Enhancement of toughness of SiC through compositing SiC-Al interpenetrating phase composites.

Silicon carbide has excellent properties such as high hardness and decomposition temperature, but its applications are limited by its poor toughness. Here, we investigate the enhancement of SiC's toughness by compositing silicon carbide-aluminum (SiC-Al) interpenetrating phase composites (IPCs) via molecular dynamics simulations. IPCs are a class of composites consisting of two or more phases that are topologically continuous and three-dimensionally interconnected through the microstructure. The Young's modulus and ultimate strength gradually increases with an increment of the volume fraction of SiC, opposite to the fracture strain. The interface between SiC and Al affects the mechanical properties of SiC-Al IPCs. When the volume fraction of SiC is less than 0.784, the attenuation rate of ultimate strength and fracture strain decreases. The attenuation rate increases when the volume fraction of SiC is more than 0.784. There are a minimum of ultimate strength and fracture strain at the 0.784, 0.7382 and 2.8610, respectively. The hardness of SiC-Al IPCs is about 48% of SiC. The change of SiC-Al IPCs hardness is more stable than that of SiC in the later stage of the nanoindentation test.

Anisotropic and temperature dependent mechanical properties of carbon honeycomb.

Carbon honeycomb (CHC) is a newly synthesized carbon allotropy with promising applications in many fields of science and engineering. In this work, we investigate the mechanical properties of CHC with focus on the anisotropicity in terms of the tilt angle θ in zigzag-armchair (x-y) plane using molecular dynamics simulations. Results show that the tensile strength of CHC ranges from 15.0 to 23.7 GPa at room temperature, which is lower than that of graphene due to the weakness on the junction. Meanwhile, except in the armchair direction, the strength of CHC reduces as the stretching direction moves away from the zigzag direction, similar to that of graphene, while the Young's modulus decreases with respect to tilt angle, opposite to that of graphene. Increasing the temperature will weaken CHC by reducing the strength, there is only a 16% reduction in the minimum strength in the x-y plane as the temperature increases from 100 to 900 K. In addition, the crack occurs first in cell axis direction then in the x-y plane, different from graphene which appears along the zigzag direction only.

Numerical Simulation of the Pouring Process in Deep-Water Flexible Pipe End Fittings.

The pouring quality of epoxy resin in the resin cavity of deep-water composite flexible pipe end fittings has a decisive effect on the performance of the end fitting, and accurate investigation of the resin flow during the pouring process can provide a reference for optimization of the pouring process so that the pouring quality can be improved. In this paper, numerical methods were employed to investigate the pouring process of the resin cavity. The distribution and evolution of defects were studied, and the influence of pouring rate and fluid viscosity on pouring quality was analyzed. In addition, based on the simulation results obtained, some local pouring simulations were conducted for the armor steel wire, the key characteristic structure of the end fitting resin cavity that has a significant influence on the pouring quality, to investigate the influence of the geometrical characteristics of the armor steel wire on the pouring quality. Based on these results, the existing end fitting resin cavity structure and pouring process were optimized, and better pouring quality was obtained.

Enhancement of Diffusion Assisted Bonding of the Bimetal Composite of Austenitic/Ferric Steels via Intrinsic Interlayers.

We investigate the effect of the intrinsic interlayers on the diffusion assisted bonding properties of the austenitic steel (stainless steel 316L) and ferric steels (Low-carbon steel Q345R) in a hot rolling process by molecular dynamics simulations and experiment. The introduction of an intrinsic interlayer (Cr or Ni) widens the diffusion region, leading to enhancement of bonding. The thickness of the diffusion region enlarges with an increase of temperature, with an enhancement factor of 195% and 108%, for Cr and Ni interlayer, respectively, at the temperature of 1800 K. Further diffusion analysis reveals the unsymmetrical diffusion near the interface. Our experimental investigation evidenced our computation discovery.

Molecular Dynamics Simulation on Creep Behavior of Nanocrystalline TiAl Alloy.

TiAl alloy represents a new class of light and heat-resistant materials. In this study, the effect of temperature, pressure, and grain size on the high-temperature creep properties of nanocrystalline TiAl alloy have been studied through the molecular dynamics method. Based on this, the deformation mechanism of the different creep stages, including crystal structure, dislocation, and diffusion, has been explored. It is observed that the high-temperature creep performance of nanocrystalline TiAl alloy is significantly affected by temperature and stress. The higher is the temperature and stress, the greater the TiAl alloy's steady-state creep rate and the faster the rapid creep stage. Smaller grain size accelerates the creep process due to the large volume fraction of the grain boundary. In the steady-state deformation stage, two kinds of creep mechanisms are manly noted, i.e., dislocation motion and grain boundary diffusion. At the same temperature, the creep mechanism is dominated by the dislocation motion in a high-stress field, and the creep mechanism is dominated by the diffusion creep in the low-stress field. However, it is observed to be mainly controlled by the grain boundary diffusion and lattice diffusion in the rapid creep stage.

