冲击拉伸过程中HDPE银纹内聚力的测定

Measurement of Cohesion Stress of HDPE Craze Under Impact Drawing

热塑性聚合物经受稳定的银纹微纤拉伸时,银纹区的迅速增厚将会迅速地引起局部绝热升温现象。预测裂尖银纹的热力学分析可以预测结晶热塑性高聚物冲击断裂阻抗。热反内聚模型用来模拟冲击拉伸过程银纹寿命或反内聚时间。文中报道了一种新型的全切痕蠕变测试法可以在银纹增厚速率高达2 m/s时测量平面银纹层的内聚力,在快速拉伸条件下高密度聚乙烯的内聚力和银纹寿命被测量,测试的结果与数值模型的预测结果是相一致的。

In a HDPE which undergoes stable craze fibril drawing, rapid thickening of the craze layer will cause highly localised adiabatic heating. A thermomeehanieal analysis, predicated on the existence of a crack-tip craze, has previously allowed both impact fracture resistance and resistance to rapid crack propagation to be predicted for crystalline thermoplastics. In terms of craze cohesion, a thermal decohesion model can be used to simulate a craze lifetime or the decohesion time during impact extension. A modified Full Notch Creep test has been developed to measure the cohesive properties of a planar, craze layer, under thickening rates of up to 2 m/s. Displacement is imposed directly on the notch surface by a rigid insert within the moulded specimen. Both the cohesive stress and the lifetime under rapid extension were measured. For the high density polyethylene tested these correlate well via the numerical model.