ULTIMATE TENSILE-STRESS OVER A ZONE - A NEW FAILURE CRITERION FOR ADHESIVE JOINTS

The objective of this work was to develop a criterion for predicting the static strength of adhesively-bonded joints. Although there is a large body of literature on this subject, no satisfactory criterion has been proposed in any publication to date. To obtain a criterion, finite element models of widely differing joint geometries were developed, in which the stresses in the adhesive bonds were calculated in great detail. These were then compared with test measurements. After examining two toughened epoxy adhesives, the authors have developed a failure criterion that predicts failure loads to within approximately 15% of measured values. This is: that the maximum principal stress must exceed the ultimate tensile stress of the adhesive material over a finite zone normal to the direction of maximum principal stress. The size of this zone is a property of the adhesive that can be determined from a combination of analysis and test.