IU Indianapolis ScholarWorks :: Browsing by Author "Yang, Shengfeng"

Browsing by Author "Yang, Shengfeng"

Now showing 1 - 10 of 10

Analysis of a discrete-layout bimorph disk elements piezoelectric deformable mirror
(SPIE, 2018-04) Wang, Hairen; Chen, Ziguang; Yang, Shengfeng; Hu, Lin; Hu, Ming; Mechanical and Energy Engineering, School of Engineering and Technology
We introduce a discrete-layout bimorph disk elements piezoelectric deformable mirror (DBDEPDM), driven by the circular flexural-mode piezoelectric actuators. We formulated an electromechanical model for analyzing the performance of the new deformable mirror. As a numerical example, a 21-actuators DBDEPDM with an aperture of 165 mm was modeled. The presented results demonstrate that the DBDEPDM has a stroke larger than 10 μm and the resonance frequency is 4.456 kHz. Compared with the conventional piezoelectric deformable mirrors, the DBDEPDM has a larger stroke, higher resonance frequency, and provides higher spatial resolution due to the circular shape of its actuators. Moreover, numerical simulations of influence functions on the model are provided.
Applying Machine Learning to Optimize Sintered Powder Microstructures from Phase Field Modeling
(2020-12) Batabyal, Arunabha; Zhang, Jing; Yang, Shengfeng; Du, Xiaoping
Sintering is a primary particulate manufacturing technology to provide densification and strength for ceramics and many metals. A persistent problem in this manufacturing technology has been to maintain the quality of the manufactured parts. This can be attributed to the various sources of uncertainty present during the manufacturing process. In this work, a two-particle phase-field model has been analyzed which simulates microstructure evolution during the solid-state sintering process. The sources of uncertainty have been considered as the two input parameters surface diffusivity and inter-particle distance. The response quantity of interest (QOI) has been selected as the size of the neck region that develops between the two particles. Two different cases with equal and unequal sized particles were studied. It was observed that the neck size increased with increasing surface diffusivity and decreased with increasing inter-particle distance irrespective of particle size. Sensitivity analysis found that the inter-particle distance has more influence on variation in neck size than that of surface diffusivity. The machine-learning algorithm Gaussian Process Regression was used to create the surrogate model of the QOI. Bayesian Optimization method was used to find optimal values of the input parameters. For equal-sized particles, optimization using Probability of Improvement provided optimal values of surface diffusivity and inter-particle distance as 23.8268 and 40.0001, respectively. The Expected Improvement as an acquisition function gave optimal values 23.9874 and 40.7428, respectively. For unequal sized particles, optimal design values from Probability of Improvement were 23.9700 and 33.3005 for surface diffusivity and inter-particle distance, respectively, while those from Expected Improvement were 23.9893 and 33.9627. The optimization results from the two different acquisition functions seemed to be in good agreement with each other. The results also validated the fact that surface diffusivity should be higher and inter-particle distance should be lower for achieving larger neck size and better mechanical properties of the material.
Atomistic Study of the Effect of Magnesium Dopants on Nancrystalline Aluminium
(2019-08) Kazemi, Amirreza; Yang, Shengfeng; Zhang, Jing; Zhu, Likun
Atomistic simulations are used in this project to study the deformation mechanism of polycrystalline and bicrystal of pure Al and Al-Mg alloys. Voronoi Tessellation was used to create three-dimensional polycrystalline models. Monte Carlo and Molecular Dynamics simulations were used to achieve both mechanical and chemical equilibrium in all models. The first part of the results showed improved strength, which is included the yield strength and ultimate strength in the applied tensile loading through the addition of 5 at% Mg to nanocrystalline aluminum. By viewing atomic structures, it clearly shows the multiple strengthening mechanisms related to doping in Al-Mg alloys. The strength mechanism of dopants exhibits as dopant pinning grain boundary (GB) migration at the early deformation stage. At the late stage where it is close to the failure of nanocrystalline materials, Mg dopants can stop the initiation of intergranular cracks and also do not let propagation of existing cracks along the GBs. Therefore, the flow stress will improve in Al-Mg alloy compared to pure Al. In the second part of our results, in different bicrystal Al model, ∑ 3 model has higher strength than other models. This result indicates that GB structure can affect the strength of the material. When the Mg dopants were added to the Al material, the strength of ∑5 bicrystal models was improved in the applied shear loading. However, it did not happen for ∑ 3 model, which shows Mg dopants cannot affect the behavior of this GB significantly. Analysis of GB movements shows that Mg dopants stopped GBs from moving in the ∑ 5 models. However, in the ∑ 3 GB, displacement of grain boundary planes was not affected by Mg dopants. Therefore, the strength and flow stress are improved by Mg dopants in ∑ 5 Al GBs, not in the ∑ 3 GBs.
