The microstructure of aluminum (Al) alloy is changed by the material process, and it strongly affects the mechanical property of the material. The final goal of our present study is to establish the mechanical model predicting the performance of the material under practical use. For this purpose, the mechanical behavior of the polycrystalline Al alloy having a notch under the monotonic and cyclic uniaxial tensile tests is investigated experimentally and numerically. A6061 Al alloy specimens obtained from T4 and T6 heat treatments are prepared which have different grain sizes and textures. The stress level of the T6 specimen in the uniaxial tensile test is larger than that of the T4 specimen whereas the elongation of the T4 specimen is larger. The clear deformation bands developed from the notch front during the cyclic test of the T4 specimen. By contrast, the deformation concentration is relaxed by polycrystalline structure-induced nonuniform deformation in the T6 specimen. The Crystalline Plasticity-Finite Element Method (CP-FEM) simulations of monotonic and cyclic tensile tests are performed using the two-dimensional plane stress polycrystalline model having different crystalline orientations and grain numbers. The stress for the model without a notch under the uniaxial tensile test decreases with increases in the deviation of crystalline orientation and grain numbers. By contrast, the decrease in the stress due to the introduction of the notch is reduced by nonuniform deformation induced by crystalline anisotropy. Localized plastic deformations occurred by crystalline anisotropy and stress concentration around the notch front induce the residual strain during the cyclic test with the maximum stress smaller than the 0.2% proof stress. A further extension of the computational model based on the back stress is required to accurately predict the mechanical behavior under cyclic loading-unloading conditions.

This study develops a crystal plasticity finite element (FE) simulation method that reproduces mechanical anisotropy caused by the microstructure of rolled materials, such as crystal orientation and dislocation distributions. The degree of orientation is defined to quantitatively evaluate the rolled microstructure’s orientation. Simulations assuming rolling are performed to map the resolved shear stress (RSS) to the increase in dislocation density. RSS estimated by the crystal orientation information and processing conditions predicts the dislocation density corresponding to the crystal orientation. Crystal plasticity FE simulations are performed considering the dislocation density distribution for each slip system and the rolling texture based on the orientation degree. The usefulness of this method is verified by comparing the results with those of conventional analysis methods.

The thermo-elastoplastic analyses considering the phase transformation are widely used to predict the residual stress and distortion going with the heat treatment. The ordinary steels often have micro segregation which affects the quenching deformation. General heat treatment simulations are not able to consider the micro segregation since the object is treated as a homogeneous mixture of multiple phases. It is necessary to perform analysis considering the effect of micro segregation in order to predict quenching deformation with high accuracy. In this paper, the elastoplastic constitutive equation expressing the effect of micro segregation with anisotropy of macroscopic material properties are formulated, and the heat treatment simulations considering micro segregation are performed based on the proposed formulation. Carburizing and quenching tests are conducted on round bars with and without micro segregation. It is confirmed that the analysis considering the effect of micro segregation with an anisotropy of transformation plasticity model reproduces the experimental results in which micro segregation increases the quenching deformation.

Dual-phase Mg alloys consisting of α-Mg phase and LPSO phase are attracting attention as structural materials of next-generation because of its high specific strength and relatively high ductility. These alloys have excellent mechanical properties attributed to kink deformation and grain refinement based on dynamic recrystallization. However, the influence of kink formation and difference in grain size on material strength of the alloys has never been clarified computationally. In this paper, a crystal plasticity Cosserat model is newly developed considering disclination density to take account of information of rotational crystal defect important for kink formation. Using the preset model, a two-dimensional FE analysis is performed for a rectangular three-crystal plate and a polycrystalline plate of the dual-phase Mg alloys with LPSO phase. Through such computation, the effects of shape of kink band and recrystallized grain size of α-Mg phase on change in material strength are numerically predicted in the process of reverse loading after compression one.

Polyamide (PA) is a semi-crystalline polymer in which the main chain is configured by repeating units of amide bonds (NHCO). The strength of PA is achieved by intermolecular hydrogen bonds between hydrogen and oxygen atoms of amide bonds. Previous studies have indicated that the thermal history conditions influent the crystallization rate and crystalline structure of PA, which affects the macroscopic mechanical properties. In this study, the relationship between the nano-micro structure of PAs and their macroscopic plastic deformation behavior was investigated. PA6 specimens were prepared with different microstructures obtained from two different crystallization processes, called the “isothermal” and “annealing” conditions, respectively. The microstructures were investigated using polarized optical microscopy and small angle X-ray scattering (SAXS), and the mechanical behaviors were evaluated using uniaxial tensile test. The SAXS measurement revealed the difference of nano-micro structures in PA6 with different thermal histories. In this study, we introduced parameters characterizing the nano-micro structure to the transient behaviors of PAs with different thermal histories. The proposed model can express the large plastic deformation behaviors of PAs with different thermal histories. We also performed the finite element (FE) simulations based on the proposed model to investigate the local plastic deformation of semi-crystalline PA. The simulation results reproduced the effects of viscoelastic-viscoplastic mechanical model based on the transient network (TN) theory.

