Three kinds of approach from macro-, meso- and micro-scopic viewpoints are summarized, in this paper, relevant to simulating the phase transformation incorporating processes. Since the fields of material structure, temperature and stress/strain induced in a body in such process are coupled each other, the ordinal way to solve independent (or, uncoupled) governing equations for transformation kinetics, heat conduction and stress analysis is insufficient, but thermodynamics-based consideration is needed to obtain the coupled equations among three fields. A transformation parameter indicating progressive phase change is introduced as one of internal parameters representing volume fraction of each phase or phase field parameter, and governing three kinds of equation for the parameter, Fourier law and stress-strain constitutive equation are derived. Thus obtained equations are applied to formulate the macroscopic finite element scheme and also the phase field method in meso-scopic sense in the framework of continuum thermodynamics. The molecular dynamics approach is also carried out to evaluate microscopic, or physical aspect of the fields. Some examples of the computer simulated processes with phase transformation are illustrated based on such three kinds of approach.
An anisotropic damage constitutive model was presented to characterize mechanical behavior of continuous fiber-reinforced ceramic matrix composites (CFCC) with two-scale damage. An overall fourth-rank damage effect tensor was introduced to account for the overall damage of the composite system. In addition, two local (matrix and fiber) fourth-rank damage effect tensors were introduced to account for the local effects of damage experienced by both the matrix and fibers. The overall and local damage tensors were correlated together using homogenization procedure. In terms of the homogenization methods, the effective elastic properties were obtained, and the stress and strain concentration factors were derived for damaged composites. The model was applied in detail to the unidirectional laminate that was subjected to uni-axial tension. The results were compared well with experimental data. The effects of important parameters such as the fiber volume fraction and the damage material parameters on the nonlinear behavior of the composites were investigated. The model provided a useful tool for understanding the overall dependence of stress-strain behavior on all the underlying constituent material properties.
For different rotationally symmetrical compressive residual stress distributions, typically found for shot peened steel surfaces, the reliability of the incremental hole drilling method is investigated by using the finite element code ABAQUS. Simulations of the hole drilling procedure were carried out in order to calculate strain relaxations at the surface due to the material removal with respect to the actual drilling depth. These calculated strain relaxation curves were evaluated by two different hole drilling evaluation methods, the integral method (IM) and the differential method (DM). The errors of the so called plasticity effect were determined by comparing the results of purely elastic simulations with those determined by elasto-plastic calculations. Obviously, the DM has principal difficulties in determining a residual stress gradient properly. The plasticity effect results for both methods in overestimated residual stress values in the surface near region.
In order to clarify the effect of tear strap in airplane fuselage on crack arrest, experimental research and numerical simulation were carried out in this study. Interaction of multiple axial pre-cracks in a pressurized fuselage was investigated using a small-scale model of an idealized fuselage. The strain between multiple cracks under the situation of rapid crack propagation was measured. The experimental results of a rupturing model fuselage represented the variations of stress intensity factors KI and KII in the mixed mode and the remote stress components σox with crack extension. Deformation at the tips of asymmetrical cracks along the stringer was analyzed by a hybrid method using a finite element analysis program, MDC DYTRAN. The recorded crack velocities were in good agreement with the results of finite element analysis. The crack kinking location, kinking angle and the off-axis crack trajectory were also predicted by numerical analysis and the validity of the calculated results was discussed in comparison with the experimental data.
