【作者】 郭翠芳；

【导师】 张淳源；

【作者基本信息】 湘潭大学 ， 一般力学与力学基础， 2003， 硕士

【摘要】 随着非线性粘弹性材料的广泛使用和材料在极端条件下的使用，在长期荷载作用下频繁出现的延迟性的灾难性的事故使得非线性粘弹性的裂纹起裂时间和裂纹扩展速度的研究成为亟待解决的问题。由于非线性粘弹性断裂问题的复杂性，对于该问题的研究还必须借助于实验。 本文的主要目的是在实验条件受限制的情况下找到观测裂纹扩展全过程的实验方法，并且在此基础上研究一种非线性粘弹性材料在小变形的情况下准静态的亚临界扩展速度问题。 本文的主要研究成果是：通过参考前人的实验方法和不断地进行试验摸索，找到了观测裂纹准静态亚临界扩展全过程的有效方法；该实验方法所需实验设备少，实验过程简单，数据真实可靠。计算出非线性弹性双悬臂梁试件的J积分；推导出非线性回复弹性双梁的J积分与非线性粘弹性双梁裂纹扩展速度的关系式；把裂纹扩展速度的理论预测和实验数据进行了比较；对不吻合的地方做了分析。 具体成果包括：1、证实了双悬臂梁试件用于非线性粘弹性裂纹扩展实验研究的优点：双悬臂梁试件在实验中能观测到的扩展过程持续时间比较长，在计算J积分时，计算方法简单；2、得到了改性聚丙烯材料用于非线性粘弹性裂纹扩展实验的两种有效的试件构形和相应的试件尺寸；采用不断改善夹具的方法使得加载稳定；3、经过连续四个多月的时间得到了一组有用的实验数据；4、得到了裂纹长度与时间的关系、裂纹扩展速度与时间的关系、裂纹扩展速度与裂纹长度的关系。5、计算了改性聚丙烯双梁对应的回复弹性J积分；得到裂纹扩展速度实验数据与J积分的关系图；6、推导了非线性回复弹性双梁J积分与非线性粘弹性双梁裂纹扩展速度的关系式；用理论公式预测了裂纹扩展速度理论值与J积分的关系图；7、最后把理论预测和实验结果做了比较。更多还原

【Abstract】 Increasingly widely use of nonlinear viscoelastic materials, use of materials under extreme conditions, along with frequent occurrence of delayed catastrophic accidents, all these make the study a pressing problem of initiation and crack growth of nonlinear viscoelastic fracture. Because of the complexity of nonlinear viscoelastic fracture, experiments are often introduced.The main purpose of this paper is to study crack growth rate of a class of nonlinear viscoelastic materials under the condition of constant load and small-strain.In this paper:The new test program is raised by referencing the existing test programs and by our trial and error; In the new test program, facilities involved in the nonlinear viscoelastic crack tests are relatively few, the test process is relatively simple and the data obtained from the experiments are credible. On this basic, the calculation of J integral of nonlinear viscoelastic double cantilever beams specimens and the parameter of fracture work of corresponding nonlinear viscoelasticity are derived. Finally, prediction and experimental result are compared.In details:1. The advantages of double cantilever beams specimens in nonlinear viscoelastic crack growth test are proved. Using these specimens, the relatively long time of crack growth process is obtained, and calculation of J integral is relatively simple.2. The two useful shapes of modified polypropylene specimens and their dimensions in nonlinear viscoelastic crack growth test are proposed. A simple loading system, which can avoid later instability, was applied for the first time.3. After more than four months continuous test, useful data have been obtained.4. Relation graphs such as between crack length and time, crack growth rate and time, crack growth rate and crack length are plotted.5. J integral of nonlinear elastic double cantilever beam specimens is calculated.6. The relationship between J integral of nonlinear elastic double cantilever beam specimens and crack growth rate of nonlinear viscoelastic double cantilever beam specimens is derived.7. Predictions of theory and results of experiments are compared, and what cause error is discussed.更多还原