FCC-HCP martensitic transformation is a known cause of transformation-induced plasticity in high manganese steels and shape memory effects in Fe-Mn-Si shape memory alloys. This paper describes the shape memory effect due to FCC-HCP martensitic transformation in Cr₂₀Mn₂₀Fe₂₀Co_40-xNi_x high-entropy alloys.Deformation behavior and low-cycle properties were investigated for Co51-xCr₂₃Mo₆Ni_x medium-entropy alloys. Alloys that underwent FCC-HCP martensitic transformation simultaneously with deformation twinning exhibited improved low-cycle fatigue life.

We will present several studies of how growing multicellular tissues shape organs, combining quantitative mechanistic models with plant experiments with respect to cell shape and division patterns. We found that the outlines of the root tip best fitted to the catenary curve across flowering plant species. Based on the physics of catenary curves, we predicted in silico and verified in vivo that the anisotropy of the cell division at root tips and the absence at the perifery are necessary and sufficient conditions for catenary-shaped organ formation. Moreover, such localized cell divisions is decoded into a globally oriented mechanical stress to shape the vascular tissue symmetry, representing a reasonable mechanism controlling the symmetry in tissue lacking cell fluidity. Finally, we will report the current progress of 3D multicellular mechanical model.

In snowy regions, trees are exposed to the mechanical stress caused by accumulated snow, therefore the effective strategies are requested for reduction of branch breakages. Various methods have been employed to prevent snow-related damages by means of support props, hanging for branches, or snow removals from the trees. During severe winter seasons with substantial snowfalls, the snow removals are physically demanding works for farmers, and the efficient and labor-saving snow damage prevention methods are required. In this study, mechanical analyses of the tree branches with various snow accumulation configurations by using the finite element modeling. The boundary conditions were considering the load pattern for assuming partial snow removal and the constraint through the implementation of support props. As the results, accurately evaluating the distribution and magnitude of bending moments on tree branch models were performed. And the suitable snow removals for the snow load reduction were proposed in the term of branch breakage prevention.

Tree branches are deformed with large deflection by mechanical loads due to wind, rain and snow weight, and also deformed by own weights. The shape of fruit tree branches is artificially planned and manually formed in cultivation process. The analyses of tree branch deformation behaviors are important for the sustainable fruit cultivation to prevent tree damages and avoid branch failures. In this study, a numerical analysis method for large bending deflection was used to evaluate the deformation of tree branch focusing on the self-weight load. The branch models were created as cantilever of straight or tapered shape with a constant elastic modulus. As the simulation results, the large bending deformation in downward direction of the long branch limited the extension length for horizontal direction. This simulation was available to estimate growth geometries of branches with bending deformation and could be used to predict the future branch configuration relating to tree vigor.

Liposomes are closed lipid bilayer membranes that have attracted attention as drug delivery carriers and cellular molecular robots. Since their mechanical properties are essential for their functionalization for such purposes, a method to evaluate their mechanical properties is desirable. Here we applied the micropipette aspiration method for liposomes prepared with two different compositions (POPC/DOPG/Cholesterol = 9/1/1 (molar ratio); Condition 1, POPC/DOPG/Cholesterol = 5/5/1; Condition 2) and numerically calculated the mechanical properties of these liposomes held at the tip of the micropipette. The mechanical properties of the aspirated liposomes, such as instantaneous elastic modulus E₀, equilibrium modulus of elasticity E_∞, and viscosity μ, were estimated by the standard linear viscoelastic model: E₀ = 239.0 ± 106.6 Pa, E_∞ = 157.0 ± 67.2 Pa, and μ = 49.7 ± 46.8 Pa･s for liposomes of Condition 1, and E₀ = 100.1 ± 84.0 Pa, E_∞ = 53.2 ± 45.3 Pa and μ = 57.1 ± 48.1 Pa･s for those of Condition 2. There was no statistically significant difference in the results between Condition 1 and Condition 2. We discussed these results along the references regarding lipid composition and solvent incorporating in the liposome membrane. The finite element method on liposome aspiration showed that the diameter of a micropipette tip holding the liposome has little effect on the liposome aspiration length. In the future, we will clarify the effect that membrane compositions and solvent on the mechanical properties of liposomes.

