Neutron Stress Imaging of Drawn Copper Tube: Comparison with Finite-Element Model
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COLD drawn seamless tubes are used for many applications, e.g., for plumbing, in heating systems, oil and gas pipes, drinking water systems, transport of medical and industrial gases, evaporators, as well as intermediate products for hydroforming and various mechanical applications.[1] For industrial production of seamless tubes, the first forming step often is piercing of the billet, for example, by extrusion. Due to vibrations of the mandrel, tolerances in positioning of the die and billet, as well as potential temperature differences within the billet, this step inherently results in variations of thickness over length, eccentricity, and ovality. These geometrical irregularities can be found downstream through the complete process route. The eccentricity E of the tube is defined as the deviation of the wall thickness from an average value (Figure 1): E ¼ tmax tmin =tave 100 pct with tmax and T. PIRLING, Instrument Scientist, is with the Institut LaueLangevin, BP 156 - 38042 Grenoble Cedex 9, France. A. CARRADO`, Associate Professor of University of Strasbourg, is with the Institut de Physique et Chimie des Mate´riaux de Strasbourg, 67034 Strasbourg Cedex 2, France. Contact e-mail: [email protected] S. BRU¨CK, Postdoctoral Student, and H. PALKOWSKI, Chair of Metal Forming, are with the Institute of Metallurgy, Clausthal University of Technology, 38678 Clausthal-Zellerfeld, Germany. This article is based on a presentation given in the symposium entitled ‘‘Neutron and X-Ray Studies for Probing Materials Behavior,’’ which occurred during the TMS Spring Meeting in New Orleans, LA, March 9–13, 2008, under the auspices of the National Science Foundation, TMS, the TMS Structural Materials Division, and the TMS Advanced Characterization, Testing, and Simulation Committee. Article published online September 16, 2008 METALLURGICAL AND MATERIALS TRANSACTIONS A
tmin the maxima and minima wall thicknesses, respectively, and tave the average wall thickness. For industrial tubes, the eccentricity lays typically around 5 to 10 pct for steel and about 5 pct for aluminum grades.[2,3] The ovality O is the deviation of the external cross section from a perfect circular shape: O ¼ dmax dmin =dave 100 pct, with dmax and dmin the maximum and minimum external diameters, respectively, and dave the average external diameter. Industrial tubes typically exhibit up to 1 pct ovality for carbon steel tubes and up to 3 pct for copper tubes.[4,5] In order to achieve the final diameter and wall thickness, the extruded tubes are reduced successively in additional cold drawing steps with or without using a plug (Figures 2(a) and (b)). Different kinds of plugs can be used to influence the wall thickness. The method is well known and described in books about metal forming processes, such as in References 6 through 8. Figure 2(a) shows an example of a running plug, Figure 2(b) shows the geometrical data of a die, where c is the so-called drawing angle and L the length of the drawing tool. The dimensions used in this investigatio
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