Development of cohesive zone models for the prediction of damage and failure of glass/steel adhesive joints

The use of mild steel/tempered glass adhesive joints has increased rapidly over recent years. Cohesive zone modelling (CZM) is used extensively for the numerical analysis and failure prediction of adhesive joints. As the bonding to the glass surface is generally weaker than the bonding to metal substrates, and therefore the development of cohesive laws by testing on different substrates generally leads to overoptimistic and non-conservative predictions. However, the interface characterisation using standardised methods for glass/steel joints is complicated due to the relatively low strength of the glass substrate leading to premature failure. This paper presents modifications proposed for the Double Cantilever Beam (DCB) and End Notched Flexure (ENF) tests used to extract traction-separation laws for glass/steel adhesive joints in fracture modes I and II. For this purpose, an in-house glass heat strengthening process was developed. The cohesive laws were validated by comparing the numerical predictions for two different adhesives with experimental tests obtained for double lap shear joints subjected to four different load cases. This is the first time, traction-separation laws were extracted and validated against experimental data using glass substrates.