Compression behavior of glass-fiber-reinforced and pure polyurethane foams at negative temperatures down to cryogenic ones

Abstract

This work experimentally addresses the effects of negative temperature on compression behavior of non-reinforced and glass-fiber-reinforced polyurethane foams. Monotonic, creep and cyclic compression tests are performed down to cryogenic temperatures. In this range, temperature is shown to influence both the Young's modulus and the yield stress, which increase with decreasing temperature. The influence is nearly the same on either reinforced or unreinforced foams, mostly due to the preferential orientation of fibers perpendicular to the compression direction. Among contributions that could explain low temperature deformation, viscoelasticity and damage are focused on. The former contribution was investigated by creep and recovery tests, which showed that a non-negligible part of the compression strain could be recovered. The latter contribution was studied from cyclic tests and scanning electron microscopy observations. Damage analyses showed that a non-negligible initial damage issued from cooling down itself prior to mechanical loading. During further compression, a decrease of the cyclic modulus was observed, significantly before the yield stress at low temperature. Generalized brittle fracture of cavity walls was suggested from micrographs. As a conclusion, damage and viscous phenomena seem to coexist down to cryogenic temperatures.