Analysis of Failure Properties and Strength of Structural Adhesive Joints with Damage Mechanics

The present paper deals with the strength and failure properties of adhe sive joints weakened by initial imperfections such as flaws or debonding of the interface. The problem is analyzed by applying the principles of the newly developed damage mechanics with suitable modifications made to accommodate the inherent physical and mechanical properties of structural adhesives. The reduction in effective load-carrying area due to damage accumulation is represented by a symmetric damage tensor of second rank that is related to the decrease of elastic modulus via a hypothesis of energy equiva lence. Damage evolution is assumed to be controlled by the dilatational part of total en ergy. The model is then implemented onto a finite element program by using the updated Lagrangian formulation. A butt adhesive joint weakened by a central crack in the adhesive is subsequently analyzed to demonstrate the potential capability of the damage model. Detailed stress and damage distributions in the near and far fields are given as functions of adherend/adhesive modulus ratio. The issue of fracture initiation angle and fracture load is also studied by applying two novel damage fracture criteria.