Fracture and Friction Characterization of Polymer Interfaces
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Understanding the interactions of polymer interfaces is essential to improve polymer-based designs, as the properties of the interface are often different than those of the bulk material. This thesis explores the interfacial interactions of polymer interfaces for two classes of materials, additive manufacturing materials and fiber-reinforced composites. Additive manufacturing (AM) refers to a number of processes which rely on data generated from computer-aided design (CAD) programs to construct components by adding material in a layer-by-layer fashion. AM continues to generate a substantial amount of interest to produce fully functional products while reducing tooling costs associated with traditional manufacturing techniques such as casting and welding. Recent advancements in the field have led to the production of multi-material printing that has the potential to create products with enhanced mechanical properties and additional functionality. This thesis attempts to characterize the fracture resistance of AM materials produced by the PolyJet process. Test standards established for mode I fracture testing of adhesive joints are adapted to evaluate the fracture resistance and interface between two printed acrylic-based photopolymers. Significant differences in fracture energy and loci of failure between the selected test configurations were observed depending on the print orientation. Failures were nominally seen to occur at the interface, alternating from one adherend interface to another in a random fashion. Results demonstrated a decreasing trend in fracture energy at slower crack propagation rates, indicating that such dependency is associated with the fracture resistance of the interface. T-peel tests conducted on specimens prepared with both constant and graded interlayers revealed enhanced peel resistance with gradient interlayers, suggesting design opportunities of enhanced fracture toughness by implementing intricate material patterns at the interface of the two photopolymers. Fiber reinforced composite (FRCs) materials have become increasingly desirable in a number of industrial applications where weight reduction is critical for increased payloads and higher performance. When manufacturing structures from these materials, the presence of friction in the composite forming process is seen to have a major effect on the finished quality. Friction between the plies, or between the composite laminate and forming tool, can be undesirable as shape distortions such as wrinkles can appear and compromise the structural integrity of the finished product. To evaluate these frictional processes, a standard rheometer is used to evaluate tool-ply friction on dry textile fabrics and graphite/epoxy prepregs over a range of temperatures, pressures, and sliding velocities. The results provide some general insights into the frictional response of composite prepregs as a function of the manufacturing environment. The materials tested are shown to have different mechanisms that govern the frictional processes. In particular, the results of friction testing on the prepreg indicate that friction comes from a contribution of both Coulomb and viscous-related mechanisms, the latter which become especially at higher temperatures.
- Masters Theses