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2018 Vol. 39, No. 6
Published: 2018-12-28
553
Research progress on conductive magnetorheological elastomers
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.039
Magnetorheological elastomer (MRE) has attracted a significant amount of attention in engineering applications due to its unique field-dependent mechanical performance. This paper presents the latest developments in MRE, with emphasis on the research status of conductive MRE in material design, mechanical behavior and applications. At first, the preparation of high performance conductive MRE and the issues involved in the design of material and structure is introduced. Then, a brief summary of the research on the magnetic-mechanic-electric mechanism and modelling is presented. Finally, the research and development of the latest devices are concluded and the potential and challenges of conductive MRE are prospected.
2018 Vol. 39 (6): 553-577 [
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578
THE DEPENDENCE OF ENERGY ABSORPTION BEHAVIOR OF CELLULAR MATERIALS ON RELATIVE DENSITY AND IMPACT VELOCITY
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.030
Cellular materials have been extensively used as core materials of impact energy absorbers and anti-blast sacrificial claddings for their lightweight and superior energy absorption capability. However, the dependence of energy absorption behavior of cellular materials on relative density and impact velocity is still unclear due to the diversity of its deformation modes and the inaccessibility of its dynamic stress-strain curve. In this paper, the dynamic energy absorption behavior of cellular materials is investigated by using the wave propagation technique, of which the main advantage is that no pre-assumed constitutive relationship is required. In the virtual Taylor impact test, the particle velocity history curves of the whole field in cellular materials are obtained, and thus the local stress and strain history profiles of cellular materials are determined based on the Lagrangian analysis method. The dynamic energy absorption behavior can be investigated by integrating local stress-strain history curves. The results show that the energy absorption behavior of cellular materials can be divided into three stages according to the deformation modes. In the stage of shock mode, the specific energy absorption of cellular materials increases linearly with the relative density since the inertia effect is dominant at this stage; in the stage of transition mode, the inertia is relatively weak, and the increase rate of the specific energy absorption decreases gradually with the increasing of relative density; in the stage of quasi-static mode, the energy absorption capacity is very weak, and it should be distinguished from the quasi-static energy absorption behavior under constant speed loading. Finally, the dynamic stress-strain state curve of cellular materials is obtained and its dependency on the relative density is further investigated. The results transpire that, with the increasing of the relative density, the dynamic densification strain under the same stress level decreases and the dynamic plastic platform stress increases.
2018 Vol. 39 (6): 578-586 [
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248
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587
TOPOLOGY OPTIMIZATION FOR STIFFENER LAYOUT OF THIN PLATE STRUCTURES BASED ON LEVEL SET METHOD
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.034
A topology optimization approach for stiffener layout of thin plate structures is proposed based on level set method. The thin plate and stiffeners are considered as plates with different bending stiffness, with use of equivalent stiffness method. Then the location of stiffeners were described by Level set method to perform topology optimization. With the objective of maximizing structural stiffness, several typical cases with various loading and boundary conditions were selected as numerical examples. The optimized stiffened plates of the proposed method were compared with optimized results in literatures to verified the validity of the proposed method. Numerical examples showed that the proposed method can provide clear stiffener layout and avoid “gray elements”.
2018 Vol. 39 (6): 587-593 [
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273
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594
Rational Criterion of Pre-estimation Distribution of Failure Regions for Fail-safe Topology Optimization of Continuum Structures
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.024
In this paper，it is pointed out that the topology optimization of continuum structures had entered a new stage since Zhou’s research in 2016. The new stage includes two points: (1) Designs of discrete structures have been benefitted from the results of the topology optimization of continuum structures. (2)At the same time, the theory of topology optimization of continuum structures can benefit from the topology optimization of discrete structures. The rational criterion of the pre-estimation distribution of failure regions is established based on geometrical analysis, that is, the upper limit and lower limit of the size of the local failure mode and the upper limit and lower limit of the space of adjacent local failure regions are given. The advantages and disadvantages of the pre-estimation distribution strategies of failure regions proposed by Janson and Zhou are analyzed according to the proposed rational criterion. Numerical examples are given to verify the relevant strategies. The results show that Janson’s strategy is too conservative to lead to unnecessary computation. Zhou's strategy with the gapless fill of failure regions can’t guarantee that all discrete members yielded by topology optimization pass the failure test, but in most cases, the optimal topology with sufficient redundancy can be obtained. While the pre-estimation distribution of failure regions satisfies the proposed rational criterion, all discrete members yielded by topology optimization can be ensured to pass the failure test and optimal topology with more redundant can be achieved. The study shows that the rational criterion for the pre-estimation distribution of failure regions provides theoretical progress in describing local failure regions for the failure-safety topology optimization continuum structures.
2018 Vol. 39 (6): 594-605 [
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182
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606
THE INTERACTION BETWEEN A SCREW DISLOCATION DIPOLE AND A LINEAR NANO CRACK IN QUASICRYSTALS
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.029
A new method is presented to get the precise results about the interaction between a screw dislocation dipole and a linear nano crack in quasicrystals. Firstly, the Gurtin-Murdoch surface/interface theory is successfully applied to nano crack problems of quasicrystal material, and the boundary model with surface stresses of phonon field and phason field is established. Secondly, the linear crack problem is turned into a unit circle orifice problem by using conformal mapping method of the complex function. Then, the exact solutions of this problem are obtained via Cauchy integral theorem. Finally, the numerical results show that surface effect will significant affects the numerical value of stress field image force and image torque of phonon field and phason field, and further changes mechanical properties of quasicrystal materials when the line crack size in quasicrystal materials is reduced to the nanometer level. Namely, the smaller crack size is, the stronger surface effect is, the greater the numerical changes of stress field and image force and image torque of phonon field and phason field. The couple arm orientation of the screw dislocation dipole has a great influence on the extreme value of the image force and its self-balance.