Atomistic Study of the Effect of Magnesium Dopants on the Strength of Nanocrystalline Aluminum
(Springer, 2019-02) Kazemi, Amirreza; Yang, Shengfeng; Mechanical Engineering and Energy, School of Engineering and Technology
Atomistic simulations have been used to study the deformation mechanisms of nanocrystalline pure Al and Al-Mg binary alloys. Voronoi tessellation was used to fully create a three-dimensional polycrystalline model with a grain size of 10 nm, while hybrid Monte Carlo and molecular dynamic simulations were used to achieve both mechanical and chemical equilibriums in nanocrystalline Al-5 at.%Mg. The results of tensile tests show an improved strength, including the yield strength and ultimate strength, through doping 5 at.%Mg into nanocrystalline aluminum. The results of atomic structures clearly reveal the multiple strengthening mechanisms related to doping in Al-Mg alloys. At the early deformation stage, up to an applied strain of 0.2, the strengthening mechanism of the dopants exhibits as dopant pinning grain boundary (GB) migration. However, at the late deformation stage, which is close to failure of nanocrystalline materials, dopants can prohibit the initiation of intergranular cracks and also impede propagation of existing cracks along the GBs, thus improving the flow stress of Al-Mg alloys.
First-Order Interfacial Transformations with a Critical Point: Breaking the Symmetry at a Symmetric Tilt Grain Boundary
(APS, 2018-02) Yang, Shengfeng; Zhou, Naixie; Zheng, Hui; Ong, Shyue Ping; Luo, Jian; Mechanical Engineering, School of Engineering and Technology
First-order interfacial phaselike transformations that break the mirror symmetry of the symmetric ∑5(210) tilt grain boundary (GB) are discovered by combining a modified genetic algorithm with hybrid Monte Carlo and molecular dynamics simulations. Density functional theory calculations confirm this prediction. This first-order coupled structural and adsorption transformation, which produces two variants of asymmetric bilayers, vanishes at an interfacial critical point. A GB complexion (phase) diagram is constructed via semigrand canonical ensemble atomistic simulations for the first time.
High Performance Thermal Barrier Coatings on Additively Manufactured Nickel Base Superalloy Substrates
(2023-08) Dube, Tejesh Charles; Zhang, Jing; Jones, Alan S.; Koo, Dan Daehyun; Yang, Shengfeng
Thermal barrier coatings (TBCs) made of low-thermal-conductivity ceramic topcoat, metallic bond coat and metallic substrate, have been extensively used in gas turbine engines for thermal protection. Recently, additive manufacturing (AM) or 3D printing techniques have emerged as promising manufacturing techniques to fabricate engine components. The motivation of the thesis is that currently, application of TBCs on AM’ed metallic substrate is still in its infancy, which hinders the realization of its full potential. The goal of this thesis is to understand the processing-structure-property relationship in thermal barrier coating deposited on AM’ed superalloys. The APS method is used to deposit 7YSZ as the topcoat and NiCrAlY as the bond coat on TruForm 718 substrates fabricated using the direct metal laser sintering (DMLS) method. For comparison, another TBC system with the same topcoat and bond coat is deposited using APS on wrought 718 substrates. For thermomechanical property characterizations, thermal cycling, thermal shock (TS) and jet engine thermal shock (JETS) tests are performed for both TBC systems to evaluate thermal durability. Microhardness and elastic modulus at each layer and respective interfaces are also evaluated for both systems. Additionally, the microstructure and elemental composition are thoroughly studied to understand the cause for better performance of one system over the other. Both TBC systems showed similar performance during the thermal cycling and JETS test but TBC systems with AM substrates showed enhanced thermal durability especially in the case of the more aggressive thermal shock test. The TBC sample with AM substrate failed after 105 thermal shock cycles whereas the one with wrought substrate endured a maximum of 85 cycles after which it suffered topcoat delamination. The AM substrates also demonstrated an overall higher microhardness and elastic modulus except for post thermal cycling condition where it slightly underperformed. This study successfully demonstrated the use of AM built substrates for an improved TBC system and validated the enhanced thermal durability and mechanical properties of such a system. A modified YSZ TBC architecture with an intermediate Ti3C2 MXene layer is proposed to improve the interfacial adhesion at the topcoat/bond coat interface to improve the thermal durability of YSZ TBC systems. First principles calculations are conducted to study the interfacial adhesion energy in the modified and conventional YSZ TBC systems. The