Global yielding as a failure criterion for bonded joints

Abstract This paper is concerned with predicting failure in adhesively bonded joints. After reviewing various methods that have been used for this purpose one technique is presented that in three independent studies has given reliable predictions of joint strength. This is based on a concept termed global yielding, which applies when a path of adhesive along the overlap region reaches the state in which it can sustain no further significant increase in applied load. Using an analysis technique such as the finite element method it is possible to ascertain the load at which this occurs fairly readily; this gives a good estimate of failure load. The three studies cited consist of experimental and analytical programmes on different types of joint. The first is concerned with the single lap joint, where this technique actually demonstrates why the strength of a joint increases with decreasing adhesive thickness. The second study is concerned with failure in double lap joints and the third with a new type of test termed the compressive shear test where it can be shown that loads considerably in excess of those expected can be sustained by eliminating the transverse tensile adhesive stresses.