Ran Ma

Ran Ma
University of Tennessee | UTK

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20
Publications
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238
Citations

Publications

Publications (20)
Article
Full-text available
We present a machine learning framework to train and validate neural networks to predict the anisotropic elastic response of a monoclinic organic molecular crystal known as Octogen (β-HMX) in the geometrical nonlinear regime. A filtered molecular dynamic (MD) simulations database is used to train neural networks with a Sobolev norm that uses the st...
Article
Full-text available
This paper introduces an explicit material point method designed specifically for simulating the micropolar continuum dynamics in the finite deformation and finite microrotation regime. The material point method enables us to simulate large deformation problems while circumventing the potential mesh distortion without remeshing. To eliminate rotati...
Preprint
Full-text available
We present a machine learning framework to train and validate neural networks to predict the anisotropic elastic response of the monoclinic organic molecular crystal $\beta$-HMX in the geometrical nonlinear regime. A filtered molecular dynamic (MD) simulations database is used to train the neural networks with a Sobolev norm that uses the stress me...
Article
Full-text available
Cyclotetramethylene-Tetranitramine (HMX) is a secondary explosive used in military and civilian applications. Its plastic deformation is of importance in the initiation of the decomposition reaction, but the details of plasticity are not yet fully understood. It has been recently shown that both the elastic constants and the critical resolved shear...
Preprint
Full-text available
We present a SE(3)-equivariant graph neural network (GNN) approach that directly predicting the formation factor and effective permeability from micro-CT images. FFT solvers are established to compute both the formation factor and effective permeability, while the topology and geometry of the pore space are represented by a persistence-based Morse...
Article
Full-text available
Phase field modeling of coupled crystal plasticity and deformation 1 twinning in polycrystals with monolithic and splitting solvers 2 Ran Ma · WaiChing Sun 3 4 Abstract For some polycrystalline materials such as austenitic stainless steel, magnesium, TATB, and HMX, 6 twinning is a crucial deformation mechanism when the dislocation slip alone is not...
Article
Full-text available
We present a machine learning approach that integrates geometric deep learning and Sobolev training to generate a family of finite strain anisotropic hyperelastic models that predict the homogenized responses of polycrystals previously unseen during the training. While hand-crafted hyperelasticity models often incorporate homogenized measures of mi...
Article
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We present a new thermal-mechanical-chemical-phase field model that captures the multi-physical coupling effects of precipitation creeping, crystal plasticity, anisotropic fracture, and crack healing in polycrystalline rock at various temperature and strain-rate regimes. This model is solved via a fast Fourier transfer solver with an operator-split...
Preprint
Full-text available
This paper is the first attempt to use geometric deep learning and Sobolev training to incorporate non-Euclidean microstructural data such that anisotropic hyperelastic material machine learning models can be trained in the finite deformation range. While traditional hyperelasticity models often incorporate homogenized measures of microstructural a...
Article
Full-text available
This paper presents the application of a fast Fourier transform (FFT) based method to solve two phase field models designed to simulate crack growth of strongly anisotropic materials in the brittle regime. By leveraging the ability of the FFT-based solver to generate solutions with higher-order and global continuities, we design two simple algorith...
Article
Fast Fourier Transform (FFT) based methods are becoming increasingly popular for modeling the texture evolution and local mechanical response of polycrystalline materials within the representative volume element (RVE). Originally, the FFT-based method was formulated through the Lippman–Schwinger (L–S) equation in terms of a homogeneous elastic refe...
Article
Full-text available
Ti-6242 is a near alpha titanium alloy, which has excellent high-temperature creep resistance and is widely used in jet engine compressors. This alloy is susceptible to creep fatigue failure under dwell loading below 473 K. The existence of microtextured regions (MTRs) contributes significantly to this fast crack propagation. Mechanical processing...
Article
Titanium alloy Ti-6242 (Ti-6Al-2Sn-4Zr-2Mo) is frequently used in the high-pressure compressor of aero engines. While exhibiting high strength at elevated temperatures, it is susceptible to dwell fatigue at temperatures below ~473 K due in part to the presence of microtextured regions (MTRs), also known as macrozones. This work investigates the rol...
Article
Fire exposure causes significant mechanical property degradation of metallic materials. This paper investigates the influence of fire exposure on mechanical response of AA5083 through in situ neutron diffraction tensile tests and crystal plasticity finite element simulations. The Mechanical Threshold Stress (MTS) model is utilized, with a focus on...
Article
In this paper, the degradation of mechanical properties of marine structural aluminum alloy AA5083 and onset of lattice plastic anisotropy subsequent to fire exposure is investigated. For virgin and fire-exposed samples, microstructural characterization is carried out for the first time and changes in lattice specific strain responses under step an...
Article
A technique named Impacting Trailed Welding (ITW) was proposed, aimed at refining the grain size of the HAZ in multi-pass welding. The key idea of ITW is to obtain a large deformation in the HAZ during one weld pass, and get it recrystallized during the next weld pass. Theoretical analysis suggests that the deformed HAZ can get completely recrystal...

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Projects

Projects (3)
Archived project
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.
Archived project
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. Post-mortem observations of specimens have revealed facet clusters along the fracture surface within the MTR. In this work, the crystal plasticity finite element method in WARP3D is used to model the processing of MTR within Ti-6242. Several configurations of MTR within representative microstructures have been simulated under single and multiple loading axes to determine the critical strain to break down the MTR and introduce more disorientation into the microstructure. 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.
Archived project
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.