西谷 弘信

き裂開口変位に基づく,大き裂伝ぱ則と小き裂伝ぱ則の相互関係に関する検討 : S45C焼なまし材の回転曲げ疲労試験

Fatigue crack growth tests were carried out in order to give a unified explanation of the formal contradiction between two fatigue crack growth laws in small and large cracks, dl/dN∝σnl and dl/dN∝ΔKm. Cracks were monitored using the plastic replica method. Crack opening displacement ranges (ΔCOD s) were measured from the positive metal replicas made from the plastic replicas. In small and large cracks having the same growth rate, the relationships between ΔCOD s near the crack tips and the distance from the crack tip were almost the same. Therefore, ΔCOD near the crack tip can be considered as the main factor controlling the crack growth rate. Based on this, the two fatigue crack growth laws can be explained consistently.

表面力を受ける接合半無限板における対数形の特異応力場 : 第1報,応力場の一般解

The stress field with logarithmic singularity is studied for the bonded wedges with a resultant configuration of a half-plane. Bogy has reported the stress field near the jointed corner tip due to arbitrary normal and shearing traction in an explicit form for the case in which the angle of the wedge γis 90°. In this study, the general expression of the stress field is given for an arbitrary value ofγ.

短炭素繊維強化ポリアミド6.6のねじり疲労過程 : 回転曲げ疲労との比較

In this paper, torsional fatigue tests and additional rotating-bending fatigue tests were carried out on the injection moulded short carbon-fiber reinforced polyamid 6.6 composites. The fatigue mechanism in the composites was clarified through successive surface observations using the replica method. Moreover, the mechanism of the torsional fatigue was compared with that of the rotating-bending fatigue. The fatigue cracks in both fatigue tests are initiated along fibers aligned in the direction of the principal stress. In the case of the rotating-bending fatigue test the fatigue crack propagates finally at right angles to the direction of the principal stress. However, the cracks initiated along the fibers in the torsional fatigue test can not propagate under high-cycle fatigue. On the other hand, the fatigue cracks initiated from fibers aligned in the direction of the principal shear stress can propagate, and reach to final fracture. From the comparison between bending and torsional fatigue tests the fatigue process of this material under the condition of an arbitrary combined stress can be estimated.

Versatile Analysis of Antiplane Shear Problems Based on Body Force Method.

A versatile method for analyzing various antiplane shear problems was presented. The method used here is based on the body force method (BFM) which is a type of boundary method. In this paper, the boundaries of an elastic body are approximated by broken lines to eliminate the necessity of using the numerical integrals. The present method is excellent in accuracy and calculation efficiency, as shown in many numerical examples.

微視的き裂の発生と伝ぱに関する統計的性質 : 続報, S20C焼ならし平滑材の回転曲げ疲労

The statistical property of the fatigue behavior was investigated for normalized 0.21% carbon steel plain specimens. An emphasis is to investigate separately the statistical properties of the initiation and propagation of microcracks through successive observations of the specimen surface by the plastic replica method. Results show that the distributions of crack initiation life and microcrack propagation life are expressed as two- or three-parameter Weibull distributions. More-over, the three-parameter Weibull distribution is well fitted to the crack length distribution, and the value of the shape parameter m in this case decreases with an increase in the relative cycle ratio N / Nf. As the main reason for the decrease in m, we can point out the decrease in the number of newly initiated cracks at each N / Nf.

Torsional Fatigue Processes of Flakes Graphite Cast Iron and Spheroidal Graphite Cast Iron : Comparison of Rotating Bending Fatigue with Torsional Fatigue

In order to clarify the fatigue behavior in plain specimens of a flake graphite cast iron (FC 25) and a speroidal graphite cast iron (FCD 45), torsional fatigue tests and optical microscopic observations were made successively, on the fatigue processes by using the plastic replica method. The process was then compared to that under rotating bending fatigue. The main results obtained are as follows. (1) The fatigue limit, in each case, is determined by the limiting condition for propagation of the microcrack initiated from graphite. (2) The ratios of the fatigue limit in reversed torsion to that in rotated bending were about 0.9 and 0.8 in FCD 45 and FC 25, respectively.

Combination of BFM and FEM for Analysis of the Stress Intensity Factor of Cracks

In this paper a combination of BFM and FEM for problems with cracks has been developed. It is found that there is always a local incompatibility of displacements or stresses on the interface of two domains in which BFM and FEM are used, respectively. The accuracy of this analysis is usually in fluenced by the incompatibility. Three types of equivalent nodal forces were compared. It is demonstrated that the equivalent nodal force defined as a resultant force between two middle points of adjacent boundary elements is useful.

S 50 C 焼入れ・焼もどし材における Paris 則の有効性 : 回転曲げによる検討

Although many papers have suggested that the growth rate of small cracks can not be determined by linear fracture mechanics, there are a few reports indicating that linear fracture mechanics can be approximately applied to determine small crack propagation. In the hard materials, it seems to be easy to satisfy the condition of small scale yielding. This means that the growth rate of small cracks in such materials can be approximately expressed as a function of the stress intensity factor. In this paper, using a heat-treated 0.54% C steel, the rotating bending fatigue tests of plain specimens with a small hole are carried out under a wide range of stress amplitudes, and the validity of Pariss rule is investigated.

浅い円弧形切欠きを有する疲労試験片ねじり, 引張り, 曲げにおける応力集中

The body force method is applied to calculate stress concentration factors of partially-circular circumferential notched cylindrical specimens subjected to torsion, tension of bending. This type specimen is used frequently for fatigue tests. The stress field induced by a ring force in an infinite body is used to solve these problems. The fundamental solutions and calculation method developed here have a wide applicability for various kinds of axisymmetric notch problems under torsion, tension or bending. Through the comparison of the present result with Neubers analytical solution for a deep hyperbolic notch, the Neubers solution is found to give a sufficient accuracy for a blunt notch in engineering use.

微小き裂伝ぱ則に及ぼす巨視的降伏の影響 : S 45 C 焼なまし材および予ひずみ材の引張圧縮による検討

The behaviors of small fatigue cracks in annealed and pre-strained 0.45% C steel specimens were investigated in order to clarify the effect of macroscopic yielding on the growth law of small cracks. The growth laws of small cracks can be expressed in the same form of dl/dN=Cσanl for the above two types of specimens. The macroscopic yielding or pre-strainning causes the change in the values of n (n=8 for not yielded specimens and 6.4 for pre-strained or yielded specimens) and the independency of stress ratio in the growth law of small cracks.