Prediction of the strength of adhesive lap joints. An investigative review

The principal methods of predicting the strength of lap shear bonded joints have been introduced for metallic and composite adherends. The early theories of Volkersen and of Goland and Reissner provided indications of the shear and transverse [peel] stresses. These equations were not easy to use and were increasingly displaced by finite element analysis [FEA]. The importance or otherwise of the high stresses around the embedded corner of the unloaded adherend were examined and shown to be the most likely cause of initial cracking, but not necessarily of joint failure. By combining an extensive experimental programme of testing both adhesives and joints with FEA, knowledge was gained of the reasons why lap shear joints fail. Some simple equations were developed with failure criteria based on yield of the adherend and/or the adhesive which produced predictions in good agreement with experimental results. Finally, the bonding of composites was considered, and it was shown that the key factor is the transverse tensile strength of the composite.