Transforming a flat physical sheet into a three-dimensional curved surface is a fundamental step for constructing functional shape-shifting surfaces. Among the methodologies relying on the emergent concepts like origami, kirigami and knitted fabric, a traditional cellular solid based meta-plate provides a versatile tool for creating a doubly curved surface by a planar bending actuation. By combining digital fabrication, physical experiment, finite element simulation (FES) and linear elasticity theory, we demonstrate how such a cellular “meta”-plate can morph into a doubly-curved shape. Generalizing the classical Lamb’s theory for the anticlastic effect in a thin elastic plate to our cellular meta-plate, we develop a scaling law for the crossover length below which the doubly-curved surface appears as b_c～b_Lamb/√ρ, where b_Lamb～√Rw, with the radius of curvature R and the plate thickness w, and ρ is the relative density of a given cellular geometry. The prediction is verified by our experiment and FES. The proposed framework is generic, highlighting the fundamental physical aspects of the mechanics of such shape-morphing surfaces, in potential application to a broad of meta-sheets.

Polyamide is a semi-crystalline polymer with different nano-micro structures and macroscopic mechanical properties depending on thermal history. In this study, polyamide specimens were prepared under isothermal and annealing conditions. The nano-micro structure was evaluated by wide angle X-ray scattering, small angle X-ray scattering (SAXS), Differential Scanning Calorimetry, and polarized light microscopy. The SAXS measurement revealed the difference of nano-micro structures in PA6 with different thermal histories. The macroscopic mechanical properties were measured by uniaxial tensile tests. Based on the measured results, the relationship between nano-micro structure and macroscopic deformation behavior was discussed and evaluated. Under the high-temperature isothermal condition where spherulites are formed, a tendency to fracture was observed without stretching after the yield stress. On the other hand, under the annealing conditions where crystal morphologies other than spherulites were formed, stretching was observed until the late stage of deformation even after the yield stress. The relationship between the lamella thickness obtained from the SAXS measurement and the maximum stress obtained from the tensile test was confirmed to be correlated under both the isothermal and annealing conditions for PA6. On the other hand, the relationship between the maximum stress and the lamella thickness of PAMXD10 was represented to be different from that of PA6.

Extended thin sheets, such as clothes and papers, easily deform under gravity and form a variety of patterns, including wrinkles, draping, and folding, as we observe on a daily basis. The equilibrium shapes of those sheets are determined by the balance between the elasticity, gravity, and external contact forces. To clarify the mechanism of the formation of undulating patterns in a heavy sheet, we investigate a so-called “blister test’’, in which a thin sheet on a rigid flat substrate is pushed at its center from below, by combining mechanical testing, optical measurements, and theory. As the vertical displacement is increased, we observe a formation of a circular delaminated region, then a wrinkled pattern, and radial crack-like delaminated patterns that are asymptotically close to the draping. We also observe an anomalous force response, such as a discontinuous change of the vertical force when the crack front reaches an edge of the sheet. We rationalize our experimental findings with a scaling argument based on the Föppl–von Kármán’s equations.

Soft robots or soft actuators can achieve complex and geometrically nonlinear deformation from simple energy inputs. Examples of energy resources are air and complex fluids. The mechanisms behind their flexible deformation are compliant structures, such as elastomer and slenderness of structures. Snap-through instabilities of slender structures enable us to design instantaneous and predictive motions of soft robots. Despite various robots and actuators, building the framework to optimize their dynamic functionality is still challenging to date. In this work, to clarify the basic mechanism of jumping soft robots, we elucidate the jumping mechanism of a hemispherical shell driven by pneumatically-controlled snap-through buckling. We study the jump height of the shell on both rigid substrates experimentally. We show that the simple scaling argument could be useful in optimizing the dynamic behavior of soft robots. Although the hemispherical shell has a seemingly simple geometry, its dynamical performance primarily relies on a complex interplay between the elasticity, geometry, and the interaction with the ground.

A simplified residual stress analysis model using the thermal shrinkage technique was developed for metal additive manufacturing of alloy tool steel for hot molds by establishing a method for setting thermal shrinkage parameters that takes into account phase transformation behavior and preheating effects. Using the developed model, we predicted the residual stress reduction obtained by changing the inter-pass temperature and preheating temperature. Meanwhile, residual stress measurements using the contour method were performed using the specimens those were manufactured under the same conditions as in the numerical analysis above. Through the comparison of these results, it was confirmed that the change trends of residual stress distributions with the inter-pass temperature and preheating temperature were in good agreement between numerical prediction and measurement, and the usefulness of the simplified residual stress analysis model for metal additive manufacturing developed was also demonstrated.

