软质聚氨酯泡沫的动态压缩力学性能和本构模型

采用Instron 9350落锤试验机研究了中低应变率下软质聚氨酯泡沫的动态压缩力学性能，分析了其应力-应变响应特征和应变率敏感性，讨论了应变率对材料应变率敏感性指数和能量吸收特性的影响，并基于实验结果建立了可准确描述其压缩力学响应的率相关本构模型。结果表明，软质聚氨酯泡沫的静动态压缩应力-应变响应具有典型的三阶段特征，且呈现出明显的应变率强化效应。准静态加载下，材料具有较高的吸能效率但能量吸收值较小，应变率对最大吸能效率和比吸能的影响较小；动态加载下，随着应变率的增加，最大吸能效率显著减小而比吸能明显增大。考虑应变率影响的修正Sherwood-Frost模型和修正Avalle模型都能够很好地表征软质聚氨酯泡沫的静动态压缩应力-应变响应，但修正Avalle模型的参数较少，更便于工程应用。研究结果可为软质聚氨酯泡沫抗冲击结构的设计和优化提供指导。

Dynamic compressive mechanical properties and constitutive models of flexible polyurethane foam

The quasi-static and dynamic compressive mechanical properties of flexible polyurethane foam were studied by using a DDL-200 electronic universal testing machine and an Instron 9350 drop-weight testing machine in a range of strain rates from 0.001 to 100 s?1. The stress-strain characteristics and strain rate sensitivity were analyzed, and the effect of strain rate on strain rate sensitivity index and energy absorption performance was discussed. Based on the experimental results, the strain rate-independent constitutive model was established to accurately describe the dynamic compressive mechanical behavior of the flexible polyurethane foam. The results show that the compressive stress-strain responses of flexible polyurethane foam exhibit typical three-stage deformation characteristics including initial elastic region, extended plateau region and final densification region, and the characteristics of material mesostructure at different deformation regions were analyzed. In addition, the material display an obvious strain rate-strengthening effect, both the yield stress and platform stress increase with the increase of strain rate, and the strain rate sensitivity index is affected by the coupling of strain rate and compressive strain. The energy absorption, energy absorption efficiency and specific energy absorption of flexible polyurethane foam at different strain rates were compared and the material shows higher energy absorption efficiency but less energy absorption, and strain rate has little effect on maximum energy absorption efficiency and specific energy absorption under quasi-static loading. With the increase of strain rate, the maximum energy absorption efficiency significantly reduces and the specific energy absorption significantly increases under dynamic loading. Both the modified Sherwood-Frost model and the modified Avalle model considering the effect of strain rate can well characterize the static and dynamic compressive stress-strain responses of the flexible polyurethane foam, but the modified Avalle model is easier to apply in engineering due to its fewer parameters. The research results can provide a guide for the design and optimization of flexible polyurethane foam on impact-resistant structures.