Molecular Dynamics Simulation on Mechanical and Piezoelectric Properties of Boron Nitride Honeycomb Structures.

Boron nitride honeycomb structure is a new three-dimensional material similar to carbon honeycomb, which has attracted a great deal of attention due to its special structure and properties. In this paper, the tensile mechanical properties of boron nitride honeycomb structures in the zigzag, armchair and axial directions are studied at room temperature by using molecular dynamics simulations. Effects of temperature and strain rate on mechanical properties are also discussed. According to the observed tensile mechanical properties, the piezoelectric effect in the zigzag direction was analyzed for boron nitride honeycomb structures. The obtained results showed that the failure strains of boron nitride honeycomb structures under tensile loading were up to 0.83, 0.78 and 0.55 in the armchair, zigzag and axial directions, respectively, at room temperature. These findings indicated that boron nitride honeycomb structures have excellent ductility at room temperature. Moreover, temperature had a significant effect on the mechanical and tensile mechanical properties of boron nitride honeycomb structures, which can be improved by lowering the temperature within a certain range. In addition, strain rate affected the maximum tensile strength and failure strain of boron nitride honeycomb structures. Furthermore, due to the unique polarization of boron nitride honeycomb structures, they possessed an excellent piezoelectric effect. The piezoelectric coefficient e obtained from molecular dynamics was 0.702   C / m 2 , which was lower than that of the monolayer boron nitride honeycomb structures, e = 0.79   C / m 2 . Such excellent piezoelectric properties and failure strain detected in boron nitride honeycomb structures suggest a broad prospect for the application of these new materials in novel nanodevices with ultrahigh tensile mechanical properties and ultralight-weight materials.

Shift of Creep Mechanism in Nanocrystalline NiAl Alloy.

We have examined the effects of temperature, stress, and grain size on the creep process including creep strain, crystal structure, dislocations and diffusions of nanocrystalline NiAl alloy through molecular dynamics simulations. A smaller grain size accelerates the creep process due to the large volume fraction of grain boundaries. Higher temperatures and stress levels also speed up this process in terms of dislocation changes and atom diffusion. In both primary creep and steady-state creep stages, atomic diffusion at the grain boundary could be seen and the dislocation density increased gradually, indicating that the creep mechanism at these stages is Coble creep controlled by grain boundary diffusion while accompanied by dislocation nucleation. When the model enters the tertiary creep stage, it can be observed that the diffusion of atoms in the grain boundary and in the crystal and the dislocation density gradually decreases, implying that the creep mechanisms at this stage are Coble creep, controlled by grain boundary diffusion, and Nabarro-Herring creep, controlled by lattice diffusion.

The Temperature-Sensitive Anisotropic Negative Poisson's Ratio of Carbon Honeycomb.

We report that carbon honeycomb, a new three-dimension carbon allotrope, exhibits large negative Poisson's ratio, as large as -0.32, in tensile revealed via molecular dynamics simulations. The Poisson's ratio of carbon honeycomb is anisotropic, and sensitive to temperature. The carbon honeycomb has phase transformation from normal to auxetic by tensile, along both zigzag and armchair directions. The critical strain for the normal-auxetic transition along the cell-axis direction reduces with respect to an increase in temperature. Combined with high strength of 50 GPa, such a unique and adjustable negative Poisson ratio suggests broad engineering applications of carbon honeycomb.

Mechanical Properties of Vacancy Tuned Carbon Honeycomb.

Carbon honeycomb (CHC) has great application potential in many aspects for the outstanding mechanical properties. However, the effect of both defects and temperature on the mechanical properties are far from reasonable understanding, which might be a huge obstacle for its promising applications as engineering materials. In this work, we investigate the effect of vacancy-type defect, which is inevitably exists in material, on the mechanical properties of CHC via reactive molecular dynamics simulations. The mechanical strength is anisotropic and decreases with the increasing temperature. CHC yield in cell axis direction since the break of C⁻C bonds on the junction. Vacancies weaken CHC by reducing the strength and failure strain. The effect of single vacancy on strength of CHC becomes more obvious with reducing temperature and is sensitive to the location and bonding of the vacancies. The maximum reduction of strength in cell axis direction is with vacancy on the middle of the wall of CHC where sp² bonds are removed. The strength is reduced by 8.1% at 500 K, 11.5% at 300 K and 12.8% at 100 K. With 0.77% defect concentration, the strength reduces 40.3% in cell axis direction but only 18.7% in zigzag direction and 24.4% in armchair direction.