Identification of Crack Damage with Wavelet Finite Element

2005 ◽  
Vol 293-294 ◽  
pp. 63-70
Author(s):  
Xue Feng Chen ◽  
Zheng Jia He ◽  
Qiang Gao ◽  
Yanyang Zi
Keyword(s):  
Finite Element ◽  
Natural Frequencies ◽  
Experimental Studies ◽  
Transient Signal ◽  
Crack Identification ◽  
Crack Location ◽  
Good Ability ◽  
Wavelet Finite Element ◽  
Elastic Fracture ◽  
Hierarchical Approximation

An improved method to identify the crack location and size is presented which takes advantages of wavelet finite element (WFE). The important property of wavelet analysis is the capability to represent functions in a dynamic multiscale manner, so solution with WFE enables a hierarchical approximation to the exact solution. WFE has good ability in modal analysis for singularity problems like a cracked beam. The crack in a beam is modeled with WFE and represented as a rotational spring. The additional flexibility caused by crack in its vicinity is evaluated according to linear and elastic fracture mechanics theory. The WFE stiffness matrix of the crack is constructed and the algorithm for crack identification through the use of vibration-based inspection (VBI) is developed. With the accurate natural frequencies obtained from the transient signal measured, graphs of crack equivalent stiffness versus crack location are plotted, by providing the first three natural frequencies as an input. The intersection of the three curves gives the crack location and size. Experimental studies of cracked shafts are presented to demonstrate the accuracy of the method. The error in identification of crack location and size are both less than 2%. This study provides the new method for the diagnosis of incipient small crack.

Crack Detection in Pipe Structures by Lifting Wavelet Finite Element Method

2009 ◽  
Vol 413-414 ◽  
pp. 143-150
Author(s):  
Xue Feng Chen ◽  
Bing Li ◽  
Zheng Jia He
Keyword(s):  
Finite Element ◽  
Crack Detection ◽  
Natural Frequencies ◽  
Uniform Mesh ◽  
Piecewise Polynomial Function ◽  
Crack Location ◽  
Wavelet Finite Element Method ◽  
Good Ability ◽  
Wavelet Finite Element ◽  
Lifting Wavelet

Due to the fact that near a crack singularity, gradients of the solution are large and are also subject to abrupt changes, so that the solution cannot locally be accurately approximated by a piecewise polynomial function on a quasi-uniform mesh. Lifting wavelet finite element has good ability in modal analysis for singularity problems like a cracked pipe. The first three natural frequencies of the cracked pipe were solved with lifting wavelet finite element, and the database for crack diagnosis was obtained. The first three measured natural frequencies were employed as inputs and the intersection of the three frequencies contour lines predicted the normalized crack location and size. The experimental examples denote the method is of higher identification precision.

scholarly journals Influence of edge crack on frequencies of thin plate in bending

2005 ◽  
Vol 27 (2) ◽  
pp. 107-117
Author(s):  
Nguyen Thi Hien Luong ◽  
Vuong Quang Giang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Thin Plate ◽  
Edge Crack ◽  
Natural Frequencies ◽  
High Accuracy ◽  
Crack Identification ◽  
The Finite Element Method ◽  
Isoparametric Element ◽  
Crack Location

This paper investigates the influence of crack location and crack length on changes in natural frequencies of bending thin plate. To perform this analysis, a computing program called CRACK-PLATE, using the finite element method based on the Ressner-Mindlin' theory of plate is developed. In order to achieve a high accuracy, an isoparametric element of Barsoum is combined with an 8-node quadrilateral isoparametric element. The numerical results show that the natural frequencies are very sensitive to the crack presence in the bending thin plate. This study is a basis for crack identification based on natural frequencies of plates.

