Review and Analysis of Cumulative-Fatigue-Damage Theories
Abstract
As the stress changes in an aircraft (or any other) structure, changes also occur in the material of the structure. Some stress changes or cycles are large enough to cause some amount of fatigue damage, even though this damage is not ordinarily discernible. There are three main problem areas in designing aircraft structures so that the accumulation of fatigue damage does not threaten safety--evaluation of cumulative damage; predicting and describing the fatigue-producing stress variations that will be experienced; and accounting for the wide scatter in fatigue life that is observed for seemingly identical test specimens and structures. The first, cumulative damage, arises because stress cycles in aircraft structures vary so greatly in size, number, and order that it is a practical impossibility to make enough tests to cover all variations. Therefore, fatigue damage caused by the many different stress cycles must be evaluated by adding up the effects of individual cycles. If we understood well enough the physical processes going on in a material during each stress cycle, this addition, or determination of cumulative effects, would be no problem. Lacking this understanding, evaluation of cumulative damage rests on theoretical methods, related in varying degree to the physical process of fatigue and to experiment. This Memorandum presents an investigation of the basic concepts of cumulative damage and of several current cumulative-fatigue-damage theories.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1963
- Accession Number
- ADA596085
Entities
People
- Lloyd Kaechele
Organizations
- RAND Corporation