Abstract:Recent progress on the polymer nanocomposites modified by graphene and functional graphene were reviewed.The preparations and properties of the nanocomposites of polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyaniline (PANI) modified by graphene were mainly discussed. The graphene modified by diphenylmethane diisocyanate (MDI), octadecyl amine (ODA), aluminum chloride (AlCl₃) and other modifications and improvement of properties of polymers after functional graphene addition were then discussed. Finally, the potential applications and prospects of graphene/polymer nanocomposites were pointed out.

Abstract:Carbon Fiber Reinforced Polymer (CFRP) composites have been successfully applied to the main load-carrying structures in aircrafts, but how to monitor the structural damage is still a key problem. In this paper, a new and promising nondestructive testing technologySymbol~B@the self-sensing detection technology based on CFRP conductive network, which has become a hot field. The principles and technical characteristics of various methods including direct current (DC) methods and alternating current (AC) methods were summarized, especially evaluating the applicable environment and damage types of all kinds of detection methods. Finally, the further research for developing a set of intelligent self-sensing detection system of CFRP structural damage was pointed out.

Abstract:This paper introduces the research status on drilling performance of drilling force,drilling temperature,machining surface quality,which presents drilling mechanism such as the material removal mechanism,defects forming mechanism and tool wearing mechanism during drilling the resin matrix fiber-reinforced composites.And it gives status of the latest research on the drilling technique and the drilling-bit improvement and an expectation of the key point on the next study of drilling technique.

Abstract:Delamination has been a subject of major concern in engineering applications of composite laminates by manufacturing defects or an impact.In this paper we investigated buckling behavior of composite laminates containing embedded delamination with circular shape.Firstly we use Rayleigh-Ritz methods to create modeling of composite laminate with the circular delamination. Through theoretical analysis,the displacement of specimen surface will be counted when the bucking happens.The bending load-dispalcement curves can be calculated at an arbitrary bending load M. After the theoretical analysis, 3D digital image correlation was used to measure the evolution of the deformation of the laminate during bending to structural failure and the resulting full-field displacement maps.The theoretical model results are in agreement with the expermental results.The theory proves to be accurate and can be used to evaluate the critical buckling load of delaminated composite laminates under pure bending.

Abstract:The three-phase ceramic powders of Ti₂AlC, TiB2 and TiC are synthesized by self-propagating high-temperature synthesis(SHS) technology. Ti₂AlC/TiB₂/TiC block multiphase ceramics are prepared by spark plasma sintering(SPS) method. The results show that Ti₂AlC is the matrix phase, and TiB₂ , TiC are dispersed on the matrix. The high density of Ti₂AlC/TiB₂/TiC block multiphase ceramic is 99.6%, the average microhardness value is 12.96 GPa, the fracture toughness value is 45.28 MPa·m1/2.

Abstract:In order to improve the oxidation resistance and thermal shock resistance properties of the TaSi₂-MoSi₂ borosilicate glass coating for porous SiCO ceramic heat insulation composite, TaSi₂-MoSi₂ borosilicate glass coating on the surface of SiCO ceramic composites was prepared by brush-air sintering method. The microstructure and phase compositions of the coatings with the content of borosilicate glass respectively of 23%,31%,38%,41% were comparative observed by XRD and SEM with EDS. The thermal cycle experiment of the coated samples was performed by heating for 5 min at 1 500℃,then taking out to cool naturally down to room temperature.The result shows that the TaSi₂-MoSi₂ borosilicate glass coating with the content of borosilicate glass of 38% has fewest holes and cracks,the mass loss of the coating is -2.1%. It can be concluded that the TaSi₂-MoSi2 glass coating with the content of borosilicate glass is 38% has the best oxidation resistance and thermal shock properties.

Abstract:The methods to reduce the distortion of ceramic fiber rigid insulation tiles during high temperature firing procedure required for coating forming were studied. The results indicate that the distortion of the tiles is caused by compressive stresses in coating. However, the distortion significantly decreases when only the coated surface of the substrate is fired at high temperature or a thicker substrate is employed during coating forming and then machined to the required final thickness. And a further decrease of the distortion is achieved when these two methods are used at the same time. Moreover, the distortion decreases with the increasing thickness of substrates independent of the method used.

Abstract:SiC_f/SiC composites were drilled by machining process and laser process. The quality of holes and the characteristics of the two processes were analysed. The results show that machining drilling can get holes with better diameter but there are serious tool wear, burr side damage problems. Laser drilling has a better efficiency but there is taper hole and the existence of heat affected zone of wall surface causes defects such as delamination and crack.