In automobile manufacturing, application of laser welding to carbon steel thin plates is an important issue to achieve weight reduction for improved power efficiency. However, solidification cracking can occur near the edge of a carbon steel plate. In this study, effect of distance from an edge of the steel plate (offset) on solidification cracking during laser welding was investigated for high-carbon steel. Melt-run welding on the S45C thin plate was performed under five offsets varying from 1.5 mm to 5.5 mm with an intervals of 1.0 mm. A steel plate was fractured along a weld line for the four offsets except 5.5 mm. A liquid film was observed on most of the fracture surfaces, while a region without the liquid film was present at a bottom base of the fracture surface. Therefore, it was considered that the crack was initiated at the bottom base of the steel thin plate along the weld line. In addition, in a thermal-elastic-plastic simulation using the finite element method, a plastic strain increment became large both at the center and, front and back surfaces of the plate for the offsets of 1.5 and 2.5 mm. Contrary, that at the center of the plate almost disappeared for the offsets of 3.5 mm and more. Furthermore, the plastic strain increment decreased as offset increased. Consequently, it is concluded that increasing offset reduces plastic strain increment on the cross-sectional plane along a weld line, leading to prevent solidification cracking.

Ttrans-Varestraint test is often used to evaluate the susceptibility to solidification cracking. Recently, however, it has become clear that the amount of strain at the rear edge of the molten pool produced in the Trans-Varestraint test is much larger than the theoretical solution obtained using the radius of curvature of the bending block and the thickness of the specimen based on material mechanics. In this study, the effects of external loading and heat input conditions on the strain behavior during the weld solidification process were quantitatively evaluated by simulating this test using finite element analysis. The results showed that the amount of strain at the rear edge of the molten pool depends on the welding heat input conditions, and that the strain increase behavior at the rear edge of the molten pool can be systematically evaluated by welding parameters concerning the welding heat input conditions.

In order to quantitatively discuss the insert material dimensional conditions in reconstitution by welding of reactor pressure vessel surveillance test specimens, the effect of heat recovery zone and heat-affected zone at the welds of the reconstituted specimens on the Charpy impact test results were investigated through numerical analysis. The results suggested that it is necessary to pay attention new conditions comparing the current standards, when welding was performed using a high energy density heat source, where the heat-affected zone and heat recovery zone are expected to be reduced due to lower heat input. Meanwhile, the effect on the Charpy impact test results when the plastic zone generated in the test before reconstitution was included in the insert material was examined by the numerical analysis. Based on the results, the dimensional conditions of the insert material when including the remaining plastic zone were also discussed.

A method for evaluating the displacement and strain field of the solidification zone was developed that uses X-ray transmission images, which were obtained by high-brilliance synchrotron radiation. The developed method is aimed to be applied to time-series X-ray transmission images, for which it is difficult to evaluate displacement and strain fields using the general DIC (Digital Image Correlation) method and combines the evaluation of optical flow using the Lucas-Kanade method and the mapping technique to grid points using the Moving Least Squares (MLS) method. Furthermore, by applying this method to actual observations, it was shown that the microstructural state, temperature state, and strain state of each region can be evaluated simultaneously. By utilizing the developed evaluation method, it will be possible to understand the behavior of welds in the high temperature range, which has been difficult to understand in the past.

To ensure the reliability of steel welds and the integrity of steel structures, it is important to detect defects by using ultrasonic testing and sizing their dimensions with high accuracy. Recently, Phased Array Ultrasonic Testing (PAUT) and Time of Flight Diffraction (TOFD) have been developed. Even when these methods are used, it is said that the location and shape of defects in welded joint affect detectability and sizing accuracy, so further accumulation of the knowledge on these effects is desirable. In this study, the detectability and sizing accuracy of defects were evaluated using PAUT and TOFD to steel multi-pass welded joint specimens with various artificial defects. The types of defects were internal defects, surface defects, and back-side defects, and the shapes were planar and cylinder. The defect detection results show that both methods can detect planar defects, while TOFD was superior in detecting internal cylinder defects. The accuracy of defect length sizing for planar defects was good in both methods. On the other hand, it was considered that the curved surface of the defect was a factor for the poor accuracy of defect length sizing. The accuracy of defect height sizing for planar defects was good in both methods regardless of the defect location, and TOFD accurately sized the height of cylinder defects.

Ductile cast iron (DCI) is characterized by an extensive strength property, which is obtained by controlling microstructural factors such as graphite conditions, matrix structure and so on. Therefore, it is likely that these microstructural factors are closely related to hydrogen storage capability and embrittlement as well.

In this study, we performed various heat treatments on the three kinds of DCIs with ferritic-pearlitic matrix structure. The effects of heat treatment and microstructural factors on hydrogen storage capability and hydrogen embrittlement in tensile fracture were investigated using hydrogen charged as-cast and heat-treated materials.

