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Context: CL-20/DNDAP cocrystal is a promising new type of explosive with exceptional energy density and detonation parameters. However, compared to TATB, FOX-7 and other insensitive explosives, it still has higher sensitivity. In order to decrease the sensitivity of CL20/DNDAP cocrystal explosive, in this article, a CL20/DNDAP cocrystal model was established, and six different types of polymers, including butadiene rubber (BR), ethylene-vinyl acetate copolymer (EVA), polyethylene glycol (PEG), hydroxyl-terminated polybutadiene (HTPB), fluoropolymer (F2603), and polyvinylidene difluoride (PVDF), were added to the three cleaved surfaces of (1 0 0), (0 1 0) and (0 0 1) to obtain polymer-bonded explosives (PBXs). Predict the effects of different polymers on the stability, trigger bond length, mechanical properties, and detonation performance of PBXs. Among the six PBX models, CL-20/DNDAP/PEG model exhibited the highest binding energy and the lowest trigger bond length, indicating that CL-20/DNDAP/PEG model had the best stability, compatibility, and the least sensitivity. Furthermore, although the CL-20/DNDAP/F2603 model demonstrated superior detonation capabilities, it should be noted that this model displayed low levels of compatibility. Overall, CL-20/DNDAP/PEG model exhibited the superior comprehensive properties, thereby demonstrating that PEG is a more suitable binder option for PBXs based on the CL20/DNDAP cocrystal. Methods: The properties of CL-20/DNDAP cocrystal-based PBXs were predicted by molecular dynamics (MD) method under Materials Studio software. The MD simulation time step was set at 1fs and the total MD simulation time was 2ns. The Isothermal-isobaric (NPT) ensemble was used for the 2ns of MD simulation. The COMPASS force field was used, and the temperature was set at 295K. [ABSTRACT FROM AUTHOR]

The molecular dynamics simulations based study of graphene (Gr) reinforced polymer nanocomposite (PNC) is a very intense research field due to the enormous range of possible applications involving such materials. Current review focuses on the reinforcing mechanisms behind the enhancement of the mechanical, thermal, and tribological properties of Gr-based PNC based on molecular dynamics (MD) simulations. It also reviews the capabilities of MD simulations to reproduce the experimentally measured materials properties and behaviour of Gr-based PNC. This review-based investigation summarizes the current literature of the MD simulation studies as well as comparisons for the tribo-thermo-mechanical properties of Gr-based PNC and identification of the suitable simulation protocols for model development, characterization, and mechanism analysis. The careful review of published MD simulation-based articles indicates that two important factors help to reproduce the experimentally measured materials properties and behaviour of Gr-based PNC. They are mainly (a) simulation models (material used for reinforcement, e.g. Gr and Gr derivatives) development and (b) simulation run parameters. In this review, details about those factors have been discussed keeping major consideration of Gr effect (e.g. shape or length, orientation, clustering, weight fraction, different layer, functionalization, and defective condition). Finally potential applications, current challenges and future prospects are discussed which can be useful to the research community. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations permit copying methodical differences of mechanical and interfacial properties outside the scope of experimental approaches. This paper reviews the effect of graphene on the mechanical properties such as Young's modulus, shear modulus, ultimate tensile strength and Young's modulus of epoxy nanocomposites via MD simulations. In MD simulation arrangement, the computational techniques are studied for dissimilar qualities of mixing a polymer matrix with graphene as the nanofiller. Subsequently, numerous papers are discussed involving graphene and its polymer nanocomposites. Furthermore, advances in molecular modeling, simulation of graphene and their nanocomposites are deliberated by considering feature charge graphene assemblies, aspect ratio, weight fraction, atomic density, molecular energy and density effect as the primary factors. It was concluded from investigations that their mechanical properties as well as interfacial properties are suitable for scientific applications. [ABSTRACT FROM AUTHOR]

