Improvement of fatigue crack growth resistance by controlled overaging in 2024‐T3 aluminium alloy

Abstract

A B S T R A C T A controlled overaging process is proposed to increase region II fatigue crack propagation resistance of 2024-T3 aluminium alloy. Overaging was achieved by subjecting the material from the initial T3 state to heat treatment at specific aging temperatures resulting in substantial reduction in hardness. Fatigue crack growth tests were subsequently performed in the intermediate ΔΚ region to assess the influence of aging treatment on fatigue crack propagation rate. The experimental results showed that overaging at high temperatures enhances the fatigue crack growth resistance of the material with regard to initial T3 state. Fatigue crack growth rates were found to decrease with increasing overaging temperature. Cyclic stress strain tests were performed to assess the impact of the performed overaging on cyclic behaviour. The results revealed that cyclic strain hardening is enhanced in the overaged material, contributing to increased fatigue crack closure levels.A 25 = elongation at fracture b = fatigue strength exponent C = parameter of Paris equation c = fatigue ductility exponent E = Young's modulus h = cyclic hardening capacity as a percentage increase of yield strength H = strength coefficient H' = cyclic strength coefficient m = Paris equation exponent n = strain hardening exponent n' = cyclic strain hardening exponent N f = fatigue life p = cumulated plastic strain P max = maximum applied load P min = minimum applied load P op = crack opening load Q = maximum amount of hardening R = stress/strain ratio V = crack opening displacement at points A,B in C(T) specimen V max = crack opening displacement at points A,B in C(T) specimen corresponding at P max V min = crack opening displacement at points A,B in C(T) specimen corresponding at P min V op = crack opening displacement at points A,B in C(T) specimen when crack surfaces come into contact β = driving rate of hardening ΔV = crack opening displacement range at points A,B in C(T) specimen Δε = total strain range Δε p = plastic strain range ΔΚ = stress intensity factor range Correspondence: A. Tzamtzis.

Improved fatigue crack growth resistance by retrogression and re‐aging heat treatment in 7010 aluminum alloy

“…The roughness data shown in Table infers that the fracture surface roughness is relatively high in RRA compared with T6 alloy suggesting higher closure in RRA leading to reduced crack growth rates. A similar observation of enhanced fatigue crack growth resistance was observed in Al‐Cu systems which was attributed to increased cyclic strain hardening, leading to higher closure levels in over aged condition …”

“…Several studies have been made on the effect of heat treatment on the fatigue crack growth behavior of various aluminum alloys. The studies made on 2xxx series aluminum alloys have shown that over aging imparts enhanced fatigue crack growth resistance . This has been attributed to cyclic strain hardening response of Al‐Cu systems in over aged condition that promotes higher crack closure, which is reported to benefit low cycle fatigue behavior.…”

“…The studies made on 2xxx series aluminum alloys have shown that over aging imparts enhanced fatigue crack growth resistance. [18][19][20][21][22] This has been attributed to cyclic strain hardening response of Al-Cu systems in over aged condition that promotes higher crack closure, which is reported to benefit low cycle fatigue behavior. A few limited studies 23,24 have highlighted the beneficial influence of the RRA treatment on the fatigue behavior of aluminum alloys.…”

A new expression for crack opening stress determined based on maximum crack opening displacement under tension–compression cyclic loading

“…And the strain hardening contributes to increased COS. The Tzamtzis research is available to support this conclusion.…”

Monotonic and low cycle fatigue behaviour of 2024‐T3 aluminium alloy between room temperature and 300 °C for designing VAWT components

“…Fatigue behaviour of various aluminium alloys and their different chemical compositions have been studied extensively. Studies mainly focused on the different fatigue behaviour of different aluminium alloys, while few of them focused on specimens under low cycle fatigue and high cycle fatigue . Numerous studies regarding the fatigue life of various aluminium alloys under different temperatures have been conducted.…”