RESIDUAL-STRESSES IN INJECTION-MOLDED AMORPHOUS POLYMERS

In the present investigation the resultant residual stresses (RS) induced by these two sources were studied in two stages. First, the flow-induced stresses were relaxed by proper heat treatment followed by quenching, resulting in only thermal stresses. The experimentally determined RS profiles in polysulfone and amorphous polyamide showed a parabolic shape and were correlated with the initial and final quenching temperatures, the glass transition temperature, and Biot Number. In the second stage, the combined effect of thermal- and flow-induced stresses was studied using injection-molded specimens prepared under a wide spectrum of molding conditions including melt and mold temperatures and injection rate and pressure. Results have indicated that the basic thermal-induced parabolic RS profiles are altered by the flow-induced stresses resulting in complicated profiles including local maxima and unbalanced RS. Finally, the tensile mechanical properties obtained for plaques molded under the various injection-molding conditions were studied and correlated in part with the previously determined RS profiles.