The Tensile Fatigue Behavior of a Glass-fiber Reinforced Plastic Composite Using a Hybrid-toughened Epoxy Matrix

Abstract

A thermosetting epoxy-polymer was modified by incorporating 9 wt% of carboxyl-terminated butadiene-acrylonitrile rubber microparticles and 10 wt% of silica nanoparticles. The tensile fatigue behavior at a stress ratio, R = 0.1 for both the neat-epoxy polymer (i.e., unmodified) and the hybrid-epoxy polymer was first investigated. The fatigue life of the hybrid-epoxy polymer was about six to ten times higher than that of the neat-epoxy polymer. Secondly, the neat- and the hybrid-epoxy resins were infused into a quasi-isotropic lay-up, E-glass fiber fabric via a ‘Resin Infusion under Flexible Tooling’ set-up to fabricate glass-fiber reinforced plastic (GFRP) composite panels. The tensile fatigue tests at a stress ratio, R = 0.1 were performed on both of these GFRP composites during which the matrix cracking and stiffness degradation were routinely monitored. The fatigue life of the GFRP composite increased by about six to ten times due to employing the hybrid-epoxy matrix, compared to employing the neat-epoxy matrix. Suppressed matrix cracking and a reduced crack propagation rate were observed in the hybrid-epoxy matrix, which resulted from the various toughening micromechanisms induced by the presence of both the rubber microparticles and silica nanoparticles. These factors were considered to contribute towards the enhanced fatigue life which was observed for the GFRP composite employing the hybrid-epoxy matrix.

Enhanced fatigue behavior of a glass fiber reinforced hybrid particles modified epoxy nanocomposite under WISPERX spectrum load sequence

“…8(c). It may be seen that, as observed earlier [24], for any given stress ratio, over the entire range of stress levels investigated, the addition of particles into the epoxy matrix enhances the fatigue life of the GFRP composite significantly.The experimental data of stress-life (S-N) curves of the GFRP composites shown in Fig. 8 were fitted to Basquin's law [46]:…”

“…5 clearly indicate the underlying mechanisms, i.e. suppressed matrix cracking, delayed initiation of 11 delamination, and reduced crack / delamination growth rate [42], for improved spectrum fatigue behavior in the GFRP-hybrid composite.It may be noted that the fatigue life enhancement is about eight to ten times under constant amplitude loads [24] whereas, it is reduced to about four to five times under WISPERX load sequence as observed in the present investigation. Load interaction effects in composites could alter the fatigue lives of composites significantly.…”

“…5 is an indication of the underlying mechanisms being operative in the composite material [24,25]. The stiffness loss in stage I and stage II results primarily from matrix cracking [24,36,39,40]. Once the matrix crack density saturates and attains the characteristic damage state (CDS) [24,36,39], the disbonds and delaminations created due to the coalescence of primary and secondary matrix cracks grow, and this leads to a further loss in stiffness.…”

“…The stiffness loss in stage I and stage II results primarily from matrix cracking [24,36,39,40]. Once the matrix crack density saturates and attains the characteristic damage state (CDS) [24,36,39], the disbonds and delaminations created due to the coalescence of primary and secondary matrix cracks grow, and this leads to a further loss in stiffness. The present results show that when both composites are subjected to same number of spectrum load blocks, the crack density is lower in the GFRP-hybrid compared to the GFRP-neat composite (see Fig.…”

From matrix nano- and micro-phase tougheners to composite macro-properties

“…Hence, such matrices may be used to produce PMC components via a RTM manufacturing route. It has been found [15,[19][20][21] that to obtain an optimum toughness, whilst maintaining other important properties, a 'hybrid' epoxy matrix polymer containing second phases of both such silica nanoparticles and rubber microparticles is frequently particularly effective. Considering the choice of the fibre reinforcement, there are clearly a very wide range of fibres that may be used in PMCs.…”