A completely nondestructive means of r-value measurement is being developed. Unlike the modul-r method, it requires no specimen removal and has potential for on-line measure-ment. The method employs noncontacting ultrasonic transducers which generate waves propagating at three different angles relative to the sheet rolling direction. A prototype instrument based on these principles has been jointly developed by researchers at Ford Motor Company and National Institute of Standards and Technology (NIST).
At present, there are correlations between ultrasonic and mechanical measurements of r̄. The ultrasonic measurements generally agree with mechanical measurements to 0.1 or better. A method based on metallurgical theories is being developed to use ultrasonic velocity measure-ments to predict not only r̄, but individual r values.
To date, all measurements have been made on static sheet. We are currently developing a device to move sheet metal at controlled velocity. This will allow simulation of on-line operation, as in a rolling mill. In addition, a circuit has been developed to automate the velocity measurements and transmit them to a computer. The eventual goal is to predict r-values from these measurements, using metallurgical theories. The predictions should be done in about 1 s, allowing for possible on-line measurement and control of r-value.