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Zhang D.,Jiangsu Key Laboratory of Engineering Mechanics | Zhang D.,Nanjing Southeast University | Jiang D.,Nanjing Forestry University | Fei Q.,Jiangsu Key Laboratory of Engineering Mechanics | And 3 more authors.
Finite Elements in Analysis and Design | Year: 2016

The mechanical behavior of honeycomb sandwich structures under low-velocity impact is of great significance. An experimental and numerical investigation on surface deformation and energy absorption subjected to low-velocity impact is undertaken. A high-speed camera system is employed to record the acceleration attenuation process of the impactor, a projection profile system is introduced to measure the surface profiles of the panel and the depth of the ultimate indentation is obtained. A three-dimensional finite element model is constructed and validated by the experimental results. Indentation characteristics and energy absorption are analyzed and in good agreement with experimental data. Effect of adhesive layers on energy absorption is discussed and the contribution of the facesheets and the honeycomb core to the energy absorption process is analyzed separately. Results shown that the effect of adhesive layers on energy absorption is non-ignorable and the honeycomb core plays a dominant role in energy absorption. Most of the energy absorbed by the honeycomb sandwich panel is expended as plastic dissipation, and the rest is transformed into strain energy. © 2016 Elsevier B.V.


Fei Q.,Nanjing Southeast University | Fei Q.,Jiangsu Key Laboratory of Engineering Mechanics | Ding J.,China Academy of Space Technology | Han X.,Nanjing Southeast University | And 3 more authors.
Journal of Vibroengineering | Year: 2012

Finite element model updating is an important research field in structural dynamics. Though a variety of updating methods have been proposed in the past decades, all the methods could be effective only on the assumption that the initial finite element model is updatable. The assumption has led to the fact that many researchers study on how to update the model while little attention is paid to studies on whether the model is updatable. This has become inevitable obstacle between research and engineering applications because the assumption is not a tenable hypothesis in practice. To circumvent this problem, the evaluation of model updatability is studied in this paper. Firstly, two conditional statements about mapping are proved as a theoretical basis. Then, two criteria for evaluation of initial models are deduced. A beam is employed in the numerical simulations. Two different initial models for the beam are constructed with different boundary conditions. The models are evaluated using the proposed criteria. The results indicate that the criteria are able to distinguish the model updatability. © Vibroengineering. Journal of Vibroengineering.


Tao J.-Y.,Nanjing Southeast University | Tao J.-Y.,Jiangsu Key Laboratory of Engineering Mechanics | Zhou Y.-D.,Nanjing Southeast University | Zhou Y.-D.,Jiangsu Key Laboratory of Engineering Mechanics | And 4 more authors.
Gongcheng Lixue/Engineering Mechanics | Year: 2016

Considering the high-temperature fatigue test for titanium alloy in three experimental conditions, namely 200℃, 0.5 kN-22.5 kN-0.5 kN testing condition, 300℃, 0.5 kN-22.5 kN-0.5 kN testing condition, and 200℃, 0.5 kN-30 kN-0.5 kN testing condition, each condition was assigned to the number of 5 to 7. By the introduction of the "Chauvenet Criterion", the test aborts the suspicious test point, and the result of the life distribution model examination is that the effective data follows a normal distribution model. On the basis of test data, the paper calculates the value of the median fatigue life and the fatigue safe life corresponding to the survival rate of 99.9%, which can be used in different project requirements. © 2016, Engineering Mechanics Press. All right reserved.


Wang M.,Nanjing Southeast University | Wang M.,Jiangsu Key Laboratory of Engineering Mechanics | Fei Q.,Nanjing Southeast University | Fei Q.,Jiangsu Key Laboratory of Engineering Mechanics | And 2 more authors.
Advances in Materials Science and Engineering | Year: 2016

Based on the assumption of quasibrittle failure under high-cycle fatigue for the metal material, the damage constitutive equation and the modified damage evolution equation are obtained with continuum damage mechanics. Then, finite element method (FEM) is used to describe the failure process of metal material. The increment of specimen's life and damage state can be researched using damage mechanics-FEM. Finally, the lifetime of the specimen is got at the given stress level. The damage mechanics-FEM is inserted into ABAQUS with subroutine USDFLD and the Python language is used to simulate the fatigue process of titanium alloy specimens. The simulation results have a good agreement with the testing results under constant amplitude loading, which proves the accuracy of the method. Copyright © 2016 Meng Wang et al.


