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SHAPE MEMORY ALLOY (SMA) HELMET RETENTION SYSTEM

Fall 2019, Academic Group Project

For Fall 2019 AME 441a: Senior Design Project at USC, my team and I decided to create a 3D printed self-fastening helmet using shape memory alloys, a relatively new material with super-elastic properties that reverts to a trained shape upon being heated up. 

 

This product tackles the problem of the additional risk that a helmet could detach from the head in a collision (and leave the head vulnerable to damage) from improper wear of helmets, such as users wearing the wrong size. 

 

Over the course of the semester, my team and I performed research on the applications and recent studies on SMAs, conducted user studies to determine the comfortable helmet pressure around a head, and designed and built several iterations of our product. Our team produced several written documents and a final exhibition poster to communicate our findings. 

 

Click on the photos below for more information. 

  1. Poster Presentation

    Final presentation to university staff members and industry members to describe the motivation, theory, results, and conclusions of our semester-long project.

  2. Roll-Off Test Setup

    The roll-off test setup was adapted from the CSPC standardized safety test to determine at what load the helmet will fall off the head. My team and I built our own stand from materials available in the lab and 3D printed a headform to simulate the head of a helmet user. A cup attached to the helmet was slowly filled with water, which was measured after the water weight at which the helmet came off of the headform. Our helmet exhibited equal effectiveness in ability to stay on the head when compared to the traditional dial-tightened helmet.

  3. Open Helmet

    The SMA coils were fitted specifically to produce the target comfort force that was determined by our user testing with a traditional dial-tightening helmet. The 3D printed quadrants of the helmet have integrated DFA features such as alignment guide channels on the top and tabs for fasteners to anchor the SMAs.

  4. Closed Helmet

    When heated (by electrical current or external heat source), the SMAs exhibit their "shape memory effect" by reverting to their trained shape, a dense coil in this case. This closes the gap between quadrants, which are held in position using a ratcheting system so that the SMAs do not need constant heating for the helmet to remain fastened.

  5. Calibration Testing Setup

    Prior to gathering data with the sensors, each individual sensor was calibrated to be able to translate the reading to a force via a microcontroller. The process of calibration was to record readings at known volumes of water to create a calibration curve, which can later be used to convert voltage data from our experiments to forces.

  6. Helmet Pressure Testing

    Pressure-sensitive resistors were aligned in four locations of the existing helmet so that we could identify the lateral and saggital forces that were deemed comfortable by users.

  7. SMA Testing Setup

    A spring force gauge measured the force resulting from changing SMA length (quantified by number of coils), power supplied to heat the coils up, and length of plastic deformation.

  8. Printed Helmet Pressure Testing

    My team and I went through several design changes and iterations to produce and viably test our product. This image depicts one of our earlier tests that demonstrated a proof-of-concept that the design could indeed fasten a helmet around a human head.

  9. SMA Testing Model

    Model of the SMA coil testing setup, created in NX prior to manufacturing. The goal of the experimental setup was to characterize the super-elastic behavior of SMA coils.

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