Papers by Author: Hironobu Nisitani

Abstract: Practically exact solutions of stress intensity factor for several two-dimensional standard specimens were calculated and shown in numeric tables. The solutions were confirmed to converge until 6 significant figures through a systematical computation of discretization analysis. The convergence analyses were carried out by using a general purpose program based on a body force method.

Abstract: The linear notch mechanics (LNM) was proposed by H. Nisitani in 1983. The concept of LNM can assure the occurrence of the same phenomena in a notched specimen and a real object. The effectiveness of LNM under the condition of small scale yielding has not been confirmed sufficiently. In this paper, the effectiveness of LNM under the condition of small scale yielding is discussed based on the results of FEM elastic-plastic analyses.

Abstract: Finite element method (FEM) is used widely for various structural problems. However, in general, it is difficult to guarantee the accuracy of results obtained by commercial software of FEM. In this paper, a practical finite element technique for calculating the stress intensity factors with high accuracy is proposed. This technique is based on the characteristics of stress field due to a crack. In this study, the proposed method is applied to 2-dimentional crack problems.

Abstract: The non-linear crack mechanics (NLCM) is a concept assuring the occurrence of the same phenomena in two cracked bodies under large scale yielding. It has been recognized that NLCM is effective in the cases of plane stress conditions. In this study, it was made clear that NLCM is effective not only in the case of plane stress condition but also in the case of plane strain condition.

Abstract: Finite element method (FEM) is used widely for various structural problems. However, in general, it is difficult to guarantee the accuracy of results obtained by commercial software of FEM. In this paper, a practical finite element technique for calculating the stress concentration factors with high accuracy is proposed in consideration of physical meaning of stress concentration, and applied to a 2-dimentional stress problem.

Abstract: In this study, it was made clear that the non-linear notch mechanics is useful not only in the case of uniaxial tension but also in the case of biaxial tension. The difference of both cases is as follows. In the former the plastic strain field near a notch root is determined by εp y0,FEM (plastic strain at a notch root) and ρ (notch root radius) alone, but in the latter case it is determined by εp y0,FEM, ρ and stress ratio k=σxn/σyn.

Abstract: It is important to know the stress intensity factor of a circumferential crack emanating from the cavity, because in some cases the fatigue strength of metals is affected by the existence of an internal cavity or an inclusion. Recently a method for calculating the highly accurate values of stress intensity factors was proposed by H. Nisitani, based on the usefulness of the stress values at a crack tip calculated by FEM. This method is called the crack tip stress method. In this study, the crack tip stress method is applied to the problem of an infinite solid having two cavities with a circumferential crack emanating from the cavity subjected to tension. The accuracy of the crack tip stress method was discussed based on some values obtained by the body force method. Moreover, a simple method for calculating the stress intensity factor of this problem was presented.