Abstract: As Carbon-fiber-reinforced SiC-matrix (C/SiC) composites are widely used in high-temperature structural applications, its mechanical behavior at high temperature is important for the reliability of structures. In this paper, mechanical behavior of a kind of 2D C/SiC composite was investigated at temperatures ranging from room temperature (20C) to 600C under quasi-static and dynamic uniaxial compression. The results show the composite has excellent high temperature mechanical properties at the tested temperature range. Catastrophic brittle failure is not observed for the specimens tested at different strain rates. The compressive strength of the composite deceases only 10% at 600C if compared with that at room temperature. It is proposed that the decrease of compressive strength of the 2D C/SiC composite at high temperature is influenced mainly by release of thermal residual stresses in the reinforced carbon fiber and silicon carbon matrix and oxidation of the composite in high temperature atmosphere.
Abstract: Adhesive joint is commonly applied to CFRP/GFRP composite tube, however, its failure rate is still high and this will limit the use of composite tube for industrial purpose. The literature study showed that the stress distribution at the joint, when loaded, is not evenly distributed and creates stress concentration at the edges. Attempts have been made by researchers to improve the joint design so that the stress would be more evenly distributed and minimize stress concentration, however, the improvement has been very limited. In this work, a comprehensive parameter study has been performed to observe the properties of adhesive joint of torque loaded tube. Based on the observation, a new type of adhesive joint is proposed which successfully reduces the stress concentration along the joint during torque loading. The analysis was performed using finite element method.
Abstract: Honeycomb materials，as a type of ultra-light multifunctional material，have been examined extensively in recent years and have been applied in many fields. This study investigated the energy absorption capacity and their mechanisms of honeycomb structures with five different cell geometry (square，triangular，circular, hexagonal，kagome). It has been shown that the honeycomb structure with kagome cells is the best choice under the targets of the energy absorption capacity, peak force and plateau stress, when relative density and cell wall thickness of the five kinds of honeycombs are the same. Besides, honeycomb with hexagonal cells and honeycomb with triangular cells are also ideal structures for energy absorption purpose.
Abstract: In this study, electrical conductive yarns were prepared by wet-spinning technique and a physically coating process. Carbon black (CB) was used to make the fiber gaining electrical conductivity. The electrical conductivity and morphological characteristics of the developed conductive fibres were studied and compared. The results show that linear resistivity of the produced conductive yarns ranges from 1 to a few hundred kΩ per centimeter, mainly depending on processing technique and substrate fibers. It is also shown that the physically coating processes will not significantly affect the mechanical properties of the fibers and yarns. These conductive yarns are lightweight, durable, flexible, and cost competitive; and able to be crimped and subjected to textile processing without any difficulty.
Abstract: A fracture mechanics algorithm, used for continuum mechanics simulations of nano-porous particle-polymer composites, is described herein. The model comprises close to a thousand ceramic particles bound together by latex polymer. These packings are generated using probabilistic methods (Monte Carlo). Pore-space arises as a function of particle shape and position coupled to the concentration and distribution of latex. Since the bridges are the weakest links in the solid state continuum, an understanding of failure behaviour is paramount for the design and optimisation of these composites. The objective of this research is to statistically characterise adhesive failure at particle-latex interfaces against cohesive failure within the latex bridges. To achieve this, a novel numerical method was developed. This method solves ordinary differential equations for vectors of force and displacement in layers through the computational packing. The model includes a scheme for non-linear elastic behaviour that evolves into a plastic flow regime. The model moreover incorporates a routine for interfacial failure between particulates and binder. Geometrical features such as solid state anfractuosity, bridge orientation, material fraction and coordination numbers are calculated from the packing output. The number of bridges straining plastically within the packing is lower than those that fracture at the interface. Fracture and failure are both related to the particle-binder coordination number. There is no evidence to suggest that decreasing the contacting sizes of binder at interfaces as well as making them thinner will lead to more plastic failure and decrease fracture. Rather, both plastic failure and fracture increase as a function of decreased contacting sizes and bulk diameters. The residual elastic modulus decreases exponentially as the number of broken connections increases.