We have shown from first-principles calculations that hydrogen concentration at the interface between the aged precipitate particles (η phase (MgZn₂), which is the strengthening phase of the Al-Zn-Mg alloy, causes semi-spontaneous interfacial debonding. Although this debonding of the precipitate is proposed as the mechanism of hydrogen-induced quasi-cleavage fracture, we have yet to directly observe actual interfacial debonding. It is also unclear how interface debonding leads to micro-damage. In this study, we will experimentally clarify the relationship between nano-scale behavior such as interface debonding and macro-scale hydrogen embrittlement such as crack propagation. A black nanovoid-like contrast was observed just below the fracture surface in the vicinity of a white contrast, which is a Zn-rich small particle. Comparing the region just below the fracture surface and the region 500 nm away from the fracture surface, more nanovoids were observed just below the fracture surface. The formation of quasi-cleavage fracture surfaces due to hydrogen embrittlement would be affected by nanovoids.

The present study utilized multi-scale 3D characterization techniques, namely, X-ray CT and FIB-SEM serial sectioning, and STEM observations to understand hydrogen-related intergranular fracture behavior in high-strength as-quenched martensitic steel. From the fracture toughness tests, we found that the crack-growth resistance decreased with increasing hydrogen content. However, the hydrogen-related intergranular cracks propagated in a stable manner even at a high hydrogen content. The X-ray CT results indicated that the fracture propagated discontinuously with a certain area of un-cracked ligaments. The crack propagation tended to be more continuous with increasing hydrogen content. The microscopic 3D analysis using FIB-SEM serial sectioning revealed that there were many fine un-cracked ligaments at the sub-micrometer scale. These fine un-cracked ligaments were not observed in the uncharged specimens. The deformation microstructure was locally evolved around the hydrogen-related crack tip. Accordingly, we can propose that the local plastic deformation and discontinuous crack propagation resulted in an apparent stable crack propagation.

When using metallic materials in hydrogen equipment, it is important to consider the issue of hydrogen embrittlement. By controlling the graphite state and microstructure of spheroidal graphite ductile cast iron, it is possible to modify its strength properties and create a material that is less susceptible to hydrogen embrittlement. In this study, we prepared ductile cast irons with different graphite sizes by adjusting the cooling rate during casting. Additionally, we tailored the matrix structure to either ferrite or pearlite through heat treatment and controlled the chemical compositions accordingly. Hydrogen absorption measurements and tensile tests were conducted on the hydrogen-charged ductile cast irons. The relationship between the microstructure and hydrogen absorption was investigated, and the hydrogen embrittlement in the tensile fractures of ductile cast iron was discussed.

Rotating bending fatigue tests were conducted on the specimens with artificially introduced defects to investigate the effect of casting defects on the fatigue strength of austenitic ductile cast iron (Ni-Resist). Either of three kinds of defects: a single drilled hole, a 3-hole defect or a circumferential notch, was introduced onto the specimens to simulate casting defects with various shapes and sizes.

After investigating the impact of such small defects, the high-cycle fatigue properties of both hydrogen-charged and uncharged materials were examined.

Aged and as received KA-STPA28, Japanese standard of Gr. 91 steel for high temperature piping, steel were tested by standard and ultra miniature creep (UMC) testing method. Time dependence of creep rate of each test were compared and the results were discussed with scanning electron microscopy (SEM) observation results of fracture surfaces and cross section of specimens. Creep rate of UMC specimens at the initial stage of tests were about 5 times higher than those of round bar specimens. By comparing relationship between modified minimum creep rate and rupture time of each tests, in case of UMC specimen, excessive creep strain corresponded to those at 3% of rupture time was considered to be accumulated during initial stage of tests. Duration time between when specimen showed corresponded to minimum creep rate and rupture was relatively longer in case of UMC specimen because of higher ductility showed at fracture. Specimen surface oxidation was well suppressed by employing appropriate Ar gas flow rate.

In this study, conducting an ultra-miniature creep (UMC) test in an argon gas environment on a modified 9Cr-1Mo steel, the size effect on creep-rupture life was discussed from the viewpoint of oxidation thinning. As a result, the maximum thickness of the oxide layer produced on ruptured UMC specimens was found to be less than 2μm. Also, calculating a life reduction rate due to the oxidation, the rate was less than 10 % at the thickness of 2μm. Therefore, it could be indicated that the oxidation had little influence on the rupture time of the UMC specimen at least within several thousand hours.

Establishment of fatigue testing standard for resin materials is discussed in this study, since no suitable standardization of low cycle fatigue tests for the materials has been proposed. Uniaxial fatigue tests were conducted to clarify the effect of various factors such as loading on fatigue strength of resin materials. Measurement of strain using a extensometer was also discussed.

