Session: ASME Undergraduate Student Design Expo

Paper Number: 174047

Laser Micromachined Auxetic Nitinol Geometries for Active Composite Systems 

Shape memory alloys (SMAs) possess the unique ability to recover large deformations either upon heating (shape memory effect) or unloading (superelasticity). These properties allow for recovery of large monolithic deformations of 6-10%, as demonstrated in our test results. A diffusionless solid-to-solid phase transformation between a low temperature martensitic state (which takes place on cooling beyond the temperature Mf) and a high temperature austenitic phase (which takes place by heating beyond the temperature Af) is responsible for the remarkable functional behaviors of SMAs. The superelastic (SE) response takes place at a constant temperature above Af, where the material is austenitic and upon loading accommodates a large amount of deformation by transforming to detwinned martensite, and upon unloading recovers this large deformation due to the reverse transformation back to austenite. The shape memory effect takes place under the Af temperature, where either the stress-induced martensite is stable upon unloading or the starting twinned martensite detwins. Upon heating this martensite beyond the Af temperature, the SMA transforms to the original undeformed austenitic shape thus ‘remembering’ its original configuration. These characteristics make them ideal for use as skeletal backbones in lightweight actuators or grippers for robotics. However, one significant obstacle to their broader adoption is the difficulty of machining them into novel shapes. This project addresses this challenge by utilizing laser micromachining to create SMA geometries that were previously unattainable. Laser micromachining is particularly attractive as it can be scaled up for mass production. The project utilizes innovative 2D lattice SMA geometries and will eventually embed them in rubbery polymers to enable locomotion in soft robotics. Soft robotics utilize compliant materials instead of rigid links, mimicking movement mechanisms found in nature. This soft system, fabricated through mass production techniques, aims to expand the practical applications of SMAs in areas such as artificial muscles, soft grippers, wearables, medical devices, and haptic devices. While we will explore the soft robot application, additional applications of such include stretch-triggered drug delivery, stretchable electronics, adaptive filters, and controlled adhesion. Our lab has prototyped an SMA actuated four-way modular robotic arm in a silicone elastomer tube. Despite the SMA actuation working successfully, one of the major problems we noticed was delamination at the elastomer-SMA interfaces.  In this work, we present characterization of auxetic SMA (in particular nitinol) geometries and the morphology of deformation transfer in elastomer-nitinol composites. Our results show that the laser cut auxetic geometries are capable of significantly increasing the magnitude and dimensionality of the underlying functional behaviors in nitinol, and that effective deformation transfer is possible in elastomers from nitinol right up to the point of fracture.

Presenting Author: Stella Maris University of Southern Maine

Presenting Author Biography: Stella Maris is a mechanical engineering undergraduate at the University of Southern Maine with a strong focus on materials science and applied research. She is currently working on an NSF-funded research internship where she investigates nitinol-elastomer composites for robotic and biomedical applications. At USM, Stella is actively involved in undergraduate research through the Composites Engineering Research Laboratory (CERL) and works as a machine shop technician. She also serves in multiple leadership roles, including President of the Engineering Student Committee and Society for the Advancement of Material and Process Engineering, Vice President and co-founder of the Society of Women Engineers chapter, and Project Director for USM’s American Society of Mechanical Engineers Chapter. Her academic and extracurricular work centers on expanding hands-on engineering opportunities, promoting equity in STEM, and developing innovative solutions through collaborative research.

Authors:

Stella Maris University of Southern Maine
Asheesh Lanba N/A
Tymur Sabirov University of Southern Maine