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

Abstract

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

Experimental analysis of new moment resisting steel connections

“…The test is performed on LRPD designed for HEB240 beams. The obtained results confirm the expected performance of LRPD constituting a fundamental step for the subsequent experimental steps mainly constituted by cyclic tests and by a deep analysis of mechanical behavior of LRPD also adopting full-field contactless analysis method as Electronic Speckle Pattern Interferometry (ESPI) [17][18][19], to obtain highly accurate strain full-field.…”

Influence of fibre orientation on pultruded GFRP material properties

“…It is noticeable that damage was limited to the middle region of the specimen through the strain gauges, especially for pultruded GFRP specimens with off-axis angle higher than 30°. The continuous filament mat has been found to be the weakest element of pultruded GFRP [40], which can influence the failure mechanism of composites with off-axis fibre orientations [41]. However, for coupons with off-axis direction lower than 30°, delamination along the roving fibre was clearly shown in each test due to the fibre-dominant behaviour.…”

Investigation of the Internal Structure of Fiber Reinforced Geopolymer Composite under Mechanical Impact: A Micro Computed Tomography (µCT) Study

“…The specimen was completely deformed, and even the regions outside the impact zone remained permanently twisted due to the impact, as is clearly shown from the top images in Figure 10 where the two "flat" parts no longer lay in the same plane. As a result, the remainder of the composite could only carry very negligible loads compared to the original value before the damage [23]. The overall image of the basalt fiber reinforced geopolymer composite is shown in Figure 11.…”

“…The impact area was observed with a fiber rupture region from the top along the direction of the central impact rupture. As a result, the remainder of the composite could only carry very negligible loads compared to the original value before the damage [23]. The overall image of the basalt fiber reinforced geopolymer composite is shown in Figure 11.…”