PLANT print issue: Shape shifting
Memory alloys rev up efficiency while reducing component weight.
Tougher corporate average fuel economy (CAFE) regulations are driving automotive manufacturers to reduce the weight of their vehicles and the use of advanced materials is helping them do so.
Highly engineered alloys that are much lighter and stronger are already replacing conventional structural components, but the application of advanced materials has taken a step forward by replacing complex multi-component devices, such as actuators, with a single piece metal called a shape memory alloy (SMA).
These “smart materials” respond dynamically to external stimuli such as heat, humidity, ultraviolet light or pressure. Although many different SMA alloys exist, the most common, composed of nearly equal parts of nickel and titanium, is commercially known as Nitinol.
SMAs are trained to remember a shape at a high temperature, then they’re cooled to a state where they’re easily unformed, but will return to the trained shape when heated. They respond passively
to ambient temperature, but can be electrically controlled to activate when heated by a current.
With more than 200 motorized parts in the average vehicle, SMAs have the potential to greatly reduce weight and improve efficiency. General Motors has incorporated one in the 2014 Corvette hatch vent – a single wire actuator that replaces a heavy motorized part, reducing weight by more than a pound (0.5 kilograms).
It opens the hatch vent when the deck lid is opened using heat from an electrical current. The wire contracts and moves a lever arm to open a vent allowing the trunk lid to close. The electrical current then switches off, the wire cools and returns to its original shape.
Existing SMAs are ideal for replacing single function actuators (on/off), but remember just one shape, making them ill-suited to replace multi-position actuators.
However, researchers at the University of Waterloo, supported by the AUTO21 Network of Centres of Excellence, have developed a breakthrough technology that makes smart materials smarter. It applies a high dose of energy to precisely adjust the temperature at which a local zone in a single SMA piece responds. The zone’s area can be as small as a few microns in width with multiple zones having discrete response temperatures. Multiple memory material (MMM) technology gives functionality to a single SMA material to make it function like a machine.
This development will greatly aid the integration of SMAs into automotive applications, replacing complex and heavy actuating systems prone to failure with a highly reliable single piece of material.
Commercialization of the MMM technology is being actively pursued by Smarter Alloys Inc., a University of Waterloo spin-off company. The company’s engineers have already fabricated more than a dozen multi-position actuators that operate with both ambient temperatures or by electronic control. The product development team is working closely with Tier 1 and Tier 2 automotive companies to design, fabricate and evaluate SMA actuators using the MMM technology.
And there is potential beyond automotive components. New frontiers for Smarter Alloys, supported by the Ontario Centres of Excellence (OCE) and National Research Council (NRC), include orthodontic, implantable medical devices, aerospace and portable electronics.
Ibraheem Khan is a former AUTO21 student researcher and president of Smarter Alloys Inc. (www.smarteralloys.com). Norman Zhou is a professor at the University of Waterloo and a project leader with the AUTO21 Network of Centres of Excellence. Visit www.auto21.ca.
This article appears in the Sept. 2013 edition of PLANT.
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