Implementation and evaluation of the shifted fracture method for crack propagation in fiber-reinforced polymer composites

Abstract

Fiber-reinforced polymer (FRP) composites are used in various engineering applications due to their many advantageous properties, but predicting failure remains challenging due to complex failure behavior. The Computational Mechanics group at TU Delft uses an inter-element cohesive zone method, referred to as the Ortiz model, to analyze microscale crack propagation. Although effective for modeling complex failure processes, the method suffers from severe mesh dependency, restricting large-scale simulations. This research implements and investigates the shifted fracture method (SFM) as an alternative to reduce mesh dependency while maintaining computational complexity. The SFM modifies key aspects of the Ortiz model, including an area correction term, crack propagation algorithm, and shifted weak form equations and cohesive zone conditions using Taylor expansions. Three versions of the SFM were tested: (1) full SFM implementation, (2) reduced SFM with only the area correction and crack propagation algorithm, and (3) an extended Ortiz model with only the area correction term. Numerical simulations show that the reduced SFM is robust, mesh-independent, and efficient in basic fracture tests. The area correction term proved critical in reducing mesh dependency. The extended Ortiz model, on the other hand, showed less accurate results in predicting cracks, despite the additions of the area correction term. Furthermore, the maximum principal tensile stress criterion for determining the crack direction was unsuitable for mixed-mode scenarios, resulting in inaccurate paths. Although the reduced SFM shows promising results, it requires further development to handle complex fracture scenarios like FRP composites. Features such as crack initiation, merging, and termination were implemented and showed potential but require further validation. This research concludes that while the reduced SFM is effective for basic testing, further refinements are needed for broader application to FRP composites.