Tensile Behaviors and Mechanical Property Analyses of T-Welded Joint for Thin-Walled Parts in Consideration of Different TIG Welding Currents Using Multiple Damage Models and Fracture Criterions: Numerical Simulation and Experiment Validation.

In order to deeply investigate the tensile properties and fracture behaviors that are obtained by tensile tests of welded joints, constitutive and damage models are imperative for analyzing the tensile behaviors. In this work, the tensile tests are conducted on the T-welded joint specimens of aluminum alloy 6061-T6, which were cut from the T-welded joints of thin-walled parts under different welding currents of Tungsten Inert Gas Welding (TIGW). A modified Johnson-Cook (J-C) model based on the original J-C equation, Swift model, Voce model, and Hockett-Sherby (H-S) model, their linear combination model, and fracture failure model are constructed and applied to simulate tensile behaviors, combined with tensile test data. What is more, the finite element (FE) simulation of tension tests is executed with the VUMAT and VUSDFLD subroutines. Compared to those results simulated with different fracture criteria and tensile experiments, the tensile strength and yield strength of T-welded joint thin-walled parts under different welding currents were achieved, and their best mean errors were only about 1%. Furthermore, the accuracy of different fracture criteria is also evaluated by the correlation coefficient and mean squared error. The results show that the combination model can accurately predict the tensile properties and fracture behaviors of T-welded joints better than the single model, especially the results simulated with the Swift-H-S model and H-S-Voce model, which are in good agreement with tensile test results, which will provide an analysis foundation for enhancing the welding assembly quality and preventing fracture failure for complex thin-walled antenna structures.

A novel method for monitoring the maxillary tooth movement during orthodontics in 3D space.

AIM: The present study aimed to develop a method for measuring 3D maxillary tooth movement during orthodontic treatment and to verify the accuracy of the method. MATERIALS AND METHODS: A 3D model analysis method was established to measure tooth movement by combining the effects of CBCT and intraoral scans. Transformation matrices were used to abstract the motion features of the teeth and translate them into translations and rotations. To test the validity and reliability of the method for clinical application, the inclination of the central incisor was measured using a 3D model analysis method and cephalometric analysis. Measurement error, correlation, and agreement between the two methods were analyzed using the Dahlberg formula, intraclass correlation coefficient, and Bland-Altman analysis, respectively. The performance of the 3D model analysis method was evaluated by monitoring the canine movement of a patient who underwent a premolar extraction. RESULTS: The measurement error was 0.58 degrees for the 3D model analysis and 2.02 degrees for the cephalometric analysis. There was no significant difference in the central incisor inclination measurements between the cephalometric and the 3D model analyses methods. A high correlation (0.974) and narrow limits of agreement (-3.55 degrees, 4.16 degrees) were obtained between the two methods. Minute movements and additional details of orthodontic tooth movements could be observed using the 3D model analysis method. CONCLUSION: The 3D model analysis method was reliable and reproducible for clinical application in monitoring the 3D maxillary tooth movement during orthodontic treatment. The trueness should be further evaluated. (Int J Comput Dent 2023;26(1): 49-0; doi: 10.3290/j.ijcd.b3818301).

Effects of Side-Chain Engineering with the S Atom in Thieno[3,2-b]thiophene-porphyrin to Obtain Small-Molecule Donor Materials for Organic Solar Cells.

To explore the effect of the introduction of heteroatoms on the properties of porphyrin materials, a new porphyrin-based derivative small-molecule donor named as PorTT-T was designed and synthesized based on alkyl-thieno[3,2-b]thiophene(TT)-substituted porphyrins. The linker bridge and end groups of PorTT-T were the same as those of XLP-II small-molecule donor materials, while the side-chain attached to the core of thieno[3,2-b]thiophene(TT)-substituted porphyrin was different. Measurements of intrinsic properties showed that PorTT-T has wide absorption and appropriate energy levels in the UV-visible range. A comparison of the morphologies of the two materials using atomic force microscopy showed that PorTT-T has a better surface morphology with a smaller root-mean-square roughness, and can present closer intermolecular stacking as compared to XLP-II. The device characterization results showed that PorTT-T with the introduced S atom has a higher open circuit voltage of 0.886 eV, a higher short circuit current of 12.03 mAcm-2, a fill factor of 0.499, a high photovoltaic conversion efficiency of 5.32%, better external quantum efficiency in the UV-visible range, and higher hole mobility.

