• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文OA文献 >Fatigue of PVC-M and PVC-M based nanocomposites
【2h】

Fatigue of PVC-M and PVC-M based nanocomposites

机译：PVC-M和PVC-M基纳米复合材料的疲劳

页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Over the years, unplasticised PVC (PVC-U) has been extensively used in the manufacturing of plastic pipes. However, in spite of offering many advantages, PVC-U pipes have been found to fracture in a brittle manner. A significant improvement in the fracture toughness properties of PVC-U pipes has been achieved by the addition of impact modifiers. This increased the use of the modified PVC materials (PVC-M), particularly in pressurized water applications. Nevertheless, since the pipes are subjected to cyclic loads during service, a potential failure of the pipes appears due to fatigue fracture of the pipe material. Therefore, in designing pipes with improved durability, it is imperative to understand the response of PVC and modified PVC to cyclic loading. Since the PVC pipes are used for transporting water, they may behave in a different manner in water and in air environments. Thus, the effect of the environment on the fatigue behavior of PVC-U and PVC-M also needs to be investigated. Modification of PVC-U with nanoparticles (i.e., CaCO3) in addition to the impact modifiers has also shown to provide promising property improvements with regards to various applications. Furthermore, improving the toughness with the addition of nanoparticles under static loading has been well researched; however, the effect of cyclic loading on fatigue properties has received limited attention. This study was undertaken to address the issues of fracture and fatigue of PVC-U and toughened variations. In this work, fatigue crack growth rates studies were conducted for two sets of materials: (1) PVC-U (monolithic) and PVC-M in air and water environments, and (2) PVC-U and PVC-CaCO3 nanocomposites in air. The PVC-M comprised of 6 pphr of chlorinated polyethylene (CPE) as an impact modifier. The fatigue tests were conducted at different frequencies (1, 7 and 20 Hz) and different R-ratios (0.1, 0.2 and 0.6), and the cyclic fatigue threshold values (ΔKth) of both PVC materials were determined at the respective frequencies. For the nanocomposite samples, the CaCO3 content was varied from 3 pphr to 20 pphr, and similar fatigue tests with similar parameters were conducted. In addition, the effect of a titanate coupling agent with 0.6 pphr on the fatigue behavior of nanocomposites was also evaluated. Crack growth mechanisms related to their morphologies were examined with light optical and scanning electron microscopes. The frequency was found to considerably affect the fatigue crack growth rate and the fatigue threshold (ΔKth) value in both materials, regardless of the testing environment. A slight difference in the crack growth rates of PVC-M and PVC-U was observed at lower stress intensity factor amplitudes (below ΔK=1MPa.m1/2) which is associated with the presence of CPE particles. It was also found that the fatigue resistance in water is higher than in air. However, the