Narrow Results

In this note, we show that special choice of the metric ansatz simplifies the equations of motion for black branes. Then we use the trick to construct charged, dilatonic black branes of Einstein–Maxwell–dilaton gravity in D = n + p + 2 dimensions, which are invariant under translation along p directions and have spherical symmetry of Sⁿ. The solutions are characterized by mass density and tension, magnetic charges, dilaton charge and coupling constant.

In this note, we apply a special metric ansatz to simplify the equations of motion for gravitational systems. Then we construct charged brane solutions in D = n+p+2 dimensions which have spherical symmetry of Sⁿ and translational symmetry along p directions. They are characterized by mass density, uniform tension and electric/magnetic charges, and nonsingular only for specific tension. In particular, we find the limits and the coordinate transformations which reduce the charged brane solutions to M2- and M5-branes. We also obtain the regularity condition for an electrically charged two-brane solution which has two tensions.

DNA's shape mostly lies on its total energy F. Its corresponding equilibrium shape equations can be obtained by classical variation method: letting the first energy variation δ⁽¹⁾F = 0. Here, we not only provide the first variation δ⁽¹⁾F but also give the second variation δ⁽²⁾F in planar case. Moreover, the general shape equations of DNA are abstained and a mistake in Zhang et al., [Phys. Rev. E70, 051902 (2004)] is pointed out.

Simulations have been carried out on [001]-oriented Ni₃Al nanowires with square cross-section with the purpose to investigate the mechanism of failure under tensile and compressive strain. Simulation results show that the elastic limit of the nanowire is up to about 15% strain with the yield stress of 5.99–6.48 GPa under tensile strain. Under the elastic stage, the deformation is carried mainly through the uniform elongation of the bonds between atoms. With more tensile strain, the slips in the {111} planes occur to accommodate the applied strain at room temperature under tensile strain. And the nanowires accommodate the compressive strain by forming the twins within the nanowires.

The manufacturing techniques of sandwich composites containing core layers of weft-knit glass fabric (WG) and weft-knit carbon fabric (WC) with carbon fabric skin layers are discussed herein. The core layers of the sandwich composites were fabricated with WG-reinforced epoxy (E) resin, WC-reinforced epoxy resin, and polyurethane foam (F). The core layer was then stacked with two pieces of carbon fabric on the top and bottom surfaces to fabricate the sandwich composites. Three sandwich composites [plain carbon fabric sandwich composite with a WG core layer (C/E/WG), plain carbon fabric sandwich composite with a WC core layer (C/E/WC), and plain carbon fabric sandwich composite with an F core layer (C/E/F)] were developed in this study. A two-step manufacturing procedure was developed to achieve sufficient adhesiveness between the skin and core layers. The tensile, flatwise compressive, and longitudinal compressive properties of these sandwich composites were measured according to referred ASTM standards on a materials test system (MTS 810). Experimental results revealed that the WC core materials displayed excellent resistance to a flatwise compressive force and the foam core material show weak resistance. Under longitudinal compression, the skin and core layer of the C/E/F specimen separated, indicating that the C/E/F specimen could not withstand longitudinal force. Moreover, the C/E/WG and C/E/WC specimens both bend at the end of the same test.

Articular cartilage is the primary structure in joints which is responsible for withstanding compressive loading; however, it is possible that cartilage also experiences localized tensile loading under various loading and boundary conditions. To date, little is known as to whether chondrocyte functions are dependent on the loading variation, especially when loading is switched from compression to tension. The purpose of this study is to examine the metabolism of chondrocytes under both compressive and tensile loadings in vitro. Our results suggest that synthesis of both collagen II and aggrecan is regulated differently by compression and tension at the mRNA level. Tensile loading significantly inhibited the mRNA expression of both collagen II and aggrecan. Since poor content of collagen II and proteoglycan has been considered a detrimental factor in the integrity of cartilage matrix, cartilage degradation and the possible formation of osteoarthritis may be the consequence of loading patterns switching from compression to tension.

In the framework of the Reissner–Simo rod theory and following Haringx’ approach for studying axial buckling in shear deformable rods, we give a mechanical interpretation of tensile instability, together with its mathematical justification, and we perform a linearized eigenvalue buckling analysis for tense planar rods. Buckled shapes and critical loads are calculated for most usual boundary conditions.

A new design of gait rehabilitation robot with cable-suspended configuration is proposed. Due to the under-constrained nature, it enables reducing the constraint feeling of patients. Cables are attached to cuffs mounted on the leg. A detailed mechanical design is presented and a kinematics model is developed. Dimensional synthesis is performed in two steps. First, the cable disposition should be determined within a range to maintain cable-suspended configuration using the minimum 2-norm solution of tensions. Second, the optimal cable disposition is achieved with the Root Mean Square of tension solutions. Gait rehabilitation robots with three or four cables are discussed and compared to determine dimensional parameters in terms of the locations of pulleys. A simulation model with ADAMS software is presented and the cable module is utilized to imitate the cable-driven system in real. Tension distribution is obtained from the simulation model, which is employed in comparison with the calculated values. The simulation results demonstrate the effectiveness of the presented method.

