Ultrasonic cracklength determination during fracture toughness testing of gray cast iron
✍ Scribed by Börje Östensson
- Publisher
- Elsevier Science
- Year
- 1972
- Tongue
- English
- Weight
- 704 KB
- Volume
- 4
- Category
- Article
- ISSN
- 0013-7944
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✦ Synopsis
When doing fracture toughness determinations on gray cast iron it is impossible to determine the length of the fatigue precrack from studies of the fracture surface. The reason for this is that the crack front is no well-defined line between ruptured and unruptured material but a zone of finite length with a continuous transition from a well-defined crack to an untracked material. This zone contains randomly distributed microcracks of the size of the grains.
Another difficulty in tests of this kind is the nonlinear stress-strain relationship of the material which makes it difficult to define the initial slcpe and thus also the secant slope of the load-COD curve.
An ultrasonic technique is developed which makes it possible to overcome the above difficulties. The method is used to determine the fracture toughness of two grades of cast iron. Different methods of precracking are used and their effect on the measured toughness values are compared. Since precracking at the crackfront is observed to occur also in planes parallel to the side surfaces of the specimen, relaxation of the thickness stress will occur. In view of this the thickness requirement for plane strain is inadequate. The consequences of this fact are discussed.