Notch tip damage zone in biaxially oriented polypropylene at low temperature
Notch tip damage zone in biaxially oriented polypropylene at low temperature
复制标题
低温双向拉伸聚丙烯缺口尖端损伤区
DOI：
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
E. Baer
中科院分区：
文献类型：
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作者：
J. Snyder;A. Hiltner;E. Baer
众所周知，双轴取向可大幅改善聚丙烯的机械性能;本研究进一步表明，机械性能的大幅改善尤其在玻璃化转变温度以下被放大。在这项研究中，在-40 °C下，在两个水平的双向取向下研究了聚丙烯在尖锐单边缺口拉伸试验期间的不可逆变形行为。无取向聚丙烯形成了一个狭窄的楔形损伤区，随着应力的增加，直到灾难性的断裂发生在一个脆性庄园。损伤区主要由垂直于加载方向生长的银纹组成。50%取向的材料最初形成楔形损伤区，随着载荷的增加而变宽。这导致在高样品延伸率下长宽比下降。试样断裂时裂纹以韧性方式稳定扩展，表现出较大的裂纹扩展阻力。80%取向的材料具有由许多分层裂纹组成的圆形损伤区。这些裂纹通过在厚度方向上分裂试样而生长。稳定的裂纹扩展占主导地位的最终失效过程与80%的取向材料显示出近三倍的无取向材料的韧性。John Wiley & Sons，Inc.
It is well established that biaxial orientation produces large improvements in the mechanical properties of polypropylene; this study further shows that the large improvements in mechanical behavior are magnified especially below the glass transition temperature. In this study, the irreversible deformation behavior of polypropylene during sharp single-edge notch tension testing has been studied at two levels of biadial orientation at −40°C. Unoriented polypropylene formed a narrow wedge-shaped damage zone that grows with increasing stress until catastrophic fracture occurs in a brittle manor. The damage zone consisted of many crazes that mainly grew perpendicular to the loading direction. The 50% oriented material initially developed a wedge-shaped damage zone that grew wider as loading increased. This resulted in a drop of the length-to-width ratio at high sample extensions. The specimen fractured with stable crack growth in a ductile manner, showing a large resistance to crack growth. The 80% oriented material had a circular damage zone that consisted of many delamination crases. These crases grew by splitting the specimen in the thickness direction. Stable crack growth dominated the final failure process with the 80% oriented material showing nearly three times the toughness of the unoriented material. © 1994 John Wiley & Sons, Inc.