Functionalization of graphene is the best way to create a high degree of dispersion and bonding to polymer matrix in order to obtain high performance composites. The effects of carboxyl (−COOH) functionalized graphene (FG) on the mechanical properties of its epoxy-based nanocomposites have been examined by molecular dynamics (MD) simulations. Simulations cells of nanocomposites with varying wt% of FG (1, 2, and 3 wt%) were constructed using Material Studio 6.0. The MD simulation findings of nanocomposites reveal that they have better mechanical properties such as elastic modulus, bulk modulus, shear modulus, and the Poisson's ratio than pure epoxy. Furthermore, the computational results of nanocomposites have been effectively confirmed with available experimental data. Therefore, the current MD simulation shows a decent computational sign for the existing experimental and simulation outcomes on mechanical properties of FG/epoxy nanocomposites. [ABSTRACT FROM AUTHOR]

In this study, the molecular dynamics method was used to explore the effects of the degradation of an adhesion agent (PEG‐TDI) in a nitrate ester plasticized polyether propellant on the compatibility and diffusibility of energetic plasticizers (NG and BTTN) and the glass transition temperature and mechanical properties of the blend system (PEG‐TDI/NG/BTTN). The radial distribution function, the mean square radius of gyration, and fractional free volume of the PEG‐TDI/NG/BTTN system under different degrees of degradation conditions were calculated. The diffusibility and compatibility of NG and BTTN, the glass transition temperature, and the mechanical properties of the blended system were then discussed. The results showed that, with aggravation of the degree of PEG‐TDI degradation, the fractional free volume in the system decreased, intermolecular hydrogen bonding and van der Waals interactions enhanced, and the size of the polymeric nematic decreased. These changes eventually caused the diffusion ability of NG and BTTN to weaken, compatibility to be enhanced, and glass transition temperature, stiffness, and yield strength of the PEG‐TDI/NG/BTTN system to increase. [ABSTRACT FROM AUTHOR]

In this study, the mechanical properties of graphene–epoxy nanocomposites were investigated using experimental tests, molecular dynamics (MD) simulation and Halpin_Tsai semi-empirical micromechanical model. To fabricate graphene/epoxy nanocomposite, specimens containing 0, 0.3, 0.5 and 0.7 weight percent (wt.%) of graphene nanoparticle (GNP), high power dispersion sonicating method and high-speed shearing were employed. Then, tensile and flexural modulus of manufactured nanocomposites were obtained, and the results illustrated that the elastic and flexural modulus of GNP/epoxy nanocomposites increased significantly until GNP was added up to 0.5 wt.% and after that, the trend of increasing elastic modulus declined which could be due to local GNP agglomerations within the nanocomposites with higher contents of filler. Furthermore, graphene, epoxy and graphene–epoxy nanocomposites were simulated by MD, and the mechanical properties of simulated graphene–epoxy nanocomposites were calculated. However, the effect of temperature and strain rate on tensile properties of graphene–epoxy nanocomposites was studied, which showed that increasing temperature decreased the strength of graphene–epoxy nanocomposites, and also increasing the strain rates led to an increase in the elastic modulus. Finally, experimental results and the Halpin_Tsai model were compared in which a good agreement between experimental and analytical results was observed. [ABSTRACT FROM AUTHOR]