He D.D.,Nanjing Southeast University | Li Z.X.,Nanjing Southeast University | Li Z.X.,Jiangsu Key Laboratory of Engineering Mechanics | Sheng H.Q.,Nanjing Southeast University | Chen C.,Nanjing Southeast University
Fatigue and Fracture of Engineering Materials and Structures | Year: 2013

Experimental analyses on the structural response caused by local fatigue damage accumulation in welded details are accomplished to perform failure process and nonlinear effect analysis at different structural levels. The experiment is carried out by using welded compact tension (CT) specimens and a scaled truss specimen, and all of them have a notch at the weld toe to facilitate damage initiation. Cyclic loads are applied to those specimens to generate accumulative fatigue damage, respectively. The process of fatigue accumulation including initiation and propagation of fatigue cracks in the welded detail and resultant structural responses of CT specimens and the truss are measured with integration of multiple testing techniques. Multi-scale experimental results show that microscopic-/mesoscopic-concentrated strain and extension of plastic zone in the vicinity of notch tip are both affected significantly by the fatigue damage accumulation and present appreciable nonlinear behaviour; however, the macroscopic response such as the frequency and stiffness parameters of the welded truss specimen are less sensitive to the low-level fatigue damage. It is concluded that the fatigue failure of the welded truss is a multi-scale progressive process due to fatigue damage trans-scale evolving, in which the local meso-damage firstly affects local strain of plastic zone in the vicinity of the notch tip, and then fatigue damage evolving from meso- to macro-scale affects nonlinear responses of the damaged components; lastly, the fatigue failure could be expected as the results of the propagation of macroscopic fatigue cracks. © 2012 Wiley Publishing Ltd.


Zhang D.,Jiangsu Key Laboratory of Engineering Mechanics | Zhang D.,Nanjing Southeast University | Fei Q.,Jiangsu Key Laboratory of Engineering Mechanics | Fei Q.,Nanjing Southeast University
Aerospace Science and Technology | Year: 2016

A numerical investigation was performed to further understand the physical significance of bird striking on a rotary jet-engine fan. A new numerical bird model considering more geometric characteristics than traditional ones was established first, during which the smooth particles hydrodynamic (SPH) method and an equation of state (EOS) were employed. The numerical method and material model were indicated to be reasonable by a validation analysis. Then, a preliminary study of a rigid target struck by a realistic bird from four different orientations including head, tail, bottom and wing sides as well as a traditional hemispherical-ended cylinder model were simulated. It was found that bird geometry and impact orientation had significant effects on impact response and kinetic energy loss of the bird. Furthermore, the same load conditions were conducted on a rotary jet-engine fan and followed by a series of parametric studies, including impact force history, kinetic energy loss of the bird, deformations of the blade tips and von Mises stresses of the blade roots. The results showed that both bird geometry and impact orientation had significant and non-ignorable influence on bird striking on a rotary jet-engine fan and bottom side was the most dangerous case. Considering more geometric characteristics of the bird and impact orientation in studies of bird strike problems was proved to be meaningful and necessary. © 2016 Elsevier Masson SAS. All rights reserved.


