Moisture-Altered Viscoelastic Response of Graphite/Epoxy Composites

Abstract

Results of experiments to evaluate the degree of moisture-induced swelling and plasticization in T300/934, T300/5209, GY70/339 composites are described. Swelling was found to be a nonlinear reversible function of equilibrium moisture content. Out-of-plane swelling was several times larger than in-plane transverse swelling in the unidirectional composites. Equilibrium moisture content was found to vary with exposure temperature as well as humidity in the 339 and 5209 matrix systems. The in-plane shear properties were determined as a function of time, temperature, and equilibrium moisture content, and master curves of temperature and moisture-compensated modulus versus time were constructed for each material. Nonsymmetric (04/904)T cross-plied laminates were employed to study the alteration of residual stresses in T300/5209 and GY70/339 as a function of temperature and moisture content. The level of residual stresses measured for a given equilibrium moisture content was found to be a function of the temperature at which the moisture was absorbed.

Some Observations on the Cured Shape of Thin Unsymmetric Laminates

“…Still others have used unsymmetric laminates to determine the effects of the environment on composites. Crossman, Mauri and Warren [19] used the curvature of 150 X 25 mm (6 X 1 in.) [04 /904 ] T laminates to study the effects of time, temperature and humidity on the residual stresses in several composite materials.…”

Research on Composite Materials for Structural Design.

“…Effects of residual stresses in composite materials can be detected by measuring curvatures of anti-symmetric laminates [2,4,23,28,[32][33][34].…”

Behavior of a viscoelastic composite plates under transient load

“…Mechanical properties of viscoelastic composite materials can be characterized by relaxation curves which are determined from tensile relaxation experiments. Experimental results for polymeric matrix composites show that modulus E 11 and Poission's ratio v 12 are insensitive to time and Young's modulus E 22 and the shear modulus G 12 have a similar time dependent behavior [20,21].…”