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

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    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, = (∂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 + = 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 on the flow localization process. To assess the effect of impurities, a Haasen plot ( 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.


    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

    Author Information:

    Christodoulou, N
    McGill University, Montreal, Quebec

    Jonas, JJ
    McGill University, Montreal, Quebec

    Canova, GR
    McGill University, Montreal, Quebec

    Committee/Subcommittee: E28.06

    DOI: 10.1520/STP28880S