Hiroshi Hikosaka

Crack length and specimen size influences on fracture strength of brittle materials

The influences of crack length and specimen size on the fracture strength of brittle materials in both tension and frictional compression are studied in the framework of the boundary element method. The coefficients representing the coupling between the cracks and finite-sized boundary are obtained in the form of algebraic expressions. The curved propagating trajectories are simulated through a stepwise propagation process. With different configurations of specimen size, crack length and frictional coefficient in compression, the related strength size effects are obtained. It is found that the usual size effects with −1/2 slope in the bilogarithmic form are only applicable to the geometrically-similar cases (with the same crack to specimen scaling ratios—assumption commonly used but not practical). For the case of the fixed specimen size with varying crack length in both tension and frictional compression, the influences of crack length on the failure stress are more severe than for those of the geometrically-similar cases.

A fundamental study on deterioration of the existing RC beam by chemical and mechanical damage

Recently, the maintenance problem of existing RC structures has increased in Japan, and it is important to estimate the total life cycle cost of structure, which includes not only construction cost but also maintenance cost. In order to accomplish this purpose, it is necessary to evaluate the durability and predict the deterioration of the existing structures accurately. In this study, the damage evolution processes caused by chemical and mechanical effects are considered by using continuum damage mechanics. Within the framework of this method, chemical damage due to the corrosion of the steel bar is considered, and the coupling effect between chemical damage and mechanical damage is calculated by introducing two independent scalar damage variables into the constitutive equation. To calculate the chemical damage evolution, diffusion process of the chloride ions that strongly affect the corrosion of the steel bar in the concrete beam is solved, and evaluate the effective cross-sectional area of the steel bar. It is found that the proposed method could evaluate the deterioration of the existing RC beam, and the change of its ultimate strength under the various exposition conditions.

Fatigue damage analysis of welded structures based on continuum damage mechanics

In this study, the fatigue damage analysis and life prediction of welded structures are carried out by using continuum damage mechanics. For high cycle fatigue, it is considered that plastic deformation and damage occurs at a microscopic scale. Therefore, a two-scale model presented by Lemaitre is introduced to evaluate the high cycle fatigue damage evolution. As it is difficult to identify the parameters directly at the micro scale, the identification method is proposed to obtain the reliable material parameters for weldment. In order to consider the effect of residual stress on fatigue behavior of welded joints, the inherent strain method is applied to determine the residual stress. The analytical results by the proposed method are compared to experimental results and it is confirmed that the proposed method could give the reliable fatigue lifetime of welded structures.