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A computational framework for modeling distortion during sintering of binder jet printed parts

Journal of Micromechanics and Molecular Physics 2021年第4期6卷 95-102页

作者： Paudel, Basil J. Conover, Dave Lee, Jung-Kun To, Albert C. Department of Mechanical Engineering and Materials Science University of Pittsburgh PA United States Ansys Inc. Canonsburg PA United States

Sintering of binder jet 3D printed (BJ3DP) parts results in significant nonlinear distortion with typical shrinkage value of 5-20%, which makes design for BJ3DP and post-machining difficult. In this work, a computational modeling framework with calibration and validation procedure is developed to simulate distortion during sintering of BJ3DP parts accurately for the first time. The computational model employs the finite element analysis with a viscoplastic constitutive model that accounts for effects of gravity and friction. A calibration procedure is proposed to obtain values of different model parameters systematically through dilatometric, gravity bending, and grain growth experiments. For model validation, four bridges with different spans and a second part with a circular hole and two free overhangs are designed. The calibration procedure is applied to develop a computational model for sintered 316L stainless steel BJ3DP parts. The displacements at various locations on the sintered parts are simulated using the calibrated model and are found to have errors less than 3.5% compared to those obtained by experiment. © 2021 World Scientific Publishing Company.

关键词： additive manufacturing binder jet distortion modeling simulation Sintering

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Application of level-set type topology optimization for defect topology identification analysis using hammering response data

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materials Today: Proceedings 2023年

作者： Kurahashi, Takahiko Koike, Towa Kishida, Masayuki Murakami, Yuki Ikeda, Fujio Department of Mechanical Engineering Institute of GIGAKU Nagaoka University of Technology Niigata Nagaoka Japan Mechanical Engineering Master's Program Graduate School of Engineering Nagaoka University of Technology Niigata Nagaoka Japan Science of Technology Innovation 5-year Integrated Doctoral Program Graduate School of Engineering Nagaoka University of Technology Niigata Nagaoka Japan Department of Civil Engineering National Institute of Technology Nagaoka College Niigata Nagaoka Japan Department of Mechanical Engineering National Institute of Technology Nagaoka College Niigata Nagaoka Japan

In this study, we presented the defect identification analysis based on the level-set type topology optimization using hammering testing data. To simulate the oscillation behavior of concrete structure, the equation of motion in three dimensions is introduced as the governing equation. The performance function is defied by the time integral of the squared residual between the computed and observed displacements. The problem is to find the defect topologies so as to minimize the performance function. In the model with a small number of observation points, it was found that nonexistent defects disappeared by using the weighted sensitivity method. In addition, it was confirmed that the model with a large number of observation points did not show the same tendency as the model with a small number of observation points because the accuracy of defect identification increased as the number of observation points increased. © 2023

关键词： Defects

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In situ structural determination of 3d and 5d perovskite oxides under high pressure by synchrotron x-ray diffraction

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Physical Review B 2023年第13期108卷 134106-134106页

作者： Jie Chen Jiaming He Yanyao Zhang Stella Chariton Vitali Prakapenka Kazunari Yamaura Jung-Fu Lin J. B. Goodenough J.-S. Zhou Materials Science and Engineering Program Mechanical Engineering University of Texas at Austin Austin Texas 78712 USA Department of Earth and Planetary Sciences Jackson School of Geosciences The University of Texas at Austin Austin Texas 78712 USA Center for Advanced Radiation Sources The University of Chicago Illinois 60637 USA Research Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science 1-1 Namiki Tsukuba Ibaraki 305-0044 Japan Graduate School of Chemical Sciences and Engineering Hokkaido University North 10 West 8 Kita-ku Sapporo Hokkaido 060–0810 Japan

