defects. To solve this problem, a processing process to increase the density of sintered compacts by cold forging has been investigated. The purpose of this study is to construct a finite element method (FEM) analysis of the powder molding and subsequent cold forging of a simple iron-based sintered body that simulates a part subjected to locally high loads. A floating die method was adopted for compaction. After powder compaction, the compacts were primary sintered and cold forged. The load-stroke diagram obtained from the cylindrical powder compaction experiment was then used to create a true stress-true strain diagram considering the density change. The analysis of the powder compaction and cold forging using the prepared true stress-true strain diagram showed that the load-stroke diagram and the relative density distribution in the surface region agreed with the experimental results.

In the industrial fields of machinery and automobiles, various seamless containers with bottoms, such as cylinders and square tubes, are processed. Deep drawing, which is one of the press forming methods, is used to process these seamless containers. Recently, to improve the functionality of containers, technological developments have been made to add value, such as high strength, light weight, corrosion resistance, heat dissipation, corrosion resistance, and formability. For example, clad materials, which are combinations of two or more materials, are used. Since it is possible to create functions and characteristics that cannot be obtained with a single metal, they are adopted as functional materials in various industrial fields. In the present study, we attempted to form a corrugated clad cup with a cross-sectional structure similar to that of cardboard. The test material was a highly corrosion-resistant pure titanium thin plate, a circular plate with a diameter of 80 to 90 mm. To form a corrugated shape, a roller ball die was developed in which steel balls were placed on the shoulder of the die. By combining it with a normal die, a corrugated clad cup was formed, and the formability was investigated. It was possible to form the clad cup with a regular wave shape. The maximum reduction in the sheet thickness was less than 10 percent. It was found that it was possible to form a lightweight, high-strength functional cup.

Neural network models corresponding to regular polygonal pyramids were generated, and tool paths for incremental forming were generated to improve forming accuracy. The learning shapes were regular tetragonal, pentagonal, and hexagonal pyramids. SUS304 sheets with dimensions of 150 mm x 150 mm x 0.3 mm were used as specimens. The Z-coordinates after positioning and the base circle radius lengths of each shape were used as shape date for learning. The base circle radius lengths were determined in three patterns with different height ranges, and three models were created. The Z-coordinate and the radius length of base circles were output as tool paths, and they were smoothed to improve surface accuracy. As a result, the forming accuracy of the formed parts excluding the flange, was improved, and the surface accuracy was improved by smoothing the generated tool paths.

Improving of forming limit of overhang shapes by incremental forming was conducted. A1050-O sheets which size of 150 mm x 150 mm and 0.5 mm thickness were used. Formed sample was evaluated with appearance, formability, strain distribution, and cross-sectional shape. By using multistage incremental forming, it was possible to form overhung shape with wall angle of 110°. For conical shape, maximum principal strain was measured in region near bottom of the formed sample. On the other hand, for square pyramid shape, the maximum principal strain was measured in area near the bottom of the formed round corner portion. Round corner portion of square pyramid shape was subject to strain in both z - direction and circumferential direction, and thus strain was larger than that in the side portion. For conical shape, the maximum wall angle of 111.5° was measured. In the case of square pyramid shape, maximum wall angle of 84.2° was measured for side and 104.6° for corner.

In this study, friction stir welding was performed by overlapping Aluminum alloy and Polyphenylene sulfide resin. Although it is considered difficult to weld metals and resins due to their different structures. The welding was confirmed by sandwiching carbon fibers for an anchor effect and resin powder, which is expected to be welded at low temperatures due to its fine particles. The welded specimens were evaluated by tensile shear tests and cross sectional observation to investigate the condition of the carbon fibers and powder. In addition, the without-probe welding process was also performed, in which the convex part at the tip of the tool, known as the probe, was not present. The advantages of the without probe method include the there is no distortion of the material due to the absence of the probes and that joining to thin plates is possible. Comparisons were made between this without probe method and the above-mentioned method with probe.

In recent years, with the widespread application of lightweight and high-strength materials in automobiles, mechanical joining technologies for dissimilar materials have been attracting attention. This paper presents a new mechanical joining technique for steel-aluminum alloys, which combines stamping and friction stir forming. First, an SPCE steel sheet was pierced by stamping with a chamfering punch to prepare a hole and placed against a backing plate after being turned over. Next, an A5083 aluminum alloy plate was put on it. Then, a rotary tool was plunged into the aluminum plate to cause the aluminum alloy to flow into the hole in the steel. A mechanical joint was performed thereby due to the tilt wall of the hole. The strength of the joint was associated with the cross-sectional shape of the hole, and it varies with punch-die clearance in the stamping. The relationship between the punch-die clearance, tensile-shear strength and cross-tensile strength was reported in the paper.

