Experimental and computational study of non-woven damage mechanics

Abstract

Non-wovens are of emerging industrial and research importance due to the characteristic high surface area, high porosity, high damage tolerance and low cost. Despite wide applications, predicting non-woven mechanical strength and toughness remains a difficult task. One difficulty is that non-wovens usually experience complex microstructure change at finite strains, which involves a combination of fiber stretching, fiber bending, fiber rotation and bond breakage. Another challenge comes from the lack of effective experimental method to characterize interfiber bond properties. Moreover, the fiber deformation in a non-woven is non-affine, which is different from a classical continuum solid. Modeling microscopic fiber deformation and bond fracture within a continuum mechanics framework is not yet well established. This dissertation contributes to understand non-woven damage mechanics and to model non-woven mechanical behaviors at finite strains. First, we present a series of mechanical tests with in-situ X-ray imaging on three versions of non-woven with different areal weights. Experimental results revealed that (1) the decrease in the number of bonds in low density materials was significant, and drastic damage occurred at a lower strain than in the high density counterparts (2) no significant fiber orientation change was observed before the peak load in high areal weight non-wovens, which suggests that the inter-fiber bonds provide strong constraints on the network structure and limit fiber rotation. Second, we present a novel combined experimental and computational approach to extract bond strength. The method proposed in this work carries the dual advantages of characterizing actual bonds in a non-woven and characterizing hundreds of bonds simultaneously. Third, we present a micromechanics based damage model which is built upon modeling single bond breaking process and linking local damage events to macroscopic behaviors. The model is able to reproduce experimentally observed behaviors include elastic slope, non-linear hardening slope, peak load and damage localization under uniaxial tensile loading as a function of network density. The proposed model bridges non-woven microstructure and macroscopic behaviors and thus can serve as an effective tool for future studies of the mechanics of fiber network materials.