The Influence of Cooling Rate on the Fracture Properties of a Thermoplastic-Based Fibre-Metal Laminate

This paper investigates the effect of varying cooling rate on the mechanical properties of a novel fibre metal laminate based on glass-fibre polypropylene. Differential scanning calorimetry (DSC) and polarised light microscopy have been used to identify differences in the matrix morphology resulting from varying the processing conditions. Additionally, the residual stresses in simple bi-material samples manufactured under different cooling conditions were quantified in order to understand the effect of the cooling rate on the mechanical properties of these multilayered materials. The results indicate that the residual stresses were greater in the fast cooled samples, whereas the degree of crystallinity was higher in slow cooled samples. The results highlight a strong link between processing conditions and mechanical properties under both fibre and matrix-dominated modes of loading. The flexural properties of the plain composites and the fibre-metal laminates were greater at the low cooling rates. Conversely, the tensile strength and interlaminar toughness for both types of material were greater for specimens manufactured using high cooling rates. Finally, faster cooling was shown to yield laminates with a superior impact resistance. It is believed that the rapid cooling of the laminates enhanced their resistance to interlaminar fracture, which in turn resulted in smaller damage areas after impact.