泡沫材料的应变率效应

Strain rate effect on the p roperties foam materials

对泡沫材料的应变率敏感性进行了系统深入的讨论,认定这种材料是应变率敏感材料,这种敏感性主要是由于泡孔的变形特性产生的。泡沫材料变形的局部化、微观惯性和致密性导致压垮应力明显提高,基体的应变率效应及泡孔的形状大小并不能对泡沫材料应变率敏感性起主导作用。

Improved SHPB method and semi-conductive gauges were used to investigate strain rate effects on the properties of foam materials. Experiments results involve quasi-static and dynamic stress-strain curves of three densities of rigid fiber-polyurethane foams, four cell sizes aluminum foams of the same density, and four densities aluminum alloy foam. All experimental results indicate that strain rate effect on foam materials is evident, although matrix, some of which are strain sensitive and some are not, cell sizes and relative density are different. It is the existing of cells that cause strain rate effect on foam materials. It can be concluded that crushing stress will be enhanced under high strain rate because of the following two reasons; (1) as impact velocity increases, the cells near the impact surface instantly are tightly compressed and therefore strain-rate will increase and the colliding speed of cell wall will enlarge, causing the crushing stress to increase; (2) The highly localized nature of crushing results in very large strain rate in crushing band and therefore micro-inertia will play a more important role causing crushing stress to increase. Another conclusion is that strain rate sensitivities of matrix and cell morphology themselves are not the main reasons for strain-rate sensitivities of foam materials.