Semi-Empirical Prediction of Turned Surface Residual Stress for Inconel 718 Grounded in Experiments and Finite Element Simulations.

The surface residual stress after machining, especially for finishing, has a vital influence on the shape stability and fatigue life of components. The current study focuses on proposing an original empirical equation to predict turned surface residual stress for Inconel 718 material, taking tool parameters into consideration. The tool cutting-edge angle, rake angle, and inclination angle are introduced for the first time in the equation based on the Inconel 718 material turning experiments and finite element simulations. In this study, the reliability of simulation parameters' setting is firstly calibrated by comparing the residual stresses and chips of the experiments and simulations. The changing trends of turned forces, temperatures of lathe tool nose, and surface residual stress with turning parameters are analyzed. Then, the predictive equation of surface residual stress is proposed considering relationships between the back-rake angle, the side-rake angle, and the tool cutting-edge angle, rake angle, and inclination angle. Moreover, the genetic algorithm optimizes the objective function to obtain the undetermined coefficients in the prediction equation. Finally, the predicted accuracy of the surface residual stress is proven by comparing the experimental, simulation, and prediction values. The results indicate that the predictive equation of surface residual stress has a good accuracy in predicting turned surface residual stress for Inconel 718 materials. The correlation coefficient, R, and absolute average error between the predicted and the simulated value are 0.9624 and 13.40%, respectively. In the range of cutting parameters studied and experimental errors, this study provides an accurate predictive equation of turned surface residual stress for Inconel 718 materials.

Semi-Empirical Prediction of Residual Stress Distributions Introduced by Turning Inconel 718 Alloy Based on Lorentz Function.

The residual stress of machined surface has a crucial influence on the performance of parts. It results in large deviations in terms of the position accuracy, dimension accuracy and service life. The purpose of the present study is to provide a novel semi-empirical residual stress prediction approach for turning Inconel 718. In the method, the bimodal Lorentz function was originally applied to express the residual stress distribution. A statistical model between the coefficients of the bimodal Lorentz function and cutting parameters was established by the random forest regression, in order to predict the residual stress distribution along the depth direction. Finally, the turning experiments, electrolytic corrosion peeling, residual stress measurement and correlation analysis were carried out to verify the accuracy of predicted residual stress. The results show that the bimodal Lorentz function has a great fitting accuracy. The adjusted R2 (Ad-R2) are ranging from 95.4% to 99.4% and 94.7% to 99.6% in circumferential and axial directions, respectively. The maximum and minimum errors of the surface residual tensile stress (SRTS) are 124.564 MPa and 18.082 MPa, those of the peak residual compressive stress (PRCS) are 84.649 MPa and 3.009 MPa and those of the depth of the peak residual compressive stress (DPRCS) are 0.00875 mm and 0.00155 mm, comparing three key feature indicators of predicted and simulated residual stress. The predicted residual stress is highly correlated with the measured residual stress, with correlation coefficients greater than 0.8. In the range of experimental measurement error, the research in the present work provides a quite accurate method for predicting the residual stress in turning Inconel 718, and plays a vital role in controlling the machining deformation of parts.

A direct Z-scheme PtS2/arsenene van der Waals heterostructure with high photocatalytic water splitting efficiency.

To overcome current serious energy and environmental issues, photocatalytic water splitting holds great promise because it requires only solar energy as an energy input to produce hydrogen. In this work, based on first-principle calculations, we studied the van der Waals heterostructure formed by PtS2 and arsenene (Are) monolayers that were successfully synthesized on a large scale at high quality. From an analysis of the migration paths of photoinduced electrons and holes, a direct Z-scheme photocatalytic mechanism is demonstrated in this heterostructure. Furthermore, the PtS2/Are direct Z-scheme heterostructure has decent band edge positions to promote the redox reaction to decompose water at pH 0. The interfacial charge difference and potential drop are presented, which further support the formation of a direct Z-scheme photocatalyst. More importantly, the PtS2/Are heterostructure has quite high solar-to-hydrogen (STH) efficiency (49.32%), significantly enhanced compared with isolated PtS2 (12.67%) or Are (10.34%) monolayers. This direct Z-scheme PtS2/Are heterostructure with excellent STH efficiency suggests its promising application as a photocatalyst for water splitting.

