Plastic Work to Heat Conversion During High-Strain Rate Deformation of Mg and Mg Alloy
- PDF / 3,045,262 Bytes
- 6 Pages / 593.972 x 792 pts Page_size
- 34 Downloads / 207 Views
e to low density and high specific strength, magnesium (Mg) and its alloys have received significant attention for structural applications including where materials are subjected to dynamic loading conditions.[1–10] During plastic deformation, a fraction of the plastic work is stored in the material, whereas the rest is converted to heat.[11–16] Determination of the fraction of the plastic work to heat conversion—the so-called Taylor–Quinney or b factor[12]—is crucial because of its important role in predicting the occurrence of thermoplastic instabilities of materials during plastic deformation.[14,15,17,18] Under quasi-static loading conditions, plastic work to heat conversion may not cause any significant temperature rise in the deforming material because heat generated can dissipate at a rate faster than the rate of deformation (i.e., isothermal conditions prevail). In contrast, plastic deformation in
DIPANKAR GHOSH, Assistant Professor, is with the Department of Mechanical and Aerospace Engineering, Old Dominion University, Norfolk, VA 23529. Contact e-mail: [email protected] OWEN T. KINGSTEDT, Postdoctoral Scholar, and GURUSWAMI RAVICHANDRAN, Professor, are with the Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125. Dipankar Ghosh was a postdoctoral scholar at California Institute of Technology during this work. Manuscript submitted August 25, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
the high-strain rate (dynamic, e_ 103 s1) loading regime can be treated as essentially an adiabatic process, and thus the plastic work to heat conversion can result in a significant temperature rise within a deforming material.[14–20] Seminal work by Farren and Taylor[11] and Taylor and Quinney[12] showed that the b factor could be conveniently assumed to be constant, b = 0.9 during deformation. However, several experimental studies revealed that b is not a constant, and changes with the plastic strain and/or strain rate.[14–16,21–24] Also, it is of note that the value of b = 0.9 or higher is typically reached only at very large plastic strains (>0.5) in previous experimental studies. With the plastic strain to failure of the Mg being quite low, typically in the order of e ~0.2,[8,9] it is expected that the b factor could be considerably smaller than 0.9. However, there are no such studies that have investigated the b factor of Mg under the dynamic loading conditions. Mg alloys such as AZ31B (3 pct Zinc, 1 pct Aluminum, and other trace elements) processed using equal channel angular extrusion (ECAE) are known to exhibit an increase of both the yield strength and ductility in comparison to pure Mg, which is attributed to the grain size refinement.[8] Therefore, it is also of interest to understand the effects of the alloying and grain size refinement on the high-rate thermomechanical coupling in the Mg-based materials. In the current work, Mg and AZ31B samples were received in the form of rectangular billets, previously subjected to ECAE using a 4Bc processing route, where a bille
Data Loading...
