Effects of defects, inclusions and inhomogeneities on fatigue strength

Steels for bearings

Quantitative evaluation of effects of non-metallic inclusions on fatigue strength of high strength steels. I: Basic fatigue mechanism and evaluation of correlation between the fatigue fracture stress and the size and location of non-metallic inclusions

Quantitative evaluation of fatigue strength of metals containing various small defects or cracks

Quantitative evaluation of effects of non-metallic inclusions on fatigue strength of high strength steels. II: Fatigue limit evaluation based on statistics for extreme values of inclusion size

The Effects of Notch Depth on the Initiation Propagation and Non-propagation of Fatigue Cracks

Evaluation of Blunting Line and Elastic-Plastic Fracture Toughness

On the fracture surface of a KIc specimen, there exists a critical stretched zone between the fatigue pre-crack and overload fracture regions. This width, SZWc, has been correlated with the critical values of various fracture mechanics parameters. On the other hand, a sub-critical stretched zone appears as the loading progresses. In this paper, the data of sub-critical stretched zone width, SZW, obtained by many researchers were summarized and the relation between SZW, as a measure of crack tip plastic blunting, and the J-integral was investigated.The followings are the summary of the results obtained.(1) The relation between SZW and J/σflow showed an apparent dependence on flow stress, σflow: there was a tendency for SZW to become smaller for the same value of J/σflow as σflow became smaller. S0, the following equation did not stand, SZW=C1J/σflow (C1: const.).(2) The change of Young's modulus, E, had little influence on the relation between SZW and J/E, and no influence of test temperature was observed. SZW was given by the following expression, SZW=89J/E(3) The above mentioned relation between SZW and J was similar to the one between the striation spacing, S, and J. Under a small scale yielding condition, S was given by the following expression, in the case that the stress ratio is 0, S=9.4J/EThat is to say, the width of the stretched zone as well as that of a striation formed by the same micromechanism of glide plane decohesion, was characterized by the very same fracture mechanics parameters.(4) If the above-mentioned relation between SZW and J is established on other materials, there is a possibility of evaluating JIc simply by measuring SZWc with a single specimen by failured overload.

A relation between crack tip plastic blunting and the j-integral

Effect of mechanical properties of material on rate of fatigue crack propagation

The relations between the fatigue strength of bearing steels in rotary bending and the shape and the distribution of inclusion were investigated. The material used were normal steel (N), normal Swedish steel (S) and steel melted in vacuum (V). Plane specimens and specimens with two kinds of groove were made from each sort of steel. The results obtained were as follows : (1) When the steel had less and smaller inclusions, its fatigue strength became higher. (2) In this experiment, the inclusion whose mean diameter was smaller than 8 μ did not affect the fatigue strength. The mean diameters of detected inclusions were 10∼40 μ for S-steel, 30∼70 μ for N-steel and 35∼130 μ for V-steel. (3) It was clarified that the fatigue life of bearing steel was affected by the mean diameter, the shape of inclusions and the distance from the surface of specimens to the inclusion. (4) The inclusions found on fatigue fracture surfaces were inspected by X-ray analyzer and it was clarified that they were composite of Si and Mn.

The Effects of the Shapes and the Distributions of Inclusions on the Fatigue Strength of Bearing Steels in Rotary Bending

Hajime Nakazawa

Papers

The Effects of Notch Depth on the Initiation Propagation and Non-propagation of Fatigue Cracks

Evaluation of Blunting Line and Elastic-Plastic Fracture Toughness

A relation between crack tip plastic blunting and the j-integral

Effect of mechanical properties of material on rate of fatigue crack propagation

The Effects of the Shapes and the Distributions of Inclusions on the Fatigue Strength of Bearing Steels in Rotary Bending