The relation between in-plane fiber waviness severity and first ply failure in thermoplastic composite laminates

Abstract

The influence of in-plane fiber waviness on the first ply failure of quasi-isotropic thermoplastic composite laminates was investigated. The failure mode and stress at first failure were studied by using a four-point bending test and an end-loaded bending (ELB) test. The experimental results confirm that no undesirable stress concentration due to load introduction occurred in the ELB test, thereby supporting the use of this test as an alternative method to measure stress at failure. The experiments demonstrated that waviness severity affects stress at first failure and compressive damage development. The stress at first failure initially decreases with increasing maximum waviness angle and levels off as the angle starts exceeding 20°. These results reinforce the hypothesis from previous research which suggests that wavy ply compressive strength is less sensitive to changes in severity at larger angles. Furthermore, it was found that kinking failure was the dominant failure mode for maximum waviness angle up to about 45°. No kink band was observed in wavy regions with maximum angles above 45° when there was another wavy region with a lower maximum angle in the same specimen. This means that failure is not necessarily initiated at the location where waviness is most severe.