Papers by Author: Yu Long Li

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Authors: Yong Kang Zhang, Yu Long Li, Hong Bing Zhang
Abstract: Identification of a bird constitutive model and its parameters is a very difficult work in bird-impact coupling solution. In order to identify the constitutive model and the parameters simultaneously, an inversion analytic model for the bird material parameters is given based on penalty function method and nonlinear optimization principle, and then combining the model preferential criterion proposed in this paper, the identification system of the bird constitutive model is established with ANSYS Parametric Design Language (APDL). Finally, the feasibility and practicability of this identification method are verified by an example.
Authors: Yong Jian Mao, Hong Jian Deng, Yu Long Li, Rong Jian He, Hong Wei Xiao, Xiao Hong Yue, Hai Ying Huang, Qing Zhou
Abstract: When a structure is irradiated by a pulsed cold X-ray with high energy density, the instantaneous deposition of energy will induce melting, vaporization, and sublimation of the outer layer of material(s). As a result, the material(s) will blow off and hence lead to a so-called blow-off impulse. This kind of impulsive load will cause high-level structural responses. In order to investigate the effects, various test simulation techniques, such as the light-initiated high explosive (LIHE) technique, the spray lead at target (SPLAT) technique and the sheet-explosive technique, were developed due to the lack of proper X-ray sources. This paper presents a rod-explosive technique developed from the sheet-explosive technique. In this technique, the main property of the explosive, i.e. the specific impulse, is determined by using a pendulum test facility. The simulation load (equivalent to the cosine-distributed specific impulse on a conical shell induced by X-ray) is designed by load discretization and impulse equivalence. Numerical simulations of structural responses to both X-ray loads and rod-explosive loads were performed for validating the test simulation technique. An application example of testing a complex structure is briefly given in the end. The rod-explosive technique has the features of low costs and rather high fidelities. It provides a new approach for testing the structural responses induced by X-ray blow-off impulses.
Authors: Yan Zhao, Fei Xu, Yu Long Li, Yoshitaka Wada
Abstract: A non-triangulation inserting particle method is presented to prevent numerical fractures of SPH computations. The particles in those regions in which numerical fractures may occur are chosen at the beginning of SPH computations. And, the chosen particles are arrayed by the two different rules respectively according to the particle position relations. When the distance between each two chosen connected particles exceeds a certain value and neither of the corresponding two particles has fractured in SPH computations, a new particle is generated between those two ones and the position relation of particles is updated. The physical quantities that the new particle carries are obtained according to some given rules. The method and the same type of method in the reference are compared. The application of the method is analyzed. Conservation of mass and Conservation of momentum of the whole system are kept in this method. Several examples are given to validate the efficiency of the method to prevent numerical fractures.
Authors: Yong Jian Mao, Yu Long Li, Han Jun Huang
Abstract: The cosine-distributed impulsive loads induced by intense soft X-ray radiation are often simulated by explosive rods in laboratory tests. The conventional design method of rods distribution needs a complicated process, by trials or optimization, to ensure the rod number as an integer. This paper proposes a simplified method based on the principle of load discretization and impulse equivalence. It has higher efficiency and more convenience, and can automatically let the rod number be an integer. This study provides an effective design tool for rod-explosive simulation tests of aerospace structures under intense soft X-ray radiation.
Authors: Zhong Bin Tang, Fei Xu, Yu Long Li, Wu Jun Xu
Abstract: A micro-scale uniaxial tension test method for measuring material mechanical properties of thin film materials is introduced in this paper. A self-developed test device is established based on the CMT8202 tension test machine. The Interference Strain/Displacement Gauge (ISDG) method is used to measure the strain in the micro-samples. The three dimensional finite element method (FEM) is utilized to optimize specimen geometry configuration and to reduce the stress concentration in specimen around grip region. The experiments are carried out for the polycrystalline copper thin film. The results show that stress-strain curves and the Young’s modulus of the thin film material can be obtained by micro-scale tension test. The Young’s modulus determined by micro-sample for polycrystalline copper thin film has a good agreement with published results.
Authors: Ling Wu, Ying Nan Guo, Yu Long Li
Abstract: The present study focuses on the mechanical performance and damage evolution of woven fabric E-glass fiber reinforced epoxy composite (7781/F155-glass/epoxy). For the identical behavior in the 0o and the 90o directions of the tested material, the mechanical experiments were performed with 0o and 45o specimens. Three kinds of tests were implemented respectively: tension test with 0o specimen, compression test with 0o specimen, and tension test with 45o specimen which represents the in-plane shear test. Tension, compression and in-plane shear damage, which are defined as the decreasing ratio of modulus, were calculated from the data of quasi-static cyclic tests. The influence of loading rate on material behaviors were investigated under three different loading rates. Although all of the three loading rates are low, it showed that the strain rate has obvious effects on the ultimate strengths and moduli of the glass fiber reinforced epoxy composite.
Authors: Yong Kang Zhang, Yu Long Li
Abstract: The 3-D finite element analysis model of beam-edge structure with spaced multiple layers under bird impact is established. Numerical simulations are implemented by using the non-linear contact-impact code ANSYS/LS-DYNA when the birds collide at three locations of the structure respectively. The failure process of the structure and the equivalent plastic strain at supports are obtained. The residual strength of the structure after impact is predicted. The results show that the front spars are penetrated or cracked after the leading edge is perforated. The equivalent plastic strain at the support is much higher when the bird impacts the structure at the central location. Both the structure deformation and failure mode from the simulation are consistent with the results of full scale test, which proves the validity of the method proposed in this paper.
Authors: Y.Z. Guo, Q. Wei, Yu Long Li
Abstract: While the super-high strength of various nanocrystalline metals (NC metals, grain size d<100 nm) has drawn great attention in the past few decades, the poor ductility has become a seemingly insurmountable obstacle for the wide application of such metals. Other limiting factors include, in particular, the high cost associated with delivering such materials. Recent efforts from various groups have brought forth strong hope that the ductility of NC metals can be greatly improved by the application of “microstructure engineering”. However, the testing methods used to evaluate the mechanical properties, especially at small scales, have invited concerns. A natural question arises as to whether the reported allegedly good ductility of many NC metals is intrinsic or extrinsic. This article attempts to critically evaluate such issues. We will examine the experimental results in conjunction with some finite element modeling on the stress state and strain measurement of specimens during mechanical testing. Factors such as sample geometry and loading mode will be critically assessed. We point out that while intrinsic ductility may be possessed by some NC metals, careful attention should be paid to how strain measurement is made.
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