Detection Of Multiple Cracks Research Articles

Nondestructive testing and crack evaluation of ferromagnetic material by using the linearly integrated hall sensor array

Magnetic flux leakage testing (MFLT), which measures the distribution of a magnetic field on a magnetized specimen by using a magnetic sensor such as a Hall sensor, is an effective nondestructive testing (NDT) method for detecting surface cracks on magnetized ferromagnetic materials. A scan-type magnetic camera, based on the principle of MFLT, uses an inclined Hall sensor array on a printed circuit board (PCB) to detect small cracks at high speed. However, the wave forms appear in a direction perpendicular to the scan because the sensors are bonded at different gradients and heights on the PCB despite careful soldering. In this paper, we propose linearly integrated Hall sensors (LIHaS) on a wafer to minimize these waves and to improve the probability of crack detection. A billet specimen is used to determine the effectiveness of the LIHaS in multiple crack detection.

Robust damage assessment of multiple cracks based on the frequency response function and the Constitutive Relation Error updating method

The aim of this paper is to present a damage assessment technique for the non-destructive detection and sizing of multiple open cracks in beams. The constitutive relation error updating method is used for the identification of the location and the size of multi-cracks in a simply supported beam.The present identification method is illustrated through numerical examples including double and triple cracks. Moreover, the efficiency and robustness of the proposed method is demonstrated through various numerical simulations in regard to the non-dimensional crack depth and the crack location.It is demonstrated that the constitutive relation error updating method can detect the number of cracks on the beam and can estimate both the crack positions and sizes with satisfactory precision, even if 10% or 20% noise levels has been added to the simulations, and only few degrees of freedom are used for the identification procedure.

定在波の直交性を考慮した補強コンクリートパイルの微細多重クラックの高精度検出

定在波の直交性を考慮した補強コンクリートパイルの微細多重クラックの高精度検出

Detection of Multiple Cracks in Triangular Cantilevers Based on Frequency Measurements

Triangular cantilevers are used as small force sensors. Prediction of location and size of multiple cracks from experimental results will be of value to users and designers of cantilever deflection force sensors. We extend a method for prediction of location and size of multiple cracks in rectangular cantilevers to deal with triangular cantilevers in this paper. The cracks are assumed to introduce local flexibility change and are modeled as rotational springs. The beam is divided into a number of segments, and each segment is associated with a damage index, which can be calculated through the relationship between the damage index and strain energy of each segment and the changes in the frequencies caused by the cracks. The location of cracks can be obtained with high accuracy with sufficient segment numbers. The size of a crack can be calculated through the relationship between the crack size and its stiffness, which can be obtained from the damage index related to the crack. The maximum error in prediction of the crack position in the case of double cracks is less than 15%, and it is less than 25% in prediction of the crack size.

Multiple Crack Detection of Concrete Structures Using Impedance-based Structural Health Monitoring Techniques

This paper presents a feasibility study for practical applications of an impedance-based real-time health monitoring technique applying PZT (Lead–Zirconate–Titanate) patches to concrete structures. First, comparison between experimental and analytical studies for damage detection on a plain concrete beam is made. In the experimental study, progressive surface damage inflicted artificially on the plain concrete beam is assessed by using both lateral and thickness modes of the PZT patches. Then, an analytical study based on finite element (FE) models is carried out to verify the validity of the experimental result. Secondly, multiple (shear and flexural) cracks incurred in a reinforced concrete (RC) beam under a third point bending test are monitored continuously by using a sensor array system composed of the PZT patches. In this study, a root mean square deviation (RMSD) in the impedance signatures of the PZT patches is used as a damage indicator.

