An Investigation of Constant Amplitude Loaded Fatigue Crack Propagation of Virgin and Pre-Strained Aluminium Alloy

The article examines and explores the impact of pre-strain on resistance to fatigue crack propagation (FCP) via analytical models. Most of the materials during service and processing have gone through preexisting strain due to strain-invigorating processes. It is an utmost priority of any low-weight and high strength structural requirement. The numerical study is based on aluminum alloy 7475 with T7375 heat treatment, which is a candidate material for the aerospace industry due to its mechanical properties. In this paper, virgin and pre-strained Aluminum7475, 2.54 & 5% are explored in the time-invariant loading for load or stress ratio (R) of 0, 0.1, and 0.4 (minimum stress/maximum stress) via fatigue crack propagation model Paris and Crack annealing model. The model selected for the study is rooted in small-scale yielding theory which is based on linear elastic fracture mechanics (LEFM) without crack closure and accounting crack closure (CL). The emphasis on crack closure behavior before and after the pre-strain of material. Effects of load ratio 0, 0.1, and 0.4 have been studied via crack closure models- Elber, Newman, and Virtual crack annealing model. A comparative study of fatigue crack propagation Paris & Crack annealing model forecast has been presented for virgin and strained conditions. The predictions are validated via experimental data. Prediction error analysis has been presented in the forecast and actual data.

Keywords: Crack annealing model, Fatigue crack propagation, Pre-strained aluminium.