Achieving Mechanical and Conductive Anisotropy in Carbon Nanotubes/Cu Composites

Cu matrix composites reinforced by Multi-walled Carbon Nanotubes (MWCNTs) were prepared aiming to enhance the mechanical performance of Cu through MWCNTs while preserving its excellent axial conductivity. The microscopic structure, mechanical performance and electroconductivity of the composites were characterized, and the related mechanism was discussed. MWCNTs dispersed uniformly in Cu matrix and arranged in the direction of drawing. The composites showed obvious orthogonal anisotropy. The mechanical properties of the composites increased with the content of MWCNTs. The composite with 10vol.% MWCNTs has the best strength and hardness, which was better than most of data in the literature. However, the highest enhancement efficiency of 3vol.%-MWCNTs/Cu composite was the highest. The main enhancement mechanism was load transmission effects and dislocation. The electroconductivity and thermal conductivity of 5vol.%-MWCNTs/Cu composite parallel to the drawing direction reached the maximum value. The main strengthening mechanism was that Ni-Cu coating on MWCNTs leads to strong interface combination between MWCNTs and Cu, which promotes the electron-phonon coupling and reduces electron or phonon scattering at the interface.

A dynamic model of laminated material extrusion additive manufacturing plate with the property of orthogonal anisotropy

Purpose The purpose of this study is to set up a dynamic model of material extrusion (ME) additive manufacturing plates for the prediction of their dynamic behavior (i.e. dynamic inherent characteristic, resonant response and damping) and also carry out its experimental validation and sensitivity analysis. Design/methodology/approach Based on the classical laminated plate theory, a dynamic model is established using the orthogonal polynomials method, taking into account the effect of lamination and orthogonal anisotropy. The dynamic inherent characteristics of the ME plate are worked out by Ritz method. The frequency-domain dynamic equations are then derived to solve the plates’ resonant responses, with which the damping ratio is figured out according to the half-power bandwidth method. Subsequently, a series of experimental tests are performed on the ME samples to obtain the measured data. Findings It is shown that the predictions and measurements in terms of dynamic behavior are in good agreement, validating the accuracy of the developed model. In addition, sensitivity analysis shows that increasing the elastic modulus or Poisson’s ratio will increase the corresponding natural frequency of the ME plate but decrease the resonant response. When the density is increased, both the natural frequency and resonant response will be decreased. Research limitations/implications Future research can be focused on using the proposed model to investigate the effect of processing parameters on the ME parts’ dynamic behavior. Practical implications This study shows theoretical basis and technical insight into improving the forming quality and reliability of the ME parts. Originality/value A novel reliable dynamic model is set up to provide theoretical basis and principle to reveal the physical phenomena and mechanism of ME parts.

Experimental Study on Improving the Mechanical Properties of Material Extrusion Rapid Prototyping Polylactic Acid Parts by Applied Vibration

Due to the stratified nature of the manufacturing process, material extrusion (ME) parts have lower mechanical properties than those fabricated by traditional technology. This is one of the most significant defects hindering the development and application of this rapid prototyping technique. In this paper, vibration was applied to the ME process by using piezoelectric ceramics for the first time to improve the mechanical properties of the built parts. The vibrating ME equipment was established, and the specimens processed in different build directions were individually fabricated without applied vibration and with different applied vibrations. To quantify the effect of applied vibration on their mechanical properties and to summarize the influencing rule, a series of experimental tests were then performed on these specimens. A comparison between the testing results shows that the tensile strength and plasticity of the specimens, especially those processed in the Z direction, can be obviously improved by applied vibration. The orthogonal anisotropy is decreased obviously. The improvement becomes greater with increasing vibration frequency or amplitude. From the microscopic point of view, it can be seen that applied vibration can reduce the part’s defects of porosity and inclusion as well as separation between layers and, thereby, improve the bonding strength.

Study of Dynamic Brittle Fracture of Composite Lamina Using a Bond-Based Peridynamic Lattice Model

We proposed a bond-based peridynamic lattice model for simulating dynamic brittle fracture of 2D composite lamina. Material orthogonal anisotropy was represented by rotating topological lattice structure instead of fiber directions. Analytical derivation and numerical implementation of the proposed model were given based on energy equivalence. Benchmark composite lamina tests are used to validate the capability of modeling dynamic fracture of the method. The peridynamic lattice model is found to be robust and successful in modeling dynamic brittle fracture of 2D composite lamina and can be extended to composite laminates by applying 3D lattice structure.

