Effect of Yarn and Fabric Structure on Air Permeability.

摘要

Permeability is the dominant functional characteristic of parachute cloth. Excessive permeability reduces deceleration rates, while too low a permeability can cause excessive loads on both the chute and the object being decelerated. High speed objects and attendent high pressure drops on chutes have necessitated the development of more rational understanding of the factors affecting permeability. The problem is very complex because of: (a) Variety of types, and thus their effects, of geometrical factors, (plain weave cloth alone, ideally, has 11 variables of construction, add to this the effects of yarn structure). (b) The type of flow through fabrics can and does change from 'simple stream-llne' flow to turbulent flow at high pressure drops. (c) The nature of the 'orifice' in fabric flow changes with pressure drop i. e., crimp interchange under biaxial tension enlarges the fabric 'pores' and can increase the flow between yarns, while increases in turbulence and flow between fibers can assume importance at high pressure drops.