THE Effect of Time and Temperature on the Mechanical Behavior of Epoxy Composites. part 1. Tangent Modulus and Stress Relaxation
MONSANTO RESEARCH CORP ST LOUIS MO
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A crosslinked epoxy resin consisting of a 60 400 weight ratio of Epon 815 and Versamid 140 and composites of this material with glass beads, unidirectional glass fibers and air foams were tested in compression and flexure to determine the effect of time and temperature on the tangent moduli and stress relaxation. Strain rates ranged from ten to the minus four power to ten to the minus one power and the temperature ranged from -1 to 107 C. Isotherms of tangent modulus versus strain rate were shifted to form master modulus curves. The modulus of a particulate filled composite or foam can be predicted from the modulus of the matrix over the entire strain rate range if one has knowledge of the reinforce-ment effect of the filler. The master curve for stress relax-ation is of the same shape as the mirror image of the modulus master curve and can be used to estimate the modulus versus strain rate ralationship if one value of modulus is known. It was concluded that the time- temperature shift factors for tangent moduli and the time-temperature shift factors for stress relaxation were identical and were independent of the type and concentration of filler as well as the mode of loading. Thus the shift factors are a property of the matrix.
- Laminates and Composite Materials