Based on molecular dynamics (MD) simulation, the binding energy, cohesive energy density (CED), bond length, and mechanical parameters were calculated for 2,6-diamino-3,5-dinitropyrazine-l-oxide (LLM-105) crystal, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystal, and their co-crystals under different temperatures. Three LLM-105/HMX patterns were constructed to investigate the influence of component proportion on structures and properties of co-crystals, in which the mole ratios of LLM-105 and HMX are 1:1, 1:2, and 2:1. The effect of temperature and components on the stability and sensitivity were investigated as well. The results show that the binding energies, CED and mechanical parameters of all the co-crystals, decrease when the temperature increases from 248 to 398 K, while their maximum N–NO2 bond length (Lmax) increases with rising temperature, indicating that the sensitivities increase and stabilities decrease when temperature rises. At all temperatures, co-crystals exhibit larger CED and shorter bond length than that of single explosive, demonstrating that they are more stable and less sensitive than single crystal, where the stability of co-crystals was ordered as 2:1>1:1>1:2. Moreover, the bulk modulus (K) and shear modulus (G) of co-crystals are lower than that of HMX, conversely, the Cauchy pressure and K/G are higher than that of HMX, implying co-crystals have better ductility. Finally, the 2:1 ratio of LLM-105/HMX co-crystal was identified as the excellent one, owning to the highest binding energy, highest CED, shortest Lmax, and greatest ductility. [ABSTRACT FROM AUTHOR]

In order to better understand the role of binder content, molecular dynamics (MD) simulations were performed to study the interfacial interactions, sensitivity and mechanical properties of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/2,4,6-trinitrotoluene (CL-20/TNT) based polymer-bonded explosives (PBXs) with fluorine rubber F2311. The binding energy between CL-20/TNT co-crystal (1 0 0) surface and F2311, pair correlation function, the maximum bond length of the N–NO2 trigger bond, and the mechanical properties of the PBXs were reported. From the calculated binding energy, it was found that binding energy increases with increasing F2311 content. Additionally, according to the results of pair correlation function, it turns out that H–O hydrogen bonds and H–F hydrogen bonds exist between F2311 molecules and the molecules in CL-20/TNT. The length of trigger bond in CL-20/TNT were adopted as theoretical criterion of sensitivity. The maximum bond length of the N–NO2 trigger bond decreased very significantly when the F2311 content increased from 0 to 9.2%. This indicated increasing F2311 content can reduce sensitivity and improve thermal stability. However, the maximum bond length of the N–NO2 trigger bond remained essentially unchanged when the F2311 content was further increased. Additionally, the calculated mechanical data indicated that with the increase in F2311 content, the rigidity of CL-20/TNT based PBXs was decrease, the toughness was improved.

Five novel poly-(phthalazinone ether sulfone ketone (PPESK) polymers were designed by introducing the sbndNO 2 , sbndNH 2 , sbndN 3 , sbndONO 2 and sbndNF 2 function groups into the polymer chain. The glass transition temperature ( T g ), density, cohesive energy density (CED), solubility parameters (δ) and mechanical properties were simulated via the molecular dynamics (MD) method for these novel polymers. The T g values of all these polymers were predicted above 500 K, and especially that of the sbndNH 2 substituted polymer close to 600 K. Cohesive energy density (CED) and solubility parameter (δ) values of these five polymers were predicted very close at 298 K, implying that they have similar solubility. The predicted Young's modulus ( E ), Bulk modulus ( K ), Shear modulus ( G ) and Poisson’s ratio ( γ ) indicate that these polymers have good mechanical properties and plastic properties, and the K/G and Cauchy pressure ( C 12 - C 44 ) indicate that they have good ductility. [ABSTRACT FROM AUTHOR]

The effects of length and content of chain branching on the mechanical properties of polyethylene (PE) in atomic scale were examined by molecular dynamics (MD) simulations. Methyl-, ethyl- and butylgroups were adopted as branched chains to distribute along PE backbones. Plastic flow deformation was captured by providing a uniaxial tensile loading at a given strain rate, which shows the characteristic of rate dependence. Current results are in reasonable agreements with existing experimental data. The statistical results show that the longer length of chain branching induces lower equilibrium density and higher yield strength of branched PE. In addition, higher content of chain branching brings higher equilibrium density and lower yield strength of branched PE. It is assumed that the distribution of dihedral angles influences the deformation of PE definitely. The non-bond interactions contribute to the load-bearing capacity of PE largely. Branched PE shows big differences on mechanical behaviours comparing with the linear one. Chain branching distribution also greatly affects the performance of PE, which needs a further discussion. [ABSTRACT FROM AUTHOR]

