Progressive Fatigue Damage Simulation in Composites based on Explicit Finite Element Formulation

Advanced polymeric composites are playing a major role in designing high-performance and lightweight vertical lift structures. However, uncertain residual strength and remaining useful life of the composite rotor and airframe structures due to complexity of failure mechanisms and susceptibility to manufacturing irregularities, which may be precursors to structural damage, impose risks that cannot be mitigated exclusively by time-consuming and costly experimental iterations. Validated analysis techniques accelerating design, certification, and qualification of composite structures are needed. Our team has been taking essential steps towards improving confidence in material qualification for laminated composites. The first step started with our reduced lamina test methods, short-beam shear and small-plate twist based on Digital Image Correlation measuring as a subset the standard material properties; and, in addition, key properties that cannot be currently measured using any standard test methods. The laminate analysis has been the second step increasing confidence in material qualification. A known weakness of the existing progressive damage analysis methods is the lack of effective techniques to predict ultimate failure. The newly developed methodology relies on Explicit finite element modelling and eliminates convergence issues due to severe non-linear discontinuities after propagation of damage beyond detectable size. This work shows preliminary results of applying this methodology to nanosilica-toughened IM7/PMT-F3GHT Open-Hole Tension strength/fatigue, Open-Hole Compression strength/fatigue, and bearing strength multidirectional laminate configurations. The ability to predict ultimate strength and fatigue for advanced material systems including IM7/PMT-F3GHT carbon/epoxy reinforced by nanosilica has been demonstrated for the first time.