IU Indianapolis ScholarWorks :: Browsing by Author "Sagar, Sugrim"

Browsing by Author "Sagar, Sugrim"

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Gaussian Process-Based Model to Optimize Additively Manufactured Powder Microstructures From Phase Field Modeling
(ASME, 2022-03) Batabyal, Arunabha; Sagar, Sugrim; Zhang, Jian; Dube, Tejesh; Yang, Xuehui; Zhang, Jing; Mechanical Engineering, School of Engineering and Technology
A persistent problem in the selective laser sintering process is to maintain the quality of additively manufactured parts, which can be attributed to the various sources of uncertainty. In this work, a two-particle phase-field microstructure model has been analyzed using a Gaussian process-based model. The sources of uncertainty as the two input parameters were surface diffusivity and interparticle distance. The response quantity of interest (QOI) was 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 interparticle distance irrespective of particle size. Sensitivity analysis found that the interparticle 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 interparticle distance as 23.8268 and 40.0001, respectively. The Expected Improvement as an acquisition function gave optimal values of 23.9874 and 40.7428, respectively. For unequal-sized particles, optimal design values from Probability of Improvement were 23.9700 and 33.3005, respectively, while those from Expected Improvement were 23.9893 and 33.962, respectively. The optimization results from the two different acquisition functions seemed to be in good agreement.
Modeling of machining process of EB-PVD ceramic coatings using discrete element method
(Elsevier, 2022-08) Zhang, Jian; Sagar, Sugrim; Dube, Tejsh; Yang, Xuehui; Choi, Hyunhee; Jung, Yeon-Gil; Koo, Dan Daehyun; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
In this work, a new discrete element model (DEM) for simulating the machining process of thermal barrier coatings is presented. The effects of cutting processing parameters, including cutting depth and cutting speed, on the cutting force and chip morphology are studied. In the model, a columnar grain microstructure mimicking the electron-beam physical vapor deposition (EB-PVD) coating is used. The results show that, as the cutting depth increases, the cutting chip morphology changes from fine powder form (ductile mode) to large chuck pieces (brittle mode). The transition depth or the critical cutting depth is determined based on the Griffith fracture criterion. The transition is also illustrated using the numbers of broken bonds and cutting energy changes in the DEM model. In the ductile mode, the number of broken bonds is increased gradually. In contrast, at larger cutting depths, the brittle mode causes a step-wise increase. Moreover, the maximum cutting force is found correlated to the cutting depth, which agrees well with an analytical solution based on fracture mechanics principles. The period in the cutting force is consistent with the diameter of the column grain. Finally, the cutting speed has little effect on the cutting force and chip morphology due to no strain rate sensitivity.
Molecular dynamics modeling of mechanical and tribological properties of additively manufactured AlCoCrFe high entropy alloy coating on aluminum substrate
(Elsevier, 2021-04-15) Yang, Xuehui; Zhang, Jian; Sagar, Sugrim; Dube, Tejesh; Kim, Bong-Gu; Jung, Yeon-Gil; Koo, Dan Daehyun; Jones, Alan; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
In this work, an improved molecular dynamics (MD) model is developed to simulate the nanoindentation and tribological tests of additively manufactured high entropy alloys (HEA) AlCoCrFe coated on an aluminum substrate. The model shows that in the interface region between the HEA coating and Al substrate, as the laser heating temperature increases during the HEA coating additive manufacturing process, more Al in the substrate is melted to react with other elements in the coating layer, which is qualitatively in agreement with experiment in literature. Using the simulated nanoindentation tests, the calculated Young's modulus of pure Al and Al with HEA coating is 79.93 GPa and 119.30 GPa, respectively. In both our simulations and the experimental results in the literature, the hardness of Al with the HEA coating layer is about 10 times higher than the Al hardness, indicating that HEA can significantly improve the hardness of the metallic substrate. Using the simulated tribological scratch tests, the computed wear tracks are qualitatively in agreement with experimental images in literature. Both our model and experiment show that the Al with HEA coating has a much smaller wear track than that of Al, due to less plastic deformation, confirmed by a dislocation analysis. The computed average coefficient of friction of Al is 0.62 and Al with HEA coating is 0.14. This work demonstrates that the HEA coating significantly improves the mechanical and tribology properties, which are in excellent agreement with the experiments reported in the literature.