results show enhanced adhesion at the bond coat/MXene interface. At the topcoat/MXene interface, the adhesion energy is similar to the adhesion energy between the topcoat and bond coat in a conventional YSZ TBC system. An alternative route is proposed for the fabrication of YSZ TBC on nickel base superalloy substrates by using the SPS technology. SPS offers a one-step fabrication process with faster production time and reduced production cost since all the layers of the TBC system are fabricated simultaneously. Two different TBC systems are processed using the same heating protocol. The first system is a conventional TBC system with 8YSZ topcoat, NiCoCrAlY bond coat and nickel base superalloy substrate. The second system is similar to the first but with an addition of Ti3C2 MXene layer between the topcoat and the bond coat. Based on the first principles study, addition of Ti3C2 layer enhances the adhesion strength of the topcoat/bond coat interface, an area which is highly susceptible to spallation. Further tests such as thermal cycling and thermal shock along with the evaluation of mechanical properties would be carried out for these samples in future studies to support our hypothesis.
Phase-field-lattice Boltzmann method for dendritic growth with melt flow and thermosolutal convection–diffusion
(Elsevier, 2021-11) Wang, Nanqiao; Korba, David; Liu, Zixiang; Prabhu, Raj; Priddy, Matthew; Yang, Shengfeng; Chen, Lei; Li, Like; Mechanical and Energy Engineering, School of Engineering and Technology
We propose a new phase-field model formulated within the system of lattice Boltzmann (LB) equation for simulating solidification and dendritic growth with fully coupled melt flow and thermosolutal convection–diffusion. With the evolution of the phase field and the transport phenomena all modeled and integrated within the same LB framework, this method preserves and combines the intrinsic advantages of the phase-field method (PFM) and the lattice Boltzmann method (LBM). Particularly, the present PFM/LBM model has several improved features compared to the existing phase-field models including: (1) a novel multiple-relaxation-time (MRT) LB scheme for the phase-field evolution is proposed to effectively model solidification coupled with melt flow and thermosolutal convection–diffusion with improved numerical stability and accuracy, (2) convenient diffuse interface treatments are implemented for the melt flow and thermosolutal transport which can be applied to the entire domain without tracking the interface, and (3) the evolution of the phase field, flow, concentration, and temperature fields on the level of microscopic distribution functions in the LB schemes is decoupled with a multiple-time-scaling strategy (despite their full physical coupling), thus solidification at high Lewis numbers (ratios of the liquid thermal to solutal diffusivities) can be conveniently modeled. The applicability and accuracy of the present PFM/LBM model are verified with four numerical tests including isothermal, iso-solutal and thermosolutal convection–diffusion problems, where excellent agreement in terms of phase-field and thermosolutal distributions and dendritic tip growth velocity and radius with those reported in the literature is demonstrated. The proposed PFM/LBM model can be an attractive and powerful tool for large-scale dendritic growth simulations given the high scalability of the LBM.
Role of disordered bipolar complexions on the sulfur embrittlement of nickel general grain boundaries
(Nature Research, 2018-07-17) Hu, Tao; Yang, Shengfeng; Zhou, Naixie; Zhang, Yuanyao; Luo, Jian; Department of Mechanical and Energy Engineering, School of Engineering and Technology
Minor impurities can cause catastrophic fracture of normally ductile metals. Here, a classic example is represented by the sulfur embrittlement of nickel, whose atomic-level mechanism has puzzled researchers for nearly a century. In this study, coupled aberration-corrected electron microscopy and semi-grand-canonical-ensemble atomistic simulation reveal, unexpectedly, the universal formation of amorphous-like and bilayer-like facets at the same general grain boundaries. Challenging the traditional view, the orientation of the lower-Miller-index grain surface, instead of the misorientation, dictates the interfacial structure. We also find partial bipolar structural orders in both amorphous-like and bilayer-like complexions (a.k.a. thermodynamically two-dimensional interfacial phases), which cause brittle intergranular fracture. Such bipolar, yet largely disordered, complexions can exist in and affect the properties of various other materials. Beyond the embrittlement mechanism, this study provides deeper insight to better understand abnormal grain growth in sulfur-doped Ni, and generally enriches our fundamental understanding of performance-limiting and more disordered interfaces.
