共查询到18条相似文献,搜索用时 195 毫秒
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聚苯乙烯断面形貌特征参量对断裂能耗的影响 总被引:3,自引:0,他引:3
对缺口聚苯乙烯试样进行了不同加载速率下的三点弯曲实验,通过对加载速率、断面特征区特征参量、断裂能耗三者间关系的分析,指出断裂表面特征形貌中的镜面区、肋状区的形成是能量消耗的主要过程.实验结果表明,随着加载速率增大,镜面区尺寸增大并逐渐趋于平缓,肋条宽度减小而肋区粗糙度增大.断裂能耗与加载速率间存在极小值现象,该极小值出现在25m/min的加载速率下,与断面形貌特征的变化正好对应;加载速率<25m/min时,断面主要由镜面区、最后断裂区组成,断裂能耗的变化取决于镜面区尺寸的变化;加载速率>25m/min时,断面由镜面区、肋区、最后断裂区组成,断裂能耗的变化主要和肋区粗糙度的变化有关. 相似文献
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测定了有机玻璃的抗裂纹增长因子K_(1C)与材料组份、拉力机夹头速度的关系。发现增塑剂和交联剂对抗裂纹性能的影响,可从聚合物分子运动能力对裂纹端点塑性屈服过程的影响说明。在对断面形态、断面层厚度、折光指数以及K_(1C)值与拉力机夹头速度关系研究之后,认为用“撕布”模式和次级断裂模式分别解释慢裂纹、快裂纹扩展过程中的实验现象是合适的。 相似文献
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不同结晶状态的聚丙烯材料的声发射研究 总被引:1,自引:0,他引:1
用MISTRAS2001声发射监测系统对加入一定量成核剂(0-2.0%)的聚丙烯材料进行冲击过程声发射研究,研究记录了冲击过程的应力-时间曲线。结果表明,在成核剂加入量为0.4%时,冲击强度出现极大值,与之相对应,其声发射信号最为丰富,声发射振铃计数最高,裂纹扩展阶段的声发射信号占主导地位,随成核剂含量增大,材料冲击断裂过程中裂纹萌生阶段AE计数呈上升趋势,而裂纹扩展阶段的AE计数呈先上升后下降的趋势,同时裂纹萌生功和裂纹扩展功也呈现相同的变化趋势,与断面特征区特征参量的变化相对应。 相似文献
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研究了聚碳酸酯(PC)和PC/ABS高分子材料的疲劳裂纹扩展规律,利用改进柔度法测量其裂纹扩展速率,采用扫描电子显微镜(SEM)观察其断口形貌,分析疲劳裂纹扩展机理.在较大裂纹扩展速率(10-6~10-3mm/cycle)范围内,PC/ABS的疲劳裂纹扩展速率可以用Paris公式da/dN=9·5587×10-5(ΔK)2·88381来描述.高分子材料PC的疲劳裂纹扩展速率约为高分子材料PC/ABS的3倍.高分子材料PC/ABS疲劳裂纹面上的特征以韧窝为主,较低裂纹扩展速率对应较小的韧窝,较高裂纹扩展速率对应较大的韧窝.高分子材料PC疲劳裂纹面有明显的不连续裂纹扩展带,其裂纹面相对较平. 相似文献
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分别制备了以L-半胱氨酸(L-cyst.)或以巯基乙酸(TGA)保护的银纳米颗粒,并用紫外-可见分光光度法和透射电子显微技术(TEM)对两种不同状态的银纳米颗粒的结构作了表征。由其吸收光谱图显示,L-cyst.和TGA保护的银纳米颗粒的吸收峰依次位于384 nm和392 nm波长处;由TEM的检测结果表明:上述2种形态银纳米颗粒的粒度大小依次在10~40 nm和20~30 nm范围内。试验中发现,以L-cyst.保护的银纳米颗粒与曙红Y之间有明显的相互作用,导致其吸收峰从384 nm红移至395 nm;以TGA保护的银纳米颗粒与曙红Y之间未见有相互反应。初步探讨了其作用机理,认为系由于结合于银纳米颗粒表面的L-半胱氨酸分子所带的正电荷与曙红Y分子上的负电荷之间的静电作用的结果。 相似文献
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芳香共聚酯B-N多种向列织构的形态研究 总被引:2,自引:1,他引:2
从一种聚芳酯B-N得到了丝状(包括细丝和粗丝)、纹影状和大理石纹状等与小分子向列液晶相似的多种织构。由于样品淬火后晶片装饰在织构上而不影响分子取向矢的分布,因而可以用化学刻蚀和电镜技术揭示其向错和取向矢图。电镜和光学显微镜的结果相互补充,表明了细丝和粗丝状织构的分子取向矢分布很不相同,是两种不同的织构,而粗化始于第二熔融降温。在这些向列织构中分别发现了S=±(1/2)和s=+1的向错的例子和平面内微区转向壁的证据。 相似文献
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One of the main challenges of the mode I double cantilever beam (DCB) test is the simultaneous determination of the applied load and displacement with the developing delamination length. The present work addresses this issue by side-view tracking the crack propagation by means of digital image correlation (DIC). Two different reduction methods were developed to determine the crack length from the DIC data. On the one hand, the crack tip position was defined by the high strain concentration in the immediate vicinity of the crack tip, and on the other hand, by crack tip opening displacement (CTOD). The data obtained enabled the calculation of the energy release rate of carbon fibre reinforced thermoplastic specimens with either run-arrest or stable crack extension. For reasons of comparability, top surface analysis (TSA), as recently reported, was also carried out. Following this approach, the crack propagation was tracked applying DIC to the top specimen surface. The methods developed showed a good correlation with both the standardised procedure and TSA. It was shown that DIC can be used as an alternative to the conventional optical measuring tools to follow the crack propagation in the mode I DCB test. 相似文献
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Within the linear viscoelastic theory, crack tip fields are calculated at various crack tip velocities. A transition from
rubbery to glassy material behavior in the vicinity of the crack tip can be observed. Shear and bulk behavior is analyzed
separately. Whereas the increase of tearing energy at higher crack tip velocities can be ascribed to the shear behavior, bulk
behavior influences the fracture mechanism. The results support experimental investigations that the instability separating
stable from unstable crack propagation is related to a change in the fracture mechanism. At low crack tip velocities, material
separation is the result of formation, growth, and coalescence of cavities. At high crack tip velocities, cavitation is suppressed
and fracture is driven by a rather brittle mechanism resulting in a decreased amount of energy to propagate the fracture process
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Published in Russian in Vysokomolekulyarnye Soedineniya, Ser. A, 2008, Vol. 50, No. 5, pp. 882–891.
