Dynamic Tensile Testing of Needle-Punched Nonwoven Fabrics

Francisca Martínez-Hergueta,Álvaro Ridruejo,Javier Llorca,Carlos González,Nik Petrinic,Antonio Pellegrino

doi:10.3390/app10155081

Abstract

The tensile testing of a needle-punched nonwoven fabric is presented. A high-sensitivity Split-Hopkinson Tensile Bar device was specifically designed for this purpose. The strain gauge measurements were combined with high-speed photography and Digital Image Correlation to analyse the deformation micromechanisms at high strain rates. The experimental set-up allowed to determine the wave propagation velocity of the as-received nonwove fabric, the evolution of the strain field with deformation and the wave interaction inside the fabric. The deformation was accommodated by the same micromechanisms observed during quasi-static tensile testing and ballistic impact, which comprised fibre straightening, rotation and sliding. Heterogeneous strain fields were developed in the nonwoven fabric as a result of the non-linear pseudoplastic response of the fabric and the internal dissipation due to the frictional deformation micromechanisms, preventing the propagation of high magnitude strain waves into the specimen. Additionally, the output forces were analysed to determine the influence of high-strain rates in the mechanical response of the nonwoven fabric, finding an increment of the stiffness for low applied strains under dynamic loading. These findings provide the basis to develop strain-rate dependent constitutive models to predict wave propagation in needle-punched nonwoven fabrics when subjected to impact loads.

Highlights

Dry fabrics based on high strength fibres such as Kevlar and Dyneema are conventionally used for soft body armour due to their high energy absorption capacity against ballistic impact [1].These materials present a very low bending stiffness due to the lack of resin, resulting in lightweight flexible textiles for personal protection [2]
This study aims to determine the dynamic response of needle-punched nonwoven fabrics subjected to in-plane tensile loads, with special emphasis on the evolution of wave propagation
The stiffness of the material was directly proportional to the fibre orientation distribution function (ODF) resulting in an equivalent increment of tangent stiffness with strain; see Figure 3a

Summary

Introduction

Dry fabrics based on high strength fibres such as Kevlar and Dyneema are conventionally used for soft body armour due to their high energy absorption capacity against ballistic impact [1]. These materials present a very low bending stiffness due to the lack of resin, resulting in lightweight flexible textiles for personal protection [2]. Their membrane response results in a large amount of energy absorption due to in-plane deformation [3]. Needle-punched nonwoven fabrics present a lower stiffness and strength (as well as processing cost) than their woven counterparts, but possess a higher deformability and excellent ballistic performance against small calibres and shrapnel [4].

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Conclusion