@article {258,
	title = {The nanogranular origin of friction and cohesion in shale-A strength homogenization approach to interpretation of nanoindentation results},
	journal = {International Journal for Numerical and Analytical Methods in Geomechanics},
	volume = {35},
	year = {2011},
	month = {Dec-10-2011},
	pages = {1854 - 1876},
	abstract = {<p>An inverse micromechanics approach allows interpretation of nanoindentation results to deliver cohesive-frictional strength behavior of the porous clay binder phase in shale. A recently developed strength homogenization model, using the Linear Comparison Composite approach, considers porous clay as a granular material with a cohesive-frictional solid phase. This strength homogenization model is employed in a Limit Analysis Solver to study indentation hardness responses and develop scaling relationships for indentation hardness with clay packing density. Using an inverse approach for nanoindentation on a variety of shale materials gives estimates of packing density distributions within each shale and demonstrates that there exists shale-independent scaling relations of the cohesion and of the friction coefficient that vary with clay packing density. It is observed that the friction coefficient, which may be interpreted as a degree of pressure-sensitivity in strength, tends to zero as clay packing density increases to one. In contrast, cohesion reaches its highest value as clay packing density increases to one. The physical origins of these phenomena are discussed, and related to fractal packing of these nanogranular materials. Copyright \&copy; 2010 John Wiley \&amp; Sons, Ltd.</p>
},
	doi = {10.1002/nag.v35.1710.1002/nag.984},
	author = {Bobko, Christopher P. and Gathier, Benjamin and J. Alberto Ortega and Franz-Josef Ulm and Borges, Lavinia and Younane N. Abousleiman}
}
@proceedings {347,
	title = {STRENGTH HOMOGENIZATION FOR COHESIVE-FRICTIONAL COMPOSITES: A LINEAR COMPARISON COMPOSITE APPROACH},
	journal = {International Workshop on Multiscale and Multiphysics Processes in Geomechanics},
	volume = {Springer Series in Geomechanics and Geoengineering},
	year = {2011},
	month = {Jan-2011},
	pages = {57 - 60},
	publisher = {Springer Berlin Heidelberg},
	address = {JUN 23-25 2010 Stanford Univ, Stanford, CA},
	abstract = {<p>In this work, we address the homogenization of cohesive-frictional strength properties of composite materials through the application of the Linear Comparison Composite (LCC) theory. The LCC methodology is implemented in a multiscale strength model relevant to geomaterials with heterogeneities associated with pore spaces and rigid-like grains. The proposed micromechanics solutions offer quantitative assessments of the effects of grain-scale properties and microstructure on the overall strength of the composite material Keywordscohesive-frictional materials\&ndash;linear comparison composite</p>
},
	isbn = {978-3-642-19629-4},
	issn = {1866-8755},
	doi = {10.1007/978-3-642-19630-0_15},
	author = {J. Alberto Ortega and Gathier, Benjamin and Franz-Josef Ulm},
	editor = {Wu, Wei and Borja, Ronaldo I.}
}
