A Semi-Automatic System for the Ultrasonic Measurement of Texture
The texture (preferred grain orientation) of rolled metal plates influences a number of important mechanical properties such as their ability to be plastically formed into complex shapes. X-ray diffraction techniques can characterize texture in great detail but are unsuitable for real time process control. Furthermore, x-rays only sample the properties of a near surface layer, whereas the average properties throughout the thickness may be of greater interest. This paper describes an alternate texture characterization approach based on ultrasonic measurements of the anisotropy of plate wave velocities. Relationships have recently been established between the macroscopic elastic constants of a rolled metal plate and the coefficients of an expansion of the crystallite orientation distribution function (CODF) in terms of generalized Legendre functions . It has also been shown that these coefficients can be determined from velocity measurements of ultrasonic plate modes [2,3]. Here a system is described which implements these ideas in a semi-automated fashion as would be required for process control applications. The measurement system consists of two sets of EMAT transducers and associated electronics, one for SHO mode measurements and the other for SO mode measurements. Each set consists of one transmitter and two receivers, separated by a fixed distance and placed at a variable angle with respect to the rolling direction of the plate. The pair of received signals are digitized and processed to determine the coefficients W400, W420 and W440, which can, in turn, be used to make first order predictions of pole figures. These steps are reviewed in detail and future directions are discussed.
KeywordsElastic Constant Pole Figure Ultrasonic Velocity Single Crystal Elastic Constant EMAT Probe
Unable to display preview. Download preview PDF.
- 2.R. B. Thompson, J. F. Smith, and S. S. Lee, Nondestructive Evaluation of Microstructure for Process Control, H.N.G. Wadley, Ed., ASM, Metals Park, OH, 1986, pp. 73–99.Google Scholar
- 3.S. S. Lee, J. F. Smith, and R. B. Thompson, “Inference of crystallite orientation distribution function from the velocity of ultrasonic plate modes”, Proceedings of the 2nd International Symposium on Nondestructive Characterization of Materials, J. F. Bussiere, Ed., (Plenum Press, NY, in press).Google Scholar
- 6.A. V. Clark, Jr., A. Govada, R. B. Thompson, G. V. Blessing, P. P. Delsanto, R. B. Mignogna, and J. F. Smith, “The use of ultrasonics for texture monitoring in aluminum alloys”, these proceedings.Google Scholar
- 7.R. J. Fields, National Bureau of Standards, private communication.Google Scholar
- 9.J. F. Smith, R. B. Thompson, D. K. Rehbein, T. J. Nagel, P. E. Armstrong, and D. T. Eash, Illustration of texture with ultrasonic pole figures, ibid.Google Scholar