Browsing by Author "Zhang, X."

Now showing 1 - 4 of 4
  • Thumbnail Image
    ItemOpen Access
    Carbon-coated fluorinated graphite for high energy and high power densities primary lithium batteries
    (Elsevier Science B.V., Amsterdam., 2010-05-01T00:00:00Z) Zhang, Qi; D'Astorg, S.; Xiao, P.; Zhang, X.; Lu, L.
    The electrochemical performances of fluorinated graphite have been improved by coating a uniform carbon layer on commercial CFx (x = 1) powder used as cathode material in lithium battery. In comparison with the cell using un-coated CFx as cathode, the cell using carbon coated CFx cathode has a higher energy density and higher power density, particularly at higher discharge current rates (1C above). This is because the conductive carbon coating provides the exterior connectivity between particles for facile electron conduciton, resulting in high rate performance.
  • Thumbnail Image
    ItemOpen Access
    Cutout shape and reinforcement design for composite C-section beams under shear load
    (Elsevier Science B.V., Amsterdam., 2009-04-30T00:00:00Z) Guo, Shijun J.; Morishima, R.; Zhang, X.; Mills, A.
    This paper reports a study of the performance of two forms of cutout and various edge reinforcements in a composite C-section beam under static shear load. Firstly, cutout shape effect on stress concentration was studied. This was followed by a comparative study of a range of reinforcement doublers, which were 20 mm wide rings made of a steel alloy or composite laminate, or by a novel fibre tow placement technique. The comparisons are made in terms of the stress and strain reductions at a hot spot at the cutout edge. Good agreement between the numerical and test results has been achieved for different cutout shapes and reinforcements, and this study has demonstrated that the cutout induced stress concentration can be reduced significantly by appropriate cutout shape and edge reinforcements. The stress reduction magnitude is found to be strongly related to the stiffness of the reinforcement rings. The diamond-shaped cutout and the fibre tows reinforcement show clear advantages over the widely adapted circular cutout and laminated ring reinforcement. These findings should contribute to future design improvement of composite aircraft structures in similar shape and loading conditions.
  • Thumbnail Image
    ItemOpen Access
    Fatigue life enhancement of aircraft structures through bonded crack retarders (BCR)
    (Cranfield University, 2015-09) Doucet, Jeremy; Irving, Phil E.; Zhang, X.
    The trend in aircraft design is to produce greener airplanes through lighter structures and/or structures with extended life and reduced maintenance. Bonded crack retarders (BCR) are one of the solutions towards that objective. BCR are reinforcing straps bonded to the structure in order to improve the fatigue and damage tolerance properties of the assembly. The aim of this study was to demonstrate that the BCR hybrid technology – beneficial for upper wing cover – could also be applied to lower wing covers. The project also focused on evaluating BCR most important parameters. The fatigue life improvement obtained from BCR was evaluated through a series of coupons and skin-stringer assemblies tested under constant and variable amplitude loading. While the coupon tests demonstrated a life improvement of only 17% under constant amplitude loading, the variable amplitude load tests performed on the skin-stringer assembly demonstrated increased fatigue lives with a factor of 5 and reduced crack growth rates with a factor of 5 to 6. A finite element calculation tool was developed in order to conduct a parametric analysis of BCR geometry through the evaluation of the substrate stress intensity factor in the case of fatigue loading. The main difficulty was to include the interacting mechanism of the substrate lead crack and the disbond of the adhesive layer. The novelty of the approach was to incorporate the fatigue delamination calculation in order to evaluate the fatigue disbond propagation with crack growth. This was embedded in a 3D finite element design tool ReSLIC (Reinforced Structures Life Improvement Calculation). A necessary step to the development of ReSLIC was the analysis of fatigue properties of the adhesive system in order to provide input data for fatigue delamination calculations. To that end, a series of fatigue tests were performed in pure Mode I, pure Mode II and mixed mode with ratios of 25%, 50% and 75% of mode II ... [cont.].
  • Thumbnail Image
    ItemOpen Access
    Predicting fatigue crack growth rate in a welded butt joint: The role of effective R ratio in accounting for residual stress effect
    (Elsevier Science B.V., Amsterdam., 2009-07-01T00:00:00Z) Servetti, Guido; Zhang, X.
    A simple and efficient method is presented in this paper for predicting fatigue crack growth rate in welded butt joints. Three well-known empirical crack growth laws are employed using the material constants that were obtained from the base material coupon tests. Based on the superposition rule of the linear elastic fracture mechanics, welding residual stress effect is accounted for by replacing the nominal stress ratio (R) in the empirical laws by the effective stress intensity factor ratio (Reff). The key part of the analysis process is to calculate the stress intensity factor due to the initial residual stress field and also the stress relaxation and redistribution due to crack growth. The finite element method in conjunction with the modified virtual crack closure technique was used for this analysis. Fatigue crack growth rates were then calculated by the empirical laws and comparisons were made among these predictions as well as against published experimental tests, which were conducted under either constant amplitude load or constant stress intensity factor range. Test samples were M(T) geometry made of aluminium alloy 2024-T351 with a longitudinal weld by the variable polarity plasma arc welding process. Good agreement was achieved.