The effect of circular holes on the natural frequencies of a beam using transverse vibration measurements method _ENG

Tariq Khalid Abdilrazzaq

doi:10.33899/rengj.2013.72817

Abstract

Defects influence in a negative way the service life of the structures. Thus, defect detection has been a considerable effort in order to eliminate this effect . In this study, the dynamical behavior of a cantilever beam, with different size of a hole, at different distances from the fixed end-for each case- have been measured, evaluated and compared with that of intact beam. It has been shown that the hole may be considered as a defect in most cases, which leads-in general- to decrease the stiffness, according to its size and place, hence affects the dynamic properties i.e., the natural frequencies and the mode shapes. A simulation process for the modal analysis using ANSYS program(release 12.1) is done in order to compare the results. In addition to that, a theoretical analysis is also done. The experimental results of the intact beam were compared with both the ANSYS program and the theoretical results. They showed an acceptable agreement between the three methods. Keywords: transverse vibration, fault detection, beam crack, beam defect, beam vibration.

Highlights

Defects may lead to under designed structures in many cases and increase the vulnerability of structures to static and dynamic loads
Literature on fault detection and condition monitoring was focused on the vibration-based method which can be classified into modal-based and signature-based methods
In modal based techniques data can be condensed from the actual measured quantities like resonant frequencies, mode shape vectors and quantities derived from these parameters for the crack detection [2]

Summary

Introduction

Defects may lead to under designed structures in many cases and increase the vulnerability of structures to static and dynamic loads. In order to identify structural damage by vibration monitoring, the study of the changes of the structural dynamic behavior due to cracks is required for developing the detection criterion [3]. Kisa & Gurel [10] proposed a numerical model that combines the finite element and component mode synthesis methods for the modal analysis of beams with circular cross section and containing multiple non-propagating open cracks. Resonance frequency shifts the power spectrum due to defects in a longitudinally vibrating beam when both ends are free investigated by Sobue et al [16] both numerical and experimental analysis. When a crack or defect exists in a beam or shaft, the stiffness is reduced and the Eigen frequencies of the system are decreased Measuring these differences can help to identify a crack. Portable field vibration analyzer in order to get the Fast Fourier Transformation to transfer the vibration from the time domain to the frequency domain

Discussion

Conclusions