TIME-DEPENDENT DEFORMATION AND DAMAGE GROWTH IN A NONLINEAR VISCOELASTIC RUBBER-TOUGHENED FIBER COMPOSITE

摘要

The constitutive theory developed by Schapery (1999) is first tailored for a continuousrnfiber composite to develop a Damage Effect Study which identifies the material parametersrnaffected by damage, thereby separating the damage and stress effects on softening. Thisrnmethod is based on 'vertical shifting' of creep-recovery data at different constant damagernstates, much like vertical shifting for the effect of stress. It is then implemented on arnrubber-toughened carbon/epoxy composite. Several significant simplifications are foundrnfor the material studied.rnA method of Acoustic Emission monitoring and waveform analysis is also developedrnas a means for tracking what is believed to be the primary damage mechanisms in thesernmaterials, matrix cracking and fiber/matrix debond. With direct monitoring, the extentrnof damage in the material does not need to be inferred from its effect on the stressstrainrnresponse. Unidirectional coupons of the rubber-toughened composite studied arernmonitored in this way for various loading histories. An interpretation of the AE data isrnproposed based on an initial population of existing flaws. Then a cumulative distributionrnfunction (CDF) of microcracking is defined and used to study effects of stress history.