An Extreme Pressure Triaxial Compression Apparatus for In-Situ Studies of Geomaterial Deformation Mechanisms
Abstract
The mechanical behavior of soils, sands, and sandstones in extreme pressure environments is critical to impact and penetration events of interest to the U.S. Army, as well as to natural hazards such as earthquakes, planetary impacts, and landslides. Hydrostatic pressures in natural hazard and Army-relevant events may reach several hundred MPa and deviatoric stresses may exceed 1 GPa. Microscale and mesoscale mechanisms contributing to macroscopic deformation in these events include grain breakage and pulverization, pore collapse, and the development of shear, dilatational, and compaction bands (collectively called deformation bands). Mechanism-based constitutive models incorporating these processes have increasingly been developed and used in the past decade, providing a reliable bridge between microscale material processes and macroscale response. However, despite rich in-situ acoustic emissions and postmortem x-ray tomography measurements in rocks subjected to confining pressures up to 400 MPa, and in-situ x-ray tomography in soils subjected to confining pressures up to 7 MPa, in-situ x-ray measurements of structure and stress in these materials in Army-relevant conditions are lacking. This measurement deficiency hinders development of predictive models and is due to challenges in miniaturizing testing instruments for x-ray environments. We propose to build a novel triaxial compression apparatus that enables in-situ laboratory and synchrotron x-ray tomography and diffraction and acoustic emissions measurements in triaxiallycompressed, variably-saturated soils, sands, and rocks with sample sizes ranging from a few millimeters to a few centimeters, sample confining pressures up to 150 MPa, and sample deviatoric stresses exceeding 1 GPa. This apparatus will enable real-time particle-resolved monitoring of grain crushing and size evolution, pore collapse, grain stress heterogeneity, and deformation band emergence and progression along various high-pressure stress paths. The apparatus will be used for a broad range of DoD-, Army-, DoE-, and NSF-relevant studies, including: (1) an investigation of the breakage, pore collapse, and deformation banding mechanisms active in variably-saturated sand at high pressures relevant to geologic flows or projectile impact; (2) studies of the brittle-toductile transition in sandstones and limestones, relevant to conditions during projectile impact of rock-buried targets and to the mechanical behavior of subsurface petroleum and hydrocarbon reservoirs; (3) calibration and validation of a mechanism-based constitutive model (based on continuum breakage mechanics) currently being developed for predicting penetration of various geomaterials. The proposed device is inspired by, but a significant advance relative to, the PIÕs current custom-built triaxial device, which permits high-resolution in-situ x-ray tomography and diffraction of geomaterials at confining pressures up to 50 MPa. The proposed device will be custom-designed and built by the PI using commercial products (Cetoni pump, Enerpac Actuator, Futek load cell). The advances enabled by the device will support the ArmyÕs interest in understanding fundamental processes of geomaterials in varied conditions, the transmission of acoustic information through geomaterials, and the development of models to understand material behavior in extreme pressures, supporting the interests of AROÕs Earth Materials and Processes Program (W911NF-17-S-002-11; POC: Julia Barzyk) and the Solid Mechanics program.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 19, 2023
- Source ID
- W911NF2310068
Entities
People
- Ryan C. Hurley
Organizations
- Army Contracting Command
- Johns Hopkins University
- United States Army