Welding and joining of NiTi based shape memory alloys (SMAs) is essential for their integration into an increasing variety of applications. The titanium elemental constituent significantly complicates joining, especially with dissimilar materials where brittle intermetallics are often formed. There have been a relatively small number of investigations of the welding of NiTi in similar and in dissimilar joints. Of these studies, a few have investigated the effect of similar welded joints on the pseudoelastic fatigue of NiTi. To the author’s knowledge there are no investigations on the effect of joining on the fatigue of thermally actuated NiTi. The current work investigates the physical, thermomechanical fatigue and shape memory properties of welded shape memory wires. The welded NiTi wires successfully achieved 86% of the base metal ultimate tensile strength. The cycle lives of the welded wires that underwent thermomechanical fatigue were significantly less than the base metal.

The revolutionary multiple memory material technology allows local modification of shape memory alloy functional properties to create monolithic actuators that exhibit several different thermomechanical characteristics. In this work, high density laser energy was used to process a monolithic piece of NiTi shape memory alloy material to allow synergistic pseudoelastic and shape memory effect behavior. The resulting actuator contains self-biasing properties eliminating the need for a separate biasing mechanism for cyclic actuation. The characteristics of these different local behaviors were analyzed using tensile testing and differential scanning calorimetry. The stress and strain amplitude of the self-biasing linear actuation was characterized with relation to input current control. This work provides proof of concept for local modification of martensitic and austenitic phases; enabling self-biasing linear actuation.

The exciting thermomechanical behavior of nickel-titanium shape memory alloys have sparked significant research efforts seeking to exploit their exotic shape memory properties. The performance capabilities of conventional nickel-titanium alloys are currently limited, however, by the retention of only one shape memory geometry. In this paper we demonstrate the application of an unprecedented manufacturing process known as Multiple Memory Material technology to create a novel monolithic nickel-titanium shape memory microgripper. In our design, actuation and gripping maneuvers are achieved by thermally activating processed material regions which possess unique shape memory transformation temperatures and shape set geometries. The existence of multiple shape memory regimes is confirmed through differential scanning calorimetry analysis and in situ resistivity measurements.

Shape memory alloys such as Nitinol, which is a group of NiTi alloys composed of nearly equiatomic nickel and titanium, finds increasing applications in many industries because of its unique properties including the shape memory effect and pseudoelasticity. In past work simple linear actuators have been developed using Nitinol wire which are actuated and controlled using resistive heating. However, traditional Nitinol materials are batch processed and a monolithic component only possesses a single set of transformation temperatures, limiting the functionality of the actuator. In this work a linear actuator processed using the novel multiple memory material processing technology is presented showing multiple transformations and dynamic actuation by resistive heating. This dynamically controlled actuation greatly improves the functionality of the Nitinol actuator allowing for the realization of new applications and improved control methods. The different transformation temperatures embedded in the monolithic wire actuator following processing are identified using thermo-analytical analysis and the dynamic application of load and displacement are presented using a custom test set-up.