Fatigue Of Metallic Materials Research Articles

A review of: “Fatigue of Metallic Materials (Second Revised Edition)” Edited by M. Klesnil and P. Lukas

(1995). A review of: “Fatigue of Metallic Materials” (Second Revised Edition) Edited by M. Klesnil and P. Lukas. Materials and Manufacturing Processes: Vol. 10, No. 2, pp. 335-336.

A new damage variable for low-cycle fatigue of metallic materials

Experimental results show that the inherent ductility in a material is deflected after cycle loading. Based on the concept of ductility deflection, a new fatigue damage variable D ψ for low-cycle fatigue is recommended in this paper. This new damage variable D ψ has definite physical meaning and can be measured with a simple experimental procedure. It can be connected directly with the usual mechanical properties of materials. D ψ increases slowly at the initial stage of cycle loading, but it increases rapidly after a definite cycle where the macroscale crack is formed. We define the turning point on the D ψ - N curve as the critical damage value D c ψ and its corresponding cycle number N is the fatigue life N f .

The Stress-Strain Relation in the Low-Cycle Fatigue of Metallic Materials under Rotating-Beam Bending

In order to find the mechanism of fatigue, it is very important to investigate the change of stress-strain relation during the fatigue process. During the past several years, the author performed a series of studies on the fatigue under the low-cycle rotating-beam bending and summarized their results. In the present report, the results of the studies are given in outlines concerning the effects of various tests conditions on the stress-strain relation and the criterion of fatigue failure. From the measurements of strain amplitude in their change in several kinds of metallic materials during the fatigue tests of the constant stress amplitude, the difference is indicated in fatigue hardening (or fatigue softening) among the materials, and the dependency of fatigue hardening (or fatigue softening) on the time rate is evaluated. Its relation to strain hardening is also discussed.

Fatigue Crack Propagation and Substructure of Tufftrided Steel

It has been pointed out by many researchers that substructure affects crack propagation in case of fatigue of metallic materials. However, the materials used in the past investigations were mostly homogeneous, and the microscopic behaviour of surface hardened materials such as tufftrided steel is only little known.In the present study, some investigations were made to obtain the relation between the crack propagation and substructure of tufftrided steel specimens with notch root through the observations of the crack propagation and the change in substructure in the vicinity of notch root and crack during the fatigue process by using the back reflection X-ray microbeam diffraction technique.The results obtained are summarized as follows;(1) The life to fracture or the period preceeding crack initiation of a tufftrided steel specimen increases remarkably as compared with that of a non-tufftrided steel specimen under the same stress amplitude.(2) The crack initiates at a comparatively early stage in the life to fracture and grows rapidly. However, when the crack tip passes through the position 1∼2mm away from the notch root, the crack propagation rate gradually decreases.(3) The substructure had already formed at the places with high content of soluted nitrogen after tufftriding, and the same substructure can be observed in the vicinity of crack tips irrespective of crack length.(4) It is evident from the observations by microbeam X-rays and by a scanning electron microscope that the plastically deformed area in the vicinity of crack in the tufftrided steel is very small and the magnitude of deformation of each crystal is also small as compared with that in the non-tufftrided steel.

Conference on the problem of fatigue of metallic materials in the case of cyclic impact loading

Conference on the problem of fatigue of metallic materials in the case of cyclic impact loading

Low-Cycle Fatigue of Aluminium Alloy due to Rotating-Beam Bending under Random and Multiple Repeated Loading

Recently, low-cycle fatigue of metallic materials has been widely studied, and several fracture criteria of fatigue have been presented as the basis for predicting low-cycle fatigue lives. The authors had previously proposed a fracture criterion of low-cycle fatigue based on strain, in stead of the Miner's linear damage rule based on S-N curve, and investigated the relation between the stress-strain behaviour and the fatigue lives by carrying out the low-cycle fatigue tests under rotary bending to measure the stress and strain during those tests, and the above mentioned criterion was verified experimentally.Although many ordinary fatigue tests have hitherto been carried out of aluminium alloys, still we have very few data of low-cycle fatigue tests of aluminium alloys performed under rotary bending. In the present report information is given of experimental studies that are usually performed on steels as applied to the studies on the aluminium alloy 17 S-T 4 under the condition of the constant- and varying-stress amplitudes. Moreover the effects of frequency distribution of loads and their sequence of application on fatigue lives were investigated. The applicability of the above criterion has been discussed by summarizing the data by means of“the reduced strain amplitude”and“the reduced stress amplitude modified by the stress correction factors”already reported.

金属材料の高温における動クリープおよび疲労

金属材料の高温における動クリープおよび疲労

Statistical Aspect in Fracture and Fatigue of Metallic Materials

Statistical Aspect in Fracture and Fatigue of Metallic Materials

The Effects of the repeating Speeds on the Fatigue of metallic Materials

1. Preface When the metallic materials were broken down due to fatigue under repeated stresses, it was previously published partially that the repeating speeds had influences upon the fatigue-curves, especially the endurance limits. But they were not investigated systematically. The causes lay, it was though, in the fact that no reliable high speed fatigue testing machine was available. In this research, some carbon steels from 0.07% to 0.6% carbon has been studied under the new Nishihara type high speed fatigue testing machine, which was designed as satisfying the purposes, and also under the old Woler type fatigue testing machine, and some other materials were also studied. 2. Effects of the repeating speeds We have studied on the range from 5, 000 rpm to 15, 000 rpm by the new Nishihara type high speed fatigue testing machine, and studied on the range from 50 rpm to 2, 000 rpm by the old Woler type fatigue testing machine. It was imperfectly known that the endurance limits were rising as the repeating speeds were rising. By this research, the facts that the endurance limits were rising as the repeating spceds were rising were confirmed, and these rates of the rising are different according to the contents of carbons or the internal crystal systems or the results of the heat treatment. When we consider all states of fatigue curve at the high stresses, the materials are fatigued sooner in the cases of repitition of high speed than of low speed, i. e. at the high stresses, the fatigue strengths are lower than at the low stresses, at the high speed repitition. But at the endurance limits, or at the lower stresses near such limits, the materials are fatigued sooner in the case of repitition of low speed than of high speed. As the cause that the fatigue strength is varied by such variations of the repeating speeds, we consider 2 causes. At the high stresses the facts that the fatigue strengths at the high speed repetitions are lower than at the low speed repetition, are considered as the next. The heat quantity which is accumlated in the material in unit time is much larger at high speed repetition than at lower speed repetition, and then the temperature of the material rises and the material is softened. So the strength becomes smaller. At the low stress near the endurance limits, the rising of temperature of the material is very much smaller, but on the contrary, the variations of the internal crystal system are larger at low speed repetition than at high speed repetition, so that the material at low speed repetition is fatigued sooner than at high speed repetition. 3. Conclusion To save the testing time of fatigue test, we perform the fatigue test under high speed repeating stresses. But by such a method, the phenomena, that the endurance limits were varied by the repeating speed, were discovered, and the facts that according to the internal crystal system of material, the rate of influences was different, was also discovered. we now believe that we must study another materials, ana discuss the effects of the repeating speed that influences the fatigue strength.