STP1231

    Automation of Fatigue Crack Growth Data Acquisition for Contained and Through-Thickness Cracks Using Eddy-Current and Potential Difference Methods

    Published: Jan 1994


      Format Pages Price  
    PDF Version (492K) 22 $25   ADD TO CART
    Complete Source PDF (15M) 22 $131   ADD TO CART


    Abstract

    A brief review of crack length measurement is made with respect to fatigue crack growth. Two contrasting, closed-loop, computer-automated systems are presented for obtaining fatigue crack growth data. A d-c potential difference method is described that can obtain long crack growth data down to threshold using a high frequency, resonance-type test machine. Measurements of load/back face strain data are made automatically while the test is running and are used to obtain values of crack closure load using two regression analyses. An automated method for measuring the crack depth, length, and profile of small cracks growing in holes using eddy currents is described. A resonance-type or a servohydraulic test machine for variable amplitude loading can be controlled by the system. The method can detect and measure cracks with depths in the range of about 0.1 to 2 mm and more than one crack can be present in a hole. Results are presented in terms of crack depth as functions of distance into the hole and angular position around the hole. The printout includes the presentation of crack profiles with increasing load cycles. Both systems can be used under constant, decreasing, or increasing ΔK and at constant R-ratio or controlled values of Kmax or Kmin. The achievement of a range of target events can be used to initiate subsequent action, and on-line control is maintained through a wide range of keyboard options. Examples of the fatigue crack growth output from long and short cracks using both systems are given for a 2024 aluminum alloy. Crack profiles are shown for reamed and cold-worked holes.

    Keywords:

    fatigue crack growth, crack closure, computer automation, eddy currents, d-c potential difference, fatigue threshold, small cracks, crack profiles, holes, backface strain, residual stresses, cold-worked holes, contained cracks, resonance test machine, aluminum alloys, test automation, fracture (materials), fatigue (materials), testing methods, data analysis


    Author Information:

    Halliday, MD
    Research fellow and former reader, Interdisciplinary Research Centre in Materials for High Performance Applications and School of Metallurgy and Materials, University of Birmingham, Birmingham,

    Beevers, CJ
    Research fellow and former reader, Interdisciplinary Research Centre in Materials for High Performance Applications and School of Metallurgy and Materials, University of Birmingham, Birmingham,


    Paper ID: STP13948S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP13948S


    CrossRef ASTM International is a member of CrossRef.