Viscoelastic Characterization of a Nonlinear, Glass/Epoxy Composite Including the Effects of Damage
AEROJET SOLID PROPULSION CO SACRAMENTO CA
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Isothermal creep and recovery tests were conducted on an epoxy resin and a glass fiber-reinforced composite made from the same bulk resin. The glassepoxy which was studied included unidirectional and laminated angle-ply composites as well as samples removed from a Minuteman III solid rocket motor case. The creep and recovery tests were carried out at a series of stress levels well into the nonlinear region at temperatures of 20,75 and 140 F for several fiber angles. Both the epoxy and glassepoxy were found to be thermorheologically complex materials with a creep compliance which may be represented by a power law in time. The linear viscoelastic principal creep compliances were determined for the glassepoxy using fourth-order tensor transformations. Using the Halpin-Tsai relationships and the rule of mixtures, the principal creep compliances were compared with those predicted by micromechanics. The experimental results were found to agree very well with the Halpin-Tsai model except at the highest temperatures and were within the upper and lower theoretical bounds on compliance. The nonlinear properties were found to depend primarily on the stress normal to the fiber. Bending tests conducted on glassepoxy beam and plate specimens brought out a strong influence of the strain gradient.
- Laminates and Composite Materials
- Solid Propellant Rocket Engines