The detections of angled surface cracks in elastic plates by using Rayleigh waves with a time-of-flight method are studied quantitatively. Based on the two-dimensional strain equations in the frequency domain, the fin...
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The detections of angled surface cracks in elastic plates by using Rayleigh waves with a time-of-flight method are studied quantitatively. Based on the two-dimensional strain equations in the frequency domain, the finite element models are established to simulate the equivalent pulsed stress generation of Rayleigh waves in the elastic plates with the angled surface cracks. At the same time, the fictitious viscoelastic properties are introduced for defining absorbing regions to avoid undesired reflections from the ends of the studied solid domains. The numerical results show that the arrival times of the reflected and transmitted Rayleigh waves are closely related to the characteristics of the angled surface cracks, which can be used for detecting the crack position, depth, and orientation angle. The propagation characteristics of these Rayleigh waves from the finite element calculations coincide well with those published experimental measurements, which validates that the finite element simulations can be used effectively for angled surface crack detections.
Encoded phased arrays have proven to be very useful for inspections in both the chemical and petrochemical industries due to their speed, repeatability, data collection capabilities and lack of environmental issues. I...
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Encoded phased arrays have proven to be very useful for inspections in both the chemical and petrochemical industries due to their speed, repeatability, data collection capabilities and lack of environmental issues. Initial work was performed on thicker walled material, as covered by ASME BP&V Section V. Emphasis is moving towards thinner walled materials, covered by ASME B31.3 and similar codes. These small diameter, thin wall tubes can now be inspected using ONDT's COBRA scanner, which has low profile and laterally focused arrays. Detection is generally not an issue with ultrasonics, particularly phased arrays, as the signal-to-noise ratio and imaging are good. The CCEV arrays, focused in the passive axis, do significantly improve horizontal sizing as the results show. However, vertical sizing capability leaves something to be desired. Specifically, smaller defects in small tubes can generate a lot larger sizing errors as a percentage of wall thickness than, say, larger defects in much larger tubes. For small defects in thin-walled tubes, precision sizing (i.e. for Fracture Mechanics approaches) is challenging.
Ultrasonic phased arrays testing for nickel-based alloy weldments meets some difficulties due to the curvilinear propagating paths will appear in this kind of joint with coarse and oriented grains. Thus, it is hard to...
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Ultrasonic phased arrays testing for nickel-based alloy weldments meets some difficulties due to the curvilinear propagating paths will appear in this kind of joint with coarse and oriented grains. Thus, it is hard to determine the proper time delay for phased arrays using the traditional focusing law which is based on the assumption that the sound beam will propagate in straight lines. In order to focus beams to any expected point in anisotropic media, we provide a modified focusing law for phased array testing by combing the ray tracing method and the least square approximation. And with the help of this modified focusing law, the proper ray path connecting each element position of phased arrays and the expected focal point in weldments can be determined so that it can control the beam focusing toward the expected point in the anisotropic weldment. Furthermore, some experimental examinations are carried out to compare the focusing ability between the traditional and the modified focusing approach. It shows that the provided focusing approach can focus more accurately than the traditional method in inspection of the nickel-based alloy weldments.
Ultrasonic scattering attenuation from voids in carbon fiber reinforced polymer (CFRP) composite materials is investigated using a 2-D Random Void Model (RVM) and the finite-difference time-domain (FDTD) method. Based...
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Ultrasonic scattering attenuation from voids in carbon fiber reinforced polymer (CFRP) composite materials is investigated using a 2-D Random Void Model (RVM) and the finite-difference time-domain (FDTD) method. Based on RVM and statistical data on voids morphology with the void contents ranging from 0.03% to 4.62%, a series of simulations for CFRP specimens are established for each void content. Using the FDTD method, ultrasonic attenuation coefficients at 1, 2.5, 5, 7.5, and 10MHz are calculated, respectively. Then, correlations among the voids morphology (shape, size, and distribution), porosity, ultrasonic frequency, and attenuation coefficient are discussed. It is found that, at fixed void content, the randomness of voids morphology in nature leads to fluctuations of attenuation coefficients. The attenuation increases with the increase of the frequency, however, the increasing rate of the attenuation varies from frequency bands. The increment rate of attenuation with increasing frequency also differs from void contents. Moreover, some unusual large voids have significant influence on the ultrasonic scattering attenuation. Calculations of attenuation coefficients from RVM at 5MHz accord with the experiments, which validated the combination of RVM and FDTD method applied to discuss the scattering attenuation from voids in composite materials. The results revealed the importance of the void morphology randomness on the ultrasonic scattering attenuation.
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