Flexural performance of shape memory alloy/CF-PEKK fiber metal laminates for aircraft morphing under varied temperature conditions

In this study, novel Fiber Metal Laminates (FMLs) were manufactured using Nickel Titanium (NiTi) sheets together with Carbon Fiber-Polyetherketoneketone (CF-PEKK) prepregs for different aerospace applications. We have investigated the effect of various temperatures on the flexural properties of NiTi/CF-PEKK FMLs. Prior to manufacture, NiTi sheets were anodized to improve the adhesion between the metal surface with the prepreg. The laminate was then compression molded in a hot-press. The flexural response of manufactured FMLs was investigated at various temperature conditions encompassing martensite and austenite phase of NiTi and glass transition temperature (T_g) of PEKK i.e. (50, 75, 100, and 175 °C). The fractographic studies were completed using optical microscopy and Scanning Electron Microscopy (SEM). The results showed that different testing temperatures have a significant impact on the flexural properties of the manufactured FMLs. Different types of failure modes were observed, ranging from brittle to ductile failure of fibers, delamination of NiTi sheets, and fiber pull-out from the matrix. The highest flexural strength (612 MPa) and flexural modulus (57.5 GPa) were observed at 100 ºC which was attributed to the higher modulus of NiTi in its austenitic phase and strong fiber-matrix interaction. However, above the glass transition temperature of PEKK, a sharp decline in the flexural response was observed due to the softness of the PEKK material and increased mobility within the prepreg layers.