Nondestructive evaluation of formability in thin steel sheets using fundamental Lamb wave

Abstract

This paper describes the nondestructive evaluation method of the Lankford value ( r̄-value) in thin steel sheets using the transit time of the fundamental Lamb wave. The ( r̄-value) in thin steel sheet depends on the texture, that is, the ( r̄-value) increases as the (111) crystal plane contained in the rolling plane increases, while it decreases as the (100) crystal plane sheet increases. The ( r̄-value) evaluation method using the averaged fundamental Lamb wave velocity in the rolling plane has already been developed by many researchers. However, this method needs different calibration curve for steel sheets produced by different manufacturing processes, because some sheets have the same ( r̄-value) but different texture, leading to a different velocity distribution. This paper describes why different Lamb wave velocities would be observed for thin steel sheets having the same ( r̄-value) and how to evaluate the ( r̄-value) by utilizing a combination of the averaged fundamental Lamb wave transit time and the characteristics of the transit time distribution. This result provides a more flexible measurement than the conventional methods and simplifies the evaluation procedures in industrial application.