Through molecular dynamics (MD) simulation, the dependencies of temperature, grain size and strain rate on the mechanical properties were studied. The simulation results demonstrated that the strain rate from 0.05 to 2 ns-1 affected the Young’s modulus of nickel nanowires slightly, whereas the yield stress increased. The Young’s modulus decreased approximately linearly; however, the yield stress firstly increased and subsequently dropped as the temperature increased. The Young’s modulus and yield stress increased as the mean grain size increased from 2.66 to 6.72 nm. Moreover, certain efforts have been made in the microstructure evolution with mechanical properties association under uniaxial tension. Certain phenomena such as the formation of twin structures, which were found in nanowires with larger grain size at higher strain rate and lower temperature, as well as the movement of grain boundaries and dislocation, were detected and discussed in detail. The results demonstrated that the plastic deformation was mainly accommodated by the motion of grain boundaries for smaller grain size. However, for larger grain size, the formations of stacking faults and twins were the main mechanisms of plastic deformation in the polycrystalline nickel nanowire. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations were carried out to study the polymer-bonded explosives (PBXs) where the explosive base was the well-known high energy co-crystal compound, 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexazaisowurtzitane/2,4,6-trinitrotoluene (CL-20/TNT), and the polymer binders were fluorine rubber (F, fluorine resin (F, polyvinyl acetate (PVAc) and polystyrene (PS), respectively. The binding energies, pair correlation functions (PCFs) and mechanical properties of the PBXs were reported. According to our theoretical results of binding energies, the compatibility of the PBXs is predicted to be in the following order: CL-20/TNT/PVAc CL-20/TNT/F CL-20/TNT/PS CL-20/TNT/F. The binding energies of the PBXs on three crystalline surfaces, (100), (001), (010), of the CL-20/TNT co-crystal were also compared: CL-20/TNT(100)CL-20/TNT(001)CL-20/TNT(010) for F, F, and PS; CL-20/TNT(001)CL-20/TNT(100)CL-20/TNT(010) for PVAc. The PCF analysis reveals that there exist H-bonds between H and O, F, and N atoms on all three interfaces and among all H-bonds, N H-bond has the fewest number. For the CL-20/TNT co-crystal, the moduli can be reduced by adding a small amount of the polymer binders but the ductility can be prolonged only by F and F. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were carried out to explore a ε-CL-20/HMX (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexazaisowurtzitane/1,3,5,7-tetranitro-1,3,5,7- tetrazacyclooctane) co-crystal-based polymer-bonded explosive (PBX) with HTPB (hydroxyl-terminated polybutadiene). The binding energies, pair correlation functions, and mechanical properties of the PBXs were reported. From the calculated binding energy, it was found that the order of the binding energies per unit surface between the crystalline surface and HTPB is (0 1 0) > (1 0 0) > (0 0 1). The pair correlation function revealed that the H···O and H···N H-bonds exist on the interfaces between the crystalline surfaces and HTPB, and the number of H∙∙∙O hydrogen bonds (H-bonds) atom pairs is ten times more than that of H∙∙∙N H-bonds. Additionally, the calculated mechanical data indicated that the stiffness of the co-crystal/HTPB PBX is weaker and its ductility is better than those of the co-crystal. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new multiple C-S-Hs model at atomic scale including C-S-H layers and water. • The strength of multiple C-S-Hs model are closer to that of cement paste at macroscale. • Low interlayer spacing greatly affects the mechanical properties of the system. • High strain rate enhances the mechanical properties of the model. • The structure of C-S-H stay intact in the composite model during tension process. Many researches have been conducted to study the properties of calcium silicate hydrate (C-S-H) using numerical modeling. However, there still exists a large gap between the mechanical characteristics of C-S-H. A new composite C-S-Hs model is proposed to more realistically represent the layered feature in this paper. Compared with regularly-arranged C-S-Hs model, larger interlayer space provides sufficient space for water adsorption and the arrangement of C-S-H cells. The random arrangement of multiple C-S-H cells and additional water molecule adsorption have a significant impact on the composite C-S-Hs system. Uniaxial tension tests with different strain rates are utilized to investigate the mechanical properties of the composite C-S-Hs model compared with those of regularly arranged C-S-H cells. The simulation results demonstrate that the mechanical properties of the composite C-S-Hs model are closer to those of cementitious materials on the macroscopic scale. The simulation results highlight the impact of strain rate and interlayer spacing on the characteristics of the multiple C-S-Hs model. The proposed composite C-S-Hs model provides a more reasonable procedure for molecular dynamics simulation of C-S-H. [ABSTRACT FROM AUTHOR]