Based on the molecular dynamics (MD) method, the single-crystalline copper nanowire with different surface defects is investigated through tension simulation. For comparison, the MD tension simulations of perfect nanowire are first carried out under different temperatures, strain rates, and sizes. It has concluded that the surface–volume ratio significantly affects the mechanical properties of nanowire. The surface defects on nanowires are then systematically studied in considering different defect orientation and distribution. It is found that the Young's modulus is the insensitive of surface defects. However, the yield strength and yield point show a significant decrease due to the different defects. Different defects are observed to serve as a dislocation source.

The mechanical properties of pipe joints are of vital importance to the performance of pipe structures. In order to further understand the whole failure process of adhesive pipe joints to maintain their good condition subjected to tensile loads, the analytical solutions are deduced in this paper, along with the parameter analysis by numerical simulations. A concise rigid-softening cohesive model was adopted to characterize the deformation of the interface. The whole failure process divided into different sections was discussed in detail and closed-form solutions of slip and shear stress were obtained. The finite element method (FEM) model for the bonded pipe joints under certain situations was established using commercial software ABAQUS, and the analytical and FEM results were accordant. The mechanism of shear stress transfer, the growth regulation of interface cracks and the mechanical performance of the joints under tensile loads were quantitatively obtained. These outcomes may help for the design, application and reinforcement of bonded pipe joints and can be compatible to other orthotropic materials.

Molecular dynamics (MD) simulations are performed to study the fracture behavior of armchair and zigzag graphene sheets with V-shaped notches subjected to tensile loading. The effects of temperature and notches depth on the fracture characteristics of the graphene sheets are examined. The results show that the cracks propagate from the notch tip along the direction perpendicular to the loading axis for armchair sheets. This is different from the zigzag graphene propagating along the direction of 45° from the loading axis. In addition, the fracture energy of zigzag graphene sheets is larger than armchair one at the same temperature condition.

Graphene has been reported with record-breaking properties which have opened up huge potential applications. A considerable research has been devoted to manipulate or modify the properties of graphene to target a more smart nanoscale device. Graphene and carbon nanotube hybrid structure (GNHS) is one of the promising graphene derivative, whose mechanical properties have been rarely discussed in literature. Therefore, the mechanical properties of GNHS is studied in this paper based on the large-scale molecular dynamics simulation. The target GNHS is constructed by considering two separate graphene layers that are being connected by single-wall carbon nanotubes (SWCNTs) according to the experimental observations. It is found that the GNHSs exhibit much lower yield strength, Young's modulus, and earlier yielding compared to bilayer graphene sheet. Fracture of GNHSs is found to initiate at the connecting region between carbon nanotubes (CNTs) and graphene. After failure, monatomic chains are normally observed at the front of the failure region, and the two graphene layers at the failure region without connecting CNTs will adhere to each other, generating a bilayer graphene sheet scheme (with a layer distance about 3.4 Å). This study will enrich the current understanding of the mechanical performance of GNHS, which will guide the design of GNHS and shed light on its various applications.

In this paper, the mechanical properties, including elastic properties, deformation mechanism, dislocation formation and crack propagation of graphene/Cu (G/Cu) nanocomposite under uniaxial tension are studied by molecular dynamics (MD) method and the strain rate dependence is also investigated. Firstly, through the comparative analysis of tensile results of single crystal copper (Cu), single slice graphene/Cu (SSG/Cu) nanocomposite and double slice graphene/Cu (DSG/Cu) nanocomposite, it is found that the G/Cu nanocomposites have larger initial equivalent elastic modulus and tensile ultimate strength comparing with Cu and the more content of graphene, the greater the tensile strength of composites. Afterwards, by analyzing the tensile results of SSG/Cu nanocomposite under different strain rates, we find that the tensile ultimate strength of SSG/Cu nanocomposite increases with the increasing of strain rate gradually, but the initial equivalent elastic modulus basically remains unchanged.

The protocols presented in this chapter focus on the micromechanical tensile testing of osteonal/interstitial bone, single trabeculae, and small animal bone specimens. Micromechanical testing of these small samples is technically challenging and often time-consuming. To alleviate the possible difficulties, the protocols for specimen preparation, apparatus and fixture design, data acquisition/interpretation, and associated techniques are provided for researchers in order to adapt these testing methodologies to their research needs.

Rubber materials are widely used in aviation, aerospace, shipbuilding, automobile and other military field. However, rubber materials are easy to aging, which largely restricts its using life. In working environment, due to the combined effect of heat and oxygen, vulcanized rubber will undergo degradation and crosslinking reaction which will cause elasticity decease and permanent deformation, so mostly rubber products are used under stress state. Due to the asymmetric structure and asymmetric stress distribution, mechanical stress may cause serious damage to molecular structure; therefore, this paper is aimed to analyze the aging behavior of rubber materials under tensile and compressive loadings, through analyzing experiment data, and adopting Gauss function to describe stress relaxation coefficient, to build an aging equation containing compression ratio parameter and aging time.