University of Illinois Urbana-Champaign

Fatigue failure predictions for complicated stress strain histories

Dowling, N. E.

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https://hdl.handle.net/2142/112063

Description

Title
Fatigue failure predictions for complicated stress strain histories
Author(s)
Dowling, N. E.
Issue Date
1971-01
Keyword(s)
  • Fatigue Failure
  • Stress-strain
  • Rain Flow Cycle Counting Method
  • Cycle Counting Methods
Abstract
A cumulative fatigue damage procedure that considers sequence and mean stress is proposed for engineering metals. Fatigue life data for prestrained specimens are used to account for sequence effects due to crack initiation. Histories with fluctuating mean stress are analyzed by determining the mean stress of each cycle. The rain flow cycle counting method, which counts all closed stress-strain hysteresis loops and cycles, is employed in the damage procedure. Axially loaded unnotched specimens of 2024-T4 aluminum were tested to failure using various complicated stress or strain control conditions. Life predictions using the proposed cumulative damage procedure were made prior to testing for 83 specimens. The predicted lives were within a factor of three of the actual lives for all of the tests and within a factor of two for more than 90% of the tests. In some of the tests there were large plastic strains, and in others the strains were predominately elastic. Some of the stress control histories were similar to the load histories for actual machines, vehicles, and aircraft in that there were irregular loadings superimposed on changes in the static level. It is shown that the use of the average mean stress to make life predictions can result in large nonconservative errors. The rain flow cycle counting method allows satisfactory predictions of the effects of different block sizes, different sequences of applying the same strain peaks, and superimposed loadings, but the use of any of the other well known cycle counting methods, such as peak counting, level crossing counting, or range counting, can result in large differences between predicted and actual fatigue lives.
Publisher
Department of Theoretical and Applied Mechanics. College of Engineering. University of Illinois at Urbana-Champaign
Series/Report Name or Number
  • TAM R 337
  • 1971-6001
ISSN
0073-5264
Type of Resource
text
Language
eng
Permalink
http://hdl.handle.net/2142/112063
Sponsor(s)/Grant Number(s)
Naval Air Development Center, Contract No. N00156-70-C-1256
Copyright and License Information
Copyright 1971 Board of Trustees of the University of Illinois

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Technical Reports - Theoretical and Applied Mechanics (TAM) PRIMARY
TAM technical reports include manuscripts intended for publication, theses judged to have general interest, notes prepared for short courses, symposia compiled from outstanding undergraduate projects, and reports prepared for research-sponsoring agencies.