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A D V A N C E D M A T E R I A L S & P R O C E S S E S | O C T O B E R 2 0 1 9 4 9 0.15 mm (not shown) revealed a clean, straight length of su- perelastic core material with good performance. Curve (c) for the 0.15-mm diameter nitinol core illustrates a measured ini- tial elastic modulus and ultimate tensile strength of 48 GPa and 1170 MPa, respectively. Curve (a) shows the distinctive 197GPa as-measured initial elasticmodulus and 2600MPa cal- culated ultimate tensile strength of the high-strength CoNiCr shell element. Note that the shell properties were calculated from superposition as follows: Nitinol core properties were measured after centerless grinding and the stress-strain data were subtracted from stress-strain data of the composite wire, followed by using the shell element area (70% of the total) for stress computation. Figure 3 provides data for an internally standardized whip test typically applied to superelastic straightened niti- nol often used in guidewire core constructs. Here, the proxi- mal end (drive end) of the 0.34-mm diameter composite wire is rotated by a given drive rotation through three rotations (1080 deg), while the distal end is tracked by a “flag” affixed to the end using optical tracking (Fig. 3a). The drive rotation is compared todistal rotationas an indicationof one-to-one con- trollability (Fig. 3b). Typically, wires that are not well-straight- ened and well-balanced in terms of residual stresses show tens of degrees in lag-snap or whip response. Performance of the wire discussed here falls within typical limits of Fort Wayne Metals SLT (straight linear torque) grades 2 to 4 processedwire. In other words, the data suggest that the wire should provide satisfactory performance ina guidewire-type control scenario. UNIQUENESS OF PROTOTYPE COMPOSITE WIRE Many patents discuss related ideas of combining high- strength, high-stiffness metals with high-elasticity metals (such as nitinol) [5-9] , but there are no known publications that discuss achievement of such properties in a composite wire. For example, Abrams [5] discussed the use of a stiff-handle Fig. 2 — Polished cross section (insert) of 35N LT (CoNiCr alloy conforming to ASTM F562 chemistry) where scale is indicated by 0.34 mm overall wire diameter (shell). Curve (a) is stress strain ex- trapolation for CoNiCr shell element, curve (b) is measured stress- strain response for overall 35N LT-DFT-30%NiTi wire, and curve (c) is stress-strain response for nitinol core element after centerless grinding to a 0.15mmdiameter. Curve (d) is higher stiffness bending response for overall DFT wire construct, and curve (e) is lower stiff- ness bending response for a 0.34-mm overall diameter superelastic nitinol wire at the same moment arm length as in (d). Fig. 3 — (a) Image of distal rotation target shown by black “flag line” with light red overlay and drive rotation with slight “lag” indicated by blue line; (b) Drive versus distal rotation of one end of the 0.34-mm 35N LT-DFT-30%NiTi wire over an approximately 1.8-m length of wire wrapped through polyethylene guide tube through 2 x 200-mm loops showing good 1 to 1 input versus output response associated with well-balanced wire straightness. 1 1 FEATURE