Loss of Stress Equivalence in the Strain-Rate Sensitivity of Flow Stress in Fine-Grain Polycrystalline Copper

✍ Scribed by Butt, M. Z. ;Ashraf, M.

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 159 KB
• Volume: 173
• Category: Article
• ISSN: 0031-8965
• DOI: 10.1002/(sici)1521-396x(199906)173:2<349::aid-pssa349>3.0.co;2-6

✦ Synopsis

The strain-rate sensitivity of flow stress (3X7 Â 10 À3 s À1 3X7 Â 10 À4 s À1 ) in fine-grain polycrystalline copper has been studied over the entire stress±strain curve at room temperature. It is observed that the yield stress varies with mean grain diameter (32 to 59 mm) in accord with the Hall-Petch relation, whereas ultimate tensile stress and fracture stress are independent of the grain size. The strain-rate sensitivity Ds of a given flow stress s depends on the grain size; it increases as grain size is increased from 32 to 59 mm. For a given grain size, the Cottrell-Stokes ratio Dsas and the product of flow stress s and associated activation volume V s remain constant in the entire stress range 50 to 210 MPa studied. Values of both Dsas and V s s depend on the grain size. The observations have been accounted for within the framework of Feltham's single barrier model of plastic flow.