Damage tolerance issues peculiar to supersonic civil transport aircraft

Abstract

International audienceThis paper presents results of experimental investigations on creep, fatigue and creep-fatigue crack growth behaviour of the 2650-T6 aluminium alloy in temperature, along with numerical simulation of stress distribution around the tip. The results will provide a preliminary database on the fatigue properties of the 2650 T6 alloy under loading representative of service conditions and predict the damage tolerance assessment of the future civil transport aircraft fuselage. Testing were carried out to evaluate the effect of creep-fatigue interaction and get insight into the damage processes. Numerical simulation of stress field around the crack tip were performed to account for the observed behaviour. The crack growth rates measured on CT specimens were correlated with the stress intensity factor K. In creep tests, an influence of the initial value of K on the low crack growth rates is shown. The behaviour is not deeply affected by temperature in the range 100-130°C. However, at 160°C, crack growth rates are faster than at 130°C due to an increase of creep contribution in local stress-strain response, that might be enhanced by ageing. In fatigue (triangular wave loading), no difference is noticed in crack growth rates at 20 and 130°C. In creep-fatigue, the crack growth rates (trapezoidal wave loading) at 130°C are faster than during creep or fatigue crack growth in a given domain of K. The fracture surfaces indicate that creepfatigue interaction is characterised by a higher portion of intergranular fracture. Thus, a detrimental creep-fatigue interaction at 130°C has to be taken into account in crack propagation law used in damage tolerance analysis. The constitutive law used in the calculations for numerical simulation was identified on the basis of cyclic relaxation tests. The computation results indicate that the von Mises stress at the beginning of dwell during creep-fatigue is higher than in the case of creep and fatigue