Evaluation of Fatigue Crack Closure from Local Compliance Measurements in Structural Steel

摘要

Two procedures developed by the present authors are applied to evaluate crack closure for structural steel. One of these (the A method) involves operations on electric signals from the load and local strain transducers, whilst the other (the D method) applies processing of the digitized compliance data. The closure levels are identified based on comparisons between the open crack compliance variations upon loading and unloading. Specially designed fatigue tests were conducted to generate fatigue crack growth data and compliance data necessary to check the performance of both methods. Parameters of the compliance data acquisition were found to significantly affect the closure levels according to the D method. For a properly chosen combination of these parameters, the D method results compare well with those from the A method obtained using a different measurement system and assumed to represent the true closure levels. The adequacy of both methods is proved by the ability of the resulting effective stress intensity factor range to correlate the observed effects of stress ratio on fatigue crack growth and to account for the post-overload transient crack growth behaviour.