QUANTITATIVE IDENTIFICATION OF ROTOR CRACKS BASED ON FINITE ELEMENT OF B-SPLINE WAVELET ON THE INTERVAL

2009 ◽  
Vol 07 (04) ◽  
pp. 443-457 ◽  
Author(s):  
XUEFENG CHEN ◽  
BING LI ◽  
JIAWEI XIANG ◽  
ZHENGJIA HE
Keyword(s):  
Finite Element ◽  
Natural Frequencies ◽  
Beam Element ◽  
Rotational Inertia ◽  
Spline Wavelet ◽  
B Spline ◽  
Rotor Systems ◽  
Crack Location ◽  
Contour Lines ◽  
Quantitative Identification

Based on finite element of B-spline wavelet on the interval (BSWI), the quantitative identification method of transverse crack for rotor systems was studied. The new model of BSWI Rayleigh–Euler rotary beam element considering gyroscopic effect and rotational inertia was constructed to solve the first three natural frequencies of the cracked rotor with high precision, and the first three frequencies solution surfaces of normalized crack location and size were obtained by using surface-fitting technique. Then the first three metrical natural frequencies were employed as inputs of the solution curve surfaces. The intersection of the three frequencies contour lines predicted the normalized crack location and size. The numerical and experimental examples were given to verify the validity of the beam element for crack quantitative identification in rotor systems. The new method can be applied to prognosis and quantitative diagnosis of cracks in the rotor system.

Natural Vibrations of a Clamped-Clamped Arch With an Open Transverse Crack

1997 ◽  
Vol 119 (2) ◽  
pp. 145-151 ◽  
Author(s):  
M. Krawczuk ◽  
W. Ostachowicz
Keyword(s):  
Finite Element ◽  
Stiffness Matrix ◽  
Edge Crack ◽  
Natural Frequencies ◽  
Element Model ◽  
Mode Shapes ◽  
Curved Beam ◽  
Natural Vibrations ◽  
Crack Location ◽  
Cracked Arch

The paper presents a finite element model of the arch with a transverse, one-edge crack. A part of the cracked arch is modelled by a curved beam finite element with the crack. Parts of the arch without the crack are modelled by noncracked curved beam finite elements. The crack occurring in the arch is nonpropagating and open. It is assumed that the crack changes only the stiffness of the arch, whereas the mass is unchanged. The method of the formation of the stiffness matrix of a curved beam finite element with the crack is presented. The effects of the crack location and its length on the changes of the in-plane natural frequencies and mode shapes of the clamped-clamped arch are studied.

scholarly journals Experimental and Finite Element Studies on Free Vibration of Skew Plates

2014 ◽  
Vol 19 (2) ◽  
pp. 365-377 ◽  
Author(s):  
C.V. Srinivasa ◽  
Y.J. Suresh ◽  
W.P. Prema Kumar
Keyword(s):  
Finite Element ◽  
Aspect Ratio ◽  
Free Vibration ◽  
Composite Laminates ◽  
Natural Frequencies ◽  
Experimental Studies ◽  
Orientation Angle ◽  
Laminated Composite ◽  
Skew Angle ◽  
Experimental Values

Abstract The present paper deals with the experimental studies carried out on free vibration of isotropic and laminated composite skew plates. The natural frequencies were also determined using QUAD8 finite element of MSC/NASTRAN and a comparison was made between the experimental values and the finite element solution. The effects of the skew angle and aspect ratio on the natural frequencies of isotropic skew plates were studied. The effects of the skew angle, aspect ratio, fiber orientation angle and laminate sequence (keeping the number of layers constant) on the natural frequencies of antisymmetric composite laminates were also studied. The experimental values of natural frequencies are in good agreement with the FE solutions. The natural frequencies are found to increase with an increase in the skew angle. The variation of natural frequencies with the aspect ratio is small and negligible both for isotropic and laminated composite skew plates.

Finite Element Modal Analysis for Steam Turbine Blade Based on ANSYS

2012 ◽  
Vol 260-261 ◽  
pp. 368-371
Author(s):  
Lu Wang ◽  
Shun Qiang Ye ◽  
Rui Meng
Keyword(s):  
Finite Element ◽  
Modal Analysis ◽  
Steam Turbine ◽  
Turbine Blade ◽  
Natural Frequencies ◽  
Crack Location ◽  
Finite Element Software ◽  
Vibration Fatigue ◽  
Steam Turbine Blade ◽  
Twisting Deformation

In response to the vibration fatigue fracture of the steam turbine blade,we construct the 3D model of cracked blade based on the actual crack location,then modal analysis is conducted to the blade with crack and one without crack using the finite element software ANSYS.Thus,we can get the respective natural frequencies and the figure of main vibration modes.The comprasion results show that the existence of the crack can make the natural frequencies of blades drop and the blades have the greatest sway and twisting deformation along the Y axis.These characteristics above can effectively identify the presence of blade cracked. It has crucial meaning for achieving cracked blade online monitoring.

