D. L. Plumley, J. E. Schaffer, Fort Wayne Metals Research Products Corporation, Fort Wayne, IN
The role of cold work reduction and its effect on fatigue properties are studied by means of rotary beam fatigue testing. Excluding the final draw pass, upstream processing parameters such as wire drawing, inter-pass annealing, and final heat treatment were held constant for all conditions investigated. Cold worked percentages between 20% and 55% in five percent increments were subjected to rotary beam fatigue testing. An analysis of the relationship between cold work deformation and fatigue are presented.
Summary: The objective of this paper will be to present the effects of multiple cold work reductions in medical grade Nitinol wires with a nominal size of 0.322mm (0.0127”). All other parameters such as interpass anneals and raw material will be held constant in order to minimize the effects. Rotary beam fatigue testing will be used to evaluate multiple strain levels ranging from 2.5% to 0.8%. Run out criteria will be set at 1,000,000 cycles with premature failures being submitted for microscopic analysis.
