Investigation of behavior of materials under repeated stress progress report 1

The investigation described herein is a basic research project undertaken at the University of Illinois in co-operation with the Office of Naval Research, U.S. Navy. The purpose of these studies is to investigate and attempt to evaluate the relative importance of a number of factors that must be considered in formulating a satisfactory explanation of the structural action and strength characteristics of machine members in repeated stress service. Information is being obtained on the effects of the following factors on the behavior of materials when subjected to repeated stressing: (a) various ranges of stress for several given states of stress; (b) the influence of specimen shape and size; (c) variation in fatigue life caused by fluctuating loads that produce a varying amplitude of repeated stress; (d) the influence of metallurgical constitution on fatigue strength and notch sensitivity; (e) strain hardening and residual stresses resulting from prior plastic deformation. Studies have also been initiated on methods of measurement and criteria for determination of damage in members subjected to repeated stress, and in devising means of studying phenomena leading to fracture in regions of a member in which the entire stress cycle is usually considered to be compressive. Tentative outlines of laboratory research problems, and detailed descriptions of apparatus, materials, and testing techniques are presented. Due to the recent inception of the program and the inherent slowness with which fatigue test data are accumulated, only brief summaries of some of the results are presented. No definite conclusions can be drawn at the present time, and this report is intended mainly to outline the nature of the work planned and in progress.Office of Naval Research, U.S. Navy, Contract N6-ori-71, Task Order I