Many experimenters fail to appreciate the significance of test system alignment during a tensile test. Poor alignment can increase data scatter and significantly influence some of the test results. In this paper a comprehensive analytical study of the misalignment problem in the plastic strain range is presented and errors caused by misalignment estimated. The results show that the stress-strain curve is not significantly affected by misalignment. However, the strains at the outer most fibers of the specimen cross-section are stongly affected by misalignment. Therefore, the effect of misalignment is most important when properties sensitive to local strain concentrations are being investigated.

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The densification kinetics of magnesium aluminate spinel during vacuum hot-pressing were studied between 1175" and 1460°C and from 500 to 5100 psi. A phenomenological rate equation, which suggests a logarithmic relation between strain rate and porosity, excellently described the observed densification. Treating porosity as an independent variable was shown to be reasonable; it does not functionally restrict porosity as a modifier of the applied stress. The strain rate dependence on porosity decreased at a porosity of approximately 0.15. Below 1350°C the densification characteristics were similar to those reported for other oxide systems. At 1450°C an increase in the stress dependence of the densification rate and an interaction between stress and porosity suggested that plastic flow by dislocation motion was an operative mechanism during densification.