Dynamic Mechanical Properties Of A Transparent Polyurethane Interlayer

Laminated glass has been developed for resisting blast and impact loads in industry to avoid serious injuries of the passengers and structures in case of an impact event. The transparent polyurethane interlayer(PUI) with excellent performance such as high transparency, resistance to climate change is finding new applications as an interlayer of windshield laminated glass of aircraft and high-speed rail to enhance structural survivability under impact loading. However, the mechanical behavior of the PUI of windshield over wide ranges of strain rates and temperatures is relatively unknown.Firstly, Dynamic Mechanical Analysis(DMA) experiments are carried out to test the glass transition temperature and dynamic viscoelastic modulus of the PUI. In addition to the temperature effect, the dynamical mechanical property of the PUI is frequency dependent. Meanwhile, the glass transition temperature of the PUI demonstrates a rise trend with the increase of frequency. The range of the glass transition temperature is from-58℃ to-40℃, which is greatly lower than the present PVB interlayer.Secondly, we mainly investigate high-rate experiment design for the PUI, in order to provide guidelines to properly carry out the Kolsky Bar experiments. Then the uniaxial compressive and tensile properties of the PUI under various strain rates(0.001 /s to 7000 /s) and various temperatures(-40℃ to 50℃) are obtained by using Micro Instron machine and Kolsky Bar. High-speed photography technique is used to study the uniform deformation of the PUI under dynamic loading conditions. The experimental results show that the compressive and tensile behavior of the PUI is sensitive to temperature and strain rate. The stress-strain curves at-40℃ exhibit the transition from a rubbery-like behavior to a glass-like behavior.Thirdly, based on the constitutive theory and the compressive experimental data, a thermal-hyper elastic-viscoelastic constitutive equation is proposed to describe the large compressive deformation response of the PUI. The proposed model is made up of two parallel mechanical elements-one component to characterize quasi-static hyper elastic behavior, and the other to define rate-sensitivity and strain history dependence. The predictions of the mechanical behavior using a hyper-viscoelastic constitutive model based on strain energy functions and hereditary approach has a good agreement with experimental results. Based on the tensile experimental results, a thermal-viscoelastic Zhu-Wang-Tang(ZWT) model is employed to describe the strain rate and temperature dependent tensile behavior of the PUI. The experimental results also reveal the time-temperature equivalence relation for the PUI. Strain rate and temperature are put together to a unified parameter by introducing a dimensionless parameter, and a unified curve reflecting the time-temperature equivalence relation is obtained.This thesis firstly investigates the temperature and strain rate dependent mechanical behavior of the transparent PUI. This study can provide material data and theoretical basis for aircraft and high-speed rail windshield resistance to impact loading.