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Published October 2007 | public
Journal Article

Experimental investigation of crack initiation in thin sheets of nitinol


An experimental investigation into the fracture properties of 160-μm-thick edge-cracked specimens of austenitic nickel–titanium (nitinol) under uniaxial tension is presented. Using the in situ optical technique of digital image correlation (DIC), strain fields directly relating to phase boundary nucleation and propagation of fracture samples were observed for the first time. The shape and size of the saturation and transformation zones as a function of loading near the crack tip were examined. An average plane strain crack initiation fracture toughness (K_C) of 51.4 ± 3.6 MPa √m for fine grained polycrystalline nitinol sheets at room temperature was measured. The extent and nature of the phase transformation obtained from DIC, combined with the relatively high value of K_C, underscores the importance of crack tip shielding in the fracture of shape memory alloys.

Additional Information

© 2007 Acta Materialia Inc. Published by Elsevier Ltd. Received 18 April 2007; accepted 18 July 2007; Available online 21 September 2007. The support of the Army Research Office (W911NF-O4- 1-0156), the National Science Foundation (DMS-0311788) and the Powell Foundation is gratefully acknowledged. It is a pleasure to acknowledge the experimental assistance received from Petros Arakelian, Vijay Chalivendra, Tracy Kidd and Min Tao throughout this work. The authors thank Correlated Solutions, Inc. for providing the DIC correlation software (Vic-2D) used in analyzing these experiments.

Additional details

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