Applied Mechanics and Materials Vol. 697

Abstract: This study presents a statistical two-scale method to predict the viscoelastic properties of composite materials with consistent random distribution of particles. The explicit formulation for predicting the effective viscoelastic relaxation modulus is given. At first, the Laplace transformation is used to the linear viscoelastic problem, the effective generalized relaxation modulus in Laplace domain for composites is derived. Then, the effective relaxation modulus in time domain is obtained by the least-square and inverse Laplace transformation. At the end of this paper, some numerical examples are given to validate that the presented method is feasible and effective.

Abstract: Micro-arc oxidation technique was studied on the surface of 2A12 aluminum alloy using AC power in this paper. The micro-arc oxidation process was divided into several periods to investigate the changes of thickness and surface morphology of oxide film that forms in different periods and record the voltage change between oxide film. The following conclusions have been found: The growth of oxide film can be divided into three stages, the first stage is the formation and disruptive discharge of amorphous oxide film, producing the ceramic oxide granules; the second stage is the formation of ceramic oxide film, the ceramic oxide granules turns into porous structure oxide film in this stage; the third stage is the growth of ceramic oxide film, the gas film forms in the oxide film’s porous structure is electric broken-down, leading higher energy discharged by micro-arc, which becomes a significant reason for promoting the growth of ceramic film.

Abstract: Ferromagnetic shape memory alloy is a kind of new smart material. Directional solidification method in producing polycrystalline Ni₂MnGa is mature and effective. In order to increase the strain of Ni₂MnGa polycrystalline prepared by directional solidification, mechanical training is an effective method. In this paper, the tests of temperature-induced strain are carried out in different directions of Ni₂MnGa prepared by directional solidification using three kinds of specimens with various mechanical training. Through analyzing the mechanical properties in different directions, the influence of mechanical training on the temperature-induced strain are investigated. Some conclusions which may provide references for the engineering applications of this material are gained.

Abstract: The binding material and concrete are prepared by desulphurization gypsum, cement, stone, sand and admixture. The performances of binding material are studied in the paper. The experimental results showed that it is absolutely feasible to prepare binding material by using cement, desulphurization gypsum and superplasticizer after drying and screening of desulphurization gypsum. The binding material was prepared by adding desulphurization gypsum replacing 10 percent cement and superplasticizer. the cement micellae compressive and bending strength of the binding material can meet the standard requirements of P.O42.5 and the binding material’s set time and soundness are up to standard. The concrete was prepared by adding desulphurization gypsum replacing 30 percent cement and superplasticizer. The concrete’s strength is up to standard of the C30 concrete, and its impermeability meets the requirement of P12. To execute the research can not only massively use waste sludge desulphurization gypsum but also solve environmental pollution.

Abstract: Plasma surface processing technology can improve the mechanical properties, the corrosion resistance and chemical properties of the parts; therefore it has been widely used in industrial field. Advanced plasma surface processing technology is also constantly innovation, high power pulsed magnetron sputtering technique has been studied and explored by many scholars in recent years, and also gradually began to be used in the industry . This paper mainly introduces the study of HiPIMS dynamic and application over the past ten years. The HiPIMS discharge mechanism research method and theory is summarized .And the influence of the preparation process parameters about voltage, pressure, pulse width and frequency to compound film performance is systematically described, a detection method for thin film by HiPIMS is also introduced. These will provide guidance for the preparation of reactive HiPIMS.

Abstract: In order to study the impact of mechanical properties of aluminum alloy that is added into carbon powder, the aluminum alloy with carbon powder were melt and test bars were cast. The mechanical properties were tested by a tensile tester, the fracture morphology were observed by SEM and the morphology of material surface and composition were checked by SEM and EDAX. The results showed that: several slip platforms were observed during bar stretching and the longer slip platform is better elongation, so the ductile of alloy was improved obliviously after adding carbon powder. Microscopic studies showed that the aluminum alloy system has been infiltrated by the carbon powder and some stable compounds were formed in the alloy systems. Overall, Carbon is added can effectively promote the toughness of the aluminum alloy and improve the mechanical properties to some extent. Keywords: Carbon powder, Cast aluminum alloy, Slip platform, Toughness

Abstract: Yb:YAG laser ceramic nanopowders were synthesized by the carbonate altogether precipitation method, and the thermal properties with structure and morphology characterized and analyzed by the measurements of TG-DTA, XRD, IRS, SEM. The results show that well-crystallized Yb:YAG nanopowders calcined at 900°C are obtained with higher sintering performance and purity, and the average diameter is in the range of 100 nm. The crystalline size grew with the increase of the heat treatment temperature. The size of powder calcined at 1100°C is about 70-150 nm with higher purity, regular shape and even particle size distribution, which is favorable for good sinterability of Yb:YAG ceramics.Key words: Yb; YAG laser ceramic powders; nanopowders synthesis; carbonate altogether precipitation method;

Abstract: The aim of this study was to investigate the valuable impact damage parameters from quasi-static indentation testing to access the low-velocity impact behaviour of ex-situ toughened composites by comparing low-velocity impact and quasi-static test results (the same boundary conditions). In terms of the delamination damage threshold load and indentation depth, quasi-static tests predicted the impact damage resistance well. However, only very conservative estimates of maximum load due to the final fibre failure under higher energy level were achieved. This phenomenon is attributed to two factors. First, energy during quasi-static indentation event is completely transformed or absorbed by the laminate, where it is stored elastically in panel bending or absorbed by the creation of damage, without the energy in the form of vibration, heat, inelastic behaviour of the impactor or the supports. Second, strain rate effect may have a remarkable influence on the fibre failure but on undamaged and delaminated damage.

Abstract: Ti(C,N)-based cermets with three carbon contents are prepared by sintering in vacuum. The effects of carbon content on the microstructure, mechanical properties and wear resistance of Ti(C,N)-based cermets were investigated. The results show that the grains refine gradually and the hard phase core becomes smaller when the carbon contents increases. The mechanical properties closely relates to the carbon content. With the increase of carbon content, the furrows created by grains cutting are getting narrower and more intensive. When the carbon content reaches 0.8%, a large quantity of wear debris bonding blocks are attached on the wearing surface. In this condition, the Ti(C,N)-based cermets are of the minimum wear weight loss and the best comprehensive mechanical property.