Research On Low Shock And Large Load Hold-down/Release Mechanism Based On Shape Memory Alloy

A number of hold-down/release mechanisms have been employed in spacecrafts,most of them are maturest pyrotechnic mechanisms in technology. However, the use ofpyrotechnic mechanisms is generally undesirable in innovative spacecraft applicationsbecause of the giant pyrotechnic shock, chemical contamination and inability to reuse,so it is imperative to develop non-pyrotechnic mechanisms to meet the strict andvariable requirements of spacecraft. Therefore the thesis, Whose application backgroundis hold-down/release action of space deployable planar antenna，research a low-shock,large-load and repetitive Shape Memory Alloy(SMA) hold-down/release mechanism.Firstly, this thesis describes the fundamental capability and influence factors ofSMA material, and then designs the basal mechanics model of SMA actuator. Accordingto the one-dimensional Brision constitutive simplification model, it is derived that themathematical relationship between strain, stress and temperature in the common casessuch as free recovering, stret alhing in constant temperature and recovering inconstrained situation. Based on electricity and thermotics theory, the temperatureresponse behavior of SMA actuator is derived. all of that is the theoretical basis of latterresearch.Several design schemes are presented aiming at different SMA actuating methods,the rotational SMA separation nut hold-down/release mechanism, which has a highermechanical efficiency for it use rolling to replace sliding to decrease the loss of friction,and has double force reduction structure, is better to meet the electric powerrequirement of current satellite, therefore the virtual prototype modal based on thescheme is established by Pro/E, the kinematics analysis of locking element and thecontact analysis that based on Elastic Contact Theory and finite element method havebeen done; the dynamic simulation of mechanism is analyzed by ADAMS, besides themain drive torque and main trigger torque are measured; finally the strength analysis ofcomponent is done by ANSYS.A series of tests of SMA performance such as phase transformation temperature,loading capacity, Modulus of Elasticity and resistivity have been accomplished. Therolling coefficient of friction of key contact surface is measured; the counterpartrelationship between tensile preload of bolt and tightening torque has been simulated bycalibration device; the principle prototype and accessory fixtures of mechansim aredesigned and manufactured; the release resistance and hold-down/release funcationhave been tested, the result of these tests show the mechanism can meet low-shock, large-load and repetitive requirement, meanwhile prove the feasibility of the relatedtheories and analysis methods.