# Strain-Rate-Dependent Tensile Behaviour and Viscoelastic Modelling of Kevlar® 29 Plain-Woven Fabric for Ballistic Applications

## TL;DR

This paper studies how Kevlar® 29 fabric behaves under different strain rates and develops a model to describe its mechanical properties for use in body armor.

## Contribution

A modified three-element viscoelastic model is proposed to capture strain-rate-dependent tensile behavior of Kevlar® 29 fabric.

## Key findings

- Tensile strength, elastic modulus, and toughness increase with strain rate, while fracture strain decreases.
- Quasi-static loading causes ductile failure with plastic flow, while dynamic loading leads to brittle fracture with axial splitting.
- The viscoelastic model accurately describes the fabric's behavior across strain rates.

## Abstract

Aramid fibre has become a critical material for individual soft body armour due to its lightweight nature and exceptional impact resistance. To investigate its energy absorption mechanism, quasi-static and dynamic tensile experiments were conducted on Kevlar® 29 plain-woven fabric using a universal material testing machine and a Split Hopkinson Tensile Bar (SHTB) apparatus. Tensile mechanical responses were obtained under various strain rates. Fracture morphology was characterised using scanning electron microscopy (SEM) and ultra-depth three-dimensional microscopy, followed by an analysis of microstructural damage patterns. Considering the strain rate effect, a viscoelastic constitutive model was developed. The results indicate that the tensile mechanical properties of Kevlar® 29 plain-woven fabric are strain-rate dependent. Tensile strength, elastic modulus, and toughness increase with strain rate, whereas fracture strain decreases. Under quasi-static loading, the fracture surface exhibits plastic flow, with slight axial splitting and tapered fibre ends, indicating ductile failure. In contrast, dynamic loading leads to pronounced axial splitting with reduced split depth, simultaneous rupture of fibre skin and core layers, and fibrillation phenomena, suggesting brittle fracture characteristics. The modified three-element viscoelastic constitutive model effectively captures the strain-rate effect and accurately describes the tensile behaviour of the plain-woven fabric across different strain rates. These findings provide valuable data support for research on ballistic mechanisms and the performance optimisation of protective materials.