Methods for Improving the Impact Resistance of Composite Materials

Abstract

A three-phase program to improve the impact resistance of composite materials was undertaken. In the first phase, the Charpy impact test was investigated for its utility in characterizing impact performance. It was found that the results of the standard Charpy test can be misleading, but the addition of instrumentation to provide load and energy histories can make this test a useful one. The importance of differentiating between initiation energy and propagation energy is shown, and a new parameter (the “Ductility Index”) is proposed, along with maximum stress and total energy, as a useful measure for comparing impact behavior of materials. The instrumented Charpy test was used to investigate impact behavior of unidirectional, epoxy-matrix composites reinforced with fibers of E-glass, Kevlar 49, and graphite. In addition, two unidirectional hybrid composite materials consisting of graphite and Kevlar 49 fibers in epoxy were investigated. Comparisons were made with quasi-static three-point bend tests. It was found that the hybrid materials had significantly higher impact energies, ductility indices, and maximum stresses than the all-graphite fiber material. Impact behavior of [±45] graphite/epoxy and hybrid Kevlar 49-graphite/epoxy panels, representative of aircraft fuselage shear panels, was studied using a ball-drop test. Results indicate a significant improvement in impact resistance with hybrid construction.

Experimental optimization of the impact energy absorption of epoxy–carbon laminates through controlled delamination

“…Beaumont et al [52] defined a dimensionless parameter called the ductility index (DI), which is found useful for ranking the impact performance of different materials under similar testing conditions. The DI is defined as the ratio between the propagation energy and the initiation energy, i.e.…”

The charpy impact fracture behavior of phenolphthalein polyether ketone

“…Its reduced viscosity in chloroform at 25°C is 0.49 dL/g. The specimens were injection-molded bars that were 55 mm long (L), 6 mm wide ( B ) , and 4 mm thick (D) and of about $D crack length (a).…”

Improving Impact Resistance of Polymer Concrete Using CNTs

“…The limited improvement in PC incorporating 1.5 wt% MWCNTs is attributed to the decrease in epoxy flowability and the difficulty to disperse this relatively high amount of MWCNTs in the epoxy resin as further discussed below. To examine effect of adding MWCNTs on the fracture behaviour of PCs, the ductility was evaluated by calculating the ductility index (DI) after (Beaumont et al 1975;Park et al 2000;Pegoretti et al 2008) for different mixes as per Eq. (4)…”