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  • Ultrasonic waves propagate in materials

    2018-11-03

    Ultrasonic waves propagate in materials at a constant velocity. This behavior allows them to be used for non-destructive investigation purposes. Different studies were conducted to determine the hardness of various materials using the velocity variations of ultrasonic wave. Tariq et al. [15] correlated the material properties, including hardness, of selected aluminum alloys with ultrasonic wave velocity variations. Bouda et al. [16], Lukomski, et al. [17], Chou et al. [18] and Rayes et al. [19] developed the correlations between ultrasonic wave velocity and steel hardness to determine the thickness average hardness. These studies showed that the velocity measurements of pulse-echo ultrasonic wave provide average hardness through the thickness of materials, but the correlations were performed using surface hardness. Isotropic materials were used in these studies, and it cyclooxygenase inhibitors was assumed that the inner hardness of samples was consistent with surface hardness. However, these correlations were not tested in industrial applications. This study aims to investigate the feasibility of through-thickness average hardness investigation method using a widely used industrial method. For this purpose, welding process, which causes the formation of irregularities in the material, is selected, and the hardness variations after welding of three different types of materials are investigated. Results of the ultrasonic method are verified by the widely used destructive surface hardness measurement method.
    Methodology The Rockwell hardness test is a simple hardness measurement technique which can be applied to a wide variety of materials [20]. The depth of a prescribed load is determined, and converted to a hardness value [21] in this technique. Eq. (1)[22] is used to calculate Rockwell hardness,where is Rockwell hardness; N is numerical constant; h is remaining depth of penetration; and S is scale division. There are various Rockwell scales that are marked by additional capital letter to . scale is used for soft and middle hardness steel, aluminum, and brass. Carbon steels with carbon content lower than 0.5 weight % are classified as soft and middle hardness steels, and consequently, scale is used in this study. The hardness measurements are performed before and after the annealing treatments and repeated 10 times. Longitudinal ultrasonic waves propagate and vibrate in the same direction and travel through a medium at constant velocity. Pulse echo technique, in which waves are transmitted and received by the same transducer, is used with this type of waves. Immersion ultrasonic systems transmit the longitudinal waves in water, as shown in Fig. 1. Echoes reflect back from the surface and back wall of a material. Computer integrated system measures the time difference between two echoes and calculates wave velocity using Eq. (2)where V is wave velocity; d is thickness; and t is time. Three sample plates of each steel type and their weld grooves are prepared according to the geometric properties given in Fig. 2. The depth of the weld groove is 3 mm with a side angle of 60°, and the width of its bottom part is 2 mm. The weld groove with a length of 93.3 mm is located in the center. Length of the weld grove is determined as one-third of length of base plate. The welding process is required to be performed using a fully automated system with common parameters for each type of steel. Submerged arc welding technique is a proper method to this end, which minimizes the possible operator errors. Dupont et al. [23] evaluated the effects of welding parameters on the arc and melting efficiency, compared various arc welding processes and determined the efficiencies of those processes, including submerged arc welding. That efficiency parameter is preferred to be used during the welding of samples. The parameters of the submerged arc welding process are given in Table 1. Other parameters are not selected according to technical investigation. They are determined according to the requirements of the operator in order to perform a real industrial application of welding process.