With recent advances in semiconductor technology, integrated circuits (ICs) have become more and more precise. Therefore, even in the low thermal expansion structure of semiconductor manufacturing equipment, the influence of minute thermal deformation cannot be overlooked. In this study, an easy-to-operate patch-type sensor with an EFPI sensor embedded in a CFRP laminate was devised, and the effect of embedding the sensor on sensing performance was experimentally verified. Measurements during manufacturing showed that the gap length variation of the EFPI was very small. On the other hand, the strain measurement results after manufacturing showed that the gap between the optical fiber and capillary during manufacturing was impregnated with resin, causing the gauge length to change. However, if the impregnation is sufficient, it is also clear that sufficient reproducibility is exhibited.

In recent years, aging infrastructure has become a serious problem. In order to repair aged infrastructures, repair work using FRP is being carried out by taking advantage of their high specific strength, excellent corrosion resistance and the possibility of on-side molding. For example, a pipe rehabilitation method using GFRP has been applied to aged sewers. This method involves underground work, so there is a possibility that uncured resin may remain due to the influence of underground water. In this study, the effects of the uncured layer thickness on the ultrasonic wave propagation characteristics of GFRP plates with an uncured layer on one side were investigated. As a result, it was found that in-plane ultrasonic velocity measurements were not sensitive to the uncured layer because in-plane ultrasonic waves mainly pass though the cured layer. It was also confirmed that the attenuation of high-frequency components due to uncured layer should be considered to understand detected waves.

In Resin Transfer Molding (RTM), the impregnation state of the fiber bundles significantly affects the quality of the molded product. Therefore, several methods have been proposed for monitoring the resin impregnation process. Our previous research demonstrated that real-time monitoring of the resin impregnation state is possible using ultrasonic techniques. In this study, we investigated the relationship between ultrasonic monitoring results and the mechanical properties of the molded products. A correlation was found between the ultrasonic monitoring results and the visual quality of the molded products. However, the mechanical properties of the molded products obtained from static tensile tests did not clearly correspond to the results of ultrasonic resin impregnation monitoring. As a results, ultrasonic monitoring can be used to evaluate the molded products with relatively good impregnation state where mechanical properties do not show significant variation in static tests.

Magnesium alloys have applications that take advantage of their dissolvable properties, such as sacrificial electrode materials and biodegradable materials. In this study, we focused on the dissolubility of magnesium alloy and attempted to develop high-strength extruded magnesium alloys with a controllable dissolution rate to suit the usage environment. As a result, by developing the melting and casting process in which Ni is added to the magnesium alloy to crystallize the Al-Ni-Mn intermetallic compounds, and the hot extrusion process in which these crystallized compounds are uniformly and finely dispersed, it has been succeeded in manufacturing the dissolvable magnesium alloy extrusions that combines dissolubility and high strength.

In this study, the monitoring method using ultrasonic waves, which has been developed in our laboratory for RTM molding, were applied to hand layup molding, and the effect of the FRP molding method on the mechanical properties of the molded products was evaluated. From the results of resin impregnation monitoring, it is confirmed that the reflected waves from the upper and lower interface of FRP layer could be detected not only in RTM molding but also in hand layup molding, indicating that ultrasonic resin impregnation monitoring is effective in hand layup molding as well. In addition, tensile tests of the molded plates with different molding methods showed that FRP molded by RTM method has lower mechanical properties than hand layup products.

Magnesium alloys are the lightest of all practical metals, and are relatively abundant in terms of resources and easier to recycle than plastics. However, compared to steel materials, magnesium alloys have low corrosion resistance and wear resistance, are prone to ignition, and are difficult to process, which are issues in their practical use. In the present study, the surface of magnesium alloys was modified by joining dissimilar materials using shot peening. The test material was an extruded magnesium alloy AZ31, and the workpiece was 50 mm in diameter and 5 mm thick. The dissimilar materials were laminated materials consisting of a resin sheet containing ceramic powder and a corrosion-resistant metal foil. The ceramic powder was alumina with a diameter of 0.1 mm. The corrosion-resistant metals were pure aluminum, pure titanium, pure copper, and pure nickel. The joining was performed using a cast steel shot with a diameter of 1 mm at a projection speed of 60 m/s and a projection time of 10 s. The joining property was evaluated by observing the cross section near the surface and by bending tests, and the wear resistance was evaluated by wear tests. The use of pure aluminum foil as an insert material and warm processing were effective in improving the joining property of the dissimilar materials. Additionally, wear tests showed improved wear resistance.

Fluoroplastic materials are difficult to decorate with normal printing methods because they repel ink and have poor adhesion due to its high water repellency. Therefore, when applying laser marking, which requires no pretreatment and allows high-speed fine processing, the surface irradiated by the laser is prone to thermal decomposition due to its high energy absorption and heat generation. Based on a heat transfer engineering concept, the work surface was cooled by thermal conduction using a laser-transparent heat sink to prevent overheating, while laser radiation caused foaming and discoloration limited to just below the surface, achieving the desired marking..