Characterization of plastic deformation in a disk bend test

A disk bend test technique has been developed to study deformation mechanis ms as well as mechanical properties. In the disk bend test, a transmission electron microscopy (TEM) disk size specimen of 3 mm diameter x0.25 mm thic k is clamped around its rim in a circular holder and indented with a tungst en carbide ball of I mm diameter on its back face. AISI 316LN austenitic st ainless steel and 9Cr-2WVTa ferritic/martensitic steel were selected as tes t materials. A model was developed to determine the average plastic strain and surface plastic strain in the disk bend test. The deformation regimes o f the plastic strain versus deflection curves corresponded to those of the load versus deflection curves. The stress state of the disk bend deformatio n was analyzed for the two test materials and compared with those of other mechanical tests such as uniaxial tensile, compact tension, and ball indent ation tests. Slip line features at the deformed surface and the correspondi ng TEM microstructures were examined for both tensile and disk bend specime ns. Differences and similarities in deformation between the disk bend and t he tensile tests are described. (C) 2001 Elsevier Science B.V. All rights r eserved.