突風学力レベルが疲労き裂進展挙動に及ぼす影響 フライトシミュレーション応力下のき裂進展の加速と遅延

Abstract

Fatigue tests were carried out on 2024-T3 aluminum alloy sheet material under 11 kinds of flight simulation loadings and its crack propagation behavior was observed. In this experiment, flight simulation loadings were made to simplify a complex stress history so that they consisted of the ground to air cycle of large stress range and gust cycles of relatively small stress range.The results obtained were as follows:(1) When the maximum stress of the ground to air cycle was equal to the maximum stress of gust cycles, the crack propagation rate under flight simulation loading was faster than that estimated by the linear damage law on the basis of crack propagation of constant stress amplitudes.(2) When the maximum stress of gust cycles was 40MPa or 80MPa lower than that of the ground to air cycle, the crack propagation rate in a short crack length was almost the same as the estimated value. With increasing crack length, the crack propagation clearly showed the retardation behavior. As the crack length increased further and approached to the critical value of final fracture, the crack propagation rate gradually recovered to the estimated values.(3) When the maximum stress of gust cycles was 120MPa or 160MPa lower than that of the ground to air cycle, the crack propagation rate under the flight simulation was nearly equal to the estimated value and the retardation behavior could not be observed in the whole range of crack propagation.(4) The retardation behavior of crack propagation was not observed just after changing the stress of the ground to air cycle to the gust stress, but the crack propagation clearly showed the retardation behavior with increasing the number of gust cycles in the same flight.