Molecular doping of blue phosphorene: a first-principles investigation.

Using first-principles calculations, we show that p-doped blue phosphorene can be obtained by molecular doping with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) and 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6-TNAP), whereas n-doped blue phosphorene can be realized by doping with tetrathiafulvalene (TTF) and cyclooctadecanonaene (CCO). Moreover, the doping gap can be effectively modulated in each case by applying an external perpendicular electric field. The optical absorption of blue phosphorene can be considerably enhanced in a broad spectral range through the adsorption of CCO, F4-TCNQ, and F6-TNAP molecules, suggesting potential of the doped materials in the field of renewable energy.

Semi-Empirical Prediction of Residual Stress Profiles in Machining IN718 Alloy Using Bimodal Gaussian Curve.

Residual stresses are often imposed on the end-product due to mechanical and thermal loading during the machining process, influencing the distortion and fatigue life. This paper proposed an original semi-empirical method to predict the residual stress distribution along the depth direction. In the statistical model of the method, the bimodal Gaussian function was innovatively used to fit Inconel 718 alloy residual stress profiles obtained from the finite element model, achieving a great fit precision from 89.0% to 99.6%. The coefficients of the bimodal Gaussian function were regressed with cutting parameters by the random forest algorithm. The regression precision was controlled between 80% and 85% to prevent overfitting. Experiments, compromising cylindrical turning and residual stress measurements, were conducted to modify the finite element results. The finite element results were convincing after the experiment modification, ensuring the rationality of the statistical model. It turns out that predicted residual stresses are consistent with simulations and predicted data points are within the range of error bars. The max error of predicted surface residual stress (SRS) is 113.156 MPa, while the min error is 23.047 MPa. As for the maximum compressive residual stress (MCRS), the max error is 93.025 MPa, and the min error is 22.233 MPa. Considering the large residual stress value of Inconel 718, the predicted error is acceptable. According to the semi-empirical model, the influence of cutting parameters on the residual stress distribution was investigated. It shows that the cutting speed influences circumferential and axial MCRS, circumferential and axial depth of settling significantly, and thus has the most considerable influence on the residual stress distribution. Meanwhile, the depth of cut has the least impact because it only affects axial MCRS and axial depth of settling significantly.

Using van der Waals heterostructures based on two-dimensional blue phosphorus and XC (X = Ge, Si) for water-splitting photocatalysis: a first-principles study.

Solar-powered production of hydrogen from water has been pursued as one of the solutions to the global energy crisis. Meanwhile, two-dimensional (2D) materials have attracted significant attention as photocatalysts. In this paper, the geometric structures, electronic band structures, band alignment, and optical properties of two novel van der Waals (vdW) heterostructures based on 2D blue phosphorus (BlueP) and 2D XC (X = Ge, Si) were systematically explored using first-principles calculations. We found that both BlueP/GeC and BlueP/SiC vdW heterostructures possess type-II band structures, which can continuously separate the photogenerated electron-hole pairs. The calculated band-edge positions suggest that the BlueP/SiC and BlueP/GeC vdW heterostructures act as potential photocatalysts for water-splitting at pH 0 and pH 7, respectively. Furthermore, XC acts as an electron-donating layer in the BlueP/XC vdW heterostructure, and the potential drop across the interface can generate a large built-in electric field across the interface; this electric field plays a crucial role in preventing the recombination of photogenerated charges. Finally, the optical properties of the BlueP/XC vdW heterostructures demonstrate that they have excellent ability to capture visible light, making them promising high-performance photocatalysts for water splitting.

Investigation of circular RNAs and related genes in pulmonary fibrosis based on bioinformatics analysis.