In contrast to the Mott transition found in RNiO3 (R= rare earths), the metal-insulator transition temperature in the perovskite NaOsO3 is not sensitive to pressure. The peculiarity may be correlated to how the crystal structure of NaOsO3 responds to high pressure, which has been rarely studied so far. The pressure-induced bond-length shrinking can increase the orbital overlap integral and therefore the electron bandwidth. However, in the orthorhombic perovskite structure, the pressure-induced bending in the bond angle Os-O-Os may compensate for the bandwidth broadening due to the bond-length shrinking in some circumstances. A recent structural study on polycrystalline NaOsO3 indicated that orthorhombic distortion is enlarged under high pressure. But, how the local structure changes under pressure remains unknown. Moreover, a highly unusual phase transition from the orthorhombic phase (Pbnm) to a polar phase (Pbn21) occurs at around 18 GPa [Sereika et al., npj Quantum Mater. 5, 66 (2020)]. Motivated by these concerns, we have done a more comprehensive structural study on NaOsO3 using single-crystal diffraction with synchrotron radiation at high pressures up to 41 GPa. Diffraction patterns over the entire pressure range can be refined well with the Pbnm structural model. Moreover, the refinement results reveal in detail how the local structures change under pressure corresponding to the enhanced orthorhombic distortion from the lattice parameters. We have carried out a systematic study for understanding the pressure effect on the orthorhombic perovskites in the context of the influences of the charge distributions in the ABO3 formula, i.e., A3+B3+O3, A2+B4+O3, and A1+B5+O3 and the B-site cations from the 3d to the 4d and 5d row of elements. To fulfill this purpose, we have revisited two families of 3d perovskites: RCrO3 and RFeO3.

关键词： Phase transitions Crystal structures X-ray diffraction

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Microwave-assisted biosynthesis of silver nanoparticles for potential antibacterial activity

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Applied Nanoscience (Switzerland) 2024年第12期14卷 1115-1124页

作者： Kala, Anuskha Uniyal, Santoshi Saini, Krati Dhyani, Reena Joshi, Deepika Verma, Rashmi Kar, Kamal K. Chamoli, Pankaj School of Basic and Applied Sciences Department of Biotechnology Shri Guru Ram Rai University Uttarakhand Dehradun248001 India School of Basic and Applied Sciences Department of Physics Shri Guru Ram Rai University Uttarakhand Dehradun248001 India Department of Physics Women Institue of Technology Uttarakhand Dehradun248007 India Siddhartha Institute of Pharmacy Uttarakhand Dehradun248013 India Advanced Nanoengineering Materials Laboratory Department of Mechanical Engineering and Materials Science Programme Indian Institute of Technology Kanpur Kanpur208016 India

The present study demonstrates the creation of silver nanoparticles (Ag NPs) in an environmentally benign manner from Cymbopogon citratus leaves extracts by employing microwave-assisted synthesis at a low power of 400 W for a short period of 180 s. The produced Ag NPs are thoroughly characterized using methods like X-ray diffraction (XRD), UV–visible spectroscopy, scanning electron microscopy (SEM), and X-ray energy dispersive spectroscopy (EDS). These Ag NPs form clusters and have unique plate-like shapes with average particle size of ~ 165 nm. To evaluate their antibacterial activity, the produced Ag NPs are tested against both gram-positive bacteria (S. aureus) and gram-negative bacteria (E. Coli, S. typhi, and Pseudomonas) at varied concentrations (1–5 mg/L). The results show strong antibacterial activity, against both gram-positive bacteria (S. aureus) and gram-negative bacteria (E. Coli, S. typhi, and Pseudomonas);and show the largest zone of inhibition diameters at 23 mm (~ 3 mg/L) and 26 mm (~ 5 mg/L) for S. aureus and Pseudomonas, respectively. The ecological potential of Cymbopogon citratus extracts as sources for the environmentally friendly synthesis of Ag NPs is highlighted in this work and the produced Ag NPs are a viable option for antibacterial treatments against pathogenic microbes. © King Abdulaziz City for science and Technology 2024.

关键词： Silver nanoparticles

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One-Pot Synthesis of Tetraarylpyrrolo[3,2-b]pyrrole Dopant-Free Hole-Transport materials for Inverted Perovskite Solar Cells

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Chinese Journal of Chemical Physics 2021年第2期34卷 217-226,I0002页

作者： Liang-sheng Duan Quan-ping Wu Yuan-yuan Xu Hui Wang Zhe Sun Yu Chen Song Xue School of Materials Science and Engineering Tianjin Key Laboratory of the Design and Intelligent Control of the Advanced Mechanical SystemSchool of Mechanical EngineeringTianjin University of TechnologyTianjin 300384China

