FRACTURE-TOUGHNESS OF ADHESIVE JOINTS .1. RELATIONSHIP BETWEEN STRAIN-ENERGY RELEASE RATES IN 3 DIFFERENT FRACTURE MODES AND ADHESIVE STRENGTHS

The three strain energy release rates, G(IC), G(IIC), and G(IIIC), of adhesive joints can be attributed to their ability to resist crack pro pagation of solids in the adhesive layer. The dependencies of G(IC), G (IIC), and G(IIIC) on crack lengths for various adhesive joints were d etermined using the double-cantilever beam specimen by a compliance me thod. The two types of adhesive strengths, i.e., adhesive tensile stre ngth and adhesive shear strength, corresponding to G(IC) and G(IIC), r espectively, were carried out at room temperature and 65% RH with a cr osshead speed of 10 mm/min. The G(IC), G(IIC), and G(IIIC) were depend ent upon crack length and had constant values irrespective of geometri c parameters of the specimen over the crack length of five times adher end thickness, 0.65 (= crack length over half a length of span) and ei ght times adherend thickness, respectively. In the region of the crack length, we determined the following increasing order of fracture toug hness: G(IC) < G(IIIC) < G(IIC). A positive correlation was found betw een adhesive tensile strength and G(IC). A significant relation betwee n adhesive shear strength and G(IIC) was not found in this work. Furth er studies are needed to clarify the relation between adhesive shear s trength and G(IIC) with general adhesives. (C) 1994 John Wiley & Sons, Inc.