Fatigue Behavior of Aramid Nonwoven Fabrics Under Hot-Press Conditions Part Ⅴ: Effect of Punching Density on Mechanical Properties

摘要

Changes in the mechanical properties and durability of a nonwoven fabric with repeated hot-press fatiguing treatment depend on the properties of the fiber material and the structure of the nonwoven. Following Part Ⅳ, which deals with fiber fineness, in this paper we focus on punching density, which greatly affects the nonwoven structure, and we discuss the influence of punching density on the mechanical properties of nonwoven fabrics after hot-press fatiguing cycles. We hypothesize that a nonwoven with greater punching density will have a larger number of fibers reaching perpendicularly across its width. This will increase fiber entanglement because more fibers will be caught by the needle. In Part Ⅳ, we found that a nonwoven fabric with more entangled fibers has a higher tensile breaking strength, so it is natural to believe that a nonwoven with a higher punching density has a higher tensile strength than one with a low punching density. The experimental results show, however, that a nonwoven with too much punching density has a lower tensile strength due to fiber breakage by too much needle punching. Thus, there is an optimum punching density that gives the highest tensile strength. Regarding compressive behavior, a nonwoven fabric with higher punching density has a small compressive strain and high compressive modulus, meaning it is stiffer. We have found that changes in tensile and compressive behaviors with hot-press fatiguing closely relate to nonwoven fiber packing factors.