Four organic smallmolecule hole transport materials(D41, D42,D43 and D44) of tetraarylpyrrolo[3,2-b]pyrroles were prepared. They can be used without doping in the manufacture of the inverted planar perovskite solar cells. Tetraarylpyrrolo[3,2-b]pyrroles are accessible for one-pot synthesis.D42, D43 and D44 possess acceptor-π-donor-π-acceptor structure, on which the aryl bearing substitutes of cyan, fluorine and trifluoromethyl, respectively. Instead, the aryl moiety of D41 is in presence of methyl with a donor-π-donor-π-donor structure. The different substitutes significantly affected their molecular surface charge distribution and thin-film morphology, attributing to the electron-rich properties of fused pyrrole ring. The size of perovskite crystalline growth particles is affected by different molecular structures,and the electron-withdrawing cyan group of D42 is most conducive to the formation of large perovskite grains. The D42 fabricated devices with power conversion efficiency of17.3% and retained 55% of the initial photoelectric conversion efficiency after 22 days in dark condition. The pyrrolo[3,2-b]pyrrole is efficient electron-donating moiety for hole transporting materials to form good substrate in producing perovskite thin film.

关键词： Pyrrole[3,2-b]pyrrole Hole-transporting materials Organic small molecules Dopant-free Perovskite solar cells

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Network evolution controlling strain-induced damage and self-healing of elastomers with dynamic bonds

arXiv

引用

arXiv 2024年

作者： Yin, Yikai Mohanty, Shaswat Cooper, Christopher B. Bao, Zhenan Cai, Wei Department of Materials Science and Engineering Stanford University StanfordCA94305 United States Department of Mechanical Engineering Stanford University StanfordCA94305 United States Department of Chemical Engineering Stanford University StanfordCA94305 United States

Highly stretchable and self-healable supramolecular elastomers are promising materials for future soft electronics, biomimetic systems, and smart textiles, due to their dynamic cross-linking bonds. The dynamic or reversible nature of the cross-links gives rise to interesting macroscopic responses in these materials such as self-healing and rapid stress-relaxation. However, the relationship between bond activity and macroscopic mechanical response, and the self-healing properties of these dynamic polymer networks (DPNs) remains poorly understood. Using coarse-grained molecular dynamics (CGMD) simulations, we reveal a fundamental connection between the macroscopic behaviors of DPNs and the shortest paths between distant nodes in the polymer network. Notably, the trajectories of the material on the shortest path-strain map provide key insights into understanding the stress-strain hysteresis, anisotropy, stress relaxation, and self-healing of DPNs. Based on CGMD simulations under various loading histories, we formulate a set of empirical rules that dictate how the shortest path interacts with stress and strain. This lays the foundation for the development of a physics-based theory centered around the non-local microstructural feature of shortest paths to predict the mechanical behavior of DPNs. © 2024, CC BY.

关键词： Dynamics

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Ionic forces and stress tensor in all-electron density functional theory calculations using an enriched finite-element basis

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Physical Review B 2022年第8期106卷 085108-085108页

作者： Nelson D. Rufus Vikram Gavini Department of Mechanical Engineering University of Michigan Ann Arbor Michigan 48109 USA and Department of Materials Science & Engineering University of Michigan Ann Arbor Michigan 48109 USA

The enriched finite-element basis—wherein the finite-element basis is enriched with atom-centered numerical functions—has recently been shown to be a computationally efficient basis for systematically convergent all-electron density functional theory (DFT) ground-state calculations. In this work, we present the expressions to compute variationally consistent ionic forces and stress tensor for all-electron DFT calculations in the enriched finite-element basis. In particular, we extend the formulation of configurational forces [P. Motamarri and V. Gavini, Phys. Rev. B 97, 165132 (2018)] to the enriched finite-element basis and elucidate the additional contributions arising from the enrichment functions. We demonstrate the accuracy of the formulation by comparing the computed forces and stresses for various benchmark systems with those obtained from finite differencing the ground-state energy. Further, we also benchmark our calculations against the Gaussian basis for molecular systems and against the linearized augmented plane wave with local orbitals basis for periodic systems.

关键词： Electronic structure First-principles calculations Band structure methods Density functional theory Finite-element method

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Machine Learning Best Practices for Soft Robot Proprioception

Machine Learning Best Practices for Soft Robot Proprioceptio...

