Mechanical and Civil Engineering Seminar

Mechanical and Civil Engineering Seminar Series

Title: Poroelastic Spherical Indentation for Material Characterization

Abstract: Spherical indentation has been commonly used as a material characterization technique to measure mechanical material properties such as hardness and toughness. Recently, spherical indentation has also been applied to characterize poroelasticity for soft materials such as hydrogel and hydrated bones in the literature. In theory, for a fully saturated porous medium with incompressible constituents, if the indenter is subjected to step loading, elastic constants can be determined from the undrained and drained limits according to the Hertzian contact solution, while hydraulic diffusivity or the coefficient of consolidation can be obtained from the transient response by matching the measured indentation force or displacement as a function of time against a master curve.

Conventional approaches of poroelasticity characterization for low permeability geomaterials in the laboratory are rather challenging and time consuming. Having an alternative such as spherical indentation could therefore be beneficial. To that end, we conduct extensive theoretical and numerical analyses to investigate the feasibility of such a concept. We will first present fully coupled poroelastic solutions derived for frictionless contact between a rigid sphere and a linear poroelastic half space with three distinct types of surface drainage conditions for both step-displacement and step-force loading as well as the master curves constructed for general porous media with compressible constituents. We show that these master curves depend on material properties through a single derived parameter only and this dependence is relatively weak for step-displacement loading. We will then discuss the effect of plastic yielding based on finite element analyses, which suggest that if the material strength is such that there is no plastic strain accumulation during the transient phase, the normalized force relaxation or transient displacement can still be approximated as poroelastic. Finally, implications from our analyses for applying poroelastic spherical indentation as an experimental methodology and its advantages will be discussed.

Bio: Dr. Haiying Huang is an Associate Professor in the Geosystems group in the School of Civil and Environmental Engineering in Georgia Institute of Technology. She obtained her B.S. from Tongji University and Ph.D. in Geological Engineering from the University of Minnesota. She then worked as a senior engineer in Schlumberger in Sugar Land, Texas, before joining the faculty in Georgia Tech. Her research is in the area of rock mechanics and geomechanics with a particular focus on earth resources engineering. Her latest work has been on development of contact models for discrete element method (DEM) to realistically model failure behaviors of quasi-brittle materials and on poroelastic spherical indentation for material characterization.

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