Young-Soon Jang

Compressed Mesh Washer Isolators Using the Pseudoelasticity of SMA for Pyroshock Attenuation

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 Ni-Ti 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.

Experimental strength of composite sandwich panels with cores made of aluminum honeycomb and foam

Composite sandwich panels with face sheets made of carbon/epoxy fabric and carbon/epoxy uni-directional prepreg were tested. The sandwich cores made by aluminum honeycomb and foam were cured with the face sheet at 180 °C. The aluminum core sandwich failed at the 40% failure strain of the face skin in the compression test. On the other hand, the foam core sandwich failed at the 100% failure strain of the face skin in the compression test. In the case of the aluminium core sandwich, nonhomogenous load distributions and fiber contents may affect the lower failure strain. Therefore, the specific compression strength of the foam core was 72% higher than the compression strength of the aluminum core. Failure mode analysis of sandwich panels made of aluminium honeycomb cores shows that shear failure leads to final failure. However, the specific flexural strength of the sandwich panels with aluminum cores had a slightly higher value than that of the sandwich panels with foam cores. Because the sandwich panel with aluminium cores had higher critical stress for the face wrinkling than the sandwich panel with foam cores due to higher compression modulus of aluminium cores than foam cores.

Development of a three-axis hybrid mesh isolator using the pseudoelasticity of a shape memory alloy

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.

Enhanced shock and vibration isolator for the attenuation of low-frequency vibration and high-frequency pyroshock loads

Launch vehicles, satellites and aircrafts often experience harsh vibration and pyroshock loads during the flight including maneuvering and separation events, which may cause the malfunction of equipped electronic devices. Furthermore, this minor malfunction can generate catastrophic failure of the whole mission. To prevent malfunction of the electronic devices from severe shock and vibration loads, elastomeric isolators are commonly applied between the electronic device and the equipment bay structure in the aerospace fields. However, this rubber type elastomeric material is vulnerable to the low-frequency vibration load which involves large amount of displacement due to its low stiffness. Recently, the present authors proposed new type of isolator, called as pseudoelastic hybrid mesh isolator. This talk introduces the key features of this new pseudoelastic hybrid mesh isolator which shows better isolation performance throughout all frequency range than conventional isolators.

Structural test of KSLV-I Payload fairing

Payload fairing(PLF) protects satellites and related equipment from the external environment. They are separated before the satellite separation. Payload fairing made of composite sandwich materials due to their considerable bending stiffness and strength-to-weight ratio. Payload fairing have compression, shear and bending load during the flight. In this study, To check the strength of PLF and connected part, structural test of PLF accomplished using an actuator and a fixture. Purpose of structural test is to verify the strength of PLF in force of separation spring and combination structural load applied. Test result shows that the PLF have an acceptable margin of safety for the combination structural load and force of separation spring.

Pyroshock Isolation Performance Test using Wiremesh Isolators

Pyrotechnic shock or pyroshock is characterized as a transient vibration phenomenon which shows large acceleration and high frequency range up to 10㎑ during the operation of separation devices where explosives are used. During the flight of a launch vehicle, pyroshock is mainly generated at several events such as satellite separation, fairing separation and stage separation. In this paper, wiremesh isolators are introduced and several types of isolators are manufactured for the performance tests. For the investigation of typical characteristics of wiremesh isolators, compressive loading tests are basically performed and pyroshock tests are accomplished to confirm pyroshock isolation ability of each wiremesh isolator by using 4㎏ dummy mass.