Numerical Prediction of Failure in Unidirectional Fiber Reinforced Composite

Fiber-reinforced polymer composites exhibit orthotropic mechanical properties and particularly low strength in the out-of-plane direction. The use of classical failure criteria that consider transverse isotropy to evaluate these composite materials implies an overestimation of their out-of-plane strength, which could lead to a nonconservative and even catastrophic design. The Molker failure criteria developed for orthotropic materials consider the LaRC05 failure modes as a basis, with two additional failure modes for the out-of-plane direction of noncrimp fiber (NCF)-reinforced composites. Given the similarity in configuration and orthotropic behavior of unidirectional fiber fabric reinforced composites to NCF-reinforced composites, Molker failure criteria are implemented and applied in this research to determine the initiation of out-of-plane failure in unidirectional fiberglass fabric composites. The criteria are programmed in the form of a module coupled to a constitutive model available in a finite element method (FEM) package. Then, the mechanical properties and failure parameters of the unidirectional fiber-reinforced composite are determined. Model validation is accomplished by comparing numerical and experimental results of out-of-plane failure in a corrugated panel. In addition, several failure criteria used in unidirectional fiber-reinforced composite that consider transverse isotropy are evaluated. The results of critical load at the onset of transverse out-of-plane failure obtained by using the Molkerorthotropic criterion prove to be superior in accuracy compared to those obtained with the criteria commonly applied to this type of materials.

Phase-Field Modeling of Damage and Fracture in Laminated Unidirectional Fiber Reinforced Polymers

The damage and fracture behavior of Fiber Reinforced Polymers (FRPs) is quite complex and is different than the failure behavior of the traditionally employed metals. There are various types of failure mechanisms that can develop during the service life of composite structures. Each of these mechanisms can initiate and propagate independently. However, in practice, they act synergistically and appear simultaneously. The difficulties that engineers face to understand and predict how these different failure mechanisms result in a structural failure enforce them to use high design safety factors and also increases the number of certification tests needed. Considering that the experimental investigations of composites can be limited, very expensive, and time-consuming, in this contribution the newly developed multi Phase-Field (PF) fracture model [1] is employed to numerically study the failure in different Unidirectional Fiber Reinforced Polymers (UFRPs) laminates, namely, fracture in single-edge notched laminated specimens, matrix cracking in cross-ply laminates, and delamination migration in multi-layered UFRPs. The formulation of the PF model incorporates two independent PF variables and length scales to differentiate between fiber and inter-fiber (matrix-dominated) failure mechanisms. The physically motivated failure criterion of Puck is integrated into the model to control the activation and evolution of the PF parameters. The corresponding governing equations in terms of variational formulation is implemented into the Finite Element (FE) code ABAQUS utilizing the user-defined subroutines UMAT and UEL.