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

The butt tensile strength of a joint that bonds two stainless steel ro ds together with an unfilled epoxy adhesive (Epon 828/T-403) has been determined for a wide range of bond thicknesses. The measured joint st rength shows a pronounced bond thickness dependence; joint strength in creases 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 stres s intensity factor, accurately predicts the observed bond thickness ef fect. This fracture criterion suggests that the strength of an adhesiv ely bonded butt tensile joint of one bond thickness can be estimated f rom strength data for a joint with a different bond thickness by the s imple relation sigma(t2)ult = sigma(t1)ult(h1/h2)1/3, where 2h(i) is b ond thickness, sigma(ti)ult is the nominal butt tensile strength, and subscript i = 1, 2 identifies the two joints with differing bond thick ness. 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, an d small scale yielding conditions hold at the interface corner.