Published Resources Details
Journal Article
- Title
- A new approach to the properties of steels in engineering
- In
- Journal of the Institution of Engineers, Australia
- Imprint
- vol. 28, no. 6, Jun 1956, pp. 161-168
- Description
This paper, No.1225, was presented before Section H of the 31st Meeting of A.N.Z.A.A.S. held in Melbourne in August, 1955.
The author, Hugh Muir, ScD BMeTE, is Senior Lecturer in the Metallurgical Department of the University of Melbourne.
Most of the work described herein was carried out at Massachusetts Institute of Technology, where the author was employed as Research Assistant in the Department of Metallurgy (1952-3). Further work has been done at the School of Mines and Metallurgy, University of Otago, under a University of New Zealand Research Grant (1953-4), and is being continued in the Metallurgy Department, University of Melbourne.
- Abstract
Recent work by the author and associates has shown that a hitherto neglected strength parameter-namely, the elastic limit-can be measured reproducibly by a load-unload method, using resistance strain gauges. The high sensitivity of the method has made it possible to distinguish the ·stress value at which the first 1 to 2 x10-6 permanent strain appears, and there is evidence that the elastic limit defined in this way is not merely a flow stress parameter of the "proof stress" type, but has real physical significance in terms of the elastic-to-plastic transition. In particular, repetition of any load just below the defined limit produces no permanent strain, whilst repeated loads of higher value produce a small strain increment at each load ·cycle. On this basis a correlation between the elastic and fatigue limits was anticipated and later demonstrated by experiment.
A comparison has been made of the effect of heat treatment and composition variables on the elastic limit and on the conventional tensile test parameters such as yield and ultimate strengths, etc. The results show that the dependence of the elastic limit on tempering temperature for hardened steels differs greatly from that observed for the conventional properties, particularly in the region of low tempering temperature and in the "500°F. brittleness" region. Thus the elastic limit has its minimum value in the fully hardened steel and rises with increasing tempering temperature to a maximum in the 500°F. range of tempering temperature (250°C. and vicinity), whilst yield and ultimate strengths decrease almost continuously with tempering temperature.
At high tempering temperatures the elastic limit and the stress strain curve in its vicinity were found to be markedly sensitive to rate of cooling from the tempering treatment. This suggests a possible correlation with temper brittleness phenomena, and further investigation of the effect is under way.
On the basis of these results, and in view of the known inadequacies of the conventional strength parameters, a case can be made out for the application of elastic limit data in engineering design, particularly at high hardness levels, and where fatigue and brittleness problems are likely.