The guided ultrasonic wave has the advantage of diagnosis on a wide area within in a short time due to the long distance propagation characteristic. However, there are many difficulties in signal analysis due to the mode conversions in the reflection from the defect and boundaries. In the use of guided waves for structure monitoring, it is necessary to understand the relation between the propagation mode and the mode of variation according to the shape of the defect. In this study, the characteristics of induced ultrasonic mode conversion is analyzed in taper defects formed from the surface of an aluminum plate. The defect depths of the plate thickness are 20, 50, and 80% and the characteristics of the reflection and transmission modes are analyzed on various defect widths, depending on the angle of change of the tapered shape. The A0 and S0 modes were selected as the excitation mode of the guided waves, the transmission and reflection coefficient amplitudes are analyzed. It is confirmed that the wavelength of the excitation mode having a large influence on the amplitude of the transmission and reflection signals generated by the taper defects depend on the shape of the defect.

In this paper, the reliability-based parameter study is carried out for the stamping process of a front rail roof member with the ultra high strength steel, considering the scatters of the material properties and the process parameters. With the reliability-based design optimization (RBDO) scheme, the springback tendency is investigated from the perturbation of the process parameters such as the sheet thickness, ultimate tensile strength, yield strength, Coulomb friction coefficient, and applied padding force. The amount of the elastic recovery along the height direction is quantified to describe the springback tendency from the analysis. The analysis shows the springback-amount scattering is not ignorable when the yield stress scatters within the similar range of the ultimate tensile strength. The analysis results fully explain the importance of controlling the scatters as well as the average yield-strength amount in the mass production of the stamped products.