头部与风挡玻璃的接触是交通事故中弱势道路使用者受到致命损伤的重要诱因，PVB薄膜的加入对提升夹层风挡玻璃的吸能特性和安全性起到关键作用。本文结合实验与理论方法，研究了风挡玻璃中间层PVB薄膜材料的力学行为和吸能特性，系统阐述了其对于夹层风挡玻璃在冲击载荷下的力学响应和吸能特性的影响机理。通过准静态和动态力学实验，得到了PVB薄膜在拉伸和压缩载荷下的力学特性，其应力-应变行为呈现出高聚物材料典型的非线性大变形特性和应变率相关效应。分析了PVB薄膜在不同加载条件下的吸能机理和失效准则。进一步地，采用动态力学分析的方法，系统研究了PVB薄膜的黏弹性及其受时间、温度的影响，计算了其玻璃化转变温度并分析了其时-温等效特性。以描述黏弹性材料本构行为的经典模型为基础，增加体现材料应变率效应的修正项，建立了可描述PVB薄膜非线性大变形和应变率相关效应的力学特性分析模型，并讨论了黏弹性项对于模型的影响。进而，考虑时间效应和温度效应，建立了PVB薄膜的黏弹性力学模型，对比分析了广义Maxwell模型和分数阶导数Maxwell模型在不同情况下的适用性。利用高速摄影方法结合落锤冲击实验系统，分析了PVB夹层玻璃在垂直平面方向冲击载荷作用下的裂纹扩展行为；分析了PVB薄膜对夹层玻璃裂纹扩展特性的影响，提出了描述夹层玻璃裂纹扩展最大速度受薄膜厚度影响的理论模型；基于统计学方法，分析了薄膜厚度对夹层玻璃宏观裂纹数量的影响。进一步地，基于头模型冲击实车风挡玻璃的实验系统，获取了冲击过程中的头部与风挡玻璃的动态响应，分析了PVB薄膜在冲击过程中的吸能机理。建立了头部冲击风挡玻璃的数值仿真模型，并将模拟结果与实验结果进行对比，得到了模型各参数的最优化取值。定义了评价风挡玻璃吸能特性的指标，在不同的冲击条件下，分析了中间层薄膜的结构属性与材料属性对风挡玻璃吸能特性的影响规律及机理，拟合得到了评价指标受各参数影响的经验公式。结合风挡玻璃在汽车设计中的具体应用，提出了其安全性设计准则。本论文在理论上揭示了PVB薄膜高聚物的黏弹性力学行为，阐明了中间层材料对夹层玻璃动态力学特性的影响机理，并在工程应用上为车用风挡玻璃夹层材料的安全性设计提供了依据。
Impact between pedestrian heads and vehicle windshields is a significant cause of fatal injuries for vulnerable road users intraffic accidents. The employment of PVB interlayer film has a great contribution to the energy absorption characteristics and crashworthiness of automotive laminated windshield. By theoretical analysis and experiments, the mechanical behavior and energy absorption characteristics of PVB film were investigated, and the mechanism of its influence on the mechanical response and energy absorption capability of laminated windshield under dynamic loading were systematically expounded.First of all, mechanical behaviors of PVB film under tensile and compressive loadings were obtained by both quasi-static and dynamic experiments. The stress-strain relationship of PVB presents a nonlinear large deformation characteristics and a strain rate effect. The energy absorption mechanism and failure criterion of PVB film under various loading conditions were analyzed. Further, the viscoelasticity of PVB film and its dependence on time and temperature were systematically investigated based on the Dynamic Mechanical Analysis method. The glass transition temperature was calculated and Time-Temperature-Superposition characteristics was analyzed. By adding correction term of strain rate effect to classical models describing viscoelastic constitutive behaviors, modified models were established which could well describe the nonlinear large deformation characteristics and strain rate dependence of PVB film. Influence of the viscoelastic term on this constitutive model was also discussed. Furthermore, with time and temperature effects in consideration, a constitutive model which can characterize the viscoelasticity of PVB film was thus established using modified Maxwell model. The applicability of Generalized Maxwell model and Fractional Derivative Maxwell model in various conditions were compared and discussed.Based on a drop-weight impact system combined with high-speed photography devices, the in-plane crack propagation behavior of PVB laminated glass under perpendicular-to-plane dynamic loading was investigated. The influence mechanism of PVB on the cracking propagation behaviors of laminated glass were clarified, and a theoretical model was suggested which expresses the influence of interlayer thickness on the maximum velocity of crack propagation. By Weibull statistical methods, the relationship between interlayer thickness and macroscopic crack amounts on laminated windshield was established. In addition, dynamic response of the impact between human head model and real automotive windshield were experimentally studied. Energy absorption characteristics of PVB film at various impact velocities, angles and directions were analyzed.An optimized numerical simulation model representing the impact process between human head and windshield was set up and validated by experimental results. Three indexes were defined to evaluate the energy absorption ability of windshield, so that the influence rule and mechanism of structure and material parameters of the interlayer were systematically investigated by finite element analysis under various impact conditions. Empirical formulas were obtained to bridge these parameters and evaluation indexes. Finally, the design criteria of windshield interlayer was suggested based on the applications of windshield in vehicle design.Results reveal the viscoelastic mechanical behavior of PVB film in theory, and explain the influence mechanism of interlayer material on dynamic mechanical behaviors of laminated glass, which may shed lights on the safety design of automotive interlayered material in engineering applications.
