The work-hardening of copper-silica: IV. The Bauschinger effect and plastic relaxation

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Abstract
Bauschinger data for dispersion-strengthened single crystals are given, and correlated with data on the dislocation microstructure and the softening effect which is prominent at room temperature in copper. The data are analysed in terms of theories presented in earlier papers, and the following conclusions have been reached: (i) the Bauschinger effect, suitably defined, can be quantitatively accounted for by the mean internal stress level in the copper matrix; (ii) the internal stress behaves as a function of strain and temperature in accord with the earlier theories, except that plastic relaxation requires a temperature-dependent initiation stress in alloys containing small particles; (iii) the softening process is the process of plastic relaxation, and is characterized by an activation energy of 0·9 eV and an activation volume of 1·5 b3; (iv) a new interpretation is given for the dislocation microstructures observed in the softened state; (v) the work-hardening in the unrelaxed state can be separated into two components, one related to energy storage and the other to heat production. Constitutive equations are given which are accurate to 10%.

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