Use of Thermosets/Thermoplastics in General Motors 4.3 Liter Vortec V6 Valve Cover I - Crush Testing and Simulation

This paper summarizes crush test results of General Motors 4.3 liter Vortec V6 valve cover currently made at Joh, a division of Gecamex Technologies Inc., through injection-compression of 25% glass reinforced epoxy vinyl ester by Cytec Industries Inc. The test consisted of displacing the middle of three central bolts to 15% of cover's height, disregarding gasket and grommet which simulates worst cover conditions. One of the production molds was modified at Build-A-Mold ltd. to allow injection of thermoplastics from four suppliers, DuPont, BASF, GE Plastics and DSM Engineering Plastics. These were crush tested in a similar manner to production covers, Dry As Molded and after moisture conditioning to 50% Relative Humidity. While thermoset covers exhibited progressive cracking, covers made out of glass reinforced nylons sustained compression whereas polyethylene terephthalate covers cracked prematurely. A three-dimensional Computer Aided Design model of the valve cover was built in Pro-Engineer by Parametric Technology Corp. and meshed using the Computer Aided Engineering pre-processor, Pro-Mesh. The data was then transferred, through a custom written FORTRAN program, to ABAQUS/Standard general purpose finite element software by Hibbitt, Karlsson & Sorensen, Inc. for non-linear analysis. Both total and incremental theories of plasticity were used to simulate non-linear elastic as well as elastic-plastic and perfectly-plastic material behavior. True stress-strain curves were generated at Sci-lab materials testing inc. using uniaxial tension specimens cut from plaques made out of production thermoset and the various thermoplastics. Statistical room temperature Young's modulus, the yield stress and Poisson's ratio were calculated as per ASTM D638 and E132. Von Mises and Tresca equivalent stress contours as well as shear and equivalent plastic strains were considered in indicating macroscopic failure around central bolt boss. Predicted failure loads of the various covers satisfactorily compared to experimental results.