Volume 28, Issue 4 (July 2005)
Development of a New Hollow Cylinder Apparatus for Stress Path Measurements over a Wide Strain Range
The development and operation of a new, automated hollow cylinder apparatus that facilitates accurate stress path measurements from the pseudo elastic domain to failure strain levels are described. Innovative sample loading mechanisms of 19.3 kN axial and 103 N · m torsional capacities facilitate rapid, precise (of the order of 10−5 % strain) displacement and rotation of the sample loading piston, with negligible compliance in the mechanisms on reversing the direction of piston motion. Both internal and external instrumentation are used to record the deformational response of the test specimen to better than 10−2 % strain. Significant differences were found between the strain values measured using the internal and external instrumentation, with the external instrumentation underestimating the true stiffness of the specimen. A series of drained stress-path tests on Leighton Buzzard sand specimens showed that predefined stress paths can be followed to an accuracy of 0.5 kPa using the new apparatus.