Jiang D.,Jiangsu Key Laboratory of Engineering Mechanics | Jiang D.,Nanjing Southeast University | Li Y.,Jiangsu Key Laboratory of Engineering Mechanics | Li Y.,Nanjing Southeast University | And 4 more authors.
Composite Structures | Year: 2015

Uncertainties are generally included in elastic parameters of the fiber reinforced textile composites. An approach on predicting the statistical characteristics of elastic modulus of braided composites using vibration test data is proposed in this paper. The method consists of two main steps, firstly estimate the initial mean values of the orthotropic elastic parameters by adopting the homogenization method, and then identify the variability of the elastic constants using a stochastic model updating algorithm with the first-order perturbation approach, the uncertain parameters are assumed as the summation of mean value and a deviation term with zero mean. A braided composite panel is employed in numerical simulations to verify the proposed method, the random samples of experimental modal data are simulated with the Latin Hypercube Sampling technique based on a reference finite element model, which is constructed by using deterministic updated elastic parameters. Results show that the mean value and standard deviation of the uncertain effective parameters of braided composite can be identified from modal data using the proposed stochastic identification method. © 2015 Elsevier Ltd.


Fei Q.,Nanjing Southeast University | Jiang D.,Jiangsu Key Laboratory of Engineering Mechanics
Conference Proceedings of the Society for Experimental Mechanics Series | Year: 2014

Finite element model updating is an important research field in structural dynamics. Though varieties of updating methods have been proposed in the past decades, all the methods could be effective only on the assumption that the initial finite element model is updatable. The assumption has led to the fact that all researchers study on how to update the model while seldom of them study on whether the model is updatable. This has become inevitable obstacle between research and engineering application because the assumption is not a tenable hypothesis in practice. Two criteria of evaluating initial models are given in this paper. A beam is employed in the numerical simulations. Two different initial models for the beam are constructed with correct and erroneous modeling of boundary condition respectively. The models are first evaluated using the proposed criteria and then updated using sensitivity based model updating method. The results indicate that the criteria are able to distinguish the model updatability. © The Society for Experimental Mechanics, Inc. 2014.


Fei Q.,Nanjing Southeast University | Fei Q.,Jiangsu Key Laboratory of Engineering Mechanics | Han X.,Nanjing Southeast University | Han X.,Jiangsu Key Laboratory of Engineering Mechanics
Journal of Vibroengineering | Year: 2012

Runyang suspension bridge is the longest suspension bridge in China with a main span of 1490 meters. During the construction of the bridge, a structural health monitoring system was installed, which was designed by the Southeast University. Since the bridge was open to traffic, quantities of structural ambient vibration responses have been recorded by the monitoring system. It is important to extract dynamic characteristics from these responses for structural assessment and maintenance. This paper presents the study on extraction of modal parameters from the Runyang suspension bridge structural health monitoring system records using wavelet analysis. Time-frequency domain modal identification using wavelet analysis is studied with an emphasis on the efficient approach for determination of the dilatation parameter. Then the wavelet analysis based method was adopted to identify dynamic properties including modal frequencies, mode shapes and damping ratios from the ambient vibration responses recorded by the monitoring system. Identified results were compared with those from Enhanced Frequency Domain Decomposition method and Stochastic Subspace Identification method. The differences between results are analyzed. Suggestions on future study are also given. © Vibroengineering. Journal of Vibroengineering.


Chen Z.-W.,Xiamen University | Chen Z.-W.,Jiangsu Key Laboratory of Engineering Mechanics
Gongcheng Lixue/Engineering Mechanics | Year: 2014

The estimation of fatigue reliability of multi-loading suspension bridges represents a challenging task in the consideration of randomness in multiple types of loading. This study presents a framework for fatigue reliability analysis of multi-loading long-span suspension bridges equipped with structural health monitoring systems (SHMS), and the Tsing Ma suspension bridge in Hong Kong is taken as a case study. A limit state function is first defined for fatigue reliability analysis. Probabilistic models of railway, highway, and wind loading are established based on the measurement data acquired from the SHMS. The daily stochastic stress responses induced by the multiple types of loading are simulated at the fatigue-critical locations of the bridge deck by using the finite element method and the Monte Carlo simulation (MCS) together with the loading probabilistic models established. The probability distribution of the daily sum of m-power stress ranges is estimated based on the daily stochastic stress responses. Finally, the fatigue failure probabilities of the bridge at the fatigue-critical locations are calculated for different time periods. The results demonstrate that the health condition of the Tsing Ma Bridge at the end of its design life will be satisfactory under current traffic conditions without growth.

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