Fatigue crack growth and crack closure in an AlMgSi alloy

Abstract

This study reports an experimental investigation of fatigue crack propagation in AlMgSi1‐T6 aluminium alloy using both constant and variable load amplitudes. Crack closure was monitored in all tests by the compliance technique using a pin microgauge. For the constant amplitude tests four different stress ratios were analysed. The crack closure parameter U was calculated and related with ΔK and the stress ratio, R. The threshold of the stress intensity factor range, ΔKth , was also obtained. Fatigue crack propagation tests with single tensile peak overloads have been performed at constant load amplitude conditions. The observed transient post overload behaviour is discussed in terms of the overload ratio, ΔK baseline level and R. The crack closure parameter U trends are compared with the crack growth transients. Experimental support is given for the hypothesis that crack closure is the main factor determining the transient crack growth behaviour following overloads on AlMgSi1‐T6 alloy for plane stress conditions.

Fatigue crack growth in thin aluminium alloy sheets under loading sequences with periodic overloads

“…As reported for single overloads in the analysed alloy [6,7] the observed crack growth trends under periodic overloads are consistent with the plasticity-induced crack closure phenomenon. Each overload produces higher monotonic plastic zone than the baseline loading.…”

“…In recent work, the authors observed that the plasticity-induced crack closure phenomenon could generally explain the crack growth behaviour following single peak overloads under both load control mode [6] and constant DK conditions [7]. The present work intends to analyse the fatigue crack growth due to several loading sequences containing periodic single overloads and to clarify if the observed behaviour can also be correlated with the crack closure phenomenon.…”

“…The majority of the work carried out in this field has been on the effects of single peak tensile overloads [3][4][5][6][7] simply because this type of loading can lead to significant load interaction effects. In contrast, other variable amplitude loading sequences have not yet been exhaustively investigated.…”

Effects of Shot-Peening and Stress Ratio on the Fatigue Crack Propagation of AL 7475-T7351 Specimens

“…This discrepancy was justified by Paris et al [24], who suggested the "partial closure model". Borrego et al [25] concluded that crack closure explained the bias of stress ratio on the fatigue crack growth rate for the 6082-T6 aluminum alloy and the influence of several load parameters for overloads interactions if the partial crack closure model is included in the analyses.…”

Finite element modelling and analysis of crack shape evolution in mode-I fatigue Middle Cracked Tension specimens

“…The experimental crack shapes were obtained by Borrego in crack closure studies [21] made in MT specimens according to the standard ASTM E647. Specimens with a fixed thickness of 3 mm were considered (the other dimensions are similar to the ones indicated in Fig.…”