Pulmonary fibrosis is a lethal inflammatory disease. In this study, we aimed to explore the potential-related circular RNAs (circRNAs) and genes that are associated with pulmonary fibrosis. Pulmonary fibrosis rat models were constructed and the fibrosis deposition was detected using hematoxylin and eosin and Masson staining. The differentially expressed circRNAs were obtained through RNA sequencing. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were further performed to uncover the key function and pathways in pulmonary fibrosis. The interaction networks between circRNAs and their downstream micro RNAs (miRNAs) and genes were constructed by Cytoscape Software. The quantitative polymerase chain reaction was performed to validate the expression of 10 candidate circRNAs and five of them were performed ringwise sequencing in pulmonary fibrosis rats. We further selected five candidate circRNAs target miRNAs and messenger RNAs and validated by real-time polymerase chain reaction. The pulmonary fibrosis models were successfully constructed according to the pathological examination. circRNAs were differentially expressed between the pulmonary fibrosis and normal pulmonary tissues. GO analysis verified that the differentially expressed circRNAs were significantly clustered in the cellular component, molecular function, and biological process. In the KEGG analysis, circRNAs were enriched in the following pathways: antigen processing and presentation, phagosome, PI3K-AKt signaling pathway, HTLV-I infection, and Herpes simplex infection. After validation in pulmonary fibrosis rat models, it was found that five of those circRNAs (chr9:113534327|113546234 [down], chr1:200648164|200672411 [down], chr5:150850432|150865550 [up], chr20:14319170|14326640 [down], and chr10:57634023|57634588 [down]) showed a relatively consistent trend with predictions. Validation of these circRNAs target miRNAs and genes showed that chr9:113534327|113546234, chr20:14319170|14326640, and chr10:57634023|57634588 were implicated in Notch1 activated transforming growth factor-ß (TGF-ß) signaling pathway. The study demonstrated that a series of circRNAs are differentially expressed in pulmonary fibrosis rats. These circRNAs, especially TGF-ß- and Notch1-related circRNAs might play an important role in regulating pulmonary fibrogenesis.

Strain-enhanced properties of van der Waals heterostructure based on blue phosphorus and g-GaN as a visible-light-driven photocatalyst for water splitting.

Many strategies have been developed to overcome the critical obstacles of fast recombination of photogenerated charges and the limited ability of semiconductor photocatalysts to absorb visible light. Considering all the novel properties of monolayered g-GaN and blue phosphorus (BlueP) which were revealed in recent studies, first-principles calculations were used to systematically investigate the structural stability, electronic energy, band alignment, band bending, and charge difference in the heterostructure formed by these two layered materials. The g-GaN/BlueP heterostructure is constructed by van der Waals (vdW) forces, and it possess a staggered band structure which induces electron transformation because of the different Fermi levels of the two layered materials. By aligning the Fermi levels, an interfacial electric field is built and it causes band bending, which can promote effective separation of photoexcited holes and electrons; the band-bending phenomenon was also calculated according to density functional theory (DFT). Moreover, effects of in-plane strain on the tuned bandgap, energy, and band edge were investigated, and the results show that the optical-absorption performance in the visible-light range can be improved. The findings reported in this paper are expected to provide theoretical support for the use of the g-GaN/BlueP vdW heterostructure as a photocatalyst for water splitting.

A van der Waals Heterostructure Based on Graphene-like Gallium Nitride and Boron Selenide: A High-Efficiency Photocatalyst for Water Splitting.

Hydrogen generation by photocatalytic water splitting has attained more and more research interests in the recent years since the solar energy can be directly transferred and stored as hydrogen. However, the search for a high-efficiency photocatalyst for water splitting is a really challenge. In this paper, we designed a novel 2D material-based van der Waals heterostructure (vdWH) composed by g-GaN and BSe, which is thermally stable at room temperature. The g-GaN/BSe vdWH has suitable band-edge positions for the oxidation and reduction reactions of water splitting at pH 0 and 7. The carrier mobility of this heterostructure is high, indicating the effective occurrence of reactions for water splitting. The g-GaN/BSe vdWH also possesses a type-II band alignment, which can promote the separation of the photogenerated electron-hole pairs constantly. Moreover, a large built-in electric field can be established at the interface, which will further prevent the recombination of photogenerated charges. In addition, the g-GaN/BSe vdWH also exhibits outstanding sunlight-absorption ability, and the biaxial strain can further enhance this ability. Thus, we conclude that the g-GaN/BSe vdWH can act as a high-efficiency photocatalyst for water splitting.