DAMPER WITH POROUS ANISOTROPIC RING

In the work on the basis of Darcy equations defining lubricant flow in porous layers, and of Reynolds modified equation the problem of an unsteady motion of viscous incompressible lubricant in the gap of a por-ous damper is under solution. A case is under consideration when a forced lubricant supply is carried out in circumferential and radial directions taking into account the influence of orthogonal anisotropy of a porous layer. As a result of the solution of the problem specified there is found a field of pressures in a porous and lubricating layer, and analytical dependences for efforts in an oil film are obtained. Besides, there is defined a module of an unbalance transmitted effort and also stationary and transient ratios of transfer. It is proved that at the forced lubricant feed in a circumferential or radial direction taking into account the influence of orthogonal anisotropy of a porous layer, a damper functions more steadily. The obtained specified calculated models al-lowed defining a number of supplementary factors and also carrying out a comparative analysis of results newly obtained and already existing ones. It confirmed a larger proximity of a new model an actual practice.

Rectangle-capped and tilted micropillar array for enhanced anisotropic anti-shearing in biomimetic adhesion

Dry adhesion observed in the feet of various small creatures has attracted considerable attention owing to the unique advantages such as self-cleaning, adaptability to rough surfaces along with repeatable and reversible adhesiveness. Among these advantages, for practical applications, proper detachability is critical for dry adhesives with artificial microstructures. In this study, we present a microstructured array consisting of both asymmetric rectangle-capped tip and tilted shafts, which produce an orthogonal anisotropy of the shearing strength along the long and short dimensions of the tip, with a maximum anti-shearing in the two directions along the longer dimension. Meanwhile, the tilt feature can enhance anisotropic shearing adhesion by increasing shearing strength in the forward shearing direction and decreasing strength in the reverse shearing direction along the short dimension of the tip, leading to a minimum anti-shearing in only one of the two directions along the shorter dimension of the rectangular tip. Such a microstructured adhesive with only one weak shearing direction, leading to well-controlled attachment and detachment of the adhesive, is created in our experiment by conventional double-sided exposure of a photoresist followed by a moulding process.

Simulation Analysis of Cutting Resistance for Cutting Tools with Different Rakes in the Strike Working Condition

Brush-cutter would always bring cutting shock in its cutting process, and its not easy to estimate the cutting resistance by usual cutting theory and methods. The present paper emulates real cutting process by using ANSYS/LS-DYNA, and orthogonal anisotropy model was used to symbolize the wood material. The result shows that the cutting tool with a 40 degrees rake is more competent than the ones with 30 degrees and 50 degrees. This result fits common cutting theories, thus the rationality of this research is proved, and a cutting resistance curve is obtained.

Analysis on Chaotic Behavior in Rock Damage Rheological Process under Uniaxial Stress

The evolutional laws of rock under uniaxial stress are studied based on damage mechanics, rock rheology mechanics and chaos theory. Firstly, the damage rheological evolution equations are set up on the base of damage mechanics under the isotropic and orthogonal anisotropy conditions. The chaotic characters are tested in the process of evolution and the chaotic effect is analyzed. The root reason of rock damaged is made clear. The creep curve of Kelvin model considering damage is illustrated by FLAC3D, and the deformation process is explained by chaos theory. It will be help to understand the mechanics property of rheology of damaged rock and predict development phases. It is also much value in solving various practical problems of geotechnical engineering and acquainting other materials’ rheology evolution..

Analytical Approach for Buckling Resistance of UOE Linepipe With Orthogonal Anisotropy Under Combined Loading

UOE linepipes have orthotropic work hardening in which the longitudinal (L-) stress vs. strain (SS) curve is different from the circumferential (C-) one. The anisotropy is emphasized by the thermal aging during the anti-corrosion coating. However, there are few studies on the effect of the circumferential mechanical properties on the compressive strain limit required in strain-based design (SBD). This paper describes the combined effect of SS curves in L- and the C-direction on the buckling resistance using the newly developed yield function to model the orthogonal anisotropy. The coupon tests after thermal aging during the anti-corrosion coating indicate that the L-SS curve can maintain the round-house type while the long yield point elongation (YPE) appears on the C-SS curve. Using these mechanical properties, FE-models demonstrate that YPE in the C-direction reduces the compressive strain limit for pipes with high diameter/thickness (D/t) under high internal pressure. Hence, SS curves in the C-direction should be considered for more reliable prediction of the buckling resistance required in long distance gas pipelines.