Equipment used in power plants undergo multiaxial loading in high-temperature environments. Therefore, a multiaxial creep investigation is important for high temperature equipment. The test method using cruciform specimen is one of the testing methods for multiaxial creep. This test method has the advantage of a wide range of multiaxial stress tests. The miniaturization of the testing specimen size will permit us to conduct testing on the small samples of materials that can be obtained from actual structural. In this paper, focusing on the shape design of the miniature creep cruciform specimen is discussed. For reducing the size of specimen, the effect of shape dimension was investigated using finite element analysis.

The small punch (SP) creep test was conducted using a newly developed testing machine capable of conducting SP test with a small disk type specimen in a high temperature hydrogen gas atmosphere. The test material used was Type 304 austenitic stainless steel. The tests were carried out at a temperature of 600°C in a hydrogen and argon gas atmosphere with an absolute gas pressure of 0.12 MPa. The experimental results showed that the SP creep rupture time was shorter in the hydrogen gas atmosphere compared to the argon gas atmosphere. This difference in rupture decreased with decreasing applied SP load. Consequently, there was no significant difference at the load level of 486 N, which was the lowest SP load in this test. It was found that the F/σ value, which was necessary parameter for comparing SP results with traditional uniaxial creep rupture results, decreased with decreasing applied SP load. The F/σ value for hydrogen gas atmosphere was consistent larger than that for argon gas atmosphere, and this larger value was closely associated with higher rupture ductility in the hydrogen gas atmosphere.

The small punch test (SPT) is a miniature test that utilizes small-diameter disk specimens, typically around 10mm in diameter. This study investigated the conversion equations proposed for determining the tensile properties of metallic materials using the SPT for their applicability to resin materials. The test specimens included thermoplastic resins such as polyamide 6 (PA6), polyethylene terephthalate (PET), polycarbonate (PC), polytetrafluoroethylene (PTFE), and thermosetting resins such as epoxy (EP) and phenol (PF). The maximum loads obtained from the SPT were found to be in the order of PC, PET, PA6, PF, EP, and PTFE, which significantly differs from the order of tensile strength. The 0.2% proof stress conversion from the SPT was determined by using the intersection point of the SP curve and a parallel line offset from the initial thickness, and the load was obtained by displacing the initial slope of the SP curve by a factor of t/10. In the SPT results for EP, the displacement velocity dependence was confirmed, as was observed in the tensile test. However, the increase in strength in response to the displacement velocity was higher for the conversion value obtained from the SPT than that from the uniaxial tensile test. This difference is presumed to be due to the uniaxial stress in the tensile test, whereas the SPT is multiaxial stress, and the sensitivity to displacement velocity differs.

This study experimentally investigates the effects of thermal treatment on the elastocaloric effects and transformation behavior of superelastic Ni-Ti alloys, with the aim of developing eco-friendly green cooling technologies as an alternative to conventional methods. We focused on tube-shaped superelastic Ni_50.8Ti_49.2 (at.%) alloy, observing that short-time aging at 400°C resulted in improved mechanical properties and enhanced elastocaloric effects. It was suggested that these changes in the properties of the Ni-Ti alloy are primarily due to the precipitate morphology of Ni₄Ti₃ nanocrystals in the NiTi single phase, which significantly impacts the transformation temperature defining cooling performance. The ability to manipulate the austenite finish (A_f) temperature range, as evidenced in our findings, suggests potential for the development of cascade elastocaloric cooling systems through thermal treatment of a single composition Ni-Ti alloy. This study underscores the potential of Ni-Ti based superelastic shape memory alloys for future environmentally-friendly cooling applications.

Additive manufacturing, as the next-generation processing technology, has the characteristic of being able to create complex parts in near-net shapes. The application of additive manufacturing is expanding in the development of space exploration, which require high strength material and complex structure. In this study, we used Directed Energy Deposition (DED), a category of additive manufacturing, to fabricate light metal specimens composed of an aluminum alloy (Al-10Si-0.4Mg) and a titanium alloy (Ti-6Al-4V). Hyper velocity impact experiments were conducted to simulate space debris collisions using a two-stage light gas gun. Further, using the layer-by-layer fabrication characteristic of additive manufacturing, we also explored the production of functionally graded materials (FGMs) of aluminum and titanium, which were difficult to join with traditional welding methods.

