Evaluation of continuous filament mat influence on the bending behaviour of GFRP pultruded material via Electronic Speckle Pattern Interferometry

Pultrusion is a process allowing the production of unidirectional (roving) fibre-reinforced polymer (FRP) structural elements with constant cross section. Recently, also civil engineers focused their attention on pultruded composite materials as alternative to traditional ones (e.g., concrete, steel). Furthermore, to improve the transverse strength and stiffness with respect to the fibres direction, continuous filament mat (CFM) is often placed within the stacking sequence. The CFM influence on the global mechanical behaviour is not considered by appropriate actual international standards. In this paper, the influence of the CFM layers on the mechanical behaviour of glass fibres pultruded composite material is investigated. In particular, the bending behaviour is analyzed by performing a four-point bending test on specimens extracted from an H-shape member. The experimental analysis was carried out via Electronic Speckle-Pattern Interferometry (ESPI) (handled by phase-stepping technique) to obtain a full-field displacement map and to numerically achieve the longitudinal strains. By imposing the equilibrium conditions and assuming the compression and tensile roving Young's moduli as constant, the CFM Young's moduli are determined. Finally, the mean stress acting on the material is obtained showing that CFM layers have to be considered to correctly evaluate the maximum stress and to optimize the design phase.