Small Punch Testing for Creep: Progress in Europe

Abstract

The small punch or disk bend test has particular value in life prediction of operating equipment since the test requires very small amounts of material (a common test specimen disk is 0.5 mm thick with a diameter of 6 to 10 mm), and usually the required volume of material can be acquired from operating equipment in a virtually nondestructive manner. The application of the small punch (SP) test for creep has gained significant interest in the last decade, primarily as a result of research in Europe. The CEN (one of three European standardization organizations recognized by the EC) has been working to develop a Code of Practice for the small punch test. The Code documents, very recently completed, focus on use of the test for creep rupture and tensile and toughness properties. This paper summarizes the European round-robin work leading to the Code of Practice and key aspects of the Code. Included is a description of the currently recommended semi-empirical interpretation of data from the multiaxially-loaded small punch test specimens, less straightforward than that from conventional uniaxial specimens. As the SP test sees more field use and as the specimen and test configurations achieve better uniformity, we can expect that its application to creep life prediction will increase.