In order to better understand the role of binder content, molecular dynamics (MD) simulations were performed to study the interfacial interactions, sensitivity and mechanical properties of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/2,4,6-trinitrotoluene (CL-20/TNT) based polymer-bonded explosives (PBXs) with fluorine rubber F2311. The binding energy between CL-20/TNT co-crystal (1 0 0) surface and F2311, pair correlation function, the maximum bond length of the N–NO2 trigger bond, and the mechanical properties of the PBXs were reported. From the calculated binding energy, it was found that binding energy increases with increasing F2311 content. Additionally, according to the results of pair correlation function, it turns out that H–O hydrogen bonds and H–F hydrogen bonds exist between F2311 molecules and the molecules in CL-20/TNT. The length of trigger bond in CL-20/TNT were adopted as theoretical criterion of sensitivity. The maximum bond length of the N–NO2 trigger bond decreased very significantly when the F2311 content increased from 0 to 9.2%. This indicated increasing F2311 content can reduce sensitivity and improve thermal stability. However, the maximum bond length of the N–NO2 trigger bond remained essentially unchanged when the F2311 content was further increased. Additionally, the calculated mechanical data indicated that with the increase in F2311 content, the rigidity of CL-20/TNT based PBXs was decrease, the toughness was improved. [ABSTRACT FROM AUTHOR]

• Mechanical properties of α, β, and γ graphyne nanotubes (GNTs) is characterized. • The role of acetylenic bonds in the mechanical properties of nanotubes is investigated. • Unlike the brittle behavior of CNTs, α-GNTs-zigzag (one type of GNTs) exhibits plastic deformation before failure. • The ductile behavior of α-GNTs-zigzag is originated from the atoms reconstruction. • The Poisson's ratio of the GNTs is calculated for the first time. • Different failure mechanisms of nanotubes based visualization of nanotubes fracture were analyzed and discussed. The mechanical properties, failure mechanisms of one-dimensional carbon allotropes including α, β, γ graphyne nanotubes (GNTs) and also conventional carbon nanotubes (CNTs) were calculated by using classical molecular dynamics simulations. The GNTs was showed unique properties due to the presence of single, double and triple bonds in their crystal lattice compared to CNTs. It was found that the α-GNT phase has had an ability for typical plastic behavior due to the presence of the acetylenic linkages and the atoms reconstruction processes. The effects of acetylenic linkages on the mechanical properties of different phases of GNTs including fracture behavior, Young's modulus, and Poisson's ratio were also investigated under uniaxial tension. Among GNTs, α-GNTs exhibited the lowest fractures stresses and Young's modulus, while γ-GNTs showed the highest fractures stress and Young's modulus. Moreover, GNTs had a higher Poisson's ratio due to possessing a higher variety of pore sizes compared to CNTs. These features made the GNTs suitable for many different applications and open up a novel view for the study of plastic carbon-based nanomaterials. As well as, based on the visualization of the nanotubes fractures, the failure mechanism of the nanotubes was analyzed and discussed. [ABSTRACT FROM AUTHOR]