3-DIMENSIONAL THERMOVISCOPLASTIC ANALYSIS OF COMPRESSION MOLDING OF SHEET MOLDING COMPOUNDS WITH FIBER VOLUME FRACTION PREDICTION

SMC (Sheet Molding Compounds) is a thermosetting material which consis ts of unsaturated polyester resin and other additives reinforced with randomly distributed chopped fiberglass strands. While the incorporati on of chopped short fiberglass strands into the thermosetting SMC resi n has added strength and stiffness to molded parts, a better understan ding of overall effects of SMC resin components, mold geometries and p rocessing variables on flow characteristics and mechanical performance of the molded parts is complicated. Thus, a three-dimensional rigid t hermo-viscoplastic finite element program including chemical reaction and fiber volume fraction prediction was developed in the present stud y and applied to the analysis of compression molding of SMC charge. Th e rheological characteristics of the SMC charge were modeled by a powe r law as a function of strain rate and temperature based on compressio n test data. To investigate the effects of dwelling time, mold closing speed, friction, and mold temperature on mold filling and curing, ser ies of three-dimensional molding simulations of the SMC charge block w ere carried out using various molding parameters such as mold closing speeds of 45 mm/min and 250 mm/min, mold temperatures of 130 degrees C and 150 degrees C, and constant shear frictional factors of 0.1 and 0 .8. The calculated fiber volume fraction distribution for plane strain condition was compared to the experimental result obtained from scann ing electron microscope available in the literature. From this study, it was found that the currently developed three-dimensional finite ele ment program coupled with heat transfer and chemical reaction can prov ide valuable information in understanding flow characteristics, fiber volume fraction distribution, and the curing behavior of SMC compressi on molding in detail.