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Research Papers

Detection of Damage in Space Frame Structures With L-Shaped Beams and Bolted Joints Using Changes in Natural Frequencies

[+] Author and Article Information
W. D. Zhu

Professor
Fellow ASME

K. He

Graduate Research Assistant
Department of Mechanical Engineering,
University of Maryland Baltimore County,
1000 Hilltop Circle,
Baltimore, MD 21250

1Corresponding author.

2Currently a structural analyst engineer at Vermeer Corporation.

Contributed by the Design Engineering Division of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received November 1, 2010; final manuscript received April 25, 2013; published online June 18, 2013. Assoc. Editor: Bogdan Epureanu.

J. Vib. Acoust 135(5), 051001 (Jun 18, 2013) (13 pages) Paper No: VIB-10-1265; doi: 10.1115/1.4024393 History: Received November 01, 2010; Revised April 25, 2013

It is difficult to use conventional nondestructive testing methods to detect damage, such as loosening of bolted connections, in a space frame structure due to the complexity of the structure and the nature of the possible damage. A vibration-based method that uses changes in the natural frequencies of a structure to detect the locations and extent of damage in it has the advantage of being able to detect various types of damage in the structure, including loosening of bolted connections. Since the vibration-based method is model-based, applying it to a space frame structure with L-shaped beams and bolted joints will face challenges ranging from the development of an accurate dynamic model of the structure to that of a robust damage detection algorithm for a severely underdetermined, nonlinear least-square problem under the effects of relatively large modeling error and measurement noise. With the development of modeling techniques for fillets in thin-walled beams (He and Zhu, 2009, “Modeling of Fillets in Thin-Walled Beams Using Shell/Plate and Beam Finite Elements,” ASME J. Vib. Acoust., 131 (5), p. 051002) and bolted joints (He and Zhu, 2011, “Finite Element Modeling of Structures With L-shaped Beams and Bolted Joints,” ASME J. Vib. Acoust., 131(1), p. 011010) by the authors, accurate physics-based models of space frame structures can be developed with a reasonable model size. A new damage detection algorithm that uses a trust-region search strategy combined with a logistic function transformation is developed to improve the robustness of the vibration-based damage detection method. The new algorithm can ensure global convergence of the iterations and minimize the effects of modeling error and measurement noise. The damage detection method developed is experimentally validated on an aluminum three-bay space frame structure with L-shaped beams and bolted joints. Three types of introduced damage, including joint damage, member damage, and boundary damage, were successfully detected. In the numerical simulation where there are no modeling error and measurement noise, the almost exact locations and extent of damage can be detected.

Copyright © 2013 by ASME
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References

Figures

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Fig. 3

(a) A bolted joint that connects two L-shaped beams through a bracket, and (b) its FE model from SDTools, with a bolted connection modeled by a solid cylinder

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Fig. 2

(a) An analytical model of the fillet in an L-shaped beam whose dimensions are shown and (b) its shell and beam element model

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Fig. 1

An aluminum three-bay space frame structure with L-shaped beams and bolted joints, and an enlarged view of its lower boundaries

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Fig. 5

A cantilever beam whose stiffness is represented by a set of nondimensional stiffness parameters, G1, G2, ⋖, and Gn.

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Fig. 4

(a) The FE model of the space frame structure in Fig. 1 and (b) an enlarged view of a bolted joint, where eight bolted connections are later loosened to hand tight

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Fig. 12

Experimental damage detection result for the undamaged space frame structure in Figs. 1 and 7

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Fig. 6

Flow chart of the damage detection algorithm using the LM method

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Fig. 7

Groups in the FE model of the space frame structure in Fig. 1

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Fig. 8

Numerical damage detection results of the space frame structure in Fig. 7 with damage introduced to a horizontal beam (group 30 in Fig. 7): (a) 65% stiffness reduction and (b) 10% stiffness reduction

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Fig. 9

Numerical damage detection results of the space frame structure in Fig. 7 with damage introduced to a bolted joint (group 24 in Fig. 7): (a) 95% stiffness reduction and (b) 10% stiffness reduction

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Fig. 10

Numerical damage detection results of the space frame structure in Fig. 7 with damage introduced to a bolted connection that connects the bottom plate to the ground (group 3 in Fig. 7): (a) 85% stiffness reduction and (b) 10% stiffness reduction

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Fig. 11

Numerical damage detection results of the space frame structure in Fig. 7 with damage introduced to a bolted connection that connects the bottom plate to the ground and a bolted joint (groups 3 and 24 in Fig. 7): (a) 85% and 95% stiffness reductions, respectively, and (b) 10% stiffness reductions

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Fig. 13

Experimental and numerical damage detection results for the space frame structure in Figs. 1 and 7, with the upper bolted connections of a diagonal beam (group 26 in Fig. 7) loosened to hand tight

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Fig. 14

Experimental and numerical damage detection results for the space frame structure in Figs. 1 and 7, with eight bolted connections in a bolted joint (group 9 in Fig. 7) loosened to hand tight

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Fig. 15

Experimental and numerical damage detection results for the space frame structure in Figs. 1 and 7, with a bolted connection that connects the bottom plate to the ground (group 4 in Fig. 7) loosened to hand tight

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