COMPARISON OF BUTT TENSILE-STRENGTH DATA WITH INTERFACE CORNER STRESS INTENSITY FACTOR PREDICTION

The butt tensile strength of a joint that bonds two stainless steel rods together with an unfilled epoxy adhesive (Epon 828/T-403) has been determined for a wide range of bond thicknesses. The measured joint strength shows a pronounced bond thickness dependence; joint strength increases by a factor of 2 as bond thickness is reduced from 2.0 to 0.25 mm. A failure criterion, based upon a critical interface corner stress intensity factor, accurately predicts the observed bond thickness effect. This fracture criterion suggests that the strength of an adhesively bonded butt tensile joint of one bond thickness can be estimated from strength data for a joint with a different bond thickness by the simple relation sigma(t2)ult = sigma(t1)ult(h1/h2)1/3, where 2h(i) is bond thickness, sigma(ti)ult is the nominal butt tensile strength, and subscript i = 1, 2 identifies the two joints with differing bond thickness. This relation applies to thin bonds when the adhesive's Poisson's ratio is between 0.3 and 0.4, the adherends are relatively stiff, and small scale yielding conditions hold at the interface corner.