A bicycle crank gear with hollow cylindrical elastic bodies has been developed to increase efficiency driving bicycles. Hollow cylindrical elastic bodies built in a crank gear are compressed by pedaling, and elastic strain energy stored in the bodies leads to improve accelerating performance of bicycle and to reduce muscle strain of human during pedaling. However, mechanism in the elastic bodies inside the gear has not yet been clarified, and its theoretical clarification is required. Assuming that a hollow cylindrical elastic body built in a bicycle crank gear is subjected to oppositely distributed pressures on the outer boundary, we have theoretically analyzed the elastic behavior of the cylinder. Considering deformation of the hollow circular cylinder in a bicycle crank gear compressed by pedaling does not recover perfectly, numerical calculations have been carried out and an effect of inner radius on changes of elastic strain energy, shrinkage and rigidity in the cylinder has been evaluated quantitatively.

Fatigue properties of an additively manufactured metal lattice structure were experimentally investigated. Fatigue specimens that have a lattice structure in their gauge section were manufactured using an aluminum alloy, AlSi10Mg, by selective laser melting powder bed fusion. The lattice structure consisted of simple cubic unit cells. Fatigue tests at room temperature in air were conducted under load control conditions with a frequency of 10 Hz and a load ratio of R = 0.1 (tension-tension) or R = 10 (compression-compression). The following achievements are reported in this manuscript: demonstrating the specimens and the testing methods; collecting basic fatigue data; understanding fundamental mechanisms of deformation and failure; evaluating an applicability of a conventional fatigue life prediction law.

A balloon-expandable stent is a mesh shape cylindrical medical device that secures blood flow by inserting and expanding a stenotic part of a blood vessel using a catheter. Co-Cr-W-Ni alloy is widely used as platform materials for balloon-expandable stents because of its excellent strength-ductility balance and corrosion resistance. Since the strut thickness of a balloon-expandable stent is about 80 to 110 μm, the grain size of the platform material is considered to have a great effect on its mechanical properties and plastic deformation behavior. In this study, we investigated the relationship between microstructure and mechanical properties in the Co-Cr-W-Ni alloy tube.

The meshed structures, whose properties vary depending on the mesh shape, are widely used in rockfall protection engineering. At present, the main method for evaluating the out-of-plane deformation behavior of meshed structures are to obtain equivalent properties by analysis, and there are few theoretical considerations. Therefore, the purpose of this study is to propose an evaluation method for out-of-plane deformation behavior based on theoretical considerations and to clarify the scope of its application. In this study, the equivalent properties of various meshed structures were calculated and used to predict the behavior of the meshed structures under out-of-plane loading. The out-of-plane behavior of various meshed structures was predicted theoretically, and the prediction accuracy was validated by using the finite element analysis (FEM).As a result, an efficient method of evaluating out-of-plane deformation according to the size of deformation was proposed and validated.

From the viewpoint of digital transformation and automation of manufacturing, manufacturing with 3D printers is attracting attention. We have developed the "GelPiPer," a platform for the fabrication of gel materials, because the ability to output a variety of materials and shapes at any location can reduce modeling time and logistics costs. In this study, we attempted 3D modeling of particulate double-network gels using a low-cost 3D gel printer and open-source software. The combination of digital transformation and gels is expected to improve the speed of gel fabrication and produce gels of the same quality, and to serve as a basis for gel processing technology in the fabrication of soft materials as well as a foundation for soft manufacturing. Two types of 3D gel printers were used in this study: a free-surface type and a pump type. As a result of using different methods depending on viscosity, it was possible to output a material with an elastic modulus more than three orders of magnitude lower than that of plastics widely used for 3D modeling in the shape desired by the user.

In this paper, the mechanical properties of two-dimensional zig-zag structure subjected to in-plane large compressive load was investigated. This structure has two counterphase layers consisted of inclined plate. The stiffness and the stored strain energy during the deformation were solved analytically based on the flexible bar theory proposed by Fly (1969). In particular, the effects of micro-architecture of the zig-zag model on these mecahnical properties were discussed. The obtained theoretical results agree fairly with FE results.

In this presentation, a numerical method for estimation of the apparent strength of a unidirectional fiber reinforced composite plate considering random fiber arrangement under the transverse tensile loading is introduced. One of the features of the presented method is the consideration of both random fields of the local apparent elastic modulus and local strength. Those apparent properties take the influence of the microstructure of composites, but the relationship of them has not been well established yet. From this fact, the influence of the correlation between them is investigated. At first, the outline of the problem setting and the methodology are introduced, and the correlation of them is discussed. Then, a strength analysis of a composite plate is demonstrated, and the influence of the presented issue on the multiscale stochastic analysis of composite is discussed.

