Pyroshock can cause malfunctions of electric components of launch vehicles or satellites, resulting in a catastrophic flight failure. This study introduces a new compressed mesh washer pyroshock isolator using the pseudoelasticity of NiTi alloy wire. The compressed mesh washer isolators were manufactured and tested to evaluate their pyroshock isolation performances. For comparison purposes, shape memory alloy compressed mesh washer isolator was also manufactured. The variations in the dynamic characteristic of the compressed mesh washer isolators due to precompressive displacements were also studied. The results showed that the natural frequency and the isolation capacity can be adjusted by controlling the precompressive displacement of the compressed mesh washer isolator. These characteristics can be used for a smart isolation system that utilizes the adjustable dynamic characteristics of the compressed mesh washer isolators.
Launch vehicles and satellites experience severe dynamic loads during flight phases. In particular, pyroshock generated from several separation events could result in malfunctions in the electric components in the launch vehicles. Shock isolators are generally applied in order to attenuate these severe shock environments; however, these isolators could amplify the low-frequency vibration generated by the engine thrust and aerodynamic loads and reduce the payload stability. When the natural frequency of the isolator is increased in order to avoid the low-frequency vibration amplification, sufficient shock attenuation could not be obtained. Thus, the isolators used in launch vehicles need to be designed with trade-offs between the low-frequency vibration amplification and the pyroshock attenuation. This article presents a novel frequency tuning method for the isolator in order to achieve both shock attenuation performance and avoidance of the vibration amplification. Compressed mesh washer isolators using the pseudoelasticity of shape memory alloy were adopted for easier attainment of the frequency tuning with a high performance in the shock attenuation.
Launch vehicles and satellites experience severe vibration and pyroshock loads during flight phases. In particular, intense pyroshock, which is generated by the actuation of separation devices, can cause malfunctions in the electronic components in launch vehicles and satellites, potentially resulting in catastrophic failure during flight. This paper introduces a new three-axis hybrid mesh isolator using the pseudoelasticity of a shape memory alloy wire that was manufactured and tested to attenuate pyroshock and vibration transmitted to the electronic components. To characterize the isolation capability, quasi-static loading tests were performed; the test results showed that the pseudoelastic effect of the shape memory alloy wire significantly absorbs energy due to the stress-induced phase transformation. The ground pyroshock test results showed a remarkable pyroshock load attenuation of the hybrid mesh isolator in all frequency ranges. The dynamic characteristics and vibration isolation performances of the mesh isolators were also verified by random vibration tests. The healthiness of the hybrid mesh isolator was also studied under a harsh vibration loading level, and the results confirmed its wide applicability without degradation of the isolation capability.
Cryogenic coolers produce undesirable micro-vibrations during on-orbit operation, which may seriously affect the image quality of high-resolution observation satellites. Micro-vibrations can be easily isolated by mounting the cooler on a vibration isolator with low stiffness to attenuate the vibration transmitted to the satellite structure. However, the structural safety of a cooler supported by an isolator with low stiffness cannot be guaranteed under the much more severe vibration condition of a launch environment. In this study, to guarantee vibration isolation performance in a launch environment while effectively isolating the micro-vibrations from the cooler on-orbit, a new type of passive vibration isolation system by using a compressed shape memory alloy mesh washer was proposed and investigated. The basic characteristics of the isolator were measured in static and free vibration tests of the isolator, and a simple equivalent model of the isolator was proposed. The effectiveness of the isolator design in a launch environment was demonstrated through sine vibration, random vibration, and shock tests.
For the design of vibration control systems of composite structures using piezo-ceramic actuators, it is necessary to obtain an accurate system model. Especially, the information related to natural modes, damping ratios and modal actuation forces appears in the governing state space equations. A refined finite element analysis based on the layerwise displacement plate theory has been performed to obtain the system parameters of composite plates with piezoelectric actuators. In this study, the present finite element method has the capability to take account of the stepped effect due to partly bonded piezo-ceramics. Also modal testing techniques have been applied to identify the system parameters experimentally. Through the comparison of numerical results with experimental data, the validity of the numerical procedures has been proved.
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