Session: 02-01: Shape Memory Alloy Actuators

Paper Number: 110390

110390 - Shape Memory Nitihf Machined Helical Springs: Balancing Displacement and Force Output for Actuation 

Traditional shape memory alloy (SMA) helical springs are manufactured from a wire stock by forming the desired helix using a shape setting procedure. Nevertheless, in the case of hard-to-work materials such as NiTiHf alloys, traditional springs are challenging to produce due to difficulties with bulk wire manufacturability. In this work, an alternative helical form, called machined springs, were investigated.  Machined NiTiHf helical springs provide excellent actuation displacement, while offering significantly more force output over traditional wire springs. The springs presented in this work are 50 mm long, 9.4 mm diameter and were machined from solid rod, giving them a unique rectangular cross section, compared to the circular cross section of a traditional wire spring. Two types of machined springs were tested: single-start and double-start. The single-start springs are typical springs with one coil. Double-start springs are unique in that they have two separate stacked coils acting in tandem to distribute the force. The double start springs provide many unique features over single-start springs, such as the ability to handle larger stresses and displacements. Both spring types were subjected to thermomechanical testing including uniaxial constant force thermal cycling (UCFTC), superelastic, blocking force, and two-way shape memory effect tests. The testing showed NiTiHf springs have very good stability, requiring less training than typical NiTi springs. These machined springs are capable of actuation displacements ranging from 12 to over 20 mm, superelastic stresses over 2.4 GPa, tensile blocking forces ranging from 750 to over 2000 N, and two-way shape memory effect with actuation displacements over 5 mm.

Presenting Author: Peter Caltagirone NASA Glenn Research Center

Presenting Author Biography: Peter Caltagirone has worked at the NASA Glenn Research Center (GRC) since 2021. He has been a postdoctoral fellow in the High Temperature and Smart Alloys Branch, working on shape memory materials. His focus is on the development of new analysis tools, design of new material forms, and research of new materials. Dr. Caltagirone is currently developing the first and only shape memory material handbook with over 60 years of curated data. Dr. Caltagirone is an active member of the joint industry-government-academia Consortium for the Advancement of Shape Memory Alloy Research and Technology (CASMART), a member of the International Organization on Shape Memory and Superelastic Technologies (SMST), a member of the American Society of Mechanical Engineers (ASME), and a member of ASM International.
Dr. Caltagirone received his Bachelor of Science in mechanical engineering in 2015, and PhD in mechanical engineering in 2021 from the Colorado School of Mines with a background in fiber reinforced composites and shape memory materials.