Based on the asymptotic homogenization theory, the multiscale finite element method (FEM) was employed in this study to investigate the mechanical properties of movable crosslinked polymer-based cellulose composites. Additionally, a design method was proposed to predict the mechanical properties under different cellulose morphologies. The study of mechanical properties primarily focused on fiber morphologies and matrix types, including factors such as fiber content, fiber aspect ratio, and different matrices. The results indicated that the elastic modulus of the composites increases with the rise in fiber content and fiber aspect ratio. Among the various matrices, the matrix with the addition of movable cross-links exhibited the highest elastic modulus. To quantify the influence of each factor on the performance, the fiber contribution rate based on strain energy was introduced. Subsequently, a predictive program, based on the linear approximation of the composite mechanical properties, fiber contribution proportion, and matrix elastic modulus, was designed and proposed. Upon validation, within a maximum error range of 10%, this design method demonstrated the ability to predict the elastic modulus of composite materials with different fiber contents and fiber aspect ratios.

In this paper, the dynamic fracture problem of a functionally graded piezoelectric material strip (FGPM strip) containing an infinite row of cracks normal to the interface between the FGPM strip and a homogeneous layer is considered. It is assumed that the electro-elastic properties of the FGPM strip vary exponentially in the thickness direction, and that the crack faces are under normal mechanical impact loadings. The integral transform techniques and the dislocation density function are employed to reduce the problem to the solution of a singular integral equation. The dynamic stress intensity factors of the internal crack and the edge crack are computed and are presented as a function of the normalized time for the various values of the nonhomogeneous and geometric parameters.

Multiferroic composites consisting of ferroelectric and ferromagnetic materials are attracting attention as a breakthrough functional material for the development of innovative devices because of their ability to produce magnetoelectric (ME) effect through mechanical strain transfer in heterostructures. In recent years, the development of polymer composites with piezoelectric (PE) and piezomagnetic (PM) particles dispersed in thermoplastic polymers as matrix has been active, with potential applications in wearable or printable devices. However, the presence of polymers in the strain transfer between PE and PM particles significantly reduces their electromagnetic properties. In this study, we applied the periodic polarization inversion structure, which was discovered by multiscale optimal design of ME ceramic composites, to PE and PM particle-dispersed polymer composites. As a result, it was found that the periodic polarization inversion structure is effective for PE and PM particle-dispersed polymer composites, and improves the transverse ME effect by a factor of 8.3 compared with the conventional stacking structure.

Magnesium (Mg) has attracted attention because of its light weight, abundant resources, and large maximum hydrogen absorption capacity of 7.6 wt.%. This study investigated the hydrogen absorption-desorption properties of Mg-based hydrogen storage alloys with Fe and reduced graphene oxide (rGO), i.e., Mg-Fe, Mg-Fe-rGO-1, Mg-Fe-rGO-2 that were prepared by mechanical alloying. PCT curve measurements showed that hydrogen was absorbed and released from all samples at 280 ℃ and 250 ℃ and at the maximum hydrogen pressure of 0.99 MPa. Mg-Fe-rGO-1 showed the highest maximum hydrogen absorption of 5.23 wt.%, which was close to the maximum hydrogen absorption of 7.6 wt.% for Mg. DSC measurements showed that hydrogen was released from all samples, and the hydrogen release temperature was lower than that of commercial MgH₂. In particular, Mg-Fe-rGO-2 showed the lowest hydrogen desorption temperature. The hydrogen desorption temperature of Mg-Fe-rGO-1 was not reduced as much as that of the other samples because the catalytic effect of Fe and rGO was not fully demonstrated due to the many rGO defects generated during MA.

Developing a numerical method to accurately simulate the brittle crack propagation phenomenon is crucial for ensuring the safety of large-scale steel structures. In this study, we have developed a strategy for analysing high-speed crack propagation in three-dimensional (3D) solids on the basis of the s-version finite element method (s-method). In the proposed strategy, the entire structure is represented by a relatively coarse global mesh, while the fine local mesh is defined in the vicinity of the crack front as an ideal structured mesh aligned with both the crack front direction and crack propagation direction to accurately simulate the crack propagation. The proposed strategy was verified by evaluating the accuracies of the local stress in dynamically propagating circular crack problems as well as those of the stress intensity factor. The results demonstrate that the proposed strategy provides unprecedented accuracy and efficiency of simulating high-speed crack propagation in a 3D solid without requiring any complicated remeshing procedures. Therefore, the proposed strategy has potential as the basis of a numeral framework for analysing high-speed brittle crack propagation problems.

In this study, a numerical simulation model that can accurately and rapidly reproduce high-speed crack propagation and arrest behavior in a three-dimensional plate structure was developed based on the s-method of finite element method. High-speed crack-arrest experiments were conducted on a specimen fabricated from acrylic resin (PMMA), and the failure criteria based on the dynamic stress intensity factor were identified through generation phase analysis using the developed model. The validity and effectiveness of the developed model were demonstrated by comparing the experimental results using PMMA with the predictions using the developed model.

