TRANSIENT THERMAL DEFORMATIONS OF THE INTERPHASE IN POLYMER COMPOSITES

Heterodyne micro-interferometry was utilized to measure out-of-plane t ransient displacements in the interphase due to thermal cycling. In-si tu measurements were made on single carbon fiber/epoxy samples with in terphases of varying glass transition temperature. Interphase properti es were tailored such that one set of samples had fibers which were co ated with a low T-g resin, another set had a higher T-g coating, and i n the third set the fibers were uncoated. The interferometric data dem onstrated that interphase T-g has a significant effect on the rate and magnitude of the thermal deformations at the fiber/matrix interface. The presence of a low T-g interphase caused an increase in the magnitu de of the thermal displacements due to a local softening of the matrix and increase in coefficient of thermal expansion. In addition, the ra te at which the displacements increase was also higher due to the redu ction in T-g. Samples with untreated fibers (no tailored interphase) b ehaved as if a low T-g interphase had formed. Experimental displacemen t profiles were also compared with finite element predictions to asses s the behavior of the tailored interphases.