The effect of crack tip local heating on the retardation of fatigue crack
| Autor: | Dong Ming-Lee, 李東明 |
|---|---|
| Rok vydání: | 1999 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 87 The retardation of fatigue crack caused by crack tip local heating was studied. Steady fatigue crack growth under constant amplitude loading would be disturbed by the sudden change in plastic zone size resulting from a single overload. However, mechanical properties of metal, such as yielding stress, Young''s modulus, etc., may vary with increasing temperature. From this consideration, the fatigue crack tip plastic zone size can be altered by locally changing the mechanical properties of this area. In order to understand the thermal effect on the retardation of fatigue crack, constant amplitude fatigue propagation tests were carried out using A5083P-O aluminum alloy specimens. Tests were performed under identical applied load, but with different levels of heat input. The a-N curves were recorded and yielded da/dN－⊿K were used to determine the degree of retardation. Also the variation in crack tip opening was recorded with CCD camera to make comparison with the effect of overload. The result show that when the heat input to crack tip was increased to a level that exceeded the threshold, the larger the heat input was the obvious retardation became, and if the heat input were large enough the crack growth would stop. Local heating method proposed in this study, is effective in retarding fatigue crack growth rate. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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