(Received 19 February 1988; accepted 9 January 1989)
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A relatively new plane-strain fracture toughness test method based on chevron-notched test specimens has created a keen interest in comparing toughness measurements by the new method against measurements by the conventional method (ASTM E 399). Tests of various aluminum alloys by the two methods have shown a divergence in test results at the higher toughness levels. The rising R-curve effect in tough aluminums has been cited as one of the factors contributing to the observed discrepancy. This paper shows why the chevron-notched test results are independent of rising R-curve effects, whereas ASTM E 399 tests often are not. The E 399 test dependence on the rising R-curve constitutes a specimen size effect, and this dependence is partly responsible for the divergence between chevron-notched and E 399 tests of tougher aluminums. The chevron-notched method produces the toughness values which would be obtained from E 399 measurements if sufficiently large E 399 specimens could be tested.
Distinguished Member of the Technical Staff, Sandia National Laboratories, Albuquerque, NM
Stock #: JTE11117J