Mechanical and ballistic analysis of aramid/vinyl ester composites

Abstract

This study focused on evaluating mechanical and dynamic-mechanical properties of polyaramid/vinyl ester composites, as a function of the fiber content. Furthermore, split Hopkinson pressure bar technique and V 50 Ballistic limit tests were performed. Composites were prepared by resin transfer molding (RTM) with different fiber content, samples being identified as AD4, AD5 and AD6 (with 4, 5 and 6 polyaramid layers, respectively). Initially, fiber, void and matrix contents were calculated and statistically analyzed, in different regions of the composites. Mechanical and dynamical mechanical properties of the composites were improved by using higher fiber content. For example, impact strength of AD6 composite was 35% higher than AD4. Moreover, increase in the fiber content promoted an increase in tenacity and stress of the composites, in the same strain rate. Velocity limit in AD6 sample was estimated in ballistics tests and it was concluded that the composite obtained could accomplish the level I requisites of ballistic protection with V 50 of 304 m.s À1 .

The effect of fluorination of aramid fibers on vinyl ester composites

“…Previous studies on vinyl-ester / aramid composites molded by RTM, with up to 67% fiber weight content, showed a void content of up to 7.03% [6], much higher than the value found here for the compression molded composite. In another study, compression molded Kevlar ® 29/epoxy composites reached fiber weight content within 54-65%, with specific weight of 1.238-1.391 g.cm −3 [1].…”

“…8) is associated with the rigidity of the material. As the temperature increases, E' values decrease due to the greater movement of chain segments [6]. As expected, the values of the pure resin are lower than those of the composites.…”

“…Previous studies on Kevlar® 29 aramid polymeric composites have reported issues related to the lack of adhesion between fibers and matrix, leading to delamination. Also, when the composites are processed by liquid molding, heterogeneity and excessive voids may also be noted due to the low permeability of the fibrous reinforcement . Indeed, aramid fibers exhibit inert and smooth chemical surfaces that lead to poor interfacial adhesion with the polymer matrix.…”

Use of the Split Hopkinson Pressure Bar on Performance Evaluation of Polymer Composites for Ballistic Protection Purposes

“…for Ballistic Protection Purposes Figure 1: Isometric view of the Hopkinson Bar, with the nomenclature of the main components 16 .…”

“…Pagnocelli et al 16 used the dynamic compression test on samples taken from 5 different regions of aramid/vynil-ester ballistic plates in order to verify if the distribution of the matrix through the fabrics occurred homogeneously during processing. The authors used σ max and J in this comparison, verifying that the peripheral regions obtained statistically equal properties, while the central region obtained mechanical property values 20% lower, an event associated to the fact that this region accumulated a larger volume of resin, making it fragile.…”