Research On Mechanical Characteristics And Energy Absorption Mechanism Of Windscreen Inter-layered Material

Impact between pedestrian heads and vehicle windshields is a significant cause offatal injuries for vulnerable road users in traffic accidents. The employment of PVBinterlayer film has a great contribution to the energy absorption characteristics andcrashworthiness of automotive laminated windshield. By theoretical analysis andexperiments, the mechanical behavior and energy absorption characteristics of PVBfilm were investigated, and the mechanism of its influence on the mechanical responseand energy absorption capability of laminated windshield under dynamic loading weresystematically expounded.First of all, mechanical behaviors of PVB film under tensile and compressiveloadings were obtained by both quasi-static and dynamic experiments. The stress-strainrelationship of PVB presents a nonlinear large deformation characteristics and a strainrate effect. The energy absorption mechanism and failure criterion of PVB film undervarious loading conditions were analyzed. Further, the viscoelasticity of PVB film andits dependence on time and temperature were systematically investigated based on theDynamic Mechanical Analysis method. The glass transition temperature was calculatedand Time-Temperature-Superposition characteristics was analyzed.By adding strain rate dependence term to classical models describing viscoelasticconstitutive behaviors, modified models were established which could well describe thenonlinear large deformation characteristics and strain rate effect of PVB film. Influenceof the viscoelastic term on this constitutive model was also discussed. Furthermore,with time and temperature effects in consideration, a constitutive model which cancharacterize the viscoelasticity of PVB film was thus established using modifiedMaxwell model. The applicability of Generalized Maxwell model and FractionalDerivative Maxwell model in various conditions were compared and discussed.Based on a drop-weight impact system combined with high-speed photographydevices, the in-plane crack propagation behavior of PVB laminated glass underperpendicular-to-plane dynamic loading was investigated. The influence mechanism ofPVB on the cracking propagation behaviors of laminated glass were clarified, and atheoretical model was suggested which expresses the influence of interlayer thicknesson the maximum velocity of crack propagation. By Weibull statistical methods, the relationship between interlayer thickness and macroscopic crack amounts on laminatedwindshield was established. In addition, dynamic response of the impact betweenhuman head model and real automotive windshield were experimentally studied. Energyabsorption characteristics of PVB film at various impact velocities, angles anddirections were analyzed.An optimized numerical simulation model representing the impact process betweenhuman head and windshield was set up and validated by experimental results. Threeindexes were defined to evaluate the energy absorption ability of windshield, so that theinfluence rule and mechanism of structure and material parameters of the interlayerwere systematically investigated by finite element analysis under various impactconditions. Empirical formulas were obtained to bridge these parameters and evaluationindexes. Finally, the design criteria of windshield interlayer was suggested based on theapplications of windshield in vehicle design.Results reveal the viscoelastic mechanical behavior of PVB film in theory, andexplain the influence mechanism of interlayer material on dynamic mechanicalbehaviors of laminated glass, which may shed lights on the safety design of automotiveinterlayered material in engineering applications.