Three-steps-meshing based multiple crack identification for structures and its experimental studies

Abstract

Multiple crack identification plays an important role in vibration-based crack identification of structures. Traditional crack detection method of single crack is difficult to be used in multiple crack diagnosis. A three-step-meshing method for the multiple cracks identification in structures is presented. Firstly, the changes in natural frequency of a structure with various crack locations and depth are accurately obtained by means of wavelet finite element method, and then the damage coefficient method is used to determine the number and the region of cracks. Secondly, different regions in the cracked structure are divided into meshes with different scales, and then the small unit containing cracks in the damaged area is gradually located by iterative computation. Lastly, by finding the points of intersection of three frequency contour lines in the small unit, the crack location and depth are identified. In order to verify the effectiveness of the presented method, a multiple cracks identification experiment is carried out. The diagnostic tests on a cantilever beam under two working conditions show the accuracy of the proposed method: with a maximum error of crack location identification 2.7% and of depth identification 5.2%. The method is able to detect multiple crack of beam with less subdivision and higher precision, and can be developed as a multiple crack detection approach for complicated structures.

A trajectory method for vibration based damage identification of underdetermined problems

“…However, there is no physical interpretation of the first assumption because damages are generally of random character, and the second assumption is valid only in case of small damages. Similar to [4], in [11], the authors assumed linear superposition for the damaged structure that is also valid for small damages. When considering FE updating techniques (e.g., implementation of metaheuristics), the complexity of the problem increases when the number and size of damages increases and the discretization becomes finer.…”

“…Yang [10] proposed a structural flexibility disassembly method to compute the perturbed parameters of the stiffness matrix, which indicate damages. In the work by Li et al [11], it was shown that the sensitivity method can be used in conjunction with a denser discretization in order to simulate crack-like defects. Yao & Pakzad [12] proposed two novel regression-based techniques that use local acceleration responses of a frame structure to estimate its local stiffness that were proven effective in their application to data collected from two laboratory specimens that are subjected to white noise excitation.…”

Model-driven fault diagnosis of slant cracks in aero-hydraulic straight pipes

“…Using equation (27), E c of the hydraulic straight pipe is calculated to be 166.77 GPa. Equations (14) to (19) show that changes in parameters, such as the crack location, depth and included angle, affect the local flexibility of the pipeline structure, which in turn changes the natural frequency. This change in the natural frequency of the structure is more distinct in a thin-walled pipeline.…”

“…Scholars have used frequency data to identify crack faults. [18][19][20] When a crack occurs in a structure, the material physical parameters change and affect the inherent characteristics of the structure. Therefore, the change in the natural frequency can be used to monitor crack damage.…”

Smoothed reduction of fracture mechanics solutions to 1D cracked models

“…Depending on the type of the examined structural system, different models (usually based on the finite element method) are utilized; cracks are usually simulated either as a springs (e.g. [1][2][3]), either by introducing local stiffness degradations expressed as modulus of elasticity reductions (see for example in [4]), or related to overall finite element stiffness e.g. [5][6][7][8] and many others.…”