Adsorption of Transition Metals on Black Phosphorene: a First-Principles Study.

Black phosphorene is a novel two-dimensional material which has unique properties and wide applications. Using first-principles calculations, we investigated the adsorption behavior of 12 different transition metals (TMs; Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au) on phosphorene. Our results showed that all of the adsorption systems have a large binding energy. The Fe-, Co-, and Au-phosphorene systems display magnetic states with magnetic moments of 2, 1, and 0.96 µB, respectively, which means that these systems are magnetic semiconductors. Adsorption of oxygen molecules on TM-phosphorene was also investigated. Interestingly, all the O2-(TM-phosphorene) systems, except O2-(Pd-phosphorene), can elongate the O-O bond, which is critical to their application as catalysts in the oxidation of CO. We also found that the adsorption of O2 molecules enables the O2-(Fe-, Ni-, Cu-, Ir-, Rh-, Ag-, and Au-phosphorene) systems to become magnetic semiconductors, and it allows O2-(Co-phosphorene) to display half-metallic state. Our results are expected to have important implications for phosphorene-based catalysis and spintronics.

Few-Layer PdSe2 Sheets: Promising Thermoelectric Materials Driven by High Valley Convergence.

Herein, we report a comprehensive study on the structural and electronic properties of bulk, monolayer, and multilayer PdSe2 sheets. First, we present a benchmark study on the structural properties of bulk PdSe2 by using 13 commonly used density functional theory (DFT) functionals. Unexpectedly, the most commonly used van der Waals (vdW)-correction methods, including DFT-D2, optB88, and vdW-DF2, fail to provide accurate predictions of lattice parameters compared to experimental data (relative error > 15%). On the other hand, the PBE-TS series functionals provide significantly improved prediction with a relative error of <2%. Unlike hexagonal two-dimensional materials like graphene, transition metal dichalcogenides, and h-BN, the conduction band minimum of monolayer PdSe2 is not located along the high symmetry lines in the first Brillouin zone; this highlights the importance of the structure-property relationship in the pentagonal lattice. Interestingly, high valley convergence is found in the conduction and valence bands in monolayer, bilayer, and trilayer PdSe2 sheets, suggesting promising application in thermoelectric cooling.

Exceptional Optical Absorption of Buckled Arsenene Covering a Broad Spectral Range by Molecular Doping.

Using density functional theory calculations, we demonstrate that the electronic and optical properties of a buckled arsenene monolayer can be tuned by molecular doping. Effective p-type doping of arsenene can be realized by adsorption of tetracyanoethylene and tetracyanoquinodimethane (TCNQ) molecules, while n-doped arsenene can be obtained by adsorption of tetrathiafulvalene molecules. Moreover, owing to the charge redistribution, a dipole moment is formed between each organic molecule and arsenene, and this dipole moment can significantly tune the work function of arsenene to values within a wide range of 3.99-5.57 eV. Adsorption of TCNQ molecules on pristine arsenene can significantly improve the latter's optical absorption in a broad (visible to near-infrared) spectral range. According to the AM 1.5 solar spectrum, two-fold enhancement is attained in the efficiency of solar-energy utilization, which can lead to great opportunities for the use of TCNQ-arsenene in renewable energy. Our work clearly demonstrates the key role of molecular doping in the application of arsenene in electronic and optoelectronic components, renewable energy, and laser protection.

Weak C-HF-C hydrogen bonds make a big difference in graphane/fluorographane and fluorographene/fluorographane bilayers.

Using density functional theory computations with van der Waals (vdW) corrections, we reveal that C-HF-C hydrogen bonding exists in graphane/fluorographene and fluorographane/fluorographane bilayers. The significant C-HF-C hydrogen bonding is strong enough to combine two separate monolayers to form the bilayer. Interestingly, both the graphane/fluorographene and fluorographane/fluorographane bilayers are metallic in the most stable stacking configuration. Applying a perpendicular electric field can effectively open a bandgap for both bilayers, and we found that the field-induced gap opening for both graphane/fluorographene and fluorographane/fluorographane bilayers can be enhanced by biaxial tensile strain. These results are expected to aid in the design of novel electronic and optoelectronic devices based on graphene materials, and they highlight the use of weak interactions for modulating band structures in two-dimensional materials.

