Development of test methods for measuring thick section tensile and compression properties of polymer matrix composites.

The use of polymer matrix composites (PMCs) has primarily involved thin membrane structures, but recent developments have seen an expansion in the use of composite materials in structural applications involving thick sections in excess of 20 mm, often complex in shape. The general perception has been to consider through thickness properties with thick composites as problematical and difficult to measure, whereas in fact an equally important issue relates to the measurement of in-plane properties and the effect of physical size of test specimens on measured data. Although extensive developmental work has been undertaken worldwide into test methods and design procedures for in-plane properties of thin laminates, there are no standard test methods available that provide guidance on testing of thick composite sections. The approach generally adopted has been to use existing standards, developed for testing small laboratory-scale specimens, with non-standard (i.e. larger) specimen geometries. A major concern relates to whether data generated from standards for relatively thin specimens are equivalent to or representative of thick section mechanical behaviour. This Measurement Note details work undertaken to develop tension and compression test methods suitable for testing ~20 mm thick carbon fibre-reinforced plastic (CFRP) laminates in support of the design of composite components comprising of thick material sections. The work has been carried out to evaluate the scaling effect of increasing coupon size (in-plane dimensions and thickness) for distributed ply laminates and effect of ply-level scaling i.e. the blocking together of plies of the same orientation.