Transient hygrothermal stresses in plates with and without cavities

The influence of coupled diffusion of heat and moisture on the transient stresses in a composite is investigated analytically where the moisture diffusion coefficient is taken to be temperature dependent while the thermal diffusion coefficient is kept constant. There is no a priori reason why moisture and temperature should be uncoupled such that each will obey the simple diffusion theory, particularly without reference made to the initial and boundary conditions of a particular situation. A study of the coupled diffusion equations was made by allowing for time-dependent changes in the humidity and temperature of the environment. The appropriate transient boundary conditions are specified on the surfaces of an infinite plate. Numerical calculations were carrie dout for the T300/5208 epoxy matrix of the graphite fibre-reinforced composite in which the non-uniformity of moisture and temperature is evaluated for sudden changes in the surface moisture and/or temperature. The coupling effect between temperature and moisture is found to be most significant when the plate undergoes a sudden change in surface temperature while the surface moisture concentration is held constant. This suggests the need to perform additional experiments for evaluating the coupled diffusion phenomenon and its influence on the mechanical behaviour of epoxy-resin composites.

Additional results are obtained for a plane body containing a circular cavity whose surface is subjected to the sudden change of temperature and/or moisture. The resulting stresses are found to fluctuate with time and used in conjunction with the strain energy density criterion for locating possible failure sites.