Indentation and penetration of glass fibre reinforced plastic laminates with phenolic matrix

In many advanced industrial fields, such as aeronautics and transportation, the study of impact resistance of the composite materials is very important. In particular, it could be useful to appreciate the damage induced in the material by an accidental impact, during the manufacturing process, the in service or the maintenance. In literature, many papers are available on this topic, in particular different reinforcements (such as glass fibre, carbon fibre and aramid fibre) and resin typology (such as epoxy and polyester) were studied. In this paper, the impact behavior of laminates made of glass fibre and phenolic resin was studied. The laminates were produced by means of autoclave forming process. Two different samples typologies were studied: orthotropic and quasi-isotropic. For both the above mentioned samples, different thickness (3, 4, 5, and 6 mm) were analyzed. Impact test were carried out using a semi-spherical indenter and a “weight drop” CEAST testing machine with full penetration and variable energy. The aim of the variable energy test is to correlate the dimension of the indentation left by the indenter on the surface with the impact energy. The indentation measurement is very important and in this work the measurements were carried out using a LEICA DCM3 confocal microscope. A dedicated software allows to measure all the dimensions of interest. The tests with variable energy confirmed that the samples with different stratification show similar behaviors respect to the energy adsorption. On the other hand, about the external damage, the quasi-isotropic specimens showed an higher resistance than the orthotropic ones in all the different thicknesses tested. Furthermore, the results obtained allow to say that the indentation depth varies as a function of the impact energy following a logarithmic law, contrarily to what happen for laminates made by epoxy resin where an exponential law was observed.