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New Corvette marks GM’s first use of heat-activated shape memory alloy to replace heavier motorized part

Corvette’s new shape memory alloy wire replaces a heavier motorized part. Click to enlarge.

As one of a number of advances to reduce its weight (90 lbs/41 kg lighter than its predecessor), the redesigned seventh-generation Chevrolet Corvette is the first vehicle to use a GM-developed lightweight shape memory alloy wire in place of a heavier motorized actuator to open and close the hatch vent that releases air from the trunk. This allows the trunk lid to close more easily than on the previous models where trapped air could make the lid harder to close.

With about 200 motorized movable parts on the typical vehicle that could be replaced with lightweight smart materials, GM says it is looking at significant mass reduction going forward.

Shape memory alloys—typically made of copper-aluminum-nickel or nickel-titanium—are smart materials that can change their shape, strength, and/or stiffness when activated by heat, stress, a magnetic field or electrical voltage. Shape memory alloys “remember” their original shape and return to it when de-activated.

In the new Corvette, a shape memory alloy wire opens the hatch vent whenever the deck lid is opened, using heat from an electrical current in a similar manner to the trunk lights.

When activated, the wire contracts and moves a lever arm to open the vent, allowing the trunk lid to close. Once the trunk lid is closed, the electrical current switches off, allowing the wire to cool and return to its normal shape, which closes the vent to maintain cabin temperature.

Smart materials like shape memory alloys offer new possibilities for many movable vehicle features. These new materials enable innovative designs and new and improved features at a lower cost than traditional motors and actuators.

—Jon Lauckner, GM’s chief technology officer

Shape memory alloy also helps remove unwanted mass, which can help improve vehicle performance and fuel economy. The wire actuator used on the new Corvette is approximately 1.1 pound (0.5 kilogram) lighter than a conventional motorized system.

The shape memory alloy used on the new Corvette represents nearly five years of research and development work on smart materials for which GM has earned 247 patents. And it is just the beginning. We have many more smart material applications in the pipeline that will bring even more improvements to our vehicles going forward.

—Paul Alexander, GM smart materials and structures researcher

As a recent example of smart material patent work, in January 2013, the US Patent and Trademark Office (USPTO) published a patent application (2013/0011806 A1) filed by GM and Dynalloy, Inc (a maker of shape memory alloy actuator technology) on an apparatus and method of controlling phase transformation temperature of a shape memory alloy. The device includes a primary wire composed of the shape memory alloy.

An activation source is thermally coupled to the wire and is operable to selectively cause the primary wire to reversibly transform from a Martensitic phase to an Austenitic phase during a cycle. The Martensite phase is a relatively soft and easily deformable phase of the shape memory alloys, which generally exists at lower temperatures. The Austenite phase, the stronger phase of shape memory alloys, occurs at higher temperatures. The temperature at which the shape memory alloy remembers its high temperature form, referred to as the phase transformation temperature, can be adjusted by applying stress and other methods.

The application notes that a loading element is connected to the wire and configured selectively to increase a tensile load on the primary wire when an ambient temperature is at or above a threshold temperature, thereby increasing the phase transformation temperature of the primary wire. In other words, the stress on the primary wire is increased only when the ambient temperature is at or above a threshold temperature.

The primary wire operates under low stress when the ambient temperature is below a threshold temperature such that a longer life cycle can be achieved. This, GM says, enables the use of relatively low cost shape memory alloy wires in certain applications which would otherwise require high cost ultra-high transition temperature shape memory alloy wires.




Over the next 40 years I see shape changing materials making massive alterations to our technological capabilities in ways that we can hardly glimpse at the moment.
Here is a write up on ferroelectric materials:

'Introducing “strain” in these materials can alter their properties and improve their performance. A lot of research in ferroelectric materials has focused on making strained thin films with alternating layers only a few nanometers thick of materials with slightly different crystal structures.

Lane Martin, a professor of materials science and engineering who leads the group describes the UI work with, “It turns out that if you put pressure on certain types of materials, the properties completely change. In our case we administer pressure by straining or stretching thin versions of these materials like one would stretch plastic wrap to fit on a bowl. You can induce things that don’t exist at ambient conditions; you can make phases and properties that don’t exist.”

UI’s thin films are made of lead zirconate titanate (commonly called PZT). The relative amounts of zirconium (Zr) and titanium (Ti) in the films determine the shape of the crystals. Traditionally, films of PZT have been made up of a single composition, grown directly on a substrate with a slightly different crystal structure to cause strain in the PZT. However, too much strain causes the PZT to revert to its original crystal structure. This limits researchers’ ability to change the properties of these materials for better device performance.

The UI group overcame this limitation by gradually shifting the concentrations of Zr and Ti as they grew the thin films, incrementally changing the crystal structure. From layer to layer, the structures are very similar, yet the composition of the PZT at the top and bottom of the film is very different, transitioning from a PZT composition with an 80% Zr to a 80% Ti. This gradual change, instead of the usual layered approach, results in little localized strain but large overall strain.

Martin explains the results, “We have taken a material with similar mechanical properties to a dinner plate, the same kind of hardness, and effectively figured out a way to stretch that plate without breaking it. With our method, we’ve been able to extend our ability to strain these materials. We go to the nanoscale so we can pull on these films and dramatically change the shape, and that affects the properties.”'



Does it continuously pull power to keep the vent open if you leave the trunk lid open?


Does any one else see how insanely complicated this design is (to say nothing of its predecessor)for what it has to do? Wouldn't a spring-loaded flap work just as well? If this is how automakers approach design issues no wonder cars and trucks are so heavy.Geesh!


So, how much does this car weigh? And, how much less than last year? I assume there was a goal to improve the car in some way by all this engineering. Does it go faster, corner better, use less gasoline? What are the resultant measurements?


Big news?


"So, how much does this car weigh? And, how much less than last year?" -- About 100 lbs less so it should be about 3100 lbs.

"I assume there was a goal to improve the car in some way by all this engineering. Does it go faster, corner better, use less gasoline?" Yes, yes, and yes. I think that what has always been amazing about the Corvette is that you can run it on a race track where it will keep up with or beat the exotic cars but you can also drive it to the grocery store or commute with it and if you keep you foot light on the accelerator, it will delivery reasonable mileage. The 2013 Corvette gets 26 MPG highway and the 2014 has not been EPA rated but GM states that it will exceed the 2013 mileage. Also, it should be noted that the Honda S2000 (no longer made) which was smaller and lighter and had a 2 liter engine was no better and the Mazda RX8 was considerably worse.


I agree with RD on this one. Simple is always better and it seems like there would be a much easier/cheaper way to do this. A spring loaded vent wouldn't let you close the trunk easier when dealing with air pressure as you slam it?

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