Experimental and numerical investigation of adhesively bonded joints in a compression–shear stress state

Adhesive joints in automotive structures often experience combined normal compression and shear in the adhesive layer due to bending, crushing, and local contact. Although cohesive zone model (CZM) is widely used to analyze such joints, conventional models mainly target mixed-mode fracture involving Mode I opening and Mode II/III shear, and do not adequately capture the effects of compressive stress on yielding, strength, and fracture. This study developed a CZM for adhesive joints under compression–shear stress states. First, tensile, shear, tensile–shear, and compression–shear tests were conducted on epoxy-bonded specimens to characterize the stress–strain behavior of the adhesive layer. The results showed that an adhesive exhibiting brittle behavior as a bulk material can exhibit elastoplastic behavior under compression–shear loading, with both yield and maximum strengths increasing as compressive stress increases. Based on the experimentally obtained maximum stresses and failure strains, the traction–separation law, yield function, and failure function in the compression–shear region was defined and implemented in LS-DYNA as a user subroutine. Finite element analyses confirmed that the proposed model reproduced the strength increase and improved the prediction of stress–strain and fracture behavior compared with a cohesive material model implemented in LS-DYNA (MAT240), demonstrating its effectiveness for progressive fracture analysis.