The intermediate heat exchanger of high-temperature-gas-cooled reactor for hydrogen production is a component that exchanges heat between primary helium gas (950℃) and secondary helium gas (300℃). This component is composed of center pipe, manifold tube plate (perforated structure) and helical heat transfer tubes, all made of nickel-based alloy Hastelloy XR. In this study, detailed inelastic analysis considering 500,000 h operation (100 cycles of 5,000 h hold time) was carried out to clarify the characteristics of inelastic behavior and creep-fatigue damage. Considering the features of these inelastic behaviors, applicability of simplified creep-fatigue evaluation method based on elastic analysis results and elastic-follow-up coefficient, which has been utilized in the Fast Breeder Reactor design guideline, is examined. Creep damage by the simplified creep-fatigue evaluation method is found to give a conservative prediction within a factor of 2, when compared with the prediction by the detailed inelastic FE analysis.

The elasto-viscoplastic deformation behavior is influenced by the temperature in general. The constitutive equation of the subloading-overstress model is extended to incorporate the temperature dependences of Young’s modulus, the isotropic hardening function and the evolutions of the kinematic hardening variable and the elastic-core and the thermal strain for metals for the range of temperature in the engineering practice in this article.

Carbon nanotubes (CNTs) and their related products have been extensively studied in the fields of cutting-edge technologies such as aerospace materials and gas sensors owing to its excellent physical properties, mechanical strength, and electrical performance. Currently, extensive studies on CNTs made it possible to achieve the stable, efficient, cheap, and large-scale manufacturing of CNTs, thereby it has been regarded as an important research topic. This study investigated the influencing factors of the experimental environment on the growth of carbon nanotubes through experimental results. After summarizing the influencing conditions and evaluating the thermal and gas flow rates optimization, CNTs with a height of 51 μm were successfully grown by controlling the temperature in repeated experimental, using the electron evaporation device and chemical vapor deposition. it was observed through scanning electron microscopy that the growth morphology of CNTs was shown and the experimental methods to improve the success rate of CNTs growth were proposed.

The authors have developed the finite element (FE) analysis program based on the implicit method to consider elasto-plasticity and cracking of brittle materials. In this study, we added thermal stress analytic function to the program because it is indispensable to simulating the mechanical behavior of the refractory under high temperatures. We focus on the sandwich structure consisting of two materials as a numerical example and derive its theoretical solution of displacement, stress, and strain to verify the validity of the thermal stress analysis. This paper shows the verification of the FE program by comparing numerical results with the theoretical ones. In addition, this paper shows the effect of the FE division and the length of the sandwich structure on the numerical results.

Recently, austenitic stainless steels are being applied to hydrogen tanks and piping due to the increasing carbon neutrality of hydrogen. The results of low strain rate tensile tests (SSRT) of austenitic stainless steel in high-pressure hydrogen gas or hydrogen-charged specimens at -120 to 200°C have reported that difference in relative reduction of area and tensile strength were small. Although the crack growth test at room temperature have been reported, the difference between the hydrogen-charged and uncharged specimens were small. However, the crack growth rate of pre-strained and hydrogen-charged specimens increases significantly. This is because austenitic stainless steel transforms into martensite due to plastic deformation, which is susceptible to embrittlement by hydrogen. In this paper, the effect of hydrogen and martensitic transformation was investigated by SSRT on austenitic stainless- steel specimens with hydrogen charging and with varying pre-strained in liquid helium. As a result, the combined effects of pre-strain and hydrogen charging were small.

This test method is proposed as one of the simple strength reliability evaluation test methods for austenitic stainless steel actual members that are used in hydrogen environment for a long period.

One of the surface modification treatments to improve fatigue life is shot peening, but it requires time and cost, and it is challenging to apply to narrow areas. Another method under study is cavitation peening, but it also takes time for the treatment. In this research, the ultrasonic cleaning peening (UCP) is considered as a method for reducing the residual stress. UCP is relatively simple and can be applied to various material shapes using an ultrasonic cleaner. In this presentation, the residual stress and hardness before and after UCP in specimens subjected to tensile residual stress by a general-purpose processing machine was discussed. The results obtained are as follows. (1) Tensile residual stress caused by cutting or grinding process tends to change to compressive residual stress due to the UCP. (2) There is a relationship between UCP and cleaning effect; the higher the cleaning effect, the higher the compressive residual stress. (3) The Vickers hardness with an indentation load of 10 N shows no change in surface hardness due to the UCP.