Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment

Wuhan, China

Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment

Wuhan, China
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Liu D.,Huazhong University of Science and Technology | Liu D.,Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment | Dunstan D.J.,Queen Mary, University of London
International Journal of Plasticity | Year: 2017

The physical basis and the magnitude of the material length scale in theories of strain gradient plasticity are crucial for accounting for size effects in the plastic behavior of metals at small scales. However, the underlying physics of the length scale is ambiguous. The length scales in strain gradient plasticity theories in which the plastic work density can be expressed as a function of the gradient-enhanced plastic strain are here derived from known physical quantities via critical thickness theory. A connection between the length scale and the fundamental physical quantities is elucidated. The combination of the strain and strain-gradient terms within the deformation theory of strain gradient plasticity is addressed. It is shown that, compared with the harmonic sum of the strain and strain-gradient terms in Fleck-Hutchinson theory, the linear combination gives a more reasonable value of length scale, several micrometers, which is close to that in the gradient theory of Aifantis. In contrast, the value of length scale in Nix-Gao theory is much larger, in the millimeter range. The length scales determined by critical thickness theory are in good agreement with those obtained by fitting to experimental data of wire torsion. © 2017 Elsevier Ltd.


Zhang X.,Huazhong University of Science and Technology | Zhang X.,Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment | Zhang H.,Wuhan Textile University
International Journal of Mechanical Sciences | Year: 2013

With appropriate design, functionally graded metallic foam can show definitely better properties than homogeneous counterpart due to its better designability. In the present work, functionally graded aluminum foam blocks subjected to ball impact are investigated numerically by using nonlinear finite element code. Blocks with different density gradient distributions, various geometric parameters and under different impact velocities are analyzed. The block with linear decreasing density gradient is found to possess excellent performance in energy absorption and outperform blocks with other density distributions under middle to high speed impact. To obtain the optimal design of the functionally graded foam block, a structural optimization problem with the objective of maximizing the crush force efficiency is solved by response surface method (RSM). The thickness and density of each layer are selected as design variables and it is interesting to find that the optimum design shows gradually decreasing density distribution. © 2013 Elsevier Ltd.


Zhang X.,Huazhong University of Science and Technology | Zhang X.,Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment | Zhang H.,Wuhan Textile University
International Journal of Impact Engineering | Year: 2014

Multi-cell columns are highly efficient energy absorbing components under axial compression. However, the experimental investigations and theoretical analyses for the deformation modes and mechanisms of them are quite few. In this paper, the axial crushing of circular multi-cell columns are studied experimentally, numerically and theoretically. Circular multi-cell columns with different sections are axially compressed quasi-statically and numerical analyses are carried out by nonlinear finite element code LS-DYNA to simulate the experiments. The deformation modes of the multi-cell columns are described and the energy absorption properties of them are compared with those of simple circular tube. Theoretical models based on the constituent element method are then proposed to predict the crush resistance of circular multi-cell specimens. The theoretical predictions are found to be in a good agreement with the experimental and numerical results. © 2013 Elsevier Ltd. All rights reserved.


Zhang X.,Huazhong University of Science and Technology | Zhang X.,Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment | Zhang H.,Wuhan Textile University | Wen Z.,Huazhong University of Science and Technology
International Journal of Impact Engineering | Year: 2014

Commercial aluminum honeycombs with various cell configurations are experimentally tested to study the influence of cell number and central angle on the out-of-plane crush resistance of the structures. The boundary effect is found to have significant impact on the crush strength of the structure when the number of cells is small and the central angle is observed to get a difference less than 10% in the strength of the honeycombs. Numerical analyses based on whole honeycomb model and Y-shaped element model are carried out to simulate the crush and deformation process of the specimens. The adhesive bonding of the double thickness foil is considered in the simulation and the numerical results show good agreement with the experimental data and theoretical predictions. Finally, the reason for the small influence of central angle on the out-of-plane strength of honeycombs is investigated and the interaction effect between wall thickness and central angle is believed to account for it. © 2014 Elsevier Ltd. All rights reserved.


Zhang X.,Huazhong University of Science and Technology | Zhang X.,Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment | Zhang H.,Wuhan Textile University
International Journal of Impact Engineering | Year: 2012

Honeycomb cellular structures and multi-cell prismatic columns are highly efficient and effective energy dissipating components and are widely used in the crashworthiness design of vehicles. Due to the complex features during large plastic deformation, only few special sections have been theoretical modeled for their energy absorption capacity under axial compression. In this paper, based on a simplified FE model, the energy absorption characteristics of angle elements with three panels are investigated by using the non-linear finite element code LS-DYNA. Theoretical models are proposed to predict the crush resistance of three-panel angle elements with different angles. Numerical results show that the proposed theoretical model can predict the energy absorption of these angle elements with good accuracy. © 2012 Elsevier Ltd. All rights reserved.