Abstract:Defects such as burrs and tear, often occur in the drilling of CFRP. Drilling characteristics of double cone drill was studied through analyzing the influence of chisel edge and primary drilling edge and secondary drilling edge on defects of hole’s entrance and exit and the influence regularity of processing parameters on tear factor. The results were compared with those of twist drill. Results show that, compared with twist drill, double cone drill is more suitable for drilling CFRP. The characteristics of double main cutting edge reduced the drilling axial force at hole’s entrance and exit, inhibited burrs and tear damages at hole’s entrance and exit. High speed drilling is favorable for minimizing the tear factor, the tear factor increases with the feed rate increasing. Through multi-linear regression analysis method, the prediction model between tear factor which is used to test hole’s entrance and exit of the two drill and process parameters were established.

Abstract:To optimize the heat treatment processing of a new super-high strength Al-Cu-Li-X alloy sheet with 2 mm thickness, the mechanical properties and microstructures of the alloy with different aging treatment were investigated. Its tensile strength kept higher than 600 MPa after a long time (20~120 h) of T8 aging with 6% pre-deformation. The strengthening phases in T8 temper were a large number of T1 (Al₂CuLi) precipitates and some (Al₂Cu) precipitates. A very small amount of S′ (Al₂CuMg) precipitates also formed in T6 aging. Pre-deformation accelerated dispersive and fine precipitation of T1 phases, but inhibited the precipitation of θ′ and S′ phases. At pre-deformation lower than 6%, the tensile strength of the T8-aged alloy was effectively increased with pre-deformation. At pre-deformation higher than 6%, with pre-deformation increasing, T1 number density was obviously increased and its size decreased, θ′ fraction reduced, and the strength enhancement caused by pre-deformation was decreased and elongation was much lowered. Excessively high pre-deformation (15%) made θ′ precipitates disappear.

Abstract:The welding between aluminum alloy and stainless steel is of practical importance for widening the application of aluminum alloys, however, it is difficult to join them using the conventional welding method because of their different physical and metallurgical properties. In this work, inertia friction welding has been used to create joints between LF6 aluminum alloy and stainless steel, and the microstructure and the mechanical properties were analyzed. The results showed that the flash of the joints was mainly caused by friction and extrusion of aluminum alloy during welding, and the microstructure in aluminum alloy side was divided into fine-grain and elongated-grain area. The EDX results displayed that the welded joint was of evident concentration gradient, and a very narrow interface diffusion layer was formed under the function of friction heat and upset force. The fracture mechanics model showed the fracture occurs at the weak area of aluminum alloy side.

Abstract:The effect of heat treatment on microstructure and mechanical properties of sand casting Mg-Gd-Y system alloys were investigated systematically by optical microscopy(OM), scanning electron microscopy(SEM) and tensile tests. The results showed that the microstructure of solutionized GW94, GW74 and GW44 Mg alloys was mainly composed of supersaturated α-Mg solid solution, residual phases of Mg₅(Gd,Y) as well as square phases formed during solution treatment.As the content of Gd addition to Mg-Gd-Y alloys increased, the volume fraction of square phases in the matrix increased. The time of reaching peak hardness decreased in the same aging temperature. The ultimate tensile strength and yield strength increased gradually (the yield strength of solutionized alloys firstly decreased and then increased), while the elongation-to-failure decreased gradually from solution treated and peak-aged alloys at room temperature to peak-aged alloys at 200 and 250℃. The peak-aged GW94 Mg alloys exhibited superior mechanical properties.The ultimate tensile strength, yield strength and elongation-to-failure of the peak-aged GW94 Mg alloys at room temperature were 300,7 MPa and 0.9%.The ultimate tensile strength, yield strength and elongation-to-failure of the peak-aged GW94 Mg alloys at elevated temperature (200 and 250℃) were 329,4MPa, 2.6% and 312,3MPa, 2.7%, respectively. The peak-aged GW94 and GW74 Mg alloys showed a abnormal behavior that the ultimate tensile strength increased with the increase of temperature.

Abstract:To study the mechanical properties of a new material with the change in temperature during the flight, a bending test is conducted in different temperatures. The result of the test indicates that in the same temperature, the mechanical properties of the material in the temperature rising period is apparently different compared with it in the cooling down period. According to test result, the relation between tensile modulus and bending modulus of the material is gained by the FEM analysis and the data is used for the FEM analysis of the new thermal-protection structure.

Abstract:The modified picture-frame experiment was applied to test and study the in-plane panel shear of Nomex honeycomb cored sandwich structure. The results show that under by the continuous shear loads from the picture frames, skin-core debonding of the sandwich structure occurred firstly and the skin materials formed to the big bubbles and wrinkles in the vertical direction ,i.e., the direction of tensile travel. With the increase of shear loads, the sandwich structure finally fractured in the transverse direction. The dispersion ratio of lower 3% gained from several experiment results indicates the effectiveness and accuracy. In addition, the fixedness between specimen and fixtures is the key factor for picture-frame experiment of in-plane panel shear. For the screw-fixed test specimen, the motion of screws driven by tensile loads induced the failure of the edges of sandwich structure.However, the specimen gained in-plane panel shear loads from picture frames were very limited indicating invalid experiment.