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

    Published: Jan 1982


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    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, = (∂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.

    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


    Author Information:

    Christodoulou, N
    McGill University, Montreal, Quebec

    Jonas, JJ
    McGill University, Montreal, Quebec

    Canova, GR
    McGill University, Montreal, Quebec


    Paper ID: STP28880S

    Committee/Subcommittee: E28.06

    DOI: 10.1520/STP28880S


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