Zhang X.,Huazhong University of Science and Technology | Zhang X.,Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment | Zhang H.,Wuhan Textile University
Thin-Walled Structures | Year: 2013

Multi-cell metal columns were found to be much more efficient in energy absorption than single-cell columns under axial compression. However, the experimental investigations and theoretical analyses of them are relatively few. In this paper, the quasi-static axial compression tests are carried out for multi-cell columns with different sections. The significant advantage of multi-cell sections over single cell in energy absorption efficiency is investigated and validated. Numerical simulations are also conducted to simulate the compression tests and the numerical results show a very good agreement with experiment. Theoretial analyses based on constitutive element method are proposed to predict the crush resistance of multi-cell columns and the theoretical predictions compare very well with the experimental and numerical results. © 2013 Elsevier Ltd.


Zhang X.,Huazhong University of Science and Technology | Zhang X.,Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment | Zhang H.,Wuhan Textile University
International Journal of Impact Engineering | Year: 2013

The present work is aimed at finding the maximum energy absorption efficiency of plates in thin-walled structures under compression. In thin-walled structures, the plates are connected with different angles and by different edge connectivity. The influences of these two major factors on the crush resistance of structures are investigated numerically by nonlinear finite element code. Two extreme modes: uniform mode and opposite mode are defined for the angle elements with different edge connectivity. The energy absorption characteristics of these two modes are investigated and a theoretical model is established to predict the energy absorption capacity of elements deforming in uniform mode. Experimental tests of multi-cell columns are conducted to validate the numerical analyses and theoretical models for angle elements. The numerical simulations and theoretical predictions of the crush resistance of multi-cell columns show a very good agreement with the experimental results. © 2013 Elsevier Ltd. All rights reserved.


Zhang X.,Huazhong University of Science and Technology | Zhang X.,Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment | Zhang H.,Wuhan Textile University
Thin-Walled Structures | Year: 2012

Energy absorption characteristics of regular polygonal columns and rhombic columns under quasi-static axial compression are investigated by using an INSTRON materials testing machine. The influence of central angle on deformation mode and mean crushing force of angle elements is studied. Numerical investigations are also carried out to study the crush resistance of polygonal columns and angle elements under quasi-static and dynamic axial compression. The numerical predicted crushing force and deformation mode of the polygonal columns are found to be in good agreement with the experimental results. In addition, based on the experiment observations, some discussion about the deformation mechanism of energy absorption is presented. © 2012 Elsevier Ltd. All rights reserved.


Huang M.,Huazhong University of Science and Technology | Huang M.,Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment | Li Z.,Huazhong University of Science and Technology | Li Z.,Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment
Journal of the Mechanics and Physics of Solids | Year: 2013

To model the deformation of single crystal nickel based superalloys (SCNBS) with low stacking fault energy (SFE), three-dimensional discrete dislocation dynamics (3D-DDD) is extended by incorporating dislocation dissociation mechanism. The present 3D-DDD simulations show that, consistent with the existing TEM observation, the leading partial can enter the matrix channel efficiently while the trailing partial can hardly glide into it when the dislocation dissociation is taken into account. To determine whether the dislocation dissociation can occur or not, a critical percolation stress (CPS) based criterion is suggested. According to this CPS criterion, for SCNBS there exists a critical matrix channel width. When the channel width is lower than this critical value, the dislocation tends to dissociate into an extended configuration and vice versa. To clarify the influence of dislocation dissociation on CPS, the classical Orowan formula is improved by incorporating the SFE. Moreover, the present 3D-DDD simulations also show that the yielding stress of SCNBSs with low SFE may be overestimated up to 30% if the dislocation dissociation is ignored. With dislocation dissociation being considered, the size effect due to the width of γ matrix channel and the length of γ' precipitates on the stress-strain responses of SCNBS can be enhanced remarkably. In addition, due to the strong constraint effect by the two-phase microstructure in SCNBS, the configuration of formed junctions is quite different from that in single phase crystals such as Cu. The present results not only provide clear understanding of the two-phase microstructure levelled microplastic mechanisms in SCNBSs with low SFE, but also help to develop new continuum-levelled constitutive laws for SCNBSs. © 2013 Published by Elsevier Ltd.


Zhu Y.,Huazhong University of Science and Technology | Li Z.,Huazhong University of Science and Technology | Li Z.,Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment | Huang M.,Huazhong University of Science and Technology | Huang M.,Hubei Key Laboratory of Engineering Structural Analysis and Safety Assessment
Scripta Materialia | Year: 2013

The coupled effects of sample size and grain size and the plastic deformation mechanisms of polycrystalline Al nanowires were investigated by molecular dynamics. With the number of grains across the diameter increasing from one to four, the 5 nm grain size nanowires showed a "smaller is stronger" effect, the 10 nm grained nanowires did not show any significant size effect, while the 20 nm grained nanowires showed a "smaller is weaker" effect. Different size effects are induced by competition between surface-mediated and grain boundary-mediated deformations. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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