MORPHOLOGICAL ALTERATIONS DURING TEXTURE-PRODUCING PLASTIC PLANE-STRAIN COMPRESSION OF HIGH-DENSITY POLYETHYLENE
MORPHOLOGICAL ALTERATIONS DURING TEXTURE-PRODUCING PLASTIC PLANE-STRAIN COMPRESSION OF HIGH-DENSITY POLYETHYLENE
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DOI：
10.1021/ma00047a023
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发表时间：
1992-10-12
期刊：
影响因子：
5.5
通讯作者：
COHEN, RE
中科院分区：
文献类型：
--
作者：
GALESKI, A;BARTCZAK, Z;COHEN, RE
单个线性聚乙烯样品的许多试样在通道模具中通过平面应变压缩变形至非常大的塑性应变。通过密度测量、偏光显微镜、透射电子显微镜、广角和小角X射线衍射等手段对变形机制进行了分析。的去卷积程序分离重叠的X-射线衍射峰和漫散射的无定形材料也适用，和极图重建从校正的数据。在压缩比为1.80时，强烈的剪切局部化出现在相对于流动方向的+/-45度处。有强有力的证据表明，层间滑动只有在低压缩比。一旦这种滑动明显耗尽，（100）[001]链滑移系统上的晶体学滑移开始。当压缩比大于1.80和3.13时，分别观察到（100）[010]横向滑移和（010）[001]链滑移过程。压缩比为2.5和3.13时的强剪切带主要来源于（100）[001]和（100）[010]滑移过程。压缩比为6.44时的形貌类似于单晶织构。进一步的变形通过（100）[001]滑动发生，并且在较小程度上通过（010）[001]链滑动发生。（110）孪晶过程显示出有限的活性，但仅在接近12的非常高的压缩比下。相关的TEM研究已经表明，当附着到薄片的初始非晶材料层旋转以垂直于加载方向时，新的长周期开始垂直于流动方向演变，开始于3.13的压缩比;这个新的长周期是通过一个明显的广泛的收缩形成的，在3.13的压缩比以上的拉伸薄片和界面平移，并且随着持续变形而逐渐变得更好地限定。有人建议，破碎的薄层是由于变形不稳定性有关的结晶和非晶层的界面拉伸阻力的增加，并开始由厚度的不规则性。由于缺陷（领带链接等）在新发展的非晶材料中，沿着链具有良好的迁移率沿着，完全织构化的准晶体样品具有连续的晶体背景，其中分离的链缺陷层构成新的长周期。也有一些证据表明，在垂直于载荷方向的平面中形成了缺陷和裂缝，这导致了与沿沿着（100）面断裂相关的拉伸脆性。
Numerous specimens of a single linear polyethylene sample were deformed by plane strain compression in a channel die to very large plastic strains. The mechanisms of deformation were elucidated by density measurements, polarized light microscopy, transmission electron microscopy, and wide-angle and small-angle X-ray diffraction. A deconvolution procedure for separating overlapping X-ray diffraction peaks and the diffuse scattering from the amorphous material was also applied, and pole figures were reconstructed from the corrected data. At a compression ratio of 1.80 intense shear localization appeared at +/-45-degrees with respect to the flow direction. There is strong evidence for interlamellar sliding only at low compression ratios. Once this sliding is apparently exhausted, crystallographic slip on the (100)[001] chain slip system sets in. At a compression ratio above 1.80 and 3.13 respectively, (100)[010] transverse slip and (010)[001] chain slip processes are observed. The strong shear bands occurring at compression ratios of 2.5 and 3.13 originated mainly from (100)[001]and (100)[010] slip processes. The morphology at a compression ratio of 6.44 resembles a monocrystal texture. Further deformation occurs by (100)[001] slip and to a lesser extent by (010)[001] chain slip. The (110) twinning process shows limited activity, but only at very high compression ratios near 12. Associated TEM studies have shown that while the initial amorphous material layers attached to the lamellae rotate to lie normal to the loading direction, a new long period starts to evolve normal to the flow direction beginning at a compression ratio of 3.13; this new long period forms via an apparent widespread pinch-off of stretched lamellae and translation of interfaces above a compression ratio of 3.13 and becomes progressively better defined with continued deformation. It is suggested that the breakup of thinned lamellae is due to a deformation instability related to the increase of interface stretching resistance of the crystalline and amorphous layers and is initiated by thickness irregularities. Because of defects (tie links, etc.) that have good mobility along the chain in the newly evolved amorphous material, the fully textured quasi-crystal sample has a continuous background of crystals with layers of segregated chain defects making up the new long period. There is also some evidence for the formation of flaws and fissures in planes perpendicular to the load direction, which causes brittleness in tension associated with fracture along the (100) planes.