Understanding the effect of block overloading on the fatigue behaviour of 2024-T351 aluminium alloy using the fatigue damage map

This work aims to provide extensive experimental evidence that reinforce the fact that block overloading can produce phenomena of either crack growth acceleration or retardation depending on its magnitude, duration and the fatigue damage stage characterising its onset. Compared to the majority of similar experimental works in the field, the investigation is based on the classification of identical overloading conditions applying to four distinct crack lengths corresponding to microstructurally short, physically short, long and very long crack conditions. The above is done in order to deliver a better understanding towards the capacity of the crack length to affect the post-overloading response, which in many cases has been hidden from the use of ΔK oriented experiments. The work, which is based on the popular 2024-T351 aluminium alloy, concludes that the effect of the aforementioned parameters on the material’s response to block overloading is complex and is represented by a mixture of acceleration or retardation mechanisms. Based on the experimental data, a sensitivity analysis is performed on the presence of load interaction mechanisms occurred or triggered by the onset and duration of overloading blocks. The boundary conditions indicating the onset of specific load interaction mechanisms have been established and incorporated into the fatigue damage map. The above methodology allows the mapping and therefore the discrimination of the overloading conditions in terms of fatigue life increase or decrease. The methodology is found to predict satisfactory the experimental results.