Abstract
The flow and fracture of rocks occurs under triaxial compressive stresses, and attempts to simulate these conditions in the laboratory were first made over 50 years ago on rock materials, marble and sandstone. Since then there have been attempts to obtain more detailed information on the increased ductility found under triaxial compression compared with uniaxial compression. It has been realized further that triaxial compression is an important factor in forming difficult metals.
In compression tests conducted under pressure, specialized techniques are necessary to obtain accurate and significant measurements of the principal parameters, load, deformation and pressure. This paper reviews other work on the subject, notes the shortcomings of some of the investigations and describes the apparatus developed at the National Engineering Laboratory. The technique described has the advantages that tests can be carried out at constant pressure up to 60 tonf/in2, and axial compressive loads and strains are measured internally, rather than externally.
The materials investigated were cast iron, a magnesium-aluminium alloy, commercially pure magnesium and an aluminium bronze. Over the pressure range 0–50 tonf/in2 the ductility of the aluminium bronze did not change but the ductility of the magnesium was increased by 20 per cent, that of the magnesium alloy by 200 per cent and that of the cast iron by 400 per cent.
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