Papers by Author: Fei Xu

Abstract: Because of the restriction of many factors such as system complexity, the maintenance and support agencies of a communication control system can not be detected and debugged faulty equipment or systems, a maintenance environment simulation and integrated detection system has been designed in this paper, which expounded system design ideas in the general scheme.

Abstract: The solar-powered platform has great application prospects with its unique characteristics of high cruising altitude and long endurance. This paper presents a high-aspect-ratio long straight composite wing structure. A 3D FEM model is used to study the mechanical performance of the wing under gust, by applying nonlinear analytical method. The wing optimization is focused on high stiffness and light weight. A wing structure of feasible strength and stiffness is obtained. Through analysis, several engineering conclusions are obtained. In addition, the instability features of the main spar are included as well.

Abstract: In this paper, the failure modes of the honeycomb sandwich structure under uniaxial compressions after impact (CAI) are analyzed through experiments and Finite Element Method (FEM). Three cases of impact damage location, two cases of impact damage depth and adhesive properties are investigated by the comparisons of corresponding non-destructive structure. Several conclusions are drawn: the failure modes and the initial damage positions obtained from experiments and FEM simulations are almost the same; the location of impact damage may affect the overall loading capabilities of the sandwich structure, whose decreasing rate peaks when the damage is at the top surface and drops when the damage is at the marginal area; different adhesive layer property of interface may lead to the failure mode change, that is, instead of honeycomb core failure, interlaminar failure will occur when the fracture energy of the adhesive layer is low; the damage level and risky location of the structure will vary relevant to the impact energy.

Abstract: Perforating parameters, such as charge density, charge quantity and shooting density, are the important factors that affect the strength security of perforation string. Finding out the relationship between this two and understanding the regularity has the guiding significance to avoid the perforating accidents. Based on the research about the strength security of perforation string at the moment of perforating, taking a perforated completion gas well as an example, by changing the perforating parameters and conducting the contrastive analysis and research, then gets the regularity understanding about the influence of the perforating parameters on the strength security of perforation string:When the charge density is more than 1.9g/m3, the amplification of peak pressure will slow down ,and the influence of charge density will decrease; When the charge quantity is more than 40 gram, the amplification of the peak pressure on the packer and the peak stress of tubing will slow down ,and the influence of charge quantity will decrease; When the shooting density is more than 20 hole/m, the amplification of peak will slow down, and the influence of shooting density will decrease.

Abstract: This paper proposed a composite damage model including the damage initiation and evolution based on strain to predict the composite intralaminar damage under impact loading. In the numerical simulation, the user material subroutine VUMAT and the cohesive-zone model are chosen to describe the composite damage model and the delamination of interfaces between different plies. ABAQUS software is used to simulate the low-velocity impact of different thickness composite laminates. It is found that the delamination shape and area, the contact force and the deflection of the impactor obtained by the numerically simulation agree well with the experimental results.

Abstract: This study presents the numerical investigation of the low-velocity impact for the foam-cored sandwich composites. Firstly, the proposed FEA model is validated by comparing the results between simulation and test. The user subroutine VUMAT and the crushable foam model are chosen to describe the damage of the face sheets and the characteristics of the foam material, respectively. The detailed damage process of the sheets and the foam is clearly shown. The sensitivity of seven parameters related to foam-core material are studied. It is shown that the yield strength, the fracture strain and the fracture displacement have significant effects on the impact-resistance of the foam-cored sandwich composites.

Abstract: Stitched foam-core sandwich structure is a new light weight sandwich structure material. In this paper, flexural testing was performed. For comparison purposes, the stitched foam-core sandwich structure with different stitch density and the unstitched foam-core sandwich structure were tested. The experimental results show the maximum failure loads was decreased owing to stitch for the flexural testing. The bending stiffness increases for stitched foam-core sandwich structure.

Abstract: Composite stiffened panels are widely used in the modern aircraft structure with the advantages of light weight, structural efficiency and good crack performance. But the stiffened panels have poor performance at thickness direction, especially for low-velocity impact. First of all, compressive tests were investigated and analyzed for two types of composite stiffened panels, which are integrated specimens and post-impact specimens. And the effect of low-velocity impact to the supporting capacity of composite stiffened panels was researched. Secondly，the finite element model was established to simulate the CAI (Compression After Impact)strength with the equivalent hole method. It is found that the analyze results match the experimental results well. According to the experimental results, structural damage and the maximum load caused by impact energy are scattering. Then the imperfect factors were introduced to reflect the initial imperfection, namely the initial deflection at thickness direction. The effect of different imperfect factors to the maximum load was discussed.

Abstract: This paper describes the mixed-mode bending test fracture toughness of composite adhesive J116-b. The test theory and experimental requirements are introduced. The fracture toughness of mode I, mode II, and different mode mixture of 0.4, 0.6, and 0.8 are obtained. It is found that the total fracture toughness is increasing with the increasing of mode mixture. It is also obtained that the technique of calculating fracture toughness by considering the influence of the weight of lever and attach apparatus is more accurate.

Abstract: The distribution of mechanical property in the weld zone of friction stir welded 7050 aluminum alloy joint along the plane perpendicular to the welding direction was experimentally investigated by the non-contact measurement method. The results show that the elastic modulus presents a W-shape distribution across the weld zone. The elastic modulus in the weld nugget zone is increased due to the grain refinement. In addition, the elastic modulus in the advancing side is slightly less than that in the retreating side possibly because of the relatively higher temperature in the advancing side during the welding process. The strength in the vicinity of weld center is decreased while the ductility is enhanced. The tensile strength and yield strength in the weld nugget zone and thermo-mechanically affected zone are significantly decreased while the elongation is increased due to the change of strengthening mechanism. In the heat affected zone the strength is decreased compared to the base material because the second phase grows up.