With the development of methane hydrate energy resources and new projects such as geological storage of carbon dioxide using hydrates (CO₂ hydrate storage), research on the mechanical properties of gas hydrate-bearing ground has been promoted. In this study, we focused on the difference in mechanical properties due to the morphology of hydrate in the void of soil, and attempted to reproduce the various mechanical tests of hydrate-bearing soils using the elasto-viscoplastic constitutive equation. In addition, by comparing the material parameters determined by fitting, the relationship between the hydrate formation process and mechanical properties was discussed.

Machined surface layer, which consist of a fine grained layer and plastically deformed layer, has significant effects on the fatigue strength on the austenitic stainless steel. Therefore, the mechanical properties of the machined surface layer are important for accurate prediction of the fatigue life. However, slight thickness of the machined surface layer makes difficult to evaluate the mechanical properties of the machined surface layer. The objective of this paper is to investigate the mechanical properties of thin machined surface layer. For this purpose, we proposed the method for evaluating the stress-strain relationship of the machined surface layer by using the surface residual axial and circumferential stresses of the as-machined round specimen obtained by X-ray diffraction. Our measurement revealed that reducing grain size and thickness of the machined surface layer make the strength higher. The increase rate in the strength of the machined surface layer is inversely proportional to the cutting speed.

The thermal stresses of the thermal barrier coatings (TBCs) under cyclic heating were measured using hard syn-chrotron X-rays of 70 keV at the beam line BL02B1 in SPring-8. We were able to quickly measure the unsteady stresses using the CdTe pixel detector which is an area detector. The two kinds of the TBC specimens were prepared. One was made by atmosphere plasma spraying (APS) and the other was made by suspension plasma spraying (SPS). The steady thermal stresses in both the APS and SPS specimens showed the same value during the heating and cooling processes. Therefore, the steady thermal stresses were caused by the miss match of the thermal expansions. The unsteady thermal stresses were larger than the steady stresses in both the APS and the SPS specimens. The unsteady thermal stresses also include the stress caused by the temperature gradient. According to the behavior of the unsteady thermal stresses measured, the thermal stress of the APS top coat did not exceed 100 MPa due to non-elastic deformation an sliding effect of lamella structure. For the SPS specimen, it was found that the tensile and compressive stresses were relaxed due to the columnar structure.

Generally, mixing models are necessary in case of estimating thermal conductivity of an intact rock from thermal conductivity of cuttings of the same rock. However, one of the problems about this is difficulty in determining suitable mixing model. To develop a simple method to determine thermal conductivity of an intact rock by thermal conductivity measured using cuttings of the rock without any mixing model, we experimentally examined relationship between thermal conductivities of rock cuttings and core samples. We used totally 15 typical rock samples and two fused silicas, including five sedimentary rocks, nine igneous rocks, one metamorphic rock, and made two categories of cuttings size distribution as ≥2 & <4 mm and <2 mm. Then, we measured thermal conductivity of water-saturated intact rock core λ_core and thermal conductivity of mixture of cuttings and water λ_probe by hot disk method and using a new measurement probe for cuttings, and also investigated relationship between two values. As a result, we found a satisfactory linear correlation and got an empirical equation between λ_core and λ_probe as λ_core=4.65λ_probe−2.38 (0.8 < λ_probe < 1.5 Wm^-1K^-1) for ≥2 & <4 mm cuttings and average relative error (RE_ave) of thermal conductivity estimation based on this equation was 6.4%. In comparison between the two categories of size distribution of cuttings, RE_ave of ≥2 & <4 mm cuttings was smaller than that of <2 mm cuttings and we concluded ≥2 & <4 mm cuttings was suitable for this method. In addition, estimation by our empirical equation was more accurate than those of previous mixing models, probably this is owing to less factors of our empirical equation which effect on the estimation. Finally, we proposed this new measurement method to determine thermal conductivity of intact rock using thermal conductivity of cuttings based on this new empirical equation without using any mixing model.