This article was submitted by the authors in English. 相似文献
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Environmental stress cracking (ESC) in poly(methyl methacrylate) under different humidity conditions has been investigated. Constant stress‐intensity factor (K) ring‐type specimens were prepared, and all specimens were equilibrated at five different humidity conditions for about two years. ESC tests were carried out under the same humidity as specimens had been stored. Acoustic emission (AE) signals during ESC tests were also measured to examine the crack‐growth behavior. The threshold K value (Kth) tended to increase with increasing humidity. At a relative humidity (RH) of 11%, crack growth occurred gradually until 40 ks under a K value of 0.70 MPam1/2, and then the crack‐growth rate began to increase and AE events were observed. A laser microscopic observation indicated that the crack extended by the coalescence between a main crack and a microcrack ahead of the main crack tip. AE signals generated are considered to be associated with the coalescence. At 98% RH, an incubation period where no crack growth was observed existed under a K value of 0.94 MPam1/2, but the crack began to grow suddenly after that incubation period. This suggests that the craze at the crack tip may become weaker with increasing loading time under high humidity. Although the crack‐growth rate at 98% RH was higher than that at 11% RH, no AE events were observed. This suggests that the crack extended stably in the craze at a crack tip, and sorbed water may make the craze growth easy. All the results suggest that two different ESC mechanisms are activated depending on sorbed water that are varied by humidity. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 1–9, 2002 相似文献
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用电子显微镜观察了聚全氟乙丙烯试料的自由表面形态结构,指出试料不同,自由表面形态也不同,有的由无规片层组成,有的则由无规和规整两种片层组成,提出了两种片层结构本质的设想,用另一些实验数据支持这种设想,根据设想所推测的试料的力学性能与实测值基本相符。 相似文献
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Gerald Pinter Ivica Duretek Nicolai Aust Reinhold W. Lang 《Macromolecular Symposia》2002,181(1):213-224
In this work the influence of three different stabiliser systems on the stress rupture behaviour of high density polyethylene (PE-HD) pipes under constant internal pressure was examined at 60 and 80°C with special consideration of the quasi-brittle failure by growth of a single crack in the failure regime preceding the global chemical degradation of the pipes. It could be proven that the pipes of the three formulations did not show global molecular and morphological differences in this failure regime and that the stabilisation was still intact. Therefore, the differences in failure times observed for the three formulations are believed to be a result of local ageing around the crack tip related to the combined influence of time, the elevated temperature, the presence of oxygen and water, and the high mechanical stresses in the immediate crack tip region. 相似文献
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Roger P. Kambour 《Journal of Polymer Science.Polymer Physics》1966,4(3):349-358
Observation of optical interference fringes at the tip of a crack in a glassy polymer allows the construction of the configurations of the crack tip and the craze that precedes it. The craze extends 25 μ beyond the crack tip in poly(methyl methacrylate) and 550 μ beyond the tip in the polystyrene studied. The craze at the crack tip in PMMA may be seen to deform elastically as much as 100% under stress before crack propagation recommences. Such deformation is estimated to account for as much as 40% of the nominal Griffith energy of crack propagation. 相似文献
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Xu Q Mayers BT Lahav M Vezenov DV Whitesides GM 《Journal of the American Chemical Society》2005,127(3):854-855
This report presents a simple and convenient method to generate nanoscale fractures (cracks) in smooth, single-crystalline Si substrates. The cracks propagated as approximately straight lines along the {100} crystal planes with controllable length defined by a stabilizing backlayer. Close to its tip, the crack presented a vertical offset of the two planes as step of smoothly decreasing height, ranging from the microscale to the atomic scale. The edges of a crack were in close contact at the tip of the crack but were separated at the edge where the crack was initiated. These steps served as ideal test features for probing the limits of the replication of soft lithography. Analysis of topography of original and replicated features (in "hard" poly(dimethylsiloxane and polyurethane) by atomic force microscopy demonstrated that steps down to 0.4 nm could be reproduced; these features approach the dimensions of atoms. 相似文献