Dimensional Stability Loss in Structures Subject to Random Vibration

Abstract eng:
Highly stable structures that are destined for space use are vulnerable to dimensional stability loss due to random vibration loads experienced during launch and ground testing. Small movements at structural interfaces and non-recoverable strains induced in metering elements can have negative implications for optical performance on-orbit. Often the dimensional stability aspects of optical bench structures are verified by environmental tests on Engineering or Protoflight Model instruments. It is proposed that a better understanding of vibration-induced structural dimensional stability loss could enable the assessment of stability loss through analysis at an early stage. To this end, several tests have been developed at RAL to assess dimensional stability loss in materials and joints in a controlled manner under random vibration. One test has been used to assess Al alloy and CFRP material samples in a 4-point bending configuration, and another has been used to assess micron-level slipping at a bolted interface. The aim of these tests was to provide useful material data, and also to assess the feasibility of predicting stability loss caused by random vibration events. It was found that the classical frequency domain random vibration Finite Element Analysis commonly performed to assess safety margins against structural failure on space structures is probably insufficient to predict instability. This is because the results are highly dependent on non-symmetry in the stress response (ie, due to gravity, pre-stress, or non-linear response). However a good correlation with test results was achieved with a time domain FEA model which incorporates nonlinear kinematic hardening rules in the materials. This paper will outline the Al alloy sample test and results, as well as propose a way to estimate random vibration-induced dimensional stability loss using static microyield test results.

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