Triaxial extensometer for volumetric strain measurement in a hydro-compression loading test for foam materials

Abstract

A new strain gauge-based triaxial extensometer (radial extensometers x, y and axial extensometer z) is presented to improve the volumetric strain measurement in a hydro-compression loading test for foam materials. By the triaxial extensometer, triaxial deformations of the foam specimen can be measured directly, from which the volumetric strain is determined. Sensitivities of the triaxial extensometer are predicted using a finite-element model, and verified through experimental calibrations. The axial extensometer is validated by conducting a uniaxial compression test in aluminium foam and comparing deformation measured by the axial extensometer to that by the advanced optical 3D deformation analysis system ARAMIS; the result from the axial extensometer agrees well with that from ARAMIS. A new modus of two-wire measurement and transmission in a hydrostatic environment is developed to avoid the punching and lead sealing techniques on the pressure vessel for the hydro-compression test. The effect of hydrostatic pressure on the triaxial extensometer is determined through an experimental test. An application in an aluminium foam hydrostatic compression test shows that the triaxial extensometer is effective for volumetric strain measurement in a hydro-compression loading test for foam materials.

Development of a material testing machine with multi-dimensional loading capability

“…Therefore, the uniaxial material testing machine (MTM) is widely used to estimate the material mechanical properties (Hessling, 2008(Hessling, , 2009. However, in the practical application, the stress state of critical parts are rarely uniaxial (Feng et al, 2010), instead, most structural parts are loaded under complex multi-directional stress state, which results in a fact that their material mechanical properties obtained by uniaxial material tests are less comprehensive and accurate. For the purpose of evaluating the mechanical properties precisely under such complicated situation, an MTM that can apply multi-dimensional load on the materials is urgently required.…”

“…Research on multi-axial loading equipment has been recently reported, including biaxial tension and compression tests (Zhang and Zhang, 2013;Smoger et al, 2012;O'Connell et al, 2012, biaxial fatigue tests (Spinelli et al, 2013), triaxial tension and compression test (Feng et al, 2010;Lee et al, 2013;Soroush and Jannatiaghdam, 2012;Cil and Alshibli, 2014). Most of the mentioned biaxial and triaxial material tests are based on the composing of orthogonal uniaxial load cell actuated by hydraulic or electric motors.…”