THE EFFECT OF ADHESIVE MODULUS ON THE PERFORMANCE OF SMC LAP SHEAR JOINTS

This study examines the effect of Young's modulus of an adhesive on it s performance in a single overlap specimen when the adherend is a shee t molding compound (SMC). A series of adhesives with various moduli we re fabricated from an epoxy resin/flexibilizer/talc/curative combinati on with moduli between 21 MPa and 6.89 GPa. The strength at break incr eased by 50% from around 2.41 MPa to 3.79 MPa when the adhesive's modu lus was reduced from 6.89 GPa to 21 MPa. Joint failure was predominant ly catastrophic failure in the SMC. Finite element analysis (FEA) for a model lap shear joint produced similar results. The analysis showed that the principal stress in the SMC, at the interface, was substantia lly reduced when the modulus of the adhesive was much lower than the S MC's modulus. Based on experimental results and FEA, the Young's modul us of the adhesive should be approximately 400 times smaller than the modulus of the SMC when the thicknesses of the SMC and adhesive are 2. 54 mm and 760 mum, respectively. Consequently, the load needed to init iate failure in the SMC was increased. These results illustrate the im portance of optimizing the material properties of the adhesive to achi eve higher performance.