benefits seen in water deteriorated under conditions of higher stress intensity factor amplitude (ΔK) and frequency. Fractographic surface analysis revealed that the basic fatigue fracture mechanism of PVC is unchanged even in the presence of CPE; the formation of craze structures. The absorption of water into the PVC matrix was evident in a water environment which leads to the formation of nodular and plasticized structures at low and high ΔK. Nevertheless, in an air environment, formations of those structures were absent. The formation of a ‘stretch’ zone in PVC-M at a high R-ratio resulted in an insignificant increment in the crack growth rates at all respective R-ratios. The trend of fatigue behaviour of PVC is consistent even in samples that had been modified with nano-CaCO3 particles, i.e. no significant deterioration in the fatigue resistance was observed compared to PVC-U. Similar results were obtained in the PVC nanocomposites that added with coupling agent. Variation in the frequency and the R-ratio levels was found to result in lower crack growth rates at higher frequencies and higher crack growth rates at higher R-ratios. Fracture surface observations showed that the fatigue fracture in the PVC nanocomposites occurred through different mechanisms; that are, through particle debonding and ligament yielding of the PVC matrix. Analysis of the crack advance mechanism in all samples (PVC-U, PVC-M, PVC nanocomposites) by microscopic observations at the crack tip process zone indicated that shear bands were not formed. Therefore, it is emphasized that craze formation and failure is the primary fatigue facture mechanism in PVC pipes, irrespective of the nature of addition phases to enhance toughening.
机译：多年来，未增塑的PVC（PVC-U）已广泛用于制造塑料管。然而，尽管具有许多优点，但是发现PVC-U管以脆性方式破裂。通过添加抗冲改性剂，可以显着改善PVC-U管的断裂韧性。这增加了改性PVC材料（PVC-M）的使用，特别是在加压水应用中。然而，由于管道在使用过程中承受周期性载荷，因此管道的潜在故障由于管道材料的疲劳断裂而出现。因此，在设计具有更高耐用性的管道时，必须了解PVC和改性PVC对循环载荷的响应。由于PVC管用于输送水，因此它们在水和空气环境中的行为可能不同。因此，还需要研究环境对PVC-U和PVC-M疲劳行为的影响。除抗冲改性剂外，还用纳米粒子（即CaCO3）对PVC-U进行了改性，从而在各种应用方面也提供了令人鼓舞的性能改进。此外，已经对通过在静态载荷下添加纳米颗粒来改善韧性进行了深入研究。然而，循环载荷对疲劳性能的影响受到了有限的关注。进行这项研究是为了解决PVC-U的断裂和疲劳以及韧性变化的问题。在这项工作中，对两组材料进行了疲劳裂纹扩展速率研究：（1）空气和水环境中的PVC-U（整体式）和PVC-M，以及（2）空气中的PVC-U和PVC-CaCO3纳米复合材料。 PVC-M包含6 pphr的氯化聚乙烯（CPE）作为抗冲改性剂。在不同的频率（1、7和20 Hz）和不同的R比（0.1、0.2和0.6）下进行疲劳测试，并在各自的频率下确定两种PVC材料的循环疲劳阈值（ΔKth）。对于纳米复合材料样品，CaCO3含量在3 pphr至20 pphr之间变化，并使用相似的参数进行了相似的疲劳测试。另外，还评估了具有0.6pphr的钛酸酯偶联剂对纳米复合材料的疲劳行为的影响。用光学和扫描电子显微镜检查了与其形态有关的裂纹扩展机理。不论测试环境如何，均发现该频率对两种材料的疲劳裂纹扩展速率和疲劳阈值（ΔKth）值都有很大影响。在较低的应力强度因子振幅（低于ΔK= 1MPa.m1 / 2）下，观察到PVC-M和PVC-U的裂纹扩展速率略有差异，这与CPE颗粒的存在有关。还发现，水中的抗疲劳性高于空气中的抗疲劳性。但是，在较高的应力强度因子振幅（ΔK）和频率较高的条件下，水中的益处会降低。分形表面分析表明，即使存在CPE，PVC的基本疲劳断裂机理也没有改变。开裂结构的形成。在水环境中，很明显水吸收到PVC基质中，导致在低和高ΔK下形成球状和增塑的结构。然而，在空气环境中，没有这些结构的形成。在高R比率下在PVC-M中形成“拉伸”区带，导致所有各个R比率下的裂纹扩展率均无明显增加。即使在已经用纳米CaCO3颗粒改性的样品中，PVC的疲劳行为趋势也是一致的，即，与PVC-U相比，未观察到疲劳强度的显着降低。在添加了偶联剂的PVC纳米复合材料中获得了相似的结果。发现频率和R比值的变化会导致较高频率下较低的裂纹扩展速率，以及较高R比下的较高裂纹扩展速率。断裂表面观察表明，PVC纳米复合材料的疲劳断裂是通过不同的机理发生的。即通过PVC基体的颗粒脱粘和韧带屈服。通过在裂纹尖端加工区的显微镜观察分析所有样品（PVC-U，PVC-M，PVC纳米复合材料）的裂纹扩展机理，表明没有形成剪切带。因此，需要强调的是，无论增强韧性的添加阶段如何，开裂和破裂是PVC管疲劳的主要机理。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号