Investigation of behavior of materials under repeated stress final report

The investigation discussed herein constituted a basic research program undertaken at the University of Illinois in cooperation with the Office of Naval Research, U. S. Navy. The purpose of these studies was 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. During the course of this research, covering the period from 1946 to 1955, over 46 technical reports were issued to disclose the findings of this study. This is submitted as a final report to summarize in a concise manner, the nature of these studies and to describe briefly some of the principal accomplishments. In general, information was obtained on the effects of the following factors on the behavior of materials subjected to repeated stressing: (a) Various ranges of stress for several given states of stress; (b) The influence of specimen shape and size; (c) The variation in fatigue life caused by fluctuating loads that produced a varying amplitude of repeated stress; (d) The influence of metallurgical structure on fatigue strength and notch sensitivity; (e) Strain hardening and residual stresses resulting from prior plastic deformation; (f) The fundamental statistical nature of fatigue data and their appropriate interpretation; (g) Basic concepts of fatigue damage in metals; (h) The influence of strain aging and changes in the inherent characteristics of the metal while being repeatedly stressed. Due to the extensive nature of the program and the wide scope of activities covered, only brief references are made to the data in the individual reports. Similarly, the details of the laboratory research programs, apparatus, materials, and testing techniques will not be discussed but are contained in the individual reports listed. In general, the results of this investigation have proved fruitful in contributing basic knowledge of the fundamental behavior of metals under repeated stressing and the application of this knowledge to the design of actual machine elements. It is hoped that this final summary of the program will serve a useful purpose as a guide to the reader in locating the detailed results of those studies from which he is interested in obtaining further information.Office of Naval Research, Department of the Navy, Contract No. N6ori-071(04), Project NR-031-00