Through thickness laser joining of continuous glass fiber fabric reinforcement

Inter laminar crack initiation and propagation is a major failure mode in structural composite applications. Manufacturing induced fiber discontinuities within a laminate composite act as stress concentrations and initiation sites of such delamination cracks. A local inter laminar reinforcement method is proposed to mitigate the effects of manufacturing induced stress concentrations and increase the local fracture toughness of the composite. A through thickness laser fusion joining process is developed for the out of plane reinforcement of glass fiber pre-forms used in the vacuum infusion fabrication of thick composite structures. Laser joining is achieved through a thermal fusion process which joins fibers within a single bundle and fiber bundles between successive woven fabric layers. Coupled two phase heat transfer and viscous flow modeling is carried out to simulate the temperature and morphology of the joining process under experimentally observed conditions. Mode I fracture toughness of through thickness reinforced composite laminates is measured experimentally and compared to un-reinforced plane weave glass composites. Laser fusion joint effects on mode I crack propagation and fracture dynamics are observed through high resolution imaging during the crack propagation process and post mortem imaging of the fracture surface. Increased delamination resistance of laser joined composites is found to be a function of the joint thickness.