Compressive fatigue response and reliability analysis of thermoplastic composite with low‐velocity impact damage

Abstract Thermoplastic composite has attracted more and more attentions for its higher fracture toughness and better damage tolerance than thermosetting composites. AS4/PEEK laminate is a representative thermoplastic composite, which has been widely used in the fabrication of fuselages and aircraft wings. In this paper, low‐velocity impact tests had been carried out on AS4/PEEK laminates. Different impact energy levels were selected for forming impact dent with depth of 1 mm for the three stacking sequences: [0/0/‐45/90/45/0/0/45/90/‐45/0]_S, [0/0/45/90/‐45/0/45/90/‐45/0]_S, and [45/‐45/0/45/90/‐45/0/45/‐45/0]_S, which were 25.5, 21.0, and 20.0 J successively. Then, compression–compression fatigue tests with stress ratio of 10 and frequency of 10 Hz were used to obtain the residual fatigue life and damage propagation. It was found that significant local buckling appeared around the impact dent, which extended perpendicular to the loading direction during the compressive fatigue loading. The increase of the transverse dimension of local buckling could be divided into three stages. The experimental results indicated that a joint Weibull distribution could be used to describe the residual compressive fatigue life of the impacted laminates. This paper assumed an equal rank relationship between the residual strength and fatigue life, and the B‐basis value of fatigue stress was calculated to ensure the reliability of the impacted AS4/PEEK laminates, which were 0.53, 0.50, and 0.53 (normalized by residual compressive stress) at 10⁶ cycles for the three kinds of laminates mentioned earlier.