Electronic properties of blue phosphorene/graphene and blue phosphorene/graphene-like gallium nitride heterostructures.

Blue phosphorene (BlueP) is a graphene-like phosphorus nanosheet which was synthesized very recently for the first time [Nano Lett., 2016, 16, 4903-4908]. The combination of electronic properties of two different two-dimensional materials in an ultrathin van der Waals (vdW) vertical heterostructure has been proved to be an effective approach to the design of novel electronic and optoelectronic devices. Therefore, we used density functional theory to investigate the structural and electronic properties of two BlueP-based heterostructures - BlueP/graphene (BlueP/G) and BlueP/graphene-like gallium nitride (BlueP/g-GaN). Our results showed that the semiconducting nature of BlueP and the Dirac cone of G are well preserved in the BlueP/G vdW heterostructure. Moreover, by applying a perpendicular electric field, it is possible to tune the position of the Dirac cone of G with respect to the band edge of BlueP, resulting in the ability to control the Schottky barrier height. For the BlueP/g-GaN vdW heterostructure, BlueP forms an interface with g-GaN with a type-II band alignment, which is a promising feature for unipolar electronic device applications. Furthermore, we discovered that both G and g-GaN can be used as an active layer for BlueP to facilitate charge injection and enhance the device performance.

Development and parameter identification of a visco-hyperelastic model for the periodontal ligament.

The present study developed and implemented a new visco-hyperelastic model that is capable of predicting the time-dependent biomechanical behavior of the periodontal ligament. The constitutive model has been implemented into the finite element package ABAQUS by means of a user-defined material subroutine (UMAT). The stress response is decomposed into two constitutive parts in parallel which are a hyperelastic and a time-dependent viscoelastic stress response. In order to identify the model parameters, the indentation equation based on V-W hyperelastic model and the indentation creep model are developed. Then the parameters are determined by fitting them to the corresponding nanoindentation experimental data of the PDL. The nanoindentation experiment was simulated by finite element analysis to validate the visco-hyperelastic model. The simulated results are in good agreement with the experimental data, which demonstrates that the visco-hyperelastic model developed is able to accurately predict the time-dependent mechanical behavior of the PDL.

Mechanical responses of the periodontal ligament based on an exponential hyperelastic model: a combined experimental and finite element method.

The V-W exponential hyperelastic model is adopted to describe the instantaneous elastic response of the periodontal ligament (PDL). The general theoretical framework of constitutive modeling is described based on nonlinear continuum mechanics, and the elasticity tensor used to develop UMAT subroutine is formulated. Nanoindentation experiment is performed to characterize mechanical properties of an adult pig PDL specimen. Then the experiment is simulated by using the finite element (FE) analysis. Meanwhile, the optimized material parameters are identified by the inverse FE method. The good agreement between the simulated results and experimental data demonstrates that the V-W model is capable of describing the mechanical behavior of the PDL. Therefore, the model and its implementation into FE code are validated. By using the model, we simulate the tooth movement under orthodontic loading to predict the mechanical responses of the PDL. The results show that local concentrations of stress and strain in the PDL are found.

Interpolating gain-scheduled H∞ loop shaping design for high speed ball screw feed drives.

This paper presents a method to design servo controllers for flexible ball screw drives with time-varying dynamics, which are mainly due to the time-varying table position and the workpiece mass. A gain-scheduled H∞ loop shaping controller is designed to achieve high tracking performance against the dynamic variations. H∞ loop shaping design procedure incorporates open loop shaping by a set of compensators to obtain performance/robust stability tradeoffs. The interpolating gain-scheduled controller is obtained by interpolating the state space model of the linear time-invariant (LTI) controllers estimated for fixed values of the scheduling parameters and a linear least squares problem can be solved. The proposed controller has been compared with P/PI with velocity and acceleration feedforward and adaptive backstepping sliding mode control experimentally. The experimental results indicate that the tracking performance has been improved and the robustness for time-varying dynamics has been achieved with the proposed scheme.