Alan T. Male

The Relative Validity of the Concepts of Coefficient of Friction and Interface Friction Shear Factor for Use in Metal Deformation Studies

The relative validity of the concepts of constant coefficient of friction (f) and constant interface friction shear factor (m) as quantitative indices for defining friction stresses existing in metal deformation operations has been investigated by means of the ring compression test technique. Material flow stress values have been determined by ring compression tests using mathematical formulae based upon both concepts in question. These have been compared with flow stress values obtained on the same material using the accurate Polakowski technique which is not based upon any mathematical concept, but which can only be carried out at ambient temperature and low strain rates. Flow stress values obtained by analyzing ring compression test results, using the concept of constant interface friction factor, were found to be consistently lower than the values obtained using the constant coefficient of friction concept, and in good agreement with results obtained using the Polakowski technique. For this reason, it...

A New Method for the Determination of Material Flow Stress Values under Metalworking Conditions

For the adequate mathematical understanding of metalworking processes and the theoretical prediction of deformation loads, there is a precise need for accurate knowledge of the basic flow stress behavior of the workpiece material under particular conditions of temperature and strain rate. This information can be obtained by means of tension, torsion, or compression testing, but because of major drawbacks with the first two methods, compression testing is most widely used.

Silver encased high temperature superconductor ribbons produced by rolling

Ribbons of silver/yttrium-barium-copper oxide/silver (Ag/YBCO/Ag), nominally 0.01 in. (0.25 mm) thick, have been fabricated by unidirectional rolling and their resulting microstructures and superconducting properties evaluated. The influence of a postfabrication sinter/oxygen replenishment anneal on their properties has been determined. Grain alignment/preferred orientation of the YBCO core was observed. Typical transport critical-current densities measured in zero field at 4.2 and 77 K were 600 and 125 A/cm/sup 2/, respectively. Preliminary experiments on the bismuth-containing high-temperature superconductors have indicated that codeformation of a silver composite billet by rolling to thin strip is easily accomplished. >

Defects at Interfaces in Co-Extruded Metals

Summary The strength of the interface between core and clad in hydrostatically co-extruded copper-clad aluminum has been measured as a function of the total extrusion ratio. It is found that the interface strength exhibits a minimum at a particular extrusion ratio. This phenomenon is investigated analytically by modeling the co-extrusion process using a finite element code, ABAQUS, to determine the stresses at the interface in the deforming region of the die and in the extruded product. These calculations show that the state of stress at this interface depends on the die geometry and on the extrusion ratio. The implications of this observation on the design of dies for co-extrusion are discussed.