FCP Report No. 42

The Effect of Selected Subcycles in Block Loading Fatigue Histories

by

Thomas J. Deves
Peter Kurath
Huseyin Sehitoglu
JoDean Morrow
Department of Theoretical and Applied Mechanics

Abstract

When considering variable amplitude histories representative of service situations, fatigue life estimates employing simple constant amplitude data and a linear damage rule are usually nonconservative. Investigators, in attempts to improve these estimates, have focused their attention on (1) event counting algorithms, (2) alteration of the baseline properties, (3) implementation of other damage summation conventions, or (4) damage criteria (i.e. strain-life, crack growth).

In this investigation, selected variable amplitude histories were chosen, and tests were conducted on smooth cylindrical laboratory specimens. Three methods of analysis were examined, (1) linear damage, (2) plastic work interaction, and (3) J-integral crack growth approach. The results of these analyses and tests are employed to further the understanding of sequence, interaction, and memory effects in fatigue. Results indicate that methods (2) and (3) provide improved fatigue life estimates.

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