Some Aspects of Flow-Stress Determination Using a Gleeble Hot Torsion Machine¶
Abstract¶
Plastic-flow response comprises an important input to the computer simulation of thermomechanical and solid-state joining processes. These processes often involve large strains, high strain rates, and transient-temperature conditions. Torsion testing in a Gleeble machine, in which the temperature is controlled by direct-resistance heating, provides an attractive method to quantify stress-strain behavior for such applications. Results from nominally-isothermal Gleeble torsion tests will be compared to those from conventional hot-compression and thin-wall-torsion tests for a nickel-base superalloy. Subsequently, the effect of axial and radial temperature non-uniformity on flow curves determined from Gleeble torsion tests will be described. Last, several novel test techniques that aim to quantify the interaction of evolving microstructure, transient heating, and plastic flow will be presented.
Bio
S.L. (LEE) SEMIATIN
Dr. Lee Semiatin is Senior Scientist (ST), Materials Processing/Processing Science in the Air Force Research Laboratory, Materials and Manufacturing Directorate. He received a BES in Mechanics from Johns Hopkins University and MS and PhD degrees in Metallurgy and Materials Science from Carnegie Mellon University.
Dr. Semiatin worked at Battelle Memorial Institute from 1978 to 1991. Here, he conducted and directed programs for a wide range of government and industry clients. A large portion of his government-sponsored work was for the Air Force Materials Laboratory and Air Force Office of Scientific Research (AFOSR). This included basic studies of the workability of difficult-to-process aerospace alloys, the fundamentals of material behavior during deformation processing, and various National Aerospace Plane (NASP) - related programs. Both the government as well as industrial programs involved a major component of technology transfer and thus working with a wide range of manufacturing companies.
In June 1991, Dr. Semiatin joined the Materials and Manufacturing Directorate as Senior Scientist for Materials Processing/Processing Science. Under his direction, R&D has been conducted in four major areas: advanced metallic, intermetallic, and nanocrystalline alloys; conventional titanium, nickel, and aluminum alloys; novel processes; and advanced modeling tools for the prediction of microstructure, texture, and damage evolution during deformation and solidification processing. The integration of various modeling, characterization, and input-data tools that underlie ICMSE form a key part of current research. These efforts have led to the development of various new forging, extrusion, and rapid heat treatment processes - some of which are utilized on a production basis. In addition, he consults regularly with a number of manufacturing vendors on material-processing problems which impact Air Force systems.
Dr. Semiatin has authored/co-authored over 400 journal papers in the area of materials processing. He has also written/edited 18 books/handbooks/conference proceedings, 27 limited distribution reports, and holds 9 patents.