Although some materials, like structural steel and titanium, appear homogenous to the naked eye, observing them under a microscope reveals thousands and thousands of grains which have their atomic crystal lattice arranged in various directions. Other materials (such carbon-fiber composites, concrete, and human bones) display their heterogeneity even to our eyes. With recent advanced manufacturing techniques, it is increasingly feasible to control these directions and phases in materials across multiple length scales, such that stronger, lighter, and more optimized properties can be achieve. Computational process models are needed to guide this expansive design space rather than heuristics. Additionally, multiscale material models that link mechanical behavior at the micro and macro scales empower the design of structural systems and components using that material in complex loading conditions and long time horizons that can’t be tested in the laboratory. These applications of interest to our group span the range of process-structure-property-performance relationships that are a hallmark of materials science research. Thus, our computational modeling group collaborates actively with experimental colleagues to address challenging problems in materials with scales, directionality, and phases to certify existing materials for longer operation and to design next-generation materials with enhanced performance.
To be updated soon.
Rock salt, a sedimentary rock classified as an evaporate, forms as a result of evaporation of inland seas or any enclosed bodies of water and can be found in nature as bedded or domal formations. Salt domes often trap oil, gas, and other minerals around their edges. Drilling through rock salt to reach oil reservoirs poses many challenges, including long-term wellbore stability/integrity, casing collapse due to lateral pressure, and drilling fluid-salt interaction. The accuracy with which the fracture behavior of any material can be simulated, including geological materials like rock, hinges upon the fidelity of both the engineering model and the geometrical representation of the cracked body. A key limitation of existing phenomenological creep models is that rock salt’s anisotropic response is not represented at the microstructural level. Presently, there is an apparent lack of crystal-orientation-sensitive models in the literature for creep and fracture in 3D rock specimens coupled with direct measurements of 3D crystal structure. Thus, this unprecedented research aims to combine nondestructive 3D x-ray diffraction (3DXRD), 3D synchrotron micro-computed tomography (SMT) in-situ experimental measurements, and 3D crystal-plasticity modeling to enhance current understanding of creep and crack formation and growth mechanisms in polycrystalline rock.
Sponsorship: National Science Foundation
Creep rupture strength is one of the high temperature material properties that are employed in establishing the allowable stresses for materials employed in pressure vessels and piping of power plant reactors. Gaining mechanistic understanding of long term deformation and degradation mechanisms such as creep, grain boundary cavitation, and thermal aging will provide guidance for model-based extrapolation of accelerated creep-fatigue experimental data. Therefore, microstructural finite element models are being pursued that combine grain boundary mechanics with dislocation density-based crystal plasticity models.
Sponsorship: Argonne National Laboratory
The titanium alloy Ti-6242 (Ti-6Al-2Sn-4Zr-2Mo) has been the structural material of choice for use in high-pressure compressors for gas turbine engines of aircraft due to its high strength-to-weight ratio and excellent high temperature mechanical properties. However, Ti-6242 is susceptible to dwell fatigue at low temperature due to crack growth on low-angle boundaries along the primary α grains, in particular small faceted cracks that link up to form a “quasi-cleavage” surface. These low-angle boundaries occur within so-called microtextured regions (MTR) that consist of many neighboring primary α grains with similarly oriented c-axes of the hexagonal close-packed atomic lattice. In-flight failures of turbine blades made from these and other titanium alloys have led to investigation of the prevalence of MTR in forged parts. In this work, the crystal plasticity finite element method in WARP3D is used to model the processing of MTR within Ti-6242. These and ongoing computational studies provide a complement to experimental data from AFRL and mill processors that demonstrate a load direction dependence on the texture evolution of this material.
Sponsorship: Air Force Research Laboratory