Fatigue Crack Identification in Tensile-Shear Spot Welded Joints by Dynamic Response Characteristics

2005 ◽  
Vol 127 (3) ◽  
pp. 310-317 ◽  
Author(s):  
G. Wang ◽  
M. E. Barkey
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Mode Shape ◽  
Crack Identification ◽  
Tensile Shear ◽  
Modal Shape ◽  
Element Analysis ◽  
Response Characteristics ◽  
Crack Location ◽  
Spot Welded

A theoretical model for the estimation of fatigue crack length of tensile-shear spot welded specimen is developed which incorporates the natural frequency and mode variation. The model is based on the concept that the propagation of cracks causes a release of strain energy, which is related to the structural modal shape. The effect of the structural mode shape and crack location is also explained. The model, experimental, and finite element results indicate that the existence of cracks cause the reduction of natural frequencies and change of natural modes, and that the mode shape of the structure and crack location will affect the magnitude of the change of these dynamic variables. The predictions of the model are compared with the experimental data and finite element analysis results and agreement is found to be consistent.

Experimental and numerical analysis of vibration frequency in sandwich composites with different radii of curvature

2017 ◽  
Vol 21 (8) ◽  
pp. 2870-2886
Author(s):  
Melis Yurddaskal ◽  
Buket Okutan Baba
Keyword(s):  
Finite Element ◽  
Numerical Analysis ◽  
Boundary Conditions ◽  
Natural Frequencies ◽  
Experimental Studies ◽  
Sandwich Panels ◽  
Mode Shapes ◽  
Sandwich Composite ◽  
Radius Of Curvature ◽  
Finite Element Software

In this study, free vibration responses of sandwich composite panels with different radius of curvature were presented numerically. The studies were carried out on square flat and curved sandwich panels made of E-glass/epoxy face sheets and polyvinyl chloride foam with three different radii of curvature. Experimental studies were used to verify the numerical results. Vibration tests were performed on flat and curved sandwich panels under free–free boundary conditions. The experimental data were then compared with finite element simulation, which was conducted by ANSYS finite element software and it was shown that the numerical analysis results agree well with the experimental ones. Effect of the curvature on natural frequencies under different boundary conditions (all edge free, simply supported, and fully clamped) was investigated numerically. Results indicated that the natural frequencies and corresponding mode shapes were affected by boundary conditions and curvature of the panel. For all boundary conditions, the variation of curvature had smaller effect on the natural frequency of the first mode than those of the other modes.

Detection of Cracks in Stationary Rotors via the Modal Frequency Changes Induced by a Roving Disc

2014 ◽  
Author(s):  
Z. N. Haji ◽  
S. O. Oyadiji
Keyword(s):  
Natural Frequencies ◽  
Crack Depth ◽  
Mode Shapes ◽  
Crack Identification ◽  
Open Crack ◽  
Suggested Approach ◽  
Rotor Systems ◽  
Crack Location ◽  
High Crack ◽  
Frequency Changes

In this study, a crack identification approach based on a finite element cracked model is presented to identify the location and depth ratios of a crack in rotor systems. A Bernoulli-Euler rotor carrying an auxiliary roving disc has been used to model the cracked rotor, in which the effect of a transverse open crack is modelled as a time-varying stiffness matrix. In order to predict the crack location in the rotor-disc-bearing system, the suggested approach utilises the variation of the normalized natural frequency curves versus the non-dimensional location of a roving disc which traverses along the rotor span. The merit of the suggested approach is to identify the location and sizes of a crack in a rotor by determining only the natural frequencies of the stationary rotor system. The first four natural frequencies are employed for the identification and localisation of a crack in the stationary rotor. Furthermore, this approach is not only efficient and practicable for high crack depth ratios but also for small crack depth ratios and for a crack close to or at the node of mode shapes, where natural frequencies are unaffected.

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