Simulation of Mechanical, Thermodynamic, and Magnetic Properties of Magnesia with Substitutional Elements for Improved Magnetic Core Coating Applications
(2019-12) Tiamiyu, Asimiyu A.; Zhang, Jing; Wei, Xiaoliang; Yang, Shengfeng
In transformers used in the electrical industry, a coating, such as magnesium oxide or magnesia (MgO), is needed to coat the magnetic ferrite core, such as silicon steel. The coating is to provide electrical insulation of the layers of the ferrite core material, in order to reduce its heat dissipation loss. The coating also separate the layers of the coiled materials to prevent their sticking or welding during high temperature uses. The goal of this thesis is to perform a modeling study to understand the mechanical, thermodynamic, magnetic and thermal properties of pure and M-doped (M stands for Mn, Co, or Ni) magnesia, thus providing a theoretical understanding of the application of this group of coating materials for transformer applications. The study has the following sections. The first section is focused on the mechanical properties of pure magnesia. Using density functional theory (DFT) based calculations, the computed Young’s modulus, Poisson’s ratio, bulk modulus, and compressibility are 228.80 GPa, 0.2397, 146.52 GPa, and 0.00682, respectively, which are in good agreement with the literature data. Using molecular dynamics (MD) simulations, the computed Young’s modulus is 229 GPa. Using discrete element model (DEM) approach, the bending deformation of magnesia is simulated. Finally, using finite element model (FEM), micro-hardness indentation of magnesia is simulated, and the computed Brinell hardness is 16.1 HB, and Vickers hardness is 16 GPa. The second section is on the thermodynamic and physical properties of pure and doped magnesia. Using DFT based simulations, the temperature-dependent thermodynamic properties, such as free energy, enthalpy, entropy, heat capacity at constant volume, and Debye temperature of magnesia, are computed. The X-ray powder diffraction (XRD) spectra of M-doped magnesia are simulated, at the doping level of 1.5%, 3%, 6% and 12%, respectively. The simulated XRD data show that peaks shift to higher angles as the doping level increases. The third section is on the magnetic properties of pure and doped magnesia. Using DFT based simulations, the calculated magnetic moments increase with the doping level, with Mn as the highest, followed by Co and Ni. This is due to the fact that Mn has more unpaired electrons than Co and Ni. The fourth section is on the thermal properties of the pure magnesia. Using the Reverse Non-Equilibrium Molecular Dynamics (RNEMD) method, the computed thermal conductivity of magnesia is 34.63 W/m/K, which is in agreement with the literature data of 33.0 W/m/K at 400 K.
Thickness Prediction of Deposited Thermal Barrier Coatings using Ray Tracing and Heat Transfer Methods
(2020-12) Dhulipalla, Anvesh; Zhang, Jing; Yang, Shengfeng; Agarwal, Mangilal
Thermal barrier coatings (TBCs) have been extensively employed as thermal protection in hot sections of gas turbines in aerospace and power generation applications. However, the fabrication of TBCs still needs to improve for better coating quality, such as achieving coating thickness' uniformity. However, several previous studies on the coating thickness prediction and a systematic understanding of the thickness evolution during the deposition process are still missing. This study aims to develop high-fidelity computational models to predict the coating thickness on complex-shaped components. In this work, two types of models, i.e., ray-tracing based and heat transfer based, are developed. For the ray-tracing model, assuming a line-of-sight coating process and considering the shadow effect, validation studies of coating thickness predictions on different shapes, including plate, disc, cylinder, and three-pin components. For the heat transfer model, a heat source following the Gaussian distribution is applied. It has the analogy of the governing equations of the ray-tracing method, thus generating a temperature distribution similar to the ray intensity distribution in the ray-tracing method, with the advantages of high computational efficiency. Then, using a calibrated conversion process, the ray intensity or the temperature profile are converted to the corresponding coating thickness. After validation studies, both models are applied to simulate the coating thickness in a rotary turbine blade. The results show that the simulated validation cases are in good agreement with either the experimental, analytical, or modeling results in the literature. The turbine blade case shows the coating thickness distributions based on rotating speed and deposition time. In summary, the models can simulate the coating thickness in rotary complex-shaped parts, which can be used to design and optimize the coating deposition process.

Browsing by Author "Yang, Shengfeng"

Results Per Page

Sort Options