Effect of temperature on the interlaminar shear strength of in-situ carbon fibre-reinforced thermoplastics measured in double beam shear tests

Out-of-plane mechanical properties play a significant role in the sizing of fibre-reinforced plastic (FRP) hydrogen tanks, where delaminations and crack propagation represent critical risks, particularly under cryogenic temperatures. A high delamination resistance is required to prevent spontaneous hydrogen permeation and leakage issues occurring in FRP hydrogen tanks. This paper presents an experimental investigation of the interlaminar properties of carbon fibre reinforced low-melt poly(aryletherketone) (CF/LM-PAEK) samples manufactured with the in-situ Automated Fibre Placement (AFP) technique. In manufacturing, the number of simultaneously deposited prepreg tapes is varied to determine its influence on the interlaminar shear properties. A five-point bending fixture (also known as double beam shear - DBS - test method) is integrated in a temperature chamber and tests are performed at temperatures between −40°C and 80°C. Using digital image correlation, the complete interlaminar shear stress versus shear strain curves and the strain at first delamination are measured. The results show a clear drop of the interlaminar shear modulus and shear strength at increasing temperature, while the strain at initiation of the delamination remains almost constant. The homogeneity and quality of the samples are also shown to be both influenced by the number of simultaneous tapes and strongly influence the measurements in DBS test.