The Adiabatic Thermoelastic Effect in Laminated Fiber Composites

The influence of material inhomogeneity and anisotropy on the reversible, adiabatic thermoelastic effect in laminated, continuous-fiber composites is investigated analytically and experimentally. The plane-stress solution for strains in a uniform laminate is combined with a simple micromechanics description of a fiber-reinforced lamina to approximate the nonhomogeneous strains in the fibers and matrix. The equations of anisotropic, linear thermoelasticity are then used to evaluate the temperature change in each of the microconstituents during an adiabatic deformation. The average temperature change of the surface plies of several carbon/epoxy laminates are computed and compared with experimental data obtained via differential infrared thermography. Results indicate that material parameters such as the volume fraction and thermoelastic properties of the microconstituent materials, the orientations of the laminae within the laminate, and the orientation of the lamina on the surface of observation affect the measurable thermoelastic response of a particular laminate. The experimental results suggested that the deformations of the polymeric composite test specimens were not perfectly adiabatic, yet the major trends in the measured thermoelastic emission patterns were nonetheless represented reasonably well by the proposed analysis. Based on the results, suggestions for further refinements to the analysis are proposed.