The purpose of health monitoring of building materials is to localize the defect during its formation to give early warnings for avoiding catastrophic failures. Here, an acoustic source localization technique for building materials is proposed using the time difference of arrival at six sensors without knowing the acoustic wave speed in the material. The proposed technique does not require solving a system of nonlinear equations; hence, greatly reduces the complexity of calculation. Finite element models of different building materials were created to verify the proposed defect localization technique. The results of numerical simulation prove the reliability of the proposed technique.
Post processes are usually needed to improve the quality and performance of ground brittle materials, and their low efficiency and high cost are greatly determined by grinding-induced roughness and subsurface damage (SSD). This raises an urgent demand to accurately predict various roughness and SSD depth. In this paper, grinding experiments are conducted on K9 glass samples with different processing parameters, including abrasive grain diameter, grinding depth, wheel speed, and feed speed. The line roughness Ra, area roughness Sa, and SSD depth are measured. Based on genetic algorithm (GA) and deep neural network, a relationship model among processing parameters, Ra, Sa, and SSD depth, is established. The model is accurate and reliable with a mean absolute percentage error MAPE < 10% and a correlation coefficient R > 0.94. The research is valuable in the evaluation of surface and subsurface integrity for ground brittle materials.
Acoustic source localization (ASL) technique is an important step for structural health monitoring (SHM). ASL in three dimensional (3D) structures is more challenging. The 3D acoustic source localization technology not only has important significance for the non-destructive monitoring of large-scale 3D structures, but also is indispensable for the spatial sound source localization problems. More unknown parameters, large number of sensors, limited known properties of the 3D structure and complex nonlinear equations greatly hinder the application and development of 3D acoustic source localization. Besides, when the acoustic signal propagates through different media in a 3D heterogeneous structure, it is refracted at the interfaces following Snell's law which makes the ASL in heterogeneous structures even more difficult. In this paper, the basic theoretical research on the acoustic source localization in 3D heterogeneous structures is carried out considering the refraction effect. A localization technique is first proposed based on the triangular pyramid sensor cluster using only the time difference of arrival (TDOA) and the location information of clusters. This technique can predict the velocity and acoustic source location with a relatively small number of sensors. A 3D finite element based numerical model of a heterogeneous structure made of two materials was analyzed to verify the proposed acoustic source localization technique. The results show the reliability of the proposed technique.
The safety of pressure vessels has been a concern in recent years. Old pressure vessels are susceptible to failure due to fatigue damage after several years of usage. Fire and spill of hazardous liquid or gas due to pressure vessel failure can cost human life and cause property damage. Therefore, monitoring these critical structures has become a problem of considerable interest. Nondestructive testing and structural health monitoring play an important role for both manufacturing and periodic inspection of pressure vessels. Acoustic emission technology is a popular and widely used technology for pressure vessel monitoring. The acoustic source localization (ASL) technique developed for the two-dimensional planar structures is applied to the surface of a cylindrical pressure vessel. The ASL on the cylindrical pressure vessel surface is performed by the time difference of arrival (TDOA) method without knowing the acoustic properties of the material. In the experiment six sensors are placed in two clusters. The location of the acoustic source is unknown, and the arrival time of the acoustic signal to each sensor is measured. After analyzing the measured data as discussed in the paper one can calculate the acoustic source position. The method is experimentally verified. The results show that the above technique can quickly and accurately locate the acoustic source position on the surface of a cylindrical pressure vessel without having the complete knowledge of the structural properties of the material.
In a nonhomogeneous specimen, if the acoustic source and receiving sensors are located in different media then the acoustic source localization becomes very difficult. In this paper, a recently developed source localization technique is extended to non-homogeneous plates by appropriately considering and modeling the refraction phenomenon. The modified technique is applied to two-layered structure. The proposed new technique gives a relatively simple way to localize the acoustic source without the need to solve a system of nonlinear equations, and thus it avoids the problem of multiplicity, converging to local minima instead of global minimum and giving wrong solution. The proposed technique works for both isotropic and anisotropic structures. The finite element simulation shows that this modified technique considering refraction at material interfaces can localize the acoustic source better than when this modification is not considered.
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