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...

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

Inhomogeneous deformation of nickel-base superalloy 〈111〉 monocrystals under compression

: The ring compression test was successfully used to determine the relative efficiency of a number of lubrication systems for the high temperature forging of Type 300A maraging steel and titanium -6 aluminum -4 vanadium alloy. The results clearly indicate the advantage of using both a glass coating on the workpiece and a grease-base lubricant on the tooling. Data obtained has identified the optimum temperature range for use of each of the three glass coatings evaluated. Inaccuracies in the application of theoretical analysis to practical ring test results, due to bulging occurring at high friction levels, can be minimized by using specimens of small ratios of internal diameter and thickness to external diameter. When such precautions are taken, the method of analysis used in this work allows a value for the interface shear of the lubricant system to be determined. Under thick film lubrication conditions, this value would be independent of the flow stress of the workpiece material.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD0726583&Location=U2&doc=GetTRDoc.pdf

T. E. Jones

Papers

The Evaluation of Glasses As Forging Lubricants