STP738

    Effect of Δa-Increment on Calculating da/dN from a versus N Data

    Published: Jan 1981


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    Abstract

    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.

    Keywords:

    fatigue, growth rate, measurement, data analysis


    Author Information:

    Ostergaard, DF
    Graduate research assistant, graduate research assistant, and Professor of Mechanical Engineering, School of Mechanical Engineering, Purdue University, West Lafayette, Ind.

    Thomas, JR
    Graduate research assistant, graduate research assistant, and Professor of Mechanical Engineering, School of Mechanical Engineering, Purdue University, West Lafayette, Ind.

    Hillberry, BM
    Graduate research assistant, graduate research assistant, and Professor of Mechanical Engineering, School of Mechanical Engineering, Purdue University, West Lafayette, Ind.


    Paper ID: STP33461S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP33461S


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