Experimental verification of a method of detection of multiple cracks in beams based on frequency measurements

A method for prediction of location and size of multiple cracks based on measurement of natural frequencies has been verified experimentally for slender cantilever beams with two and three normal edge cracks. The analysis is based on energy method and representation of a crack by a rotational spring. For theoretical prediction the beam is divided into a number of segments and each segment is considered to be associated with a damage index. The damage index is an indicator of the extent of strain energy stored in the rotational spring. The crack size is computed using a standard relation between stiffness and crack size. Number of measured frequencies equal to twice the number of cracks is adequate for the prediction of location and size of all the cracks. The accuracy of prediction of crack details is encouraging. The maximum error in predicting location of cracks decreases with an increase in the number of cracks. It is less than 10% and 20% for two and three cracks respectively. The maximum error in predicting the crack size is less than 12% and 30% respectively for the two cases. A strategy to overcome failure in the prediction for cases with one of the cracks located near an anti-node has been suggested.

Detection of multiple cracks using frequency measurements

A method for detection of multiple open cracks in a slender Euler–Bernoulli beams is presented based on frequency measurements. The method is based on the approach given by Hu and Liang [J. Franklin Inst. 330 (5) (1993) 841], transverse vibration modelling through transfer matrix method and representation of a crack by rotational spring. The beam is virtually divided into a number of segments, which can be decided by the analyst, and each of them is considered to be associated with a damage parameter. The procedure gives a linear relationship explicitly between the changes in natural frequencies of the beam and the damage parameters. These parameters are determined from the knowledge of changes in the natural frequencies. After obtaining them, each is treated in turn to exactly pinpoint the crack location in the segment and determine its size. The forward, or natural frequency determination, problems are examined in the passing. The method is approximate, but it can handle segmented beams, any boundary conditions, intermediate spring or rigid supports, etc. It eliminates the need for any symbolic computation which is envisaged by Hu and Liang [J. Franklin Inst. 330 (5) (1993) 841] to obtain mode shapes of the corresponding uncracked beams. The proposed method gives a clear insight into the whole analysis. Case studies (numerical) are presented to demonstrate the method effectiveness for two simultaneous cracks of size 10% and more of section depth. The differences between the actual and predicted crack locations and sizes are less than 10% and 15% respectively. The numbers of segments into which the beam is virtually divided limits the maximum number of cracks that can be handled. The difference in the forward problem is less than 5%.

Multiple Surface Crack Detection Using A. C. Potential Drop Method.

This paper studies the multiple crack detection by a. c. potential method. Alternating currents from 200 Hz to 5000 Hz were applied to artificially cracked specimens of Incone 1738 LC superalloy having 1-5 cracks with 50-500 μm depth, and a. c. potentials raised by the cracks were measured at respective frequencies. The potentials had a linear relationship against the frequency and the gradient and intercept of the relationship depended on the number of cracks and crack depth. A new a. c. method was proposed for determining the number of cracks and crack depth by utilizing the frequency dependency of the gradient and intercept. The frequency dependency of the gradient and intercept from FEM analysis agreed with the experiment results qualitatively.

Experimental crack identification using electrical impedance tomography

This paper addresses the problem of practical crack identification in electrically conducting specimens using only boundary measurements. The method is commonly referred to in the literature as Electrical Impedance Tomography (EIT). Crack identification is determined from the electrical impedance distribution, which amounts to solving an inverse problem, starting from boundary measurements. Whereas this kind of inverse problem has been extensively addressed in its theoretical and numerical aspects, there is a scarcity of experimental results aimed at examining the applicability of the method for real conditions. We present new experimental results, based on a simple identification methodology. The efficiency and limitations of this method are assessed through a series of numerical simulations and laboratory experiments on two-dimensional geometries. Following a preliminary numerical validation stage, actual crack detection is carried out on a discrete network of resistors, as an approximation to Laplace's equation. Next, experiments are carried out on a continuous conductive medium, containing one and two flaws. Our results show that EIT is a promising candidate for crack identification in real life conditions with a potential for multiple crack detection.

Image Processing for Stress Cracks in Corn Kernels

ABSTRACT AN image processing algorithm was developed for detecting stress cracks in corn kernels using a commercial vision system. White light in back-lighting mode with black-coated background having a small aperture for the light provided the best viewing conditions. The kernel images, when processed using the algorithm developed, produced white streaks corresponding to the stress cracks. Double stress cracks were the easiest to detect. Careful positioning of the kernel over the lighting aperture was necessary for satisfactory detection of single and multiple stress cracks.