Rotors and discs used in low-pressure turbines must be made of a material possessing high strength and toughness and be capable of manufacturing extremely large components. For these reasons, 3.5% NiCrMoV steel is widely used. It has been previously reported that intergranular stress corrosion cracking in this material is initiated in wet deaerated steam when the temperature reaches approximately 400K. As no rotor and disc material with high strength and toughness that can serve as a substitute for 3.5 NiCrMoV steel has been found, efforts to resolve this problem have been conducted to reduce material strength and lower the susceptibility to stress corrosion cracking. The purpose of this study was to elucidate a relationship between material strength and intergranular stress corrosion cracking susceptibility. Slow strain rate tests (SSRT) were performed in a neutral atmospheric environment at a test temperature of 403K. The results were as follows: (1) The SSRT found that, as the 0.2% offset strength decreased, the area of the intergranular fracture was reduced. For the test specimen with an 0.2% offset strength of 777 MPa, only a tiny intergranular fracture was observed; at 0.2% offset strengths of 697 MPa and below, cracking disappeared completely. (2) From the precipitation status of the two carbides M3C and M7C3 precipitated at the grain boundaries, it was found that the disappearance of the M3C carbide coincided with the disappearance of the intergranular fracture. From this observation, it is thought that differences in composition of these carbides have an effect on the susceptibility of 3.5% NiCrMoV steel to stress corrosion cracking. (3) It was confirmed that the M3C carbide disappears when the 0.2% offset strength is approximately 700 MPa or below, and that these materials achieve the target value for increased resistance to intergranular stress corrosion cracking in neutral environments.
In this paper, the tension-torsion multiaxial creep-fatigue lifetime for CMSX-2 nickel base single crystal superalloy at 1173K is described. Strain controlled tension-torsion low cycle fatigue tests with various hold times were carried out using hollow cylindrical specimens, the axis of which coincides with the  crystallographic direction. An introduction of the hold time into the torsion tests was more detrimental to the lifetime than that into the tension tests. The Von Mises' equivalent strain range gave a larger scatter for the correlation of creep-fatigue lifetimes. The relationship between elastic strain range and creep-fatigue lifetime had a strong dependency on the principal strain ratio. But those between plastic strain and the lifetime, and creep strain and the lifetime had almost no dependency on the principal strain ratio. A linear damage rule yielded an accurate lifetime estimation in the tension tests, but substantially overestimated the lifetimes in the torsion tests. A new simple lifetime prediction method, taking account of anisotropy of the elastic modulus, was proposed. The method predicted the experimental lifetime within a factor of 3 scatter band. Cracks in the tension tests propagated in the principal strain direction but those in the torsion tests propagated in the maximum shear direction. In the torsion tests, cracks were only observed in the soft zones predicted by numerical analyses.
For effective production of crystallized carbon (T-component) usable for electromagnetic shielding (EMS) from Lignocresol (LC) by nickel-catalyzed carbonization, the promotion effect of calcium co-loaded was investigated in the reaction at 900°C for 1h. It was shown that suitable loadings of nickel and calcium were both 8 wt% for char in terms of the formation of T-component and EMS capacity, and the Ca/Ni ratio of 1.0 was also optimal for other nickel loadings. A similar aspect was observed in the same carbonization of acid-demineralized alkali lignin (DAL) used for comparison. These results supported a previously proposed interaction between nickel and calcium and made the action and role of calcium clear.
Powders in the ZrO2-MxOy and [20CeO2-80ZrO2 (mol%)]-MxOy system were prepared from zirconium sulfated slurry. The components MxOy are 1-16 groups of metal oxides in the Periodic Table including transition and rare earth. The influence of MxOy addition on specific surface area (SA) and oxygen storage capacity (OSC) was investigated. It was found that, compared with additive-free powders, the powders containing La, Pr, Nd, Sm, Eu, Gd, Tb or Dy had high SA values at 1000°C. On the other hand, the powders containing V, Cr, Co, Ni or Cu had high OSC values at 610°C and 1000°C. It may be concluded that the powders containing rare earth metals show high SA values and those containing transition metals show high OSC values exhibiting high thermal stability.
The existing freezing and thawing test method of structural concrete leaves much room for improvement from the viewpoint of materials science research; that is, the concrete specimen is too large and heavy and the testing procedure is so time-consuming that the test itself cannot be practically used for evaluation of durability. Thus, the authors have reported that the standard cylindrical specimen (∅10×20cm)is the best type for the quality control of concrete and that the accelerative test method using the exposure temperature of ±5°C has been developed. The surface defect ratio has been defined on the basis of the fact that the gradual process of surface deterioration, namely, the popping-out, is fundamentally related to the internal destruction of concrete. This paper deals with the relationship between the relative dynamic modulus of elasticity, the number of freezing and thawing cycles, and the surface defect ratio. Thus it proposes a practical evaluation method of the compressive strength of structural concrete, which uses a new durability index of the surface defect ratio.