Abstract
Releasing and deployment maneuvers carried out during space satellites launching are usually performed by utilizing pyrotechnics loads. However, it is considered convenient to replace this technique by others not requiring explosives (Non Explosive Actuators-NEA). This is mainly due to the necessity of reducing highshock and vibrations induced levels, also avoiding the contamination of sensible instruments because of dust and gas release during explosion. In addition, the avoidance of risks associated with storage and manipulation of explosives and the possibility of performing device retesting prior to final mounting are desirable qualities. Among NEA devices, those exploiting the singular mechanical behavior of Shape Memory Alloys (SMA) have reached commercial maturity. In this study, the performance of a NEA device that uses the mechanical stress generated upon reverse transformation of a mechanically constrained SMA actuator (constrained recovery effect) to generate the controlled fracture of a notched bolt is analyzed. Firstly, the mechanical components of the system are described, and the main problems associated with its design are introduced. Then, the results of the experimental characterization performed on a NiTi SMA cylindrical tube actuator with 12.7 and 7.8 mm outer and inner diameter respectively, are presented. After an activation stage in which the cylinder is compressed to induce the martensitic phase (or re-orient the existing martensitic phase), the temperature is raised while a constant displacement condition is imposed. For temperatures near 120 oC, a loads increment of 35 kN (440 MPa) is obtained. The repetition of this loading-unloading-heating-cooling cycle does not generate any important deterioration in the material response. Keywords: Constrained Recovery, SMA actuators, NiTi, Release systems.
Highlights
Deployment and releasing maneuvers in satellites launching were typically carried out by pyrotechnic loads remotely activated through the fracture of an union element
A non explosive actuator (NEA) device consists of a union element, a fixing system and an actuator mechanism which is in general a piece made of a material which changes a property upon the application of heat provided by an electric current
Actuators made from a hollow bar of NiTi Shape Memory Alloys (SMA) previously subjected to suitable thermal treatments
Summary
Deployment and releasing maneuvers in satellites launching were typically carried out by pyrotechnic loads remotely activated through the fracture of an union element This method, though broadly adopted due its simplicity and rapid response, presents serious drawbacks mainly associated with the high shock levels induced after the explosion, responsible of failure in many spatial missions in the past [1]. A NEA device consists of a union element, a fixing system and an actuator mechanism which is in general a piece made of a material which changes a property upon the application of heat provided by an electric current. In this case, a device inspired in the Frangibolt design was adopted for its study, utilizing a NiTi SMA actuator as the kernel element. Experiments included the measurement of load and displacement levels attainable by the actuators, as their behavior stability and reproducibility upon repetition of operative cycles
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