A Multi-Scale Multi-Physics Modeling Framework of Laser Powder Bed Fusion Additive Manufacturing Process
(Elsevier, 2018-05) Zhang, Jing; Zhang, Yi; Lee, Weng Hoh; Wu, Linmin; Sagar, Sugrim; Meng, Lingbin; Choi, Hyun-Hee; Jung, Yeon-Gil; Mechanical Engineering, School of Engineering and Technology
A longstanding challenge is to optimize additive manufacturing (AM) process in order to reduce AM component failure due to excessive distortion and cracking. To address this challenge, a multi-scale physics-based modeling framework is presented to understand the interrelationship between AM processing parameters and resulting properties. In particular, a multi-scale approach, spanning from atomic, particle, to component levels, is employed. The simulations of sintered material show that sintered particles have lower mechanical strengths than the bulk metal because of their porous structures. Higher heating rate leads to a higher mechanical strength due to accelerated sintering rates. The average temperature in the powder bed increases with higher laser power. The predicted distortion due to residual stress in the AM fabricated component is in good agreement with experimental measurements. In summary, the model framework provides a design tool to optimize the metal powder based additive manufacturing process.
Numerical Simulation of Impact Behavior of Ceramic Coatings Using Smoothed Particle Hydrodynamics Method
(ASME, 2021-04) Zhang, Jian; Lu, Zhe; Sagar, Sugrim; Choi, Hyunhee; Jung, Yeon-Gil; Park, Heesung; Koo, Dan Daehyun; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
In this work, the impact behavior of an alumina spherical particle on alumina coating is modeled using the smoothed particle hydrodynamics (SPH) method. The effects of impact angle (0 deg, 30 deg, and 60 deg) and velocity (100 m/s, 200 m/s, and 300 m/s) on the morphology changes of the impact pit and impacting particle, and their associated stress and energy are investigated. The results show that the combination of impact angle of 0 deg and velocity of 300 m/s produces the highest penetration depth and largest stress and deformation in the coating layer, while the combination of 100 m/s and 60 deg causes the minimum damage to the coating layer. This is because the penetration depth is determined by the vertical velocity component difference between the impacting particle and the coating layer, but irrelevant to the horizontal component. The total energy of the coating layer increases with the time, while the internal energy increases with the time after some peak values, which is due to energy transmission from the spherical particle to the coating layer and the stress shock waves. The energy transmission from impacting particle to coating layer increases with the increasing particle velocity and decreases with the increasing inclined angle. The simulated impact pit morphology is qualitatively similar to the experimental observation. This work demonstrates that the SPH method is useful to analyze the impact behavior of ceramic coatings.
Simulation of Spatters Sticking Phenomenon in Laser Powder Bed Fusion Process Using the Smoothed Particle Hydrodynamics Method
(American Society of Mechanical Engineers, 2021-11) Meng, Lingbin; Sun, Tao; Dube, Tejesh; Sagar, Sugrim; Yang, Xuehui; Zhang, Jian; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
In this work, a smoothed particle hydrodynamics (SPH) method is developed to simulate the spattering phenomenon in the laser powder bed fusion (L-PBF) process. First, an experiment using the high-speed synchrotron X-ray full-field imaging is conducted to acquire in-situ images during the L-PBF process. Then, a scenario is selected from the X-ray image as a case study of the SPH model. In the case study, a particle is ejected and melted by the metal vapor, impacts with another particle, solidifies, and sticks to the other particle to form a rigid body. As a result, the trajectories of the two particles match well with the experimental observation. The evolution of velocity and temperature of the particle is extracted from the simulation for analysis. The SPH model can be a useful alternative to computational models of simulating the spattering phenomenon of L-PBF.
Smoothed Particle Hydrodynamics Modeling of Thermal Barrier Coating Removal Process Using Abrasive Water Jet Technique
(ASME, 2022-09) Zhang, Jian; Yang, Xuehui; Sagar, Sugrim; Dube, Tejesh; Koo, Dan Daehyun; Kim, Bong-Gu; Jung, Yeon-Gil; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
In this work, a new smoothed particle hydrodynamics (SPH)-based model is developed to simulate the removal process of thermal barrier coatings (TBCs) using the abrasive water jet (AWJ) technique. The effects of water jet abrasive particle concentration, incident angle, and impacting time on the fracture behavior of the TBCs are investigated. The Johnson–Holmquist plasticity damage model (JH-2 model) is used for the TBC material, and abrasive particles are included in the water jet model. The results show that the simulated impact hole profiles are in good agreement with the experimental observation in the literature. Both the width and depth of the impact pit holes increase with impacting time. The deepest points in the pit hole shift gradually to the right when a 30-deg water jet incident angle is used because the water jet comes from the right side, which is more effective in removing the coatings on the right side. A higher concentration of abrasive particles increases both the width and depth, which is consistent with the experimental data. The depths of the impact pit holes increase with the water jet incident angle, while the width of the impact holes decreases with the increase in the water jet incident angle. The water jet incident angle dependence can be attributed to the vertical velocity components. The erosion rate increases with the incidence angle, which shows a good agreement with the analytical model. As the water jet incident angle increases, more vertical velocity component contributes to the kinetic energy which is responsible for the erosion process.
