Technical Reports

Strain-Life Fatigue Analysis

  • 01
  • Sep
  • 1984
AUTHOR: Jen C. Shang
OFFICE: RPD
REPORT NUMBER: R-589
SUBJECT: Rail and Infrastructure Integrity
KEYWORDS: Design Methodology, Local Plastic Strains, Materials
ABSTRACT: The strain-life approach to characterize the fatigue behavior of materials and its applications to railroad equipment design have been investigated. A logical means of accounting for local plastic strains, which are the cause of fatigue failures, has been given, and constitutive relations between strain and fatigue life were also developed. Moveover, a concept of cyclic material characteristics was introduced; mean stresses were taken into account by a simple modification of the strain-life equation; and a technique to include the effect of geometric notches was presented. A combination of the above analytical tools with an adequate cycle counting technique, such as rainflow, which accrues closed hysteresis loops permits prediction of fatigue initiation life of materials under random road environments. In addition, a general overview of current fatigue analysis methodologies using the stress-life and strain-life approaches and the fracture mechanics formulation, is presented in relation to their design philosophy, benefits and pitfalls when applied to the railroad industry.
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