Finite Element Analysis and Computational Fluid Dynamics Verification of Molten Pool Characteristics During Selective Laser Melting of Ti-6Al-4V Plates.

The finite element (FE) method is used to characterize the thermal gradient, solidification rate, and molten pool sizes of Ti-6Al-4V plates in the process of selective laser melting (SLM). The results are verified by using the computational fluid dynamics (CFD) simulation. The proposed FE model contains a series of toolpath information that is directly converted from a G-code file, including hatch spacing, laser power, layer thickness, dwell time, and scanning speed generated by using Slic3r software from a CAD file.

Optimized XGBoost Model with Small Dataset for Predicting Relative Density of Ti-6Al-4V Parts Manufactured by Selective Laser Melting.

Determining the quality of Ti-6Al-4V parts fabricated by selective laser melting (SLM) remains a challenge due to the high cost of SLM and the need for expertise in processes and materials. In order to understand the correspondence of the relative density of SLMed Ti-6Al-4V parts with process parameters, an optimized extreme gradient boosting (XGBoost) decision tree model was developed in the present paper using hyperparameter optimization with the GridsearchCV method. In particular, the effect of the size of the dataset for model training and testing on model prediction accuracy was examined.

Dynamic Behavior of Rotation Transmission Nano-System in Helium Environment: A Molecular Dynamics Study.

The molecular dynamics (MD) method is used to investigate the influence of the shielding gas on the dynamic behavior of the heterogeneous rotation transmission nano-system (RTS) built on carbon nanotubes (CNTs) and boron nitride nanotube (BNNT) in a helium environment. In the heterogeneous RTS, the inner CNT acts as a rotor, the middle BNNT serves as a motor, and the outer CNT functions as a stator. The rotor will be actuated to rotate by the motor due to the interlayer van der Waals effects and the end effects.

Enhanced mechanical properties of 4H-SiC by epitaxial carbon films obtained from bilayer graphene.

Graphene exhibits excellent mechanical properties under atomically thin thickness, which made it very suitable for nanoelectromechanical systems that had high requirements for the thickness of coatings. The epitaxial bilayer graphene on the 4H-SiC (0001) surface presents high stiffness and hardness comparable to diamond. However, due to structural transition occurring at the nanoscale, it is difficult to elucidate reinforcement mechanisms using experimental methods.

Micromechanical Modeling of Damage Evolution and Mechanical Behaviors of CF/Al Composites under Transverse and Longitudinal Tensile Loadings.

This paper investigates the progressive damage and failure behavior of unidirectional graphite fiber-reinforced aluminum composites (CF/Al composites) under transverse and longitudinal tensile loadings. Micromechanical finite element analyses are carried out using different assumptions regarding fiber, matrix alloy, and interface properties. The validity of these numerical analyses is examined by comparing the predicted stress-strain curves with the experimental data measured under transverse and longitudinal tensile loadings.

The Martensitic Transformation and Mechanical Properties of Ti6Al4V Prepared via Selective Laser Melting.

This article investigated the microstructure of Ti6Al4V that was fabricated via selective laser melting; specifically, the mechanism of martensitic transformation and relationship among parent β phase, martensite (α') and newly generated β phase that formed in the present experiments were elucidated. The primary X-ray diffraction (XRD), transmission electron microscopy (TEM) and tensile test were combined to discuss the relationship between α', β phase and mechanical properties. The average width of each coarse β columnar grain is 80⁻160 μm, which is in agreement with the width of a laser scanning track.

Oscillators based on double-walled armchair@zigzag carbon nanotubes containing inner tubes with different helical rises.

A novel approach is presented to improve the oscillatory behavior of oscillators based on double-walled carbon nanotubes containing rotating inner tubes applied with different helical rises. The influence of the helical rise on the oscillatory amplitude, frequency, and stability of inner tubes with different helical rises in armchair@zigzag bitubes is investigated using the molecular dynamics method. Our simulated results show that the oscillatory behavior is very sensitive to the applied helical rise.

Exciton and Trion Dynamics in Bilayer MoS2.

The control of exciton and triondynamics in bilayer MoS2 is demonstrated, via the comodulations by both temperature and electric field. The calculations here show that the band structure of bilayer MoS2 changes from indirect at room temperature toward direct nature as temperature decreases, which enables the electrical tunability of the K-K direct PL transition in bilayer MoS2 at low temperature.

Homogenized finite element analysis on effective elastoplastic mechanical behaviors of composite with imperfect interfaces.

A three-dimensional (3D) representative volume element (RVE) model was developed for analyzing effective mechanical behavior of fiber-reinforced ceramic matrix composites with imperfect interfaces. In the model, the fiber is assumed to be perfectly elastic until its tensile strength, and the ceramic material is modeled by an elasto-plastic Drucker-Prager constitutive law. The RVE model is then used to study the elastic properties and the tensile strength of composites with imperfect interfaces and validated through experiments.

Steered molecular dynamics simulations on the peeling and shearing of carbon nanotubes on a silicon substrate.

Steered molecular dynamics simulations were performed to investigate the peeling and shearing behavior of a single-walled carbon nanotube lying on a silicon substrate. Both the constant velocity and the constant force methods were applied to explore the adsorption of carbon nanotube and silicon substrate, and the efficiency of the two simulation methods was compared via a few representative examples. We examined the influences of the peeling angle, the shearing velocity, the initial distance between the carbon nanotube and the substrate, the connection point with the virtual ideal spring, the tube radius, as well as the 5-7-7-5 and radius defect of the carbon nanotube.