Impact Mechanics of PMMA/PC Multi-Laminates with Soft Polymer Interlayers
The main purpose of this thesis is the systematic, experimental investigation of how a soft interlayer affects the impact response and energy dissipation mechanisms of all-polymer multi-laminates. An instrumented, intermediate impact velocity experimental setup with strain rates on the order of 100 s-1, is used to assess the impact mechanics of three-layered samples consisting of a poly(methyl methacrylate) (PMMA) front, polymer interlayer or adhesive, and polycarbonate (PC) back layer. Instrumentation of the gas gun is achieved with a shock accelerometer measuring contact force and optical displacement sensors recording deflection. Previous impact research utilizing instrumented gas guns by Levy and Goldsmith, and Delfosse et al. have measured contact force, but did not record simultaneous out-of-plane displacement. Signals acquired are temporally aligned allowing for insight into the response of the multi-laminate during impact, which is inaccessible with typical gas guns.
Impact testing is completed on bonded and unbonded sample configurations, with two thermoplastic polyurethane and four polyacrylate interlayers. Quantitative metrics from force and displacement signals, along with post-impact damage observations, are used to compare impact performance between configurations and impact velocities (12 and 22 m/s). In general, the presence and bonding of an interlayer increases impact resistance by mitigating and localizing the impact load. The interlayers are characterized at various strain rates in tension, compression, and shear adhesion. In tension, all interlayers display rate dependence, non-linearity, and hysteretic behavior showing varying degrees of increasing energy dissipation with strain rate. Several trends between sample fracture and energy absorption mechanisms, quasi-static and low rate interlayer response, and metric results are established and discussed.