In this paper, the effect of water cooling on mechanical properties and microstructure of AA5086 aluminum joints during friction stir welding is investigated. For doing so, the mechanical and microstructural behavior of samples welded both in air and in water was analyzed. Tests were performed involving both butt and lap welds and the results were compared. The effect of rotational speed at constant feed rate of 50 mm/min and changing rotational speed ranging from 250 to 1250 r/min was investigated. The results showed a significant change in the tensile behavior of the butt-welded specimens due to water cooling. In addition, welding was performed at constant spindle speed of 800 r/min and various traverse speeds (25 mm/min to 80 mm/min) to determine the effect of feed rate. The strength increases at first, but then decreases dramatically along with the feed rate which is due to the occurrence of a groove defect. Results showed some generally positive impacts of water cooling which are discussed in terms of tensile results, hardness distributions and microstructure analysis.

Lamb waves are ultrasonic-guided waves with applications in inspection and monitoring of plate-like structures. These waves can be used for detecting, locating, and sizing of defects. In this paper, a new method is proposed for in situ measurement of the location and size of circle-like corrosion defects in thin plates. A novel technique for omnidirectional generation of Lamb waves is also proposed. The probe is placed on at least three different points around the defect and the arrival times of reflected echoes are measured. An algorithm then estimates the location and size of the defect based on the arrival times of reflected echoes. A finite element model is also developed for modeling the process and studying various aspects of the method. The proposed method is then tested on an aluminum plate. The center location and radius of a 5-mm hole in a 0.5-mm thick aluminum plate is estimated with uncertainties of ±1 mm (1%) and ±0.25 mm (5%), respectively. Various aspects of the proposed method are discussed, and uncertainties in measurements are estimated. Effectiveness of the proposed method is also assessed by sizing actual corrosion defects. The proposed method is fast, flexible, and portable and shows better accuracy in comparison to similar existing methods.

A mathematical model for the scattering of a symmetric [Formula: see text] Lamb wave mode from a circular cavity in an isotropic plate is developed that can handle both symmetric and asymmetric single- and double-sided blind holes. The theoretical formulation is based on Mindlin and Poisson plate theories. A finite element model is also utilized to extract the scattering patterns of Lamb waves from various cases of a generalized circular cavity. Two-dimensional FFT analysis is used to determine the transmitted and reflected Lamb wave modes when the incident wave interacts with either symmetric (through-hole and double-sided blind hole) or asymmetric (blind hole and double-sided blind hole) cavities. Results indicate that the remaining thickness of a cavity zone and the type of a cavity are two key parameters in the scattering pattern. For asymmetric cavities, the shape of the scattering pattern of the mode-converted [Formula: see text] mode does not vary significantly. However, the amplitude of the scattering pattern shows noticeable changes in the out-of-plane component of the displacement. Results obtained from the proposed theory and finite element model are in good agreement with previously published data.