Experimental evaluation of laminated glass interlayer polymers at various strain rates and temperatures
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The use of blast-resistant glazing, such as laminated glass in buildings can greatly reduce, if not eliminate, the hazard of flying glass shards. In a failure event, fractured glass shards adhere to the polymer interlayer, and do not fly or fall. Under dynamic loading scenarios such as blast, the interlayer deforms largely, providing post-cracking energy absorption to the laminated glass system. When properly designed, laminated glass polymer interlayers are capable of maintaining the integrity of the building envelope in extreme events such as blasts or hurricanes, protecting the interior from damage. Analytical and experimental research exists in the literature in the area of blast-resistant glazing; however, more research on the dynamic response of polymer interlayer materials is necessary to understand the post-cracking behavior of blast-resistant window systems. Therefore, the main objective of this research is to experimentally evaluate the high strain rate and temperature effects on the dynamic response of pre-laminated PVB and SG polymers. The results of this research are expected to enhance the engineering design methods and numerical modeling of laminated glass windows subjected to dynamic loading. A drop weight testing apparatus was used in this research for evaluating PVB and SG samples under various loading rates and at different temperature ranges. Quasi-static testing of the materials was performed using a servo hydraulic testing machine in order to evaluate the effects of dynamic loading on the engineering stress-strain response and energy absorption capabilities of the interlayer materials. The results show that dynamic loading significantly affects the engineering stress-strain response and energy absorption of the materials. Under quasi-static loading, PVB behaves in a highly non-linear, hyperelastic manner; however, the dynamic response of PVB is bilinear and viscoelastic. Dynamic loading of SG increases the initial modulus of the response by about 20% and pseudo-yield strength by about 60%, resulting in far greater energy absorption than the quasi-static response at the same strains. The effect of strain rate variation effects the initial linear region of the response of PVB more than the response after pseudo-yielding. In general, as strain rate increases, the initial modulus and pseudo-yield strength increase, resulting in increased total strain energy. Temperature effects are more prominent than the effect of strain rate variation on the dynamic response of PVB. At colder temperatures, the initial linear elastic response is predominant, and at elevated temperatures, the secondary viscoelastic response is predominant. The results of this thesis provide valuable findings regarding the dynamic response of interlayer polymers, but additional tests are still needed to develop statically reliable results. A wider range of strain rates is recommended to better understand the strain rate effects on the dynamic response of interlayer materials. More precise temperature control, and elimination of initial strains due to prestressing, are necessary to accurately characterize the temperature effects on the dynamic response of interlayer materials.