I n t r i n s i c D e v i c e s I n c o r p o r a t e d
I n t r i n s i c D e v i c e s I
n c o r p o r a t e d
Active
Fasteners
In most cases
our products are used as permanent or semi-permanent fasteners. The alloy is
chosen such that the fastener will exert clamping force over the entire ambient
temperature range the assembly will experience. For
disassembly, the fastener is brought below normal ambient temperature using
a coolant. For alloy H, liquid nitrogen is used and for Alloy D, HFC spray coolant
or liquid nitrogen is used.
UniLok rings and Intrinsic's other products can also be used to perform fastening or unfastening functions in response to changes in ambient temperature. For example, a UniLok ring can clamp and immobilize a mechanism when the device is overheated in a fire. Alternately, a shape memory element can actuate a release mechanism when exposed to elevated temperature. This might be used to deploy an instrument or to breach a pressure vessel to render it non-propulsive or non-explosive. A shape memory fastener can also hold an object securely at normal ambient temperatures and release it when deployed to a colder environment. Illustrations of various applications are given below.
Electrically controlled, rather than ambient temperature sensing, release mechanisms are also possible. In this case power is applied to an electric heater to bring the shape memory element to its recovery temperature.
Here a UniLok ring shrinks when heated above ambient temperature, gripping a rod to immobilize it. Typically Alloy G or N rings are used for this type of application, giving nominal lock temperatures of 105°C or 125°C respectively.
|
 |
In this configuration, an SMA ring is used as a self releasing snap ring. When the device is heated above normal ambient temperature, the ring shrinks, disengaging from the outer shoulder. This sort of release mechanism can be used for fire suppression systems and insensitive munitions. Nominal release temperatures of 105°C or 125°C are typically specified. The release temperature depends on the load and the design of mating components as well as on the shape memory ring. The tolerance on release temperature could be as low as ±5°C with a favorable design. A tolerance of ±10°C to ±15°C is more typical. |
 |
An alternate release mechanism is pictured here. The two cylinders are joined by a snap fit. When exposed to elevated temperature, the memory metal ring compresses the collet, disengaging its fingers from the groove in the outer cylinder. Release temperatures are the same as the illustration above. |
 |
Shape memory washers can be produced to expand in length when heated and contract in length when cooled. If such a washer is incorporated into a bolted joint, it provides a means of tightening and loosening the joint in response to temperature. One potential use is as a "thermal conduction switch" to provide a good thermal path between a heat source and a radiator panel while heat is being generated. When the heat source is inactive, the heat flow path is decoupled to prevent excess cooling of the heat source. See the description of work done at JPL in NASA Tech Briefs. |
 |
In this case, the ring relaxes on cooling, releasing the pin. Release temperatures in the range of -20°C to -120°C can be achieved. |
 |
Copyright
2003 Intrinsic Devices, Inc. All rights reserved.
UniLok®
is a registered trademark of Intrinsic Devices, Inc.