This thesis contains a study which has been conducted using fracture mechanics parameters to describe crack and craze growth behaviour in PMMA under the influence of liquid environment. The text of this work is divided into two main parts: Part I has two component chapters; Chapter 1 contains a general introduction to environmental fracture in polymers. Chapter 2 outlines the basis of fracture mechanics concepts used in the analysis of results, and contains a literature review on the failure behaviour of PMMA in dry and wet environment. The survey includes results from dead load tests and monotonically increasing displacement conditions. Part II contains the work which has been undertaken to investigate the environmental fracture of PMMA. This part is subdivided into four phases. Phase I describes an effective method which is successfully used to monitor craze growth in PMMA under the influence of dead load and methanol environment. In the same chapter (3) the results together with the discussion are given. Phase II gives results obtained from crack propagation tests in PMMA in air and liquid environments. These tests are performed under monotonically increasing load-point displacement conditions using the double torsion technique which is described in Chapter 4. Chapter 5 contains the experimental results and shows that in dry tests, crack propagation is stable with characteristic KC and crack speed values. To the contrary, tests performed in methanol have developed unstable cracking which is identified with a sequence of rapid jumps. Phase III follows here where the mechanism which constitutes these jumps is determined. This is done with the aid of the K/v relationship obtained during a crack jump. The linear compliance analysis for the test piece geometry in Chapter 6, together with an experimental technique developed to measure rapid load drops, given in Chapter 7, provide the basis for the measurement of the K/v values. In Phase IV a mathematical model is proposed in Chapter 8, which successfully identifies the various stages which occur during the fracture of PMMA both dry and in methanol. A thorough fractographic study is carried out in Chapter 9 in support and completion of the model, with further evidence given from acoustic emission results, shown in Chapter 10. As an alternative environmental condition, fracture tests are performed in distilled water and crack propagation results are given in Chapter 11. These have shown similar crack jumping mechanism to that in methanol.
|Date of Award||1980|