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The interfaces between graphene and graphane play an important role in developing graphene-graphane-based electronic devices. We identify three most common types of graphane-graphene interface, and perform atomistic simulations to determine three key parameters that characterize the interface structural properties: mismatch strain, tilt angle, and interfacial stress. Further through atomistic simulations, we find that the composite sheets can develop complex morphologies, such as ripples, warps and wedges. These morphologies can be accurately reproduced by our finite-element modeling with interfacial properties explicitly included. We further show that mismatch in the lattice parameters between graphene and graphane is the dominant factor that causes the complex morphologies. Our work provides a quantitative framework for analyzing and designing graphene-graphane composite sheet architectures, and further for exploring their electronic properties. [ABSTRACT FROM AUTHOR]

A three-dimensional concurrent atomistic/continuum analysis is performed to study the stress distributions in an epitaxial island. The island and the adjacent substrate are modeled by the molecular dynamics method, and the surrounding zone is modeled by the finite element method in which the nonlinear elasticity is governed by the atomic potential. An overlapping zone is defined to be the location where the atomistic and continuum models exchange necessary material information. It is found that the nonlinear elasticity based on the atomic potential is required for a smooth stress transition in the overlapping zone, and that the linear elasticity assumption significantly overestimates the stress levels at moderate and high loading levels. The implications of the present results on surface roughening driven by strain energy are discussed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this work, the extended finite element method (XFEM) is for the first time coupled with face-based strain-smoothing technique to solve three-dimensional fracture problems. This proposed method, which is called face-based smoothed XFEM here, is expected to combine both the advantages of XFEM and strain-smoothing technique. In XFEM, arbitrary crack geometry can be modeled and crack advance can be simulated without remeshing. Strain-smoothing technique can eliminate the integration of singular term over the volume around the crack front, thanks to the transformation of volume integration into area integration. Special smoothing scheme is implemented in the crack front smoothing domain. Three examples are presented to test the accuracy, efficiency, and convergence rate of the face-based smoothed XFEM. From the results, it is clear that smoothing technique can improve the performance of XFEM for three-dimensional fracture problems. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents a general formulation for simulating the singular stress field at the vicinity of the crack-tip for linear fracture mechanics problems, based on the edge-based smoothed finite element method (ES-FEM) settings. This novel "singular ES-FEM" makes use of the unique feature offered by the ES-FEM that only the assumed displacement values (not the derivatives) are required to compute the stiffness matrix of the discretized system. The present singular ES-FEM method uses a basic mesh of linear triangular elements and a layer of novel "five-noded crack-tip elements" sharing the crack-tip node. The five-noded crack-tip element has one additional node on each of the edges connected to the crack-tip, and the locations of the "edge-node" can be arbitrary. A number of examples are analyzed and the results demonstrate that the present singular ES-FEM is generally softer and much more accurate than the existing FEM. The stress intensity factors obtained using the singular ES-FEM are very stable for different area-integration paths designed around the crack-tip. The present singular ES-FEM is found an excellent alternative to the standard FEM for fracture problems. [ABSTRACT FROM AUTHOR]

A constitutive model for thermoplastic polymeric materials and its finite element implementation are presented. The model was verified by both tensile and indentation experimental results. In addition, a five-step indentation scheme, which is able to separate time-dependent plastic deformation from elastic and visco-elastic–plastic deformations, was formulated to extract the complete list of parameters in the constitutive model. Four types of indentation tests on polymethylmethacrylate (PMMA), following the five-step and other schemes, were performed. Experimental data were used to extract all the parameters in the model and verify the five-step test scheme. Good agreement between the experimental results and model prediction indicate that the five-step indentation scheme is a practical approach to determine the mechanical properties of thermoplastic polymers. [ABSTRACT FROM AUTHOR]

Biological materials in nature serve as a valuable source of inspiration for developing novel synthetic materials with extraordinary properties or functions. Much effort to date has been directed toward fabricating and understanding bio-inspired nanocomposites with internal architectures mimicking those of nacre and collagen fibril. Here we establish simple and explicit analytical solutions for both upper and lower bounds of the elastic properties of biocomposites in terms of various physical and geometrical parameters including volume fraction and moduli of constituents, and aspect ratio and alignment pattern of stiff reinforcements. Numerical analyses based on the finite element method are performed to validate the derived elastic bounds. [ABSTRACT FROM AUTHOR]