The weldability of dissimilar materials is strongly influenced by their physical properties such as density, surface tension, and viscosity especially at the molten state. Therefore, it is essential to quantitively measure these properties for deeply understanding and simulating complicated melting pool behaviors. In this study, Electrostatic Levitation (ESL) method was employed to directly measure these physical properties of four materials: cast iron (C: 3%), carbon steel (C: 0.3%), Ni alloys (weld wire), and their mixed material in weld metal. The density of base metals and weld wire decreases linearly with increase of the temperature. The magnitude of density is largest for Ni alloy, smallest for cast iron and the middle for carbon steel. The density of weld metal, the material mixed from base metals and weld wire, has the magnitude between carbon steel and cast iron. The measured surface tension shows an increasing relationship with temperature when the temperature is lower than a certain value (1 270~1 450 °C) and decreases when temperature exceeds the certain value. The rarely reported surface tension for the mixed material in weld metals was successfully measured here. Since the difference of surface tension between the base metals and the weld metal is large, the molten shape is asymmetrical in actual welding. This may be concerned with the uneven Marangoni convection in the cast iron and carbon steel. The viscosity in a wide range of temperature was measured and it decreases with temperature increase as it in conventional alloys. It was found that the Arrhenius plot could be used to approximate the temperature dependent viscosity for base metals, Ni-alloy and their mixed material in weld metal.

In this study, thermal barrier coating (TBC) specimens were atmospheric plasma sprayed with NiCoCrAlY and 8 mol% Y₂O₃-ZrO₂ powders as the bond coat and the top coat, respectively. The TBC specimens were exposed to high temperatures at 1373 K for 0, 500 and 1000 hours. For stress measurements, the diffraction by transmitted X-rays of 70 keV synchrotron X-ray micro-beam was used. The diffraction patterns from the 224+422 lattice planes were measured using a double exposure method, and the stress values were determined using a direct method. As a result, the residual stress distribution of the top coat from the surface to the interface was obtained. No significant residual stress was generated in the as-sprayed top coat, but after 500 h of high temperature exposure, a large compressive residual stress was generated in the top coat. In balance with this, a large tensile residual stress was generated in the bond coat. After 1000 h of high temperature exposure, the residual stresses in the top coat and bond coat were released near the interface.

The wall clay, which is a component of Tsuchikabe, is mixed with straw to prevent cracking caused by drying shrinkage and to improve workability during construction by plasterers. However, it is known that mixing straw improves workability but also reduces the uniaxial compressive strength of the wall clay. In recent years, due to changes in rice cultivation processes, it has become difficult to obtain straw as a material for Tsuchikabe, leading to the search for alternative fiber materials. In this study, we manufactured three types of micro-fibrillated cellulose (MFC) with different pulping processes from native herbaceous plants and evaluated their effectiveness as reinforcing materials for wall clay. Additionally, as a comparison, we added mechanically fibrillated cellulose nanofibers (CNF) derived from purified cellulose fibers to the wall clay and conducted evaluations. Adding MFC or CNF to the wall clay reduced its flowability. The cracking ratio of the dried wall clay test specimens was significantly lower in the specimens containing MFC or CNF, which contain almost no lignin, than in the specimens without fibers, indicating that uniform drying shrinkage occurred. Compression test results showed increased uniaxial compressive strength and toughness in specimens containing MFC or CNF. Particularly, specimens containing MFC, which has almost no lignin and high hemicellulose content, exhibited the highest uniaxial compressive strength and elastic modulus. The compressive strain was increased as the fiber diameter decreased, suggesting that the fibers formed a network structure between the soil particles. These results indicate that MFC and CNF, which contain almost no lignin, act as reinforcing agents that simultaneously prevent cracking in wall soil and enhance compressive strength. Since MFC and CNF can be produced from all higher plants, they are expected to be utilized as new reinforcing materials to replace traditional straw.

Tensile and rotating bending fatigue tests were conducted on SUS304 and SUS316L specimens with precisely controlled grain size and plastic strain, and both fatigue and static strength data were obtained. The relationship between fatigue properties and static strength was then investigated. It was found that, in specimens with a fully recrystallized microstructure, both static and fatigue strengths followed the Hall–Petch relationship. Moreover, SUS304 exhibited fatigue strength comparable to SUS316L despite its lower static strength. This behavior is considered to result from secondary hardening associated with stress-induced martensitic transformation during the fatigue process. X-ray diffraction analysis confirmed that martensitic transformation occurred in SUS304 after 10⁴ cycles at the stress level corresponding to the fatigue limit, and the tendency for martensitic transformation was independent of grain size. Microstructural changes in the early stage of fatigue process were examined using EBSD analysis, which revealed that plastic flow occurred near the surface while martensitic transformation had not yet initiated. Furthermore, when the S–N data were normalized by yield stress, it was found plastic strain and texture introduced by cold rolling significantly increased static strength, whereas the improvement in fatigue strength was relatively small.

