Fatigue crack propagation tests with single tensile peak overloads have been performed in 6082-T6 aluminium alloy at several baseline DK levels and stress ratios of 0.05 and 0.25. The tests were carried out at constant DK conditions. Crack closure was monitored in all tests by the compliance technique using a pin microgauge. The observed transient post-overload behaviour is discussed in terms of overload ratio, baseline DK level and stress ratio. The crack closure parameter U was obtained and compared with the crack growth transients. Experimental support is given for the hypothesis that plasticity-induced closure is the main cause of overload retardation for plane stress conditions. Predictions based on crack closure measurements show good correlation with the observed crack growth rates for all the post-overload transients when discontinuous closure is properly taken into account.

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.

In this study low-cycle fatigue tests were performed in two AlMgSi aluminium alloys with different chemical composition, namely 6082-T6 and 6060-T6 alloys, using standard round specimens and tube specimens, respectively. The tests were undertaken in strain control with a strain ratio R e ¼ À1. The cyclic stress-strain curves were determined using one specimen for each imposed strain level. The low-cycle fatigue results are used for the characterisation of the cyclic plastic response and the fatigue live of the alloys. Moreover, the geometry of the hysteresis loops and the occurrence of Masing behaviour are also analysed. The observed behaviour is discussed in terms of the chemical composition of the alloys (Mg 2 Si hardening particles and Mn dispersoid content) and fracture mechanisms. Alloy 6060-T6 exhibits nearly ideal Masing behaviour, while alloy 6082-T6 presents significant deviations from the Masing model. The type of cyclic deformation behaviour in AlMgSi alloys seems to be influenced by the dispersoid phase.

No abstract

Fatigue crack propagation tests in constant amplitude loading, as well as with single peak overloads, have been performed in AlMgSi1-T6 aluminium alloys with different Mn and Cr contents. Crack closure was monitored in all tests by the compliance technique using a pin microgauge. A moderate stress ratio and a strong material dependence effects on the fatigue crack growth were observed. These effects are discussed in terms of the different dominant closure mechanism (plasticity-induced closure or roughness-induced closure). Roughness-induced closure dominates crack closure in the alloys with higher contents of Mn and Cr elements. In the alloy with a lower content of these elements, plasticity-induced closure is dominant. When roughness-induced closure is the prime pre-overload closure mechanism, the retardation effect is decreased in comparison to when plasticity-induced closure is dominant.