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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 | J A N U A R Y 2 0 1 6 3 2

(a)

Fig. 3 — No statistically significant difference, at a 95% confidence level, in joint tensile strength with reduction in cross-sectional area. This shows joint consistency.

(b)

(c)

Fig. 4 — Lateral stiffness testing on 0.014-in. diameter guidewire with LRM solid-state joint, compared to competitive guidewire with hypotube joint.

(d)

Fig. 5 — SEM image of fracture surface, post tensile testing. Lowmagnification (200×) of hypotube joint and LRM solid-state joint, respectively (a) and (b); high magnification image (2000×) of NiTi wire side of hypotube joint and LRM solid-state joint, respectively (c) and (d). solid-state weld joint failed at or near the joint interface, Fig. 5(b). The frac- ture surface of the LRM solid-state weld exhibits micro-roughness and dimples

hypotube joint design exhibits sharp transitions that could cause kinks and performance degradation. The lateral stiffness graph shows the seamless nature of the LRM guide- wire at around 40 cm from the distal tip. A direct change in stiffness occurs at the solid-state weld joint. Conversely, the graph shows that the sample guidewire with the 3-cm long hypotube joint has a less desirable stiffness load profile.

Table 1 summarizes the tensile data for 0.014-in. diameter LRM solid- state welded guidewires. The LRM joint exhibits high tensile strength compared to the hypotube adhesive joint. Figures 5(a) and 5(c) show that the failure mode for the hypotube joint design was ad- hesive failure, with subsequent core pullout from the hypotube. Therefore, the Nitinol wire end exhibits a smooth shear cut surface, Fig. 5(c). The LRM