Abstract: This paper analyses the effect of ageing on the oxidation behavior of 6061Al/SiC composite material at temperatures ranging from 500 to 800 K. Also aluminum coating is employed as protective coating in order to improve the oxidation resistance of the composite. SEM, EDAX, XRD and stepped oxidation measurement techniques are used to study the oxidation behavior and to characterize the composite specimens. Oxidation of the composite material without protective coatings is seen to be very rapid during the initial stages of exposure to the high temperatures but subsequently slowed down due to the formation of a protective surface layer of oxide. Among the artificially aged composites, peak aged specimens are more prone to oxidation. The oxidation was especially severe above 600 K. The interface between the matrix and reinforcement particles and the grain boundary regions of the matrix enhance this oxidation process since they provided sites for oxidation initiation. Aluminum coating on the composite obtained by DC magnetron sputtering technique, reduce the oxidation rate effectively since the interface regions between the matrix and reinforcement, grain boundary regions of the matrix are unexposed to the atmosphere. Aluminum coating provides better oxidation resistance for the artificially aged composites.
Abstract: To understand the damage mechanism and obtain the fatigue life of the oriented sheets of polymethyl methacrylate (PMMA) glasses, the quasi-static compression tests and the constant amplitude fatigue testing with two notch stress concentration factors are carried out respectively, using the CSS44100 electromechanical universal materials testing machines and a MTS servohydraulic testing machine. The damage region and fracture section of the deformed and failed sheet samples are examined with the aid of an optical microscopy. The results show that, 1) the oriented PMMA glasses drawn through vertical bi-direction have remarkable thermomechanical anisotropic characteristic, that is, it has the higher hardness and strength along the normal direction of the sheet panel, it will burst out and scatters into bigger pieces under the perforation; 2) the S-N curve of the oriented sheet specimens shows that its fatigue life is not sensitive on the notch at lower amplitude stress levels; and 3) the crack initiation of the oriented PMMA glasses often originates the interbeds area or mid region of the notch edge under fatigue cycle loading.
Abstract: For numerical simulation, the shear strength reduction technique (SSRT) is often used to evaluate slope or landslide stability. According to numerical computation results of slopes or landslides analyzed by SSRT, it can be found that with increase of the shear strength reduction factor, some of the soil elements will yield gradually to form a connected plastic zone, which is the potential slip surface of the slope or landslide. In view of the plastic resistance of soils, formation of the connected plastic zone does not always indicate that the landslide is about to failure. Other auxiliary criterion is necessary to predict whether a slope or landslide is in a critical state or not. Here, difference of the incremental percent of horizontal displacement of the outcropping slip surface node is regarded as the auxiliary indicator to distinguish the critical state of slopes or landslides after formation of the potential slip surface. With the ideas mentioned above, stability of a fossil landslide, Xietan landslide has been analyzed for the natural and the long-term reservoir water level conditions. Factors of safety of Xietan landslide by the numerical method have been compared with that by the limit equilibrium method, which indicates that the method used here for evaluating stability of Xietan landslide is feasible. Because numerical method has more advantages over the limit equilibrium method, the approach for evaluating stability of landslide here can be applied to more complicated or three-dimensional landslides or slopes further.
Abstract: The elastic stress and strain fields of a finite-thickness plate containing two interacting holes are systematically investigated using the finite element method. The maximum stress and strain concentrations occur on the mid plane only in the thin plates. They do not occur on the mid plane and their locations are different in the same plate for the thick plates. The values of the maximum stress and the strain concentration factor and their locations depend on the distance between the two holes and the plate thickness. The stress and the strain concentration factor are different, even if in an elastic state. The stress concentration factor and the strain concentration factor on the plate surface decrease rapidly with increasing thickness and becomes lower than the values corresponding to the plane stress state and the values of the mid plane. They are too low to reflect the overall stress concentrations as the plate thickness increases. The differences between the maximum value and the surface value of the stress concentration factor, the strain concentration factor increase rapidly and tend to their respective constant values with increasing plate thickness. These constant values depend on the distance between the two holes and the difference of the stress concentration factor is larger than that of the strain concentration factor in the same plate.