聚丙烯拉伸性能测试及再屈服行为

Uniaxial Tensile Properties Testing and Re-yield Behavior of Polypropylene

为明确热塑性塑料塑性变形阶段加载-卸载-再加载的力学行为,采用注塑成型方法制备了哑铃型聚丙烯试样,进行了单轴拉伸实验。实验结果表明:所制备的试样具有良好的性能稳定性,试验结果重现性好,应力-应变曲线符合部分结晶热塑性塑料的一般行为。通过不同应变速率测试结合断口形貌扫描电子显微镜(scanning electron microscope,SEM)观察,表明应变速率超过50 mm/min时,试样由韧性断裂转变为脆性断裂,断口形貌由穿晶断裂形貌转变为河流花样形貌。聚丙烯的加载-卸载-再加载测试表明,在低应变速率情况下,塑料在再加载之后的应力-应变曲线存在明显的再屈服行为,与金属的包辛格效应存在明显不同。加载-卸载-再加载的应力-应变曲线会出现第二个屈服点,其屈服应力低于第一屈服应力,并且其数值与卸载点应变无关。研究结果为热塑性塑料塑性阶段的加工和使用提供理论支持。

In order to clarify the mechanical behavior of loading-unloading-reloading in the process of plastic deformation of polypropylene(PP),dumbbell-type polypropylene samples were prepared by injection molding,and uniaxial tensile experiments were carried out.The experimental results show that the prepared specimens have good stability,and the result of the tensile test has good reproducibility,and the stress-strain curve conforms to the general behavior of partial crystalline thermoplastics.Through different strain rate tests combined with scanning electron microscope(SEM)observation of fracture morphology,it is shown that when the strain rate exceeds 50 mm/min,the specimen changes from ductile fracture to brittle fracture,and the fracture morphology changes from perforation fracture morphology to river pattern morphology.The loading-unloading-reloading test results show that the PP specimens have an obvious re-yield behavior under the condition of low strain rate,which is significantly different from the Bauschinger effect of the metal materials.The second yield point is presented by the stress-strain curve of the loading-unloading-reloading test,and the second yield stress is lower than the first,and the value of the second yield stress is independent of the strain of the unload point.The research results provide theoretical support for the processing and application of thermoplastic plastics in the plastic deformation stage.