In order to investigate the effect of shot peening treatment on notched material, a rotating bending fatigue test was conducted on notched specimens made of vacuum-carburized SCM420H steel, with a stress concentration factor of approximately 1.76. In this study, four types of shot peening conditions were prepared: normal shot peening (SP), fine particle shot peening (FPP), super fine particle peening (SFPP) and double shot peening of SP and FPP (DSP). All shot peening treatments improved the fatigue limit to the same level as that of the non-peened smooth specimen. The internal stress distribution, accounting for both notch-induced stress concentration and residual stress, was investigated to examine the correlation between crack initiation behavior and fatigue limit. For SP treated specimens that do not undergo significant plastic strain, the fatigue limit can be explained by calculating the sum of applied load stress and residual stress, while considering the decay of residual stress. For DSP treated specimens that undergo significant plastic strain, it is difficult to explain the fatigue limit simply by calculating the sum of the applied load stress and residual stress; however, it can be explained based on the results of finite element analysis. Additionally, the fatigue properties of DSP-treated specimens were further enhanced by blast polishing.

The reuse of carbon fibers (rCFs) recovered from waste carbon fiber reinforced plastics (CFRPs), which volume is expected to increase, is becoming increasingly important. When rCFs are used to reproduce CFRPs, it is essential to evaluate the tensile strength reliability at the fiber bundle (FB) level. This study aims to clarify the effects of frictional stress on the FB tensile strength reliability. A stochastic model based on a Markov process was proposed to describe the tensile fracture behavior of FBs. The key advantage of employing the Markov process lies in its ability to discretize the fracture process into multiple states, each representing FBs with varying number of broken fibers as a function of applied stress. Furthermore, each state is characterized by a probability, enabling the analysis of FB strength reliability. The proposed model was applied to stress–strain curves obtained from tensile tests of FBs consisting of 12,000 CFs. The model exhibited good agreement with the experimental results and enabled estimation of both the Weibull parameters for CF strength and the friction coefficient. Finally, the effect of frictional stress on strength reliability was analyzed. The results found that frictional stress improves the overall strength reliability of FB.

Probabilistic model is newly developed to estimate temporal variation of debonding probability on CFRP adhesive reinforcement under random deterioration of the an adhesive in the reinforcement. First, a probabilistic model for describing debonding of bonded CFRP caused by spatially random variation of the adhesive thickness is briefly reviewed. Next, random deterioration model is proposed for describing temporal deterioration of the integrity of the adhesive material, where temporally random differential equation is given based upon extended Kachanov law for the deterioration. Then, a hybrid approach is proposed, based upon two probabilistic models, to estimate temoporal variation of debonding probability on the reinforcement. Finally, numerical examples are shown for quantitative analysis on the temporal variation of the debonding probability. Further, a simple example of application for a reliability-based design using the newly proposed model is discussed.

A fast Monte Carlo simulation scheme is newly developed for fatigue failure under random overloads, which is based upon an importance sampling technique using a probability measure transformation. A probabilistic model proposed by the authors is applied to describe fatigue crack growth under random overloads, in which a two-criteria failure condition consisting of a fatigue fracture mode as well as a ductile fracture mode is taken into the model. Then, an importance sampling measure is newly proposed as a mixture measure of “double mode”, one is for estimating probability associated with fatigue mode and the other is for probability associated with ductile mode. Numerical examples are shown for demonstrating the proposed simulation scheme, which clarifies that (i) the proposed method can accurately estimate extremely small failure probabilities (such as order of 10^{－ 5}) and (ii) it achieves a significant improvement in computational efficiency, which can reduce the computing time to approximately 1/50 of that required by a large-scale crude Monte Carlo simulation.

Recent advances in materials design have been greatly accelerated by the combination of computational science and data science. However, the high computational cost remains a serious problem. One possible solution is gradient-based optimization in chemical space using fractional nuclear charges, where the atomic number is treated as a continuous variable. Although this concept is promising, pseudopotentials for such virtual atoms are not available in existing databases and must be generated manually. In this study, we have developed a system to automatically optimize pseudopotential parameters for fractional nuclear charges by using Bayesian optimization. The objective function is defined as the mean squared error of the logarithmic derivative between all-electron and pseudo wavefunctions. Pseudopotential generation is performed using the ADPACK code. As a benchmark, we first applied our method to aluminum with a nuclear charge of 13.0. The optimized pseudopotential showed a smaller delta gauge value compared to the default one in OpenMX. We then extended the optimization to nuclear charges from 13.0 to 14.0 in steps of 0.2. For each case, we calculated the bulk energy and confirmed the validity of the generated pseudopotentials.