Low cycle fatigue and creep–fatigue interaction in short fibre reinforced aluminium alloy composite

Abstract

The high temperature low cycle fatigue resistance and the creep–fatigue interaction (CFI) behaviour in terms of the effects of prior fatigue exposure on the subsequent creep behaviour are evaluated and reported for a short alumina fibre (Saffil) reinforced aluminium alloy (Al–12Si–CuMgNi) matrix composite at 623 K. The prior fatigue to study the CFI behaviour was imparted in the form of low cycle fatigue loading in a fully reversed, total strain controlled loading up to a quarter of fatigue life at a total strain amplitude of 0·006 (the plastic strain amplitude at half-life is 0·004), corresponding to a plastic strain energy per cycle value of 0·46 MJ m–3. Subsequently, isothermal tensile creep tests were conducted at 623 K to evaluate the minimum creep rate, rupture time and strain to failure as a function of applied creep stress. Also examined were the fracture features as well as the nature and extent of damage that occurs during low cycle fatigue and creep–fatigue loading. The results obtained on the composite material are compared with those of the matrix aluminium alloy to bring out the effects of reinforcement. The results showed that the reinforcement causes significant loss in high temperature low cycle fatigue resistance in terms of fatigue ductility and cyclic energy parameters. Prior fatigue loading was seen to cause a small but consistent decrease in the creep resistance, which is attributed to the combined effects of mechanical loading and microstructural damage from prior fatigue loading.