Session: Virtual Presentations in Acoustics, Vibration, and Phononics

Paper Number: 96717

96717 - Investigation on Dispersion Characteristics of Elastic Waves in Steel Strands Based on Floquet Boundary Conditions Method 

Steel strands has the advantages of good bending performance, strong impact resistance, stable and reliable operation, etc. As a load bearing structure, the health of steel strands directly affects the stability and safety of the entire structure. Therefore, it is extremely important to detect the damage of in-service steel strands.Due to the influence of the helical structure, the contact effect between the wires and the influence of the applied load, it is difficult to solve the wave problem of the steel strand using the governing equations and boundary conditions from a purely theoretical point of view. With the maturity of finite element software and the advancement of computer technology, semi-analytical finite element formulation (SAFE) and Floquet Boundary Condition (Floquet BC) method have become effective methods for analyzing complex structures. The steel strands are usually a simple straight stranded wire consisting of a straight core and a layer of helical wires. When using SAFE to solve the dispersion characteristics of steel strands, it is necessary to convert the equilibrium equation from the Cartesian coordinate system to the torsional coordinate system, which is a very tedious process. The Floquet BC method can replace the whole with a single repeatable substructure without rewriting the equilibrium equation, which is more general and simpler than the SAFE method.

In this work, a twisted coordinate system is first established. Steel strands can also be regarded as a periodic structure due to their special helical structure. A useful twisting coordinate system can be obtained from,where is the helical step of the outer helix. It corresponds to a system for which theplane (cross-section plane) rotates around and along theaxiswith an axial periodicity L. According to Treyssède 's research, such a coordinate system can be used for the analysis of steel strands. Then the dispersion characteristics of the steel strands are obtained by simple wavenumber conversion. The power of the Floquet BC method is that the equations are solved by the finite element software, because the Floquet BC method only affects the propagation term, which is the same, whatever the nature of the waveguide. It is not necessary to develop the equations for each specific problem and to generate complex codes to get the dispersion relations. Therefore, when the Floquet BC method is applied to the helical waveguide, only the wave number needs to be converted. This method has been verified in the dispersion analysis of single helix and steel strands and will provide a new research method for the propagation characteristics of elastic guided waves in complex waveguides.

Presenting Author: Hongyan Zhang Tianjin University

Presenting Author Biography: Hongyan Zhang earned her Bachelor’s degree in Measurement and Control Technology and Instruments at School of Physics, Liaoning University. She is currently continuing her research as a MS at State Key Laboratory of Precision Measurement Technology and Instrumentation, Tianjin University. Her interests include acoustic field analysis of complex waveguide and quantitative nondestructive testing.

Authors:

Hongyan Zhang Tianjin University
Jian Li Tianjin University
Shili Chen Tianjin University
Yang Liu Tianjin University