SYMPOSIA PAPER Published: 01 January 1981
STP33461S

Effect of Δ -Increment on Calculating from versus Data

Source

Data from a previously reported study were analyzed to determine the effect of the Δa-increment on the error in calculating the fatigue crack growth rate from recorded a versus N data. The data had been recorded from 68 replicate fatigue crack growth tests on center crack panels of 2024-T3 aluminum alloy using a Δa-increment of 0.2 mm. Two different differentiation methods were considered, the secant method and the quadratic seven-point incremental polynomial method. The influence of the Δa-increment was determined by evaluating da/dN using all the data, every second, every fourth, every eighth, and every sixteenth data point. The minimum error for calculating da/dN was found to be for Δa between 0.8 and 1.6 mm. An evaluation of the type of distribution for da/dN showed that of the five distributions considered no single distribution adequately represented all da/dN regardless of the Δa-increment.

Author Information

Ostergaard, DF
School of Mechanical Engineering, Purdue University, West Lafayette, Ind.
Thomas, JR
School of Mechanical Engineering, Purdue University, West Lafayette, Ind.
Hillberry, BM
School of Mechanical Engineering, Purdue University, West Lafayette, Ind.
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Details
Developed by Committee: E08
Pages: 194–204
DOI: 10.1520/STP33461S
ISBN-EB: 978-0-8031-4804-8
ISBN-13: 978-0-8031-0717-5