Temperature-Dependent Charpy Impact Property of 3D Printed 15-5 PH Stainless Steel
(Taylor & Francis, 2021) Sagar, Sugrim; Zhang, Yi; Choi, Hyun-Hee; Jung, Yeon-Gil; Zhang, Jing; Mechanical and Energy Engineering, School of Engineering and Technology
In this study, the impact property of 3D printed 15-5 PH stainless steel was investigated at low (77 K), room (298 K), and high temperatures (723 K) using integrated experimental and modelling studies. The finite element model was based on the Johnson-Cook phenomenological material model and fracture parameters. The experimentally measured impact energies are 0.01, 6.78 ± 4.07, and 50.84 ± 3.39 J cm−2, at the low, room, and high temperatures, respectively. The experimental and modelling predicted impact energies are in good agreement. The microstructures show that the steel exhibits a brittle behaviour at low and room temperatures as indicated by a transgranular fracture, but changes to a more ductile behaviour at high temperatures as illustrated by microvoid coalescence induced facture morphology.
Temperature-dependent impact properties of 3D printed 15-5 stainless steel
(2018-05) Sagar, Sugrim; Zhang, Jing; Tovar, Andres; El-Mounayri, Hazim
Since the conception of three dimensional (3D) printing circa 40 years ago, there has been the proliferation of several additive manufacturing (AM) technologies that enable its use in everyday applications such as aerospace, medicine, military, oil and gas and infrastructure. In order to improve its applicability and growth, 3D printed materials are subjected to the same or even higher levels of scrutiny for its mechanical behavior as its conventionally manufactured counterpart. One of the most important mechanical properties is toughness or the ability of a material to undergo large strain prior to fracture when loaded. The toughness of a material can be correlated to its impact energy or the increase in internal energy due to impact. In this study, the impact properties, including the toughness of 3D printed 15-5 stainless steel were investigated at low temperature (77 K), room temperature (298 K) and high temperature (723 K) using experimental and numerical modeling of the Charpy impact test. In addition, ballistic impact simulations were performed to determine the applicability of 3D printed 15-5 stainless steel in the defense industry. The 15-5 stainless steel specimens were printed (horizontal-build) using the direct metal laser sintering (DMLS) technique, cooled or heated to the specified temperature, then tested in accordance with the ASTM E23-2016b [1] standard. The Johnson-Cook (J-C) phenomenological material model and fracture parameters were used in the numerical modeling. The cross-sectional microstructures of surfaces and impact energies of the Charpy impact test were examined. For the ballistic impact simulations, a 3D printed 15-5 stainless steel typical plate was investigated at the same temperatures as the Charpy impact test. A typical missile using the J-C properties at room temperature (298 K) was assigned an initial velocity of 300 ms-1 for each plate temperature. The fracture surface investigation (microsurface analysis as well as visual inspection) and impact energy values of the Charpy impact test show that the 3D printed 15-5 stainless steel exhibited brittle behavior at low and room temperatures, but transitioned into a more ductile behavior at high temperature. At 77 K, 298 K and 723 K, the experimental Charpy impact test results were 0.00 J/cm2, 6.78±4.07 J/cm2 and 50.84±3.39 J/cm2 respectively; whereas the simulated impact energy were 1.05 J/cm2, 10.46 J/cm2 and 47.07 J/cm2 respectively. Hence, the impact energy for the experimental and numerical simulations were in good agreement; especially at higher temperatures. Consistent with the results from the Charpy impact test, the ballistic impact simulations show an increase in the impact energy, elastic plastic strain and deflection of the plate with an increase in temperature indicating brittle-to-ductile behavior. The high exit velocity at low and room temperature may not make the plate attractive in defense in its current configuration; however, at the high temperature, the exit velocity reduction was significant.

Browsing by Author "Sagar, Sugrim"

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