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Ultrasonic Phased Arrays are an emerging technology in nondestructive testing and evaluation. Some important factors affecting on the performance of these probes include, positioning elements in probe, number of elements, distance between two elements, elements length, and time delays to excite probe elements. The type of linear phased array probes is a prevailing type in which elements placed side by side and longitudinally. In this paper based on analyzing the existent laws in design and performance of the phased array probes related to the propagation of ultrasonic waves, an improved dimensional design for ultrasonic linear phased array probes, as well as improvement of the sequence of time delays to excite the probe elements are done. In order to evaluate the performance of the probe with improved design in comparison with a similar ordinary probe, an ultrasonic phased array test is simulated using FEM-based ABAQUS software. By numerical simulations, the performance of the probe with improved design versus the ordinary probe for propagating the guided waves in a thin square aluminum plate is compared. In first part, the attenuation coefficient of the received signals of reflected wave is evaluated, and in second part, the performance of the probes for radial scanning is compared. Results of both simulations confirm that the performance of the probe with improved design is much better than the similar ordinary one. Specially, the probe with improved design propagates the ultrasonic waves with the maximum head wave energy, and steers them with higher accuracy towards a determined direction.

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Turbomachinery, specially gas turbines and axial compressors, play an important and vital role in energy producing and transmission industries. Thus, probable defects must be detected and measured in a timely manner, in order to prevent expensive costs of repair and maintenance. In this paper, a gas turbine blade-disc connection model, that is one of the most important and sensitive gas turbine parts, has been inspected using phased array ultrasonic non-destructive testing method. In manufactured mockup specimen, a crack with 4 and 8 millimeters length, has been created in two steps, followed by the length effect study on inspection results. Comparison of acquired signals in different angles for each crack length with acquired signals got from the healthy model in the same angles, has been employed for crack sizing purposes. The increase in the amplitude of crack reflected signals and the decrease in the amplitude of signals related to the wall behind the crack versus increase in the inspection angle, in ultrasonic phased array testing, has been utilized for extracting a novel feature for crack length estimation. Experimental results show that it is possible to evaluate the crack length in the complicated fir-tree geometry of the disc connection area to the blade, with the amount of error less than 10%, using the extracted feature.