SEDL / STP / STP1357-EB / STP15837S

Nonlinear Viscoelastic Behavior of Rubber-Toughened Carbon and Glass/Epoxy Composites

Bocchieri, RT
Graduate Research Assistant and Professor, The University of Texas at AustinThe Offshore Technology Research Center, AustinAustin, TXTX

Schapery, RA
Graduate Research Assistant and Professor, The University of Texas at AustinThe Offshore Technology Research Center, AustinAustin, TXTX

Pages: 28    Published: Jan 2000

Download this paper for $25 PDF (632K)          View License Agreement
Abstract

A previously-developed constitutive equation for nonlinear viscoelastic materials is first used to characterize mathematically the ply-level stress-strain behavior of a rubber-toughened carbon/epoxy composite. Emphasized are some practical aspects of carrying out such a characterization. Constant stress rate tests are used to derive first-loading material response in the dry state, at room temperature. It is found for a large portion of the loading curve that the shear and transverse compliances can be described by a quasi-elastic model expressed in terms of a single scalar function of stress state, a ratio of compliances, a time or rate exponent, and two elastic terms. This model offers a simple way to incorporate nonlinearity and time dependence in a material model for limited loading conditions. Results are then compared to those for a glass/epoxy composite with the same rubber-toughened resin system. Special considerations for using off-axis coupons are examined and unique tabbing is employed to derive material properties out to high stress levels. The consistency of the carbon/epoxy characterization is checked by comparing experimental stress-strain response to results not used in the characterization. Behavior of the two composite systems is compared and checked for consistency using a micromechanical model.