Simulation methodology for fracture processes of composite laminates using damage-based models

Abstract

Fiber-reinforced polymer composite (FRP) laminates have found increasing use in advanced industrial applications. However, the limited knowledge and validated material models of the failure processes of the laminated composites continue to pose challenges in ensuring reliability and integrity of the structures. This research aims at establishing a validated simulation methodology for fracture assessment of FRP composite laminates. The approach accounts for the failure processes and the associated damage mechanisms through finite element (FE) simulations. The FE model development considers the existence of the physical interfaces between the laminas due to the manufacturing processes. A hybrid experimental-computational approach is developed for systematic implementation of the simulation methodology. Different combinations of the failure modes were observed, including matrix cracking-crushing, fiber/matrix interface debonding, interface multi-delamination, and fiber fracture-buckling. Local material failure is modeled by a damage initiation event followed by the evolution of the damage to fracture. Two types of damage-based models are investigated; the continuum damage model encompassing the multi-damage criteria for the FRP composite lamina and the cohesive zone model for interface delamination. A full derivation of the continuum damage model for the anisotropic material is given and employed for prediction of the damage evolution in the lamina. A series of experiments on CFRP and GFRP composite laminate specimens are conducted to establish the flexural and fracture behaviors of the materials. Complementary 3D FE models of the specimens and test setups are developed. Two different FE-based models, namely the conventional and Prepreg model, are developed and examined for GFRP and CFRP composites. Results show that accurate prediction of elastic-damage behavior and the progressive damage process in FRP composites depend on the chosen FE-based model of the FRP composite laminates and the damage-based material model used. The flexural test of a 12-ply antisymmetric CFRP composite beam specimen under four-point bending displayed the occurrence of multiple failure events. These include matrix cracking at lamina No. 9 (90o), and delamination at interfaces No. 8 (-45o/90o) and No. 9 (90o/45o). In addition, intralaminar multi-failure events are predicted in lamina No. 1 (-45o) due to matrix shear and fiber buckling failures. FE simulation of the test predicted an accurate flexural response with less than 4% average error when compared with measured data, along with similar multiple failure zones in the specimen. Damage dissipation energy is used to illustrate the quantity of the overall progressive damage in FRP laminas, interfaces and the laminated composite. The simultaneous use of lamina and interface damage models in the FE simulation of the FRP composite laminate is recommended in view of the occurrence of multiple intralaminar-interlaminar failure modes and fractures under general loading conditions.