MODELING DEFORMATION AND DAMAGE CHARACTERISTICS OF WOVEN FABRIC UNDERSMALL PROJECTILE IMPACT

Fabrics comprising highly oriented polymers possess high impact resist ance and are often used in flexible armour applications. As these mate rials are viscoelastic, accurate modelling of their impact and perfora tion response requires formulation of constitutive equations represent ing such behaviour. This study incorporates viscoelasticity into the f ormulation of a model to analyse the impact of small spherical project iles on plain-woven PPTA poly(p-phenylene-terephthalamide) fabric. The fabric is idealized as a network of viscoelastic fibre elements and a three-element viscoelastic constitutive model is used to represent po lymer behaviour. Viscoelastic parameters are used to reflect intermole cular and intramolecular bond strengths as well as the static mechanic al properties of fibres. Results of the theoretical analysis were comp ared with data from experimental tests on fabric specimens subjected t o projectile impact ranging from 140 m/s to 420 m/s. Predictions of th e threshold perforation velocity and energy absorbed by the fabric sho wed good agreement with experimental data. The proposed analysis is ab le to model deformation development and rupture of the fabric at the i mpact point. Fraying and unravelling of yarns are also accounted for. The study shows that a knowledge of static mechanical properties alone is insufficient and results in gross underestimation of impact resist ance. An important parameter identified is the crimping of yarns. Yarn s in woven fabric are not initially straightened out and hence part of the stretching in fabric is due to the straightening of yarns. The ef fect of crimping was found to be significant for high impact velocitie s.