Laser Joining of Continuous Glass Fiber Composite Preforms

Abstract

A laser fusion joining method is investigated for the purpose of through thickness strengthening of fiber pre-forms used in the vacuum infusion fabrication of thick composite structures. Laser joining is achieved without filler materials to replace adhesives, pins or stitches used in conventional composite fabrication.A two step joining process is developed to fuse fibers within a single bundle and between multiple fiber bundles. Finite element analysis is used to investigate the joint strength with respect to joint morphology. Joint strength is found to be a function of the fiber contact angle and packing density at the joint interface. Tensile tests show that laser joined fiber bundles exhibit higher strength than comparable fastening methods. Lessons learned from the axial joining of fiber bundles are applied to joining in the radial and thickness directions of 3d pre-form architectures. Flow induced joint morphology and densification effects observed in the axial direction indicate the need for a two step joining process in the thickness direction. Fiber compaction effects on joint strength in the axial direction motivate the need for high fiber packing fraction at joint interfaces in the thickness direction. INTRODUCTIONComposite pre-preg fabrication involves placing densely packed resin infused tapes of reinforcement fibers in layers (laminates) and then curing to produce thin shell structures. Composite components manufactured from pre-preg processes exhibit high fiber packing fraction and high strength along the fiber directions, but offer little strength perpendicular to the fiber directions. Laminates of pre-preg construction contain no fiber reinforcements aligned in the thickness direction due to the layer by layer assembly process. Thus, pre-preg fabrication is undesirable for making composite parts requiring high through thickness strength and fracture toughness. One method for improving the through thickness strength of pre-preg constructed components is to insert metal pins through layers of pre-preg prior to curing [1,2]. Mechanical pinning increases through thickness strength, relying on matrix load transfer mechanisms between the fibers and pins. The insertion of metal pins into a stack of pre-preg lamina displaces the fibers in the lamina and introduces

An Integrated Approach to Additive Manufacturing Simulations Using Physics Based, Coupled Multiscale Process Modeling

“…The preprocessing tools available from this software are also applicable for solving thermomechanical fields in other closely related joining and material processing phenomenon such as laser joining and surface treatment [19][20][21][22] or for using these tools in already existing predictive algorithms [23] specially designed for solving these phenomenon where the above-mentioned tools could be used to provide a seamless transition from fine to coarse scale simulation domain.…”

Thermomechanical Modeling of Laser Spot Welded Solar Absorbers

“…Recently, a number of numeri cal models have been developed to study thermal and mechanical phenomena during laser processes. These models were used to evaluate temperature distributions and to predict the weld pool shape, the melting zone, and the dimensions of the HAZ [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], In some studies, a fully or sequentially coupled thermal-stress analysis was also carried out to determine the thermal deformations-distortions and the residual stress-strain fields [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. Most of these investigations are limited to problems associated with continuous or single spot laser welding in butt-, lap-, or T-joint specimens; the mechanical effects of LSW in manufactur ing processes of large industrial structures, such as solar absorb ers, have not been investigated so far.…”

The Laser Interlaminar Reinforcement of Continuous Glass Fiber Composites

“…The model concurrently solves the compressible Navier Stokes equations for viscous fluid flow, phase field (Cahn Hilliard) equations for two phase immiscibility and velocity dependent heat equations, as discussed in detail in a previous paper [17]. The numerical model is validated using experimental results of the reinforcement morphology.…”

“…A major challenge to the fusion processing of fibrous systems is the high surface area and low relative density of the initial material, causing glass to flow away from the focal volume during laser processing. The effects of surface tension induced flow of glass fiber systems during laser heating has previously been investigated by Tan et al [17]. The inter-laminar reinforcement method devised in this work relies on the fusion bonding of a dense bead of soda lime glass between layers of fabric preform to overcome the flow behavior inherent in the fiber system.…”

“…The component of F in the thickness direction is zero given the anisotropic tendency of molten glass to flow along the fiber directions [17].…”