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IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)

作者： Annan Zhang Tsun-Hsuan Wang Ryan L. Truby Lillian Chin Daniela Rus MIT Computer Science and Artificial Intelligence Laboratory (CSAIL) Massachusetts Institute of Technology Cambridge MA USA Department of Materials Science and Engineering and Mechanical Engineering Northwestern University Evanston IL USA

Machine learning-based approaches for soft robot proprioception have recently gained popularity, in part due to the difficulties in modeling the relationship between sensor signals and robot shape. However, to date, there exists no systematic analysis of the required design choices to set up a machine learning pipeline for soft robot proprioception. Here, we present the first study examining how design choices on different levels of the machine learning pipeline affect the performance of a neural network for predicting the state of a soft robot. We address the most frequent questions researchers face, such as how to choose the appropriate sensor and actuator signals, process input and output data, deal with time series, and pick the best neural network architecture. By testing our hypotheses on data collected from two vastly different systems–an electrically actuated robotic platform and a pneumatically actuated soft trunk–we seek conclusions that may generalize beyond one specific type of soft robot and hope to provide insights for researchers to use machine learning for soft robot proprioception.

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Grain boundaries amplify local chemical ordering in CrCoNi

arXiv

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arXiv 2025年

作者： Geiger, Ian Tian, Yuan Han, Ying Bi, Yutong Pan, Xiaoqing Cao, Penghui Rupert, Timothy J. Materials and Manufacturing Technology University of California IrvineCA92697 United States Department of Materials Science and Engineering University of California IrvineCA92697 United States Department of Mechanical and Aerospace Engineering University of California IrvineCA92697 United States Hopkins Extreme Materials Institute Johns Hopkins University BaltimoreMD21218 United States Department of Materials Science and Engineering Johns Hopkins University BaltimoreMD21218 United States

Local chemical ordering plays an important role in the behavior of complex concentrated alloys, yet its characterization remains challenging due to the nanoscale dimensions and scattered spatial distribution of the ordered domains. This study explores the potential of grain boundaries as microstructural anchor points that amplify chemical ordering and enable the formation of compositional nanopatterns in CrCoNi. Using hybrid Monte Carlo/molecular dynamics simulations, we reveal the development of distinct compositional waves with ordering vectors normal to grain boundaries, extending to lengths greater than 6 nm. These waves manifest as periodic enrichment and depletion patterns, with strong Ni depletion near the Ni-segregated grain boundary accompanied by Co and Cr enrichment. Analogous to surface-driven phase separation, the concentration waves emanating from the boundaries gradually attenuate as they propagate into the grain interior. This behavior highlights the interplay between boundary-dictated directional ordering and the isotropic, untemplated domain growth within the grain. This work advances our fundamental understanding of grain boundary-mediated ordering phenomena and offers a pathway for more precise experimental characterization of local chemical ordering in CCAs. © 2025, CC BY.

关键词： Phase separation

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Applying a Capacitated Heterogeneous Fleet Vehicle Routing Problem with Multiple Depots Model to Optimize a Retail Chain Distribution Network

Applying a Capacitated Heterogeneous Fleet Vehicle Routing P...

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2022 IEEE International Conference on Industrial engineering and engineering Management, IEEM 2022

作者： Fernando, W. Madushan Thibbotuwawa, Amila Perera, H. Niles Chandima Ratnayake, R.M. University of Moratuwa Center for Supply Chain Operations and Logistics Optimization Katubedda10400 Sri Lanka University of Stavanger Department of Mechanical and Structural Engineering and Materials Science StavangerN-4036 Norway

ISBN: (数字)9781665486873

ISBN: (纸本)9781665486873

Planning and operating retail chain distribution processes is becoming more challenging, due to the increasing demand and urban congestion. This research applied a Capacitated Heterogeneous Fleet Vehicle Routing Problem with Multiple Depots (CHFVRPMD) model to optimize a retail chain distribution network with a real-world road network. The model attempts to obtain a distribution plan that minimizes the total distribution cost. A hybrid solution algorithm was proposed to solve the CHFVRPMD model. The solution algorithm was developed by combining the heuristic and metaheuristic methods. A case study was carried out to collect actual data to test the proposed optimization model and the solution algorithm. All the input parameters were estimated using a real-world industry application, to minimize the gap between the theoretical model and the real-world applicability. Computation experiments demonstrate the proposed hybrid solution algorithm's effectiveness in optimizing the CHFVRPMD model in a feasible computational time. The overall findings reveal that the CHFVRPMD model has achieved about 10.7% savings in daily distribution cost, in optimizing the selected retail distribution network. The proposed model and solution algorithm assist industry practitioners to mitigate transport inefficiencies in retail distribution networks. © 2022 IEEE.

关键词： Vehicle routing

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