### STP765: Determination of First and Second Order Work-Hardening and Rate-Sensitivity Coefficients for Oxygen-Free, High-Conductivity (OFHC) Copper and 99.99 Percent Aluminum

Christodoulou, N

*McGill University, Montreal, Quebec*

Jonas, JJ

*McGill University, Montreal, Quebec*

Canova, GR

*McGill University, Montreal, Quebec*

Pages: 16 Published: Jan 1982

**Abstract**

In order to provide data for process modeling, work-hardening and rate-sensitivity coefficients of the first and second order were determined for oxygen-free, high-conductivity copper and 99.99 percent aluminum. For this purpose, tension tests were carried out at room temperature and with constant rates of deformation varying from 5 × 10^{−4} to 1 s^{−1}. In each test, a constant true strain rate was applied at the minimum cross-section of specially machined samples by means of a computer-interfaced, servo-controlled hydraulic testing machine. The work-hardening coefficient, *H* = (*∂* ln *σ/∂ε)˙ε*, the rate sensitivity of the work-hardening rate, *Bσ* = (*∂H/∂* ln *˙ε*)^{σ}, and the curvature term, *C* = −(*∂H/∂* ln *σ*)^{˙ε}, were determined from the flow curves of continuous tests. By performing strain rate changes at constant structure *τ* and measuring the immediate stress changes, the “instantaneous” rate sensitivity, *M* = (*∂* ln *σ/∂* ln *˙ε*)^{τ}, was also established. The dependence of the coefficients derived in this way on stress and strain rate is described. From the variation of *M* with *σ* and *˙ε*, the coefficients *P* = −(*∂M/∂* ln *˙ε*)^{σ} and *Q* = (*∂M/∂* ln *σ*)^{˙ε} were evaluated. It was determined that an additional strain of 0.2 had to be imposed on the sample to take it from the UTS condition (*H* = 1) to the condition *H* + *Bσ* = 1. The latter is associated with the onset of flow localization, and the additional strain of 0.2 is a measure of the retarding effect of *Bσ* on the flow localization process. To assess the effect of impurities, a Haasen plot (*Mσ* versus *σ*) was constructed, which indicated that the copper was solution hardened due to the presence of ≅200 ppm of Ag + Mg + S, while there was no effect of solutes in the aluminum.

**Keywords:**

state variables, plastic deformation, flow localization, instantaneous rate sensitivity, work hardening, dynamic recovery, solute hardening, OFHC copper, 99.99 percent aluminum, constant strain rate, computerized servo-controlled testing, strain rate change testing, stress and strain rate dependence of rate sensitivity and work hardening coefficient

**Paper ID:** STP28880S

**Committee/Subcommittee:** E28.06

**DOI:** 10.1520/STP28880S

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