Nano and neutron science applications for geomechanics

Abstract

Recent advances in experimental characterization techniques offer unique opportunities to evaluate mechanical properties of geomaterials. In this paper, authors introduce two such techniques that have significant potential to impact geomechanics community. The technique of using Instrumented indentation testing using nano-indenter to evaluate hardness and modulus of individual sand particles is introduced. Use of the measured data from nanoindenter on individual sand grain in modelling its assembly using numerical methods such as the discrete element method (for example PFC-2D) is addressed. Modulus for two silica sands with varying particle shape is presented for the depth of indentation in the range of 100 to 1000 nanometers. Use of neutron science for solving relevant problems to geotechnical engineering is also described in this paper. Neutrons are subatomic particles with no electric charge having duality and interacts with atomic nuclei, while X-ray interacts with electrons. Neutrons thus have significantly higher penetration power for most geo-materials when compared to X-rays and are sensitive to hydrogen. Use of neutrons for solving a new class of problems including non-destructive evaluation of strain at particle level while the assemblage is subjected to target stress conditions, and imaging applications including flow through partially saturated porous medium are presented.

3D Experimental Measurement of Lattice Strain and Fracture Behavior of Sand Particles Using Synchrotron X-Ray Diffraction and Tomography

“…Although they are powerful, the major shortcoming of these imaging techniques is their inability to measure interparticle forces and strain within particles. Neutron imaging and diffraction was employed to determine the lattice strain of silica sand and steel balls (Penumadu et al 2009;Wensrich et al 2014). This approach required averaging the lattice strain for an assembly of particles within a gauge volume or measuring elastic strain of each particle by employing a gauge volume corresponding to particle size.…”

Strain tensor determination of compressed individual silica sand particles using high-energy synchrotron diffraction

“…Most of the neutron diffraction images in the literature are blurred with a resolution an order of magnitude lower than CT images. For example, Penumadu et al [20] used neutron diffraction to measure lattice strains in the bulk of silica sand and found a significant difference between the global and lattice strainstress relationship. Frischbutter et al [21] used the same technique to measure lattice strain in geological samples and found a significant difference between lattice strain and strain measured by strain gauges.…”

Novel Techniques to Simulate and Monitor Contaminant–Geomaterial Interactions

“…Furthermore, the investigations conducted by Kadali et al [75] were instrumental in demonstrating the utility of X-ray diffraction analysis for establishing residual normal and shear stresses on the soil grains when they get exposed to the elevated temperatures [199,204,205,221]. These researchers were also successful in demonstrating the potential of nanoindentation, which is mostly employed by material scientists for characterization of metals, in identifying the changes undergone by the fine-and coarse-grained soils when they get exposed to elevated temperatures [27,132]. A typical load versus displacement response of a soil exposed to different temperatures is depicted in Fig.…”