Mode I fracture modeling of elastomer toughened polymers, adhesive joints, and composite materials

Analytical models are developed to correlate Mode I fracture toughness of polymer based material systems with microstructural energy dissipation mechanisms occurring around the crack tip. The material systems include elastomer toughened polymers, polymer adhesive joints, and polymer composite materials. In the Mode I fracture modeling of toughened polymers and their adhesive joints, the total energy dissipation caused by three dominant damage modes, namely, plastic shear band formation, plastic void growth, and plastic deformation of the entire matrix resin, is used as the basis to derive the analytical expression for the Mode I fracture toughness of these material systems. In the Mode I interlaminar fracture modeling of toughened polymer composites, interfacial failure at the fiber-resin interface is considered as an additional energy dissipation mechanism. Numerical results are presented, and compared with the available experimental data for some typical polymer material systems. The parametric results involving a number of material and microstructural variables indicate some very interesting trends, and provide some guidelines toward achieving optimum fracture toughness values for these types of material systems. In the analysis of polymer adhesive joints, numerical results show that L the proposed models can predict well the effects of adhesive thickness on the Mode I fracture toughness of toughened epoxy adhesive joints. It is emphasized that the proposed models can be used to quantitatively evaluate the contributions of various energy dissipation mechanisms on the Mode I interlaminar fracture toughness for many kinds of polymer composite laminates. The results of the analysis show that the energy dissipation due to the interfacial failure at the fiber-resin interface plays an important role in the interlaminar crack growth resistance of these composite systems. It is concluded that the control of the thickness of the resin-rich layer and the fiber volume fraction is a key to the enhancement of the Mode I interlaminar fracture toughness of the polymer composite systems. Further validity and use of the proposed theoretical models require experimental and/or analytical evaluation of all the unknown parameters.