The microstructure of 3D printed composites is inherently different than traditional composites due to the manufacturing process. The differences influence morphological characteristics such as the ...contour of the cross-section of the fiber and alter the macroscopic behavior of 3D printed parts. This article investigates the microstructural morphology of 3D printed nylon reinforced with continuous carbon fibers and the effect of microstructural irregularities on the macrostructural elastic response through stochastic homogenization modeling. The contour of the carbon fibers is extracted from scanning electron microscopy (SEM) micrographs available in the literature and used to generate realistic and ideal (ellipsoidal, circular) contours in a stochastic manner using a new methodology. Furthermore, a novel method is introduced to generate single- and multiple-fiber representative volume elements (RVEs) in finite element (FE) software for the approximation of the effective elastic properties. To minimize the computational effort associated with the full numerical modeling of multiple-fiber RVEs, a novel semi-analytical approach is demonstrated based on the numerical estimation of stiffness contribution tensors and the implementation of analytical effective field methods. The results of the numerical and semi-analytical models are compared with analytical models and exhibit a good agreement.
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•New methodology for generating stochastic fiber contours.•Novel method for modeling single- and multiple-fiber Representative Volume Elements.•Novel approach for semi-analytical effective field methods.
Based on the successful applications of the first-principles calculations method in many fields, the electronic structures, elastic properties, fracture toughness, and thermal properties of M23C6 ...carbides are studied using first-principles calculation based on density functional theory (DFT) in this research. The results of cohesive energy and the formation enthalpy exhibit the thermodynamic stability of these M23C6 carbides. The electronic properties indicate that the bond of M23C6 carbides shows the mixture characteristic of metallic and covalent bonds. Polycrystalline elastic properties, hardness and fracture toughness show that these M23C6 carbides are ductile, tolerant to damage, and elastic anisotropic. The probable cleavage plane and slip system are (110) plane and {100} 〈100〉 for Ti23C6, V23C6, Cr23C6, and Co23C6, while that are (100) plane, {110} 〈110〉 for Mn23C6, Fe23C6 and Ni23C6. Moreover, lattice thermal conductivity and its dependence on temperature are discussed.
•These M23C6 carbides are mechanically stable, ductile, resistant to crack, tolerant to damage, and elastic anisotropic.•The probable cleavage plane and slip system for M23C6 (M = Ti, V, Cr, and Co) carbides are (110) plane and {100} .•The calculated kph and kmin manifest that M23C6 carbides are potential high-temperature TBC materials.
Covellite, the CuS, is a unique compound owing to both superconducting and metallic behavior at different temperatures. We model and characterize the elastic, electronic and associated properties of ...the CuS launching the state-of-art first-principles calculations taking the exchange and correlation energy functionals based on the gradient generalized approximation and hybrid functionals. After settling the crystal structure, we find elastic constants and related mechanical constants. As the crystal satisfies the stability criterion, so we compute the sound velocity, Debye temperature and lower bound of the thermal conductivity also. The electronic bands dispersion and the density of states exhibit the metallic behavior of the compound. The isotropic and the anisotropic parts of the electron momentum density are calculated by means of the Compton profiles. The isotropic Compton profile is compared with our measurement deploying the 5Ci 241Am spectrometer based on the 59.54 keV gamma-rays and a good agreement is found. The anisotropies in the directional Compton profiles are also presented. The Mulliken population analysis is performed to see nature of bonding and occupied charges on the crystallographically distinct Cu and S atoms in CuS.
•First attempt to report the directional and spherically averaged Compton profiles of CuS using LCAO method.•First attempt to investigate experimental Compton profiles of CuS using 59.54 keV gamma-rays.•First attempt to investigate elastic properties of CuS using first principle method based on LCAO technique.•First attempt to investigate thermodynamic properties of CuS using calculated elastic parameters.•The theoretical results are well synchronized with the experimental investigations.
