Some insights into the impact fatigue damage behaviour in laminated composites

Abstract

An experimental method for impact fatigue of low energy was devised to provide some insights into the impact fatigue damage behaviour and characterize the response of laminated glass/polyester composites under conditions of increasing impact energy and increasing number of impacts. The impact frequency and subsequent projectile velocity of an impact fatigue apparatus specially designed and fabricated was varied to provide a spread of incident energies. The internal damage as a consequence of repeated impacts was investigated at five different levels of incident impact energy in the range of 3 -7J, with the laminated specimens. The results indicated that the laminates suffered severe microstructural damage under impact fatigue, including cracking of the resin, delaminations, crushing and fracture of the glass fibres. Macroscopic failure mode can also be observed, such as; formation of spherical crater and propagating crack at the back face of plates, formed by the tensileshearing failure of fibre bundles at the weaving level. The delamination behaviour in the laminated specimens depended largely upon the level of incident energy. Well-defined impact fatigue (E-N f ) behaviour, showing an endurance limit at above 10 4 impact cycles, has been demonstrated.

Rupture by impact-induced fatigue of a copper foil strip embedded in a multifunctional composite material

“…The impactor has a hemispherical head, 15 mm in diameter, and a mass M of 5.7 kg. This machine was used in previous works by Ouroua et al, 25 Azouaoui et al 2,4 and Mouhoubi et al 5,6 A description of the experimental setup is given in (Figure 2). The assembly used for holding the test samples is generally used for the evaluation of puncture strength in plastic materials.…”

“…The repeated impacts induce damages characterized by the formation of craters on the impacted surface (front surface) and delamination of the non-impacted surface (back surface). The method for measuring these damages is similar to that used in previous works by Ouroua et al, 25 Mouhoubi et al 5,6 and Azouaoui et al 2,4 Before the impact fatigue test, nine test samples were singled out to do pre-impact fatigue testing, where for each energy level (E i ¼ 2, 3, and 4 J) three samples were impacted until total rupture of the composite. The aim of this preliminary test was to define an average number of impacts to total failure of the composite material, which was used to determine when to stop the machine, periodically, to collect damage data during the impact cycles.…”

“…The behavior of these materials under cyclic dynamic loads such as repeated shocks has always been a center of interest to designers and researchers. [2][3][4][5][6][7][8][9]11,25 Tests of shock-driven fatigue allow the study of the effects of the number of impacts and the accumulated impact energy on the damage of composite materials. Studies of the effect of impact energy on the life span of layered glass-polyester materials, where plots of fatigue curves showed a classical fatigue behavior, were reported in Refs.…”

“…Studies of the effect of impact energy on the life span of layered glass-polyester materials, where plots of fatigue curves showed a classical fatigue behavior, were reported in Refs. 2,25 Rupture processes in a layered hybrid material with metallic inserts are divers and can be described only if we know: the strength criteria of each constituent of the composite material, the state of constraints and deformations in the material, the phenomena of crack propagation in the microstructure, and the nature of the interface between the composite matrix, armor, and metallic insert.…”

“…Following the works reported in Refs., 2,3,5,25 we developed this study with the main goal to quantitatively determine the lifespan, strength, behavior and electrical failure of a glass-epoxy composite with embedded copper foil strip when subjected to periodic impact stress. This was accomplished by experimentally determining the evolution of the various damage parameters such as the delamination area, and the width and depth of the crater that form under such stress.…”