Abstract: Based on the photographic observation and analysis of different cross section of the materials, it is found that both the section of normal and warp yarns are rectangular in shape, the sections of weft yarns are the convex lens in shape, the weft and normal yarns are kept straight along their directions, the warp yarns are wavy. 3D images and geometry model of normal yarns reinforced 2.5D woven materials are established. This model can be used to calculate the fiber volume fraction of each yarn system. Compared with the experimental data, the computational results show excellent agreement. The work will lay the foundation for prediction of mechanical properties.
Abstract: The finite element software ANSYS was employed to create a finite element model of the cracked wing beam integrated structure, and the stress field of the crack tip was got by the material nonlinearity (elastic-plastic) analysis method. Based on the maximum tensile stress theory criteria, the crack deflection angle was obtained. The crack deflection angles with different geometry parameters (crack length, wed thickness, the height-thickness ratio of the stringer, cross-sectional area, and the location of the stringer) of the wing beam integrated structure were calculated and compared with each other. So the influences of the geometry parameters of the wing beam integrated structure on the crack deflection were studied. The crack deflection angles obtained in elastic analyzing and elastic-plastic analyzing were compared to investigate the effects of the material property on the crack deflection angle.
Abstract: This paper investigates the stability issues of functionally graded material (FGM) panels subjected simultaneously to both aerodynamic and thermal loads. Finite Element Method is employed to model the panel structures and the supersonic aerodynamics is calculated by the first-order piston theory. The critical buckling temperature elevation of the panels is at first predicted. The nonlinear static analysis of the panels is then implemented at certain interval of temperature elevation before buckling onset to obtain structural stiffness matrix. The flutter speed of the panels with updated stiffness matrix corresponding to a certain temperature elevation is estimated. The results show that the FGM panels can offer beneficial effects, especially prevention from buckling. However, if FGM panels integrated with TPS are to be applied on supersonic vehicles, one should pay more attention to the boundary conditions to guarantee the dynamic stability.
Abstract: In this experiment, blast furnace slag fine aggregate that was produced by 3 different steel factory was been used in high-strength concrete, and mechanical properties of high-strength concrete were studied. The concrete using the blast furnace slag fine aggregate is admitted the increase of compressive strength as well as the case of the river sand when the water cement ratio is reduced, and the compressive strength can attain 100N/mm2. The strength of concrete using blast furnace slag fine aggregate is lower than the strength of concrete using natural river sand as fine aggregate, and the strength of concrete using mixture fine aggregate is middle of strength used river sand and strength used blast furnace slag fine aggregate. The crushing value of blast furnace slag fine aggregate is bigger than the natural river sand, and it could influence the strength of high-strength concrete using blast furnace slag fine aggregate.
Abstract: In conventional image enhancement methods, the noises and overshoot occur which degrade the image quality significantly accompanied with transient improvement. To obtain high quality image enhancement, a novel transient improvement with overshoot suppression and noise reduction is proposed. It employs a Laplacian of Gaussian operator and a Sobel operator to achieve transient improvement, and uses a nonlinear clamp filter in luminance and a median filter in chrominance for overshoot suppression. Experimental results indicate that it can achieve better transient improvement and sharpen the blurred edge effectively while suppressing or preventing overshoot.
Abstract: Filament-wound composites are more and more frequently used for pressure tanks and motor cases. It is essential to study their mechanical properties, especially the properties at peculiar shaped locations. A carbon fiber wound pressure vessel structure was chosen to investigate by experiment and finite element method in our program, respectively. Considering the vessel deformation, internal pressure load was added step by step so that the changing stiffness matrix and changing geometric conditions could be calculated in simulation process. In our experiment, the pressure vessel with strain gauges was tested under internal pressure to get strain data at some typical locations. And a finite element model was built with software ANSYS considering the structural deformation of the pressure vessel. Under internal pressure, it is found that fibers in the cylinder part of the vessel are in tension and fibers in partial dome region are bent and transversely compressed. The simulated results also are in good agreement with experimental results.
Abstract: Third generation Al-Li alloy 2195 and 2198 were studied. The material properties of these two Al-Li alloy were compared with traditional alloy 2024; damage tolerance properties was tested and compared with 2024 as well. Microstructure of parent material and welded sample was studied and compared. Crack growth rate was tested and compared. Some conclusions were drawn: Al-Li alloy had a great strength and damage tolerance; local inhomogeneities microstructure in welded samples, which created the difference of damage tolerance and the tendency of crack growth rate in welded samples.
Abstract: Structural reaction analysis under frequent earthquake and rare earthquake was carried out using time- history method. Every single-tower structure was chosen as an analysis modal, which can reflect real structural reaction. The results show that seismic response decreases obviously and story shear force and overturning moment are far less than that of aseismic structures. Horizontal reduction coefficient is lower under rare earthquake. Story drift is mainly centralized at isolator layer, which approaches zero on superstructure. The isolated structure shows whole translational motion. Reduction degree of seismic response for the three towers is more or less from each other.
Abstract: Tear propagation is the typical fracture mode of fabric laminates, which is affected by stress and damage size. With the use of high strength fabrics, high performance laminates emerge continually. In this paper, tear propagation of a high strength fabric laminate coating polyurethane used in high altitude lighter-than-air vehicle (LTA) is studied. Cross-shaped specimens, central size 5cm×5cm, are scissored out to test tear propagation strength in biaxial stress by a tailor-made testing machine. The damnification is a cut slit in weft direction, warp fibers cut off. The cut slit is in the middle of specimens, including 0cm (scatheless specimens), 1cm, 2cm and 3cm in length. Tear propagation is observed and the strength is noted simultaneously to gain the mechanical properties of the fabric laminate. The tensile strength of the laminate is 424N/cm, and it descends to 263N/cm in cut slit length of 1cm. Subsequently, two methods based on stress field and linear elasticity fracture mechanics are introduced to analyze the tear strength, which is validated well by test results, and the coefficients of empirical formulae are obtained. It is useful to analyze the limit length and the limit stress for the fabric laminate with initial damage.
Abstract: SiC coated Ni nanocapsules were prepared by arc evaporating the mixture of Ni and SiC powders in Ar and H2 atmosphere. HRTEM shows the as-prepared nanoparticles form in a core¬¬¬-shell structure, with the size of nanoparticles in range of 20-50nm and the thickness of the shell 2-6nm. X-Ray and X-ray photoelectron spectroscopy show core consist of Ni, while the shell consists of SiC. The core-shell structure can prevent Ni nanoparticles from oxidation and agglomeration. The electromagnetic characters were measured by Agilent 8722ES microwave network analyzer in the band of 2-18GHz. The reflection loss R(dB) of less than –20 dB was obtained in the frequency range of 3.8-11.1GHz with absorber thickness of 2.5–5mm, An optimal reflection loss of –33.4dB was reached at 7.4GHz with an absorber thickness of 3.5mm.In addition, the optimal RL obviously shifts to the lower-frequency range with increasing thickness of the layer.