Response of a Tensegrity Simplex in Experimental Tests of a Modal Hammer at Different Self-Stress Levels

Leszek Małyszko,Andrzej Rutkiewicz

doi:10.3390/app10238733

Leszek Małyszko, Andrzej Rutkiewicz

Open Access

https://doi.org/10.3390/app10238733

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Journal: Applied sciences	Publication Date: Dec 6, 2020
Citations: 2	License type: CC BY 4.0

Affiliation: University of Warmia and Mazury in Olsztyn

Abstract

The natural frequencies and eigenmodes of the tensegrity simplex are determined experimentally in impact hammer tests. To study an effect of prestressing, the tests are carried out on a physical model 1.2 m high and 0.5 m diameter with build-in transducers for measuring actual values of forces in cables at 13 prestress levels. The recorded data for each pre-stress level from three three-axial accelerometers are combined to extract the first five natural frequencies and modes by means of the method of experimental modal analysis. It was experimentally confirmed that the first rotational frequency depends on the pre-stress level and its sensitivity to the self-stress state is high enough to be successfully used in vibrational health monitoring. A proprietary formula was proposed for the relationship between frequency and the pre-stress level to control the dynamic properties of the simplex. An excellent comparison between the experimental results of the frequency and the formula was obtained. A comparison of numerical results of the finite element method with truss element and experiment is also shown.

Highlights

Tensegrity structures are built from compressed struts and tensioned cables
A known example of these types of structure is a tensegrity column composed of several moduli, each of them being a tensegrity simplex (Figure 1)
For the difference is less than 25%, which may be acceptable at the moment, considering the very complex level greater than 1.5 kN the difference is less than 25%, which may be acceptable at the moment, mass distributions in the physical model

Summary

Introduction

Tensegrity structures are built from compressed struts and tensioned cables. External loads can only be applied at the nodes, which connect elements using ball joints. The system stability and load-bearing capacity is obtained after inducing the prestressing force in its elements. From the mechanical point of view, tensegrities can be regarded as a special class of spatial truss. A known example of these types of structure is a tensegrity column composed of several moduli, each of them being a tensegrity simplex (Figure 1). The tensegrity simplex as the fundamental three-dimensional module of low complexity is often called the regular minimal tensegrity prism [1]

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