2018 Vol. 39 (6): 606-613 [
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170
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614
Computational investigation of mixed-mode I/II fracture behavior of CTS specimen
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.033
The SIFs solutions of CTS specimen are used to investigate the I/II mixed-mode fracture behavior, but they are not applicable for the deflected crack. In this study, three dimensional fracture analyses of CTS specimen for mixed-mode I/II loading are performed using finite element method (FEM). To simulate the real conditions, the contacts between the contact surfaces of the loading device, specimen and the pins. Comparison between the FEM results and the solutions for SIFs of CTS specimen were done for verification of the proposed simulation method. The crack growth paths of the CTS specimen for all loading angles are simulated by following the MTS principle. The SIFs of the crack front with the crack growth length were given, and the reason of the crack growth paths not perpendicular with the direction of the traction force was found. The mixed-mode crack growth rate can be obtained by combining the proposed SIFs results with thea-N test results.
2018 Vol. 39 (6): 614-625 [
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289
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626
Experimental and numerical study on three-point bending of adhesive multi-cell tubes
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.019
A novel type of easily prepared adhesive multi-cell tube is investigated experimentally and numerically in this paper. The deformation and energy absorption performance of the multi-cell tubes under three-point bending loads are analyzed. The quasi-static three-point bending tests reveal that the energy absorption capacity of adhesive multi-cell tubes is generally higher than the summation of their constituent single-cell tubes and in some case up to 70% can be achieved due to the effect of adhesive. Numerical simulations of the three-point bending tests are conducted by LSDYNA. The simulated deformation pattern and punch force-displacement curves are in good agreement with experiment results. In addition, three different interface conditions are simulated to analyze and compare the response of adhesive multi-cell tubes. Results show that energy absorption characteristics of adhesive multi-cell tubes are comparable to traditional multi-cell tubes if there is no obvious adhesive detachment. Otherwise the performances of adhesive multi-cell tubes will be seriously weakened.
2018 Vol. 39 (6): 626-633 [
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146
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634
Analysis of flutter instability of cantilever carbon nanotubes conveying fluid
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.028
Fluid-conveying carbon nanotubes (CNTs) have attracted much attention and they are used in nano-electromechanical systems (NEMS) and biomedical applications. In this work differential transform method (DTM) is used to study the vibration behavior of fluid conveying single-walled carbon nanotube (SWCNT). Based on the theories of elasticity mechanics and nonlocal elasticity, taking into account the flow-induced inertia, Coriolis and centrifugal forces along the nanotube, an elastic nonlocal Bernoulli-Euler beam model is developed for thermal-mechanical vibration and instability of a cantilever single-walled carbon nanotube (SWCNT) conveying fluid. The governing partial differential equations of motion and associated boundary conditions are derived by Hamilton's principle. The resulting eigenvalue problem is then solved, and some numerical examples are presented to investigate the effects of fluid velocity, nonlocal parameter and temperature change on the critical flow velocities and flutter instability of system. Numerical results show that the nonlocal small-scale parameter makes the fluid-conveying CNT more flexible. More importantly, the addition of a temperature field leads to much richer dynamical behaviors of the CNT system. It can be concluded that the temperature change can shift the unstable mode in which flutter instability occurs first at sufficiently high flow velocity from one to another. Furthermore, detailed results are demonstrated that at low or room temperature, for the SWCNT, the critical flutter flow velocity increases as the temperature change increases, on the other hand, while at high temperature the critical flow velocity decrease as the temperature change increases. Thus, the results of the present study may facilitate further analyses of nonlocal vibration, and thus the design of nanotubes in the presence of a temperature field. Our results maybe beneficial for the fabrication of smart nanostructures that can be employed to transport fluidic drug to diseased areas, where a low temperature field may help the fluid to flow in a suitable stream.
2018 Vol. 39 (6): 634-641 [
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130
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642
Secondary development and application of rock water-damage creep model based on FLAC3D
DOI: 10.19636/j.cnki.cjsm42-1250/o3.2018.018
Abstract：In order to study the effect of water content on rock creep, the water switch and the creep damage threshold are introduced into a new creep model named rock water-damage creep model, through which the coupling of water deterioration and creep damage is realized on constitutive relation. The rock water-damage creep model has good imitative effect by comparison with the triaxial compression creep test results of a soft rock, and the variation laws of the model parameters with the water content are inversed by Levenberg-Marquardt (LM-UGO) algorithm. In the environment of C++ language and Fish language in FLAC3D, through deducing its constitutive equation in three-dimensional difference form, the rock water-damage creep model is secondarily developed by the interface of FLAC3D. After validating its accuracy by an engineering example, the rock water-damage creep model is used in numerical simulation to reflect that the roadway stability is gradually weakened with the increase of water content in surrounding soft rock.
2018 Vol. 39 (6): 642-651 [
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155
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