Tensile Failure Analysis of Unidirectional Fiber-reinforced Composite Laminates with Inter-tow Gap

Abstract

In fiber-reinforced plastic (FRP) composites, fibers can be used in the form of woven fabrics or tape laying. When fiber tows are woven into fabrics or fiber tapes are placed by automated fiber placement (AFP) technique, gaps naturally occur between two adjacent fiber tows or tapes, which have an influence on geometry of fiber fabric, fiber volume fraction, and mechanical properties of FRP composites. The gaps are defect in the FRP composites since they are filled by polymers with much lower mechanical property than that of fiber. In AFP techniques, gaps have been reported as most probable defects. And from tensile testing of unidirectional FRP composite laminates in this study, it was observed that failure of off-axis plies mainly occurs along the gaps. Object of this research is to simulate failure along inter-tow gaps in unidirectional FRP composite laminates under tensile loading, which was achieved by separate modeling of fiber tows and inter-tow gaps. Research consists of three steps: geometrical modeling, micromechanics, and progressive failure analysis. At first step, dimension of fiber tow and inter-tow gap were measured by using optical microscope. Based on their dimension and stacking sequence of laminates (fiber orientation), geometry of them is mathematically modelled in the form of nodes and elements for finite element analysis. At second step, mechanical properties of impregnated fiber tow were calculated based micromechanics. Calculated properties of impregnated fiber tow and measured properties of polymer were applied at fiber tow element and inter-tow gap element, respectively. At third step, virtual tensile testing of FRP laminate was conducted by using finite element method. With incremental extension, progressive failure analysis was performed, consisting of stress analysis based on classical laminate theory, failure analysis based on maximum tensile criteria and Von Mises criteria. Finally, mechanical behavior and failure of FRP composite laminates were compared between simulation and experimental results.