EFFECT OF CYCLIC COOLING TO LOW-TEMPERATURES ON THE ADHESIVE STRENGTHOF FIBER-THERMOPLASTIC MATRIX JOINTS

The adhesive strength tau of the interface between the polyarylene sul fone PSK-1 and a steel wire 150 mm in diameter was measured using a pu ll-out technique after cyclic cooling of the joints from room temperat ure down to liquid nitrogen temperature. All specimens were prepared r ender isothermal conditions (300 degrees C, 30 min) without applying p ressure. The number of cycles N of plunging in liquid nitrogen reached 900. All measurements were taken at room temperature with constant lo ading rate. The joint areas S were varied within a wide range. It was found that ten cooling cycles do not cause any appreciable change in t he values of tau (Figs. 1-3). After 100 cooling cycles, the adhesive s trength losses reached 30-45% (Figs. 1-3). After 810 cycles, the fiber -matrix interface is almost totally destroyed (Fig. 1). As the number of cycles N increases, the character of the dependence of the adhesive strength tau on the joint area changes. when N < 100, the values of t au are reduced as the interfacial surface area increases; when N = 810 , the adhesive strength does nor depend on S. The main factor that gov erns the reduction in adhesive strength is assumed to be residual ther mal stresses. Analysis of the data obtained here and earlier shows tha t the behavior of polymer-fiber systems after cyclic cooling down to l ow temperatures is the same for both network and linear polymer matric es. The origin of this behavior also seems to be the same for all poly mer-fiber adhesive joints.