无规共聚聚丙烯材料的断裂损伤性能研究

发布时间：2018-07-10 12:21

本文选题：PP-R材料 + 断口显微形貌　；参考：《昆明理工大学》2017年硕士论文

【摘要】：自二十世纪60年代意大利化学家Giulio Natta等人相继研制出聚丙烯(简称PP)材料以来,世界各国大量的科研工作者们从来没有停止过对其各项力学、化学、电学等方面等基础性研究工作。如今,经改性得到的无规共聚聚丙烯(简称PP-R)材料逐渐被广泛应用于日常生活和工程应用等领域。例如,建筑行业与给排水管道、汽车领域的保险杆等重要结构部件等。从现有已获的国内外相关文献中获悉,PP-R材料在准静态、动态(冲击载荷下)的断裂性能(特别是裂纹扩展性能)以及损伤机理方面的研究还比较稀少。这导致PP-R材料的近一步应用带来一定阻碍作用。而断裂、损伤机理的研究在进行抗断裂设计、结构失效评定以及结构剩余寿命评估等方面均有重要意义。为此,本课题选取了 PP-R材料,采用实验、数字图像相关方法以及有限元方法,研究其断裂损伤机理。本文主要的研究工作和成果分为以下几个方面:1)首先对于不同机械预制裂纹位置(中心裂纹、偏离中心20mm、偏离中心40mm)的试件,进行Ⅰ型疲劳裂纹预制。分别得到两类不同预制裂纹长度的PP-R试件。试验过程中发现,在不同跨度下,PP-R材料依然存在增韧迟滞现象。2)以相同的位移控制速度,对三种经过预制疲劳裂纹的PP-R试件施加准静态载荷,完成复合型裂纹扩展试验。以此得到载荷F与裂纹扩展量△a之间的关系曲线图,分析这三种加载方式下材料的断裂形式。发现裂纹停留在迟滞区的试件准静态裂纹扩展量比突破迟滞区的裂纹扩展量少很多。3)准静态加载试验下采用数字图像测量技术,应用VIC-2D软件分别计算三类PP-R试件准静态工况下裂纹启裂状态以及裂纹扩展至最大状态的位移场、应变场;并进行可靠性分析。4)完成三类试件在不同高度下的落锤冲击试验。用高速摄像机获取试件的动态裂纹扩展路径,并拍摄试件启裂时的散斑图像,经VIC-2D软件处理,得到PP-R试件裂纹启裂状态下的位移场和应变场,并对其进行可靠性分析。5)通过扫描电子显微镜(SEM)分别对准静态试验条件下与冲击试验条件下的三类试件进行断口形貌分析,并得到PP-R材料在准静态裂纹稳定扩展阶段的断裂、损伤形式;在准静态载荷作用下裂纹快速扩展形式;在冲击载荷作用下裂纹快速扩展的断裂、损伤形式。6)利用Franc3D与ABAQUS软件相结合的方法,计算裂纹尖端附近的应力场、应变场、位移场、裂纹尖端张开位移(COD)以及应力强度因子,并与数字图像相关方法的计算结果进行对比分析。
[Abstract]:Since the Italian chemist Giulio Natta and others developed polypropylene (PP) materials in the 1960s, a large number of researchers around the world have never stopped working on its mechanics and chemistry. Electrical and other aspects of basic research work. Nowadays, the modified random copolymerization polypropylene (PP-R) materials have been widely used in daily life and engineering applications. For example, the construction industry and water supply and drainage pipes, automobile safety bar and other important structural components. It has been learned from the relevant literatures at home and abroad that there are few studies on the fracture properties (especially crack propagation properties) and damage mechanism of PP-R materials under quasi-static and dynamic (under impact load). This leads to the further application of PP-R materials to a certain extent. However, the study of fracture and damage mechanism is of great significance in the design of anti-fracture, the evaluation of structural failure and the evaluation of structural residual life. Therefore, the PP-R material is selected to study the fracture damage mechanism of PP-R material by means of experiments, digital image correlation method and finite element method. The main work and results of this paper are as follows: 1) first of all, mode I fatigue crack prefabrication is carried out for specimens with different mechanical precast crack positions (central crack, 20mm off-center, off-center 40mm). Two kinds of PP-R specimens with different crack lengths were obtained. During the test, it is found that toughening hysteresis still exists in different span of PP-R material. (2) at the same displacement control speed, three kinds of PP-R specimens subjected to precast fatigue crack are subjected to quasi-static load, and the composite crack growth test is completed. The relationship between the loading F and the crack propagation a is obtained, and the fracture modes of the materials under these three loading modes are analyzed. It is found that the quasi-static crack propagation of the specimen with a crack remaining in the hysteresis region is much less than that of the specimen with a crack break through the hysteresis region. The digital image measurement technique is used in the quasi-static loading test. VIC-2D software is used to calculate the crack initiation state and the displacement field and strain field of crack propagation to the maximum state in quasi-static condition of three kinds of PP-R specimens, and the reliability analysis (.4) is carried out to complete the impact test of three kinds of specimens at different heights. The dynamic crack propagation path of the specimen was obtained by high speed camera, and the speckle image of the specimen was taken. The displacement field and strain field of the PP-R specimen under crack initiation were obtained by VIC-2D software. The fracture morphology of three kinds of specimens under static test condition and impact test condition were analyzed by scanning electron microscope (SEM), and the fracture of PP-R material was obtained at the stage of quasi-static crack stable growth. Damage form; crack rapid growth under quasi-static loading; crack fracture under impact load, damage form .6) the stress field and strain field near the crack tip are calculated by using Franc3D and Abaqus software. The displacement field, crack tip opening displacement (COD) and stress intensity factor are compared with the calculated results of digital image correlation method.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O346.1

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