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Fracture toughness tests to BS 7448 and BS EN ISO 12737


BS 7448 'Fracture mechanics toughness tests' is published in four parts:

- Part 1 (1991): 'Method of determination of KIc, critical CTOD and critical J values of metallic materials'

- Part 2 (1997): 'Method for determination of KIc, critical CTOD and critical J values of weld in metallic materials'

- Part 3 (2005): 'Method for determination of fracture toughness of metallic materials at rates of increase in stress intensity factor greater than 3MPa √ms-1

- Part 4 (1997): 'Method for determination of fracture resistance curves and initiation values for stable crack extension in metallic materials'

BS 7448 supersedes previous test standards, which were restricted to measurement of KIc (BS5447) or critical CTOD (BS5762) only. BS 7448 Part 2 has itself recently been superseded by ISO 15653:2010 'metallic materials – method of tests for the determination of quasistatic fracture toughness of welds'.

BS EN ISO 12737:2005 'Metallic materials - determination of plane-strain fracture toughness' has been published by the International Standards committee for determining the plane strain fracture toughness of homogeneous metallic materials.

In general terms, the ISO specification is the same as BS 7448 Part 1, and includes many of the same figures and requirements. For conditions where it is appropriate to determine KIc alone, BS 7448-1 refers to the testing method in BS EN ISO 12737. The tolerances on the test parameters and specimen dimensions are the same in many instances, but ISO 12737 allows more variation in fatigue crack shape than BS 7448 Part 1.

However BS EN ISO 12737 does not make any particular recommendations about the testing of welds (unlike BS 7448 Part 2 and ISO 15653), it is specifically for KIc testing and does not address ductile or higher toughness materials. BS 7448 allows KIc, CTOD or J to be determined from the test results. The ISO 12737 standard specifies fewer details to be given in the test report, nor does not make it a requirement to report where any of these fail to meet the validity limits, unlike BS 7448.

Further information

FAQ: What is a fracture toughness test?

FAQ: Are there any differences between fracture toughness tests carried out to BS 7448 and those using ASTM E1820?

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