The existing longitudinal structural model of shield tunnels usually simplify the tunnel as a Euler-Bernoulli beam on elastic foundation, which ignores the shearing dislocation between rings. To ...model the dislocation between rings, this paper proposed a soil-tunnel interaction model based on the Timoshenko beam simplified model (TBSM) of tunnel on Vlasov foundation. The governing differential equation and the closed-form solution for TBSM on Vlasov foundation subjected to any given pressure are derived with consideration of two types of boundary conditions. The proposed model was adopted to analyze the behaviors of a shield tunnel subjected to external forces transferred from surcharge load on the ground surface. Factors influencing the longitudinal behavior of shield tunnels are discussed. The factors include the equivalent of shear stiffness, location of load application, and the rotational stiffness of the joint between tunnel and station. The results indicated that Euler-Bernoulli beam model underestimates deformation and overestimates the internal forces in the tunnel structure. When the load application is close to the station, with the decrease of the distance between the load and the station will lead to a slightly decrease of the maximum settlement of the tunnel, and an increase of the maximum internal forces and the maximum joint deformation. A stiffer joint between tunnel and station will cause greater internal forces at the location of joint.
A two-node method is proposed in this paper to predict the effective elastic properties of periodic cellular truss materials based on the traditional representative volume element (RVE) method. ...Through the two-node method, the original unit cell with multiple boundary nodes is transformed into a new equivalent unit cell with only two boundary nodes, and the effective elastic properties of the original unit cell can be indirectly obtained by the new equivalent unit cell. The accuracy of the present method is theoretically and numerically validated by using the asymptotic homogenization (AH) method and experimentally validated by the quasi-static uniaxial compression tests of the 3D printed cellular structures. Both theoretical and numerical results show that the present two-node method is more accurate and easier to implement than the traditional RVE method and the AH method when the size of the unit cell is negligible relative to the size of the macrostructure. For periodic cellular truss materials with rod elements, the present method can provide results with the same accuracy as the AH method but with more efficiency. For periodic cellular materials with beam elements, the present method can provide more accurate lower bound of the effective elastic properties than the traditional RVE method. The uniaxial compression tests results show that the elastic modulus of the equivalent structure obtained by the two-node method is almost the same as its original structures and is in good agreement with the calculation results obtained by the AH method.
•A method is proposed to predict the effective elastic properties of periodic cellular truss materials.•The method is easier to implement than the AH method but with the same accuracy.•The method provides more accurate lower bound of effective elastic properties than the RVE method.•Several 3D cellular structures are designed, manufactured and compressed, and the experimental results are in good agreement with the calculation results.
This paper presents the semi-analytical solution for the transverse local fields and overall transverse properties of composite materials with aligned multiple cylindrical nanofibers. The interface ...between each fiber and the matrix is treated as a material surface described by the Steigmann–Ogden model, which accounts for the effects of surface tension as well as for membrane and bending stiffness of the surface. Assuming a plane strain setting, the problem is formulated in the transverse plane as an infinite elastic matrix with multiple circular inhomogeneities subjected to a uniform far-field load. The expressions for all elastic fields in the composite system are obtained analytically in the form of infinite series expressions. The Maxwell methodology is used to obtain the overall transverse elastic properties. The goal of this work is twofold: (a) to study the influence of the interactions between the inhomogeneities on the local fields and overall transverse properties of the composite system, and (b) to reveal the connection of the Steigmann–Ogden model (with zero surface tension) to a specific uniform interphase layer model. The results presented in this paper demonstrate that for fiber composite materials with medium to high volume fractions, the influence of the interactions can be significant.
•A doping design method of contact materials is proposed with first-principles calculations.•Cu16Cr15W1, Cu16Cr15Os1 and Cu16Cr13Co3 were selected as reinforced doped alloys.•Cu16Cr15W1, Cu16Cr15Os1 ...and Cu16Cr13Co3 have a higher melting point than Cu16Cr16.•The mechanical properties of the doped alloys are generally better than Cu16Cr16.
In this paper, a first-principles design approach for ablation-resistant contact materials was developed. Take Cu16Cr16 for example, the melting point was used as the criterion to screen the improved doped alloys, and mechanical properties were computed to guarantee that the designed doped alloys satisfy the contacts' operational requirements. This technique revealed that Cu16Cr15W1, Cu16Cr15Os1, and Cu16Cr13Co3 have stronger properties than Cu16Cr16 in terms of melting point and resistance to deformation, which can be utilized to enhance the ablation resistance and mechanical strength of the contacts. Simultaneously, the doped alloys' brittleness guarantees the welding resistance of the contacts. As a result, strengthening contact materials can be made from these doped alloys.
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