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2014 Vol. 35, No. 1
Published:
1
Thermal buckling and critical temperature analysis of sandwich panels with metal-truss core
This article presents a theoretical analysis and parametric discussion of thermal buckling of sandwich panels with metal truss core under clamped and simply-supported boundary conditions, when subject to uniform thermal loading, by using Ressiner model and assuming the truss core is a continuous material. We ignore the flexural rigidity and bending stiffness of the core, and consider the shear stiffness of the core is the shear stiffness of the sandwich panel. By using the double Fourier expansion of the virtue deformation mode, we get the critical temperature of sandwich panels under clamped boundary, which cannot be analytical solved. The theoretical results are in good agreement with those of the finite element analysis. Then we discuss the influence of cell configuration of lattice-framed materials, the relative density of truss core, and panel thickness on critical buckling temperature.
2014 Vol. 35 (1): 1-7 [
Abstract
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374
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8
THE STUDY OF WAVE PROPAGATION IN THE AIR-COUPLED COMPOSITE LAMINATE
In this paper, the wave propagation in the air coupled composite laminate is studied. The amplitude and phase of the transmission coefficient along with frequency under any incident angle was solved and calculated by the potential function method from the fundamental wave equation with the air-solid boundary condition. The experimental platform was established to measure the transmission coefficient of any incident angle based on MATLAB. Simultaneously the transmission coefficients of composite samples were measured and the experimental results agreed well with those of theoretical calculations. Therefore, the validity of the proposed theoretical solution of the air-coupled wave propagation and the experimental measurement technique are demonstrated.
2014 Vol. 35 (1): 8-14 [
Abstract
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209
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15
The scattering of SH Wave on the Array of Periodic Cracks in a Piezoelectric Substrate Bonded a Half-Plane of Functionally Graded Materials
The interaction of SH wave with the array of periodic cracks in a piezoelectric substrate bonded to a functionally graded materials (FGM) coatings is considered. The governing equations along with permeable crack boundary, regularity and continuity conditions across the interface are reduced to a coupled set of Hilbert singular integral equations which are solved approximately by applying Cheyshev polynomials. Numerical results for the normalized dynamic stress intensive factors (NDSIF) and the normalized electric displacement intensive factors (NEDIF) are presented. The effects of geometric parameters and the physical parameters, and the effects of frequency and angles of SH wave on the NDSIF and the NEDIF are discussed.
2014 Vol. 35 (1): 15-20 [
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181
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21
Modeling and Parameter Study of PWAS-induced Lamb wave based on Spectral Finite Element
A three-layer spectral finite element model, consisting of piezoelectric wafer active sensor (PWAS), adhesive layer and base structure, is developed to study PWAS-induced Lamb wave propagation in structures. Based on different beam theories for different layers, governing equations and force boundary conditions are derived for the coupled PWAS-adhesive layer-base structure system, by which spectral finite element model is established. Compared with the conventional finite element method, the developed model is proved to obviously improve calculation efficiency and have high accuracy in modeling Lamb wave propagation. Output voltage versus exciting frequency, the length and thickness of PWAS and the thickness of adhesive layer is analyzed, which may provide some references for PWAS and Lamb wave-based active health monitoring technology.
2014 Vol. 35 (1): 21-29 [
Abstract
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195
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30
A CRACK PROPAGATION PATH ANALYSIS METHOD OF RANDOM CRACKED STRUCTURE
There are many uncertainty factors such as crack length, material properties and external load, etc in cracked structure, and the crack propagation path uncertainty analysis is necessary for a better understanding of their mechanical properties including damage and fracture and predicting the performance and reliability. This paper proposes a crack propagation path analysis method in random cracked structure, which is suitable for mixed-model load. The method takes into consideration the randomness of crack length, material properties and external load, etc and adopts the Monte Carlo method to random sampling from random parameter space. The scaled boundary finite element method is adopted to calculate the stress intensity factors and simulate the crack propagation path. On this basis, a statistical analysis method is presented to obtain the crack propagation path statistical properties in random cracked structure. Finally two numerical examples are presented for verification of the validity of the proposed method.
2014 Vol. 35 (1): 30-38 [
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182
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39
Mechanical Behavior of Frozen Soil with Uniaxial Dynamic Loading
Investigation of dynamic behavior of frozen soil is of great importance to artificial ground freezing method in underground engineering, etc. In this article, split Hopkinson pressure bar (SHPB) is employed to investigate the dynamic character of artificial frozen soil under uni-axial stress condition. Tests are conducted at the temperature of -3, -8,-13,- 17,-23 and -28℃ and strain rates from 300 to 1200s-1. The stress-strain curves at different conditions were obtained. The uni-axial stress-strain curves of frozen soil show brittle character. The compressive strength of frozen soil shows positive strain-rate and negative temperature sensitivity，and the final strain of frozen soil shows positive strain-rate sensitivity over the range of strain rates and temperature employed. The thermal effect of frozen soil is greater with higher loading strain rates. The strain rates sensitivity of frozen soil is higher with lower temperature. The viscoelastic damage model mentioned in this article can describe the stress strain relation of frozen soil under dynamic loading.
2014 Vol. 35 (1): 39-48 [
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187
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49
Stability analysis of spatial beam based on corotational formulation
Based on the element independent corotational formulation (EICR), a geometrically linear shear locking free Timoshenko beam element was extended to the geometrically nonlinear analysis of spatial beams with arbitrarily large displacements and rotations but small strain. On considering the non-communitativity of finite rotations in three-dimensional analysis, which means that rotational degrees of freedom can't be updated by addition rule as vector quantities, therefore, the quaternion was used to store and update the rotational degrees of freedom. And a modified Riks arc-length method suitable for three-dimensional geometrically nonlinear analysis with large rotations was also presented. Several numerical examples for geometrical nonlinear analysis of spatial beams using the present beam element were also presented and the results demonstrate that the proposed element and methods are efficient and accurate.
2014 Vol. 35 (1): 49-56 [
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199
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57
A MUTI-RESOLUTION TIMOSHENKO BEAM ELEMENT FORMULATION
A multi-resolution beam element with bending based on the Timoshenko theory is proposed. The multi-resolution analysis (MRA) performance of the element is formulated out of a nesting displacement subspace sequence, whose basis functions are constructed of scaling and shifting on the interval [0,1] of node shape functions extended from the traditional interval [0,1] to the [-1,1]. The MRA property enables this one proposed element to be re-meshed freely just by means of adjusting its resolution level, thus modulating its analysis accuracy accordingly. The extended shape functions make all the sub-elements connect together at the nodes as a whole as the initial proposed element in the re-meshing process, that is, the stiffness, the mass matrices and the equivalent node loading vectors can be obtained automatically without being reassembled artificially，thus, being seen as a technical secret for assembling artificially of node-related items in global matrix formation by the conventional. In addition, the proposed beam element can deal with the boundary conditions conveniently just as a conventional Timoshenko beam element does. In this sense, the MRA concept is fulfilled for the first time for a Timoshenko beam element and the mathematic essence, a nesting displacement subspace sequence, is found for meshing of beam structure in this paper.
2014 Vol. 35 (1): 57-62 [
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378
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63
ELASTO-PLASTIC UNIFIED SOLUTIONS FOR COMBINED THICK WALL CYLINDER BASED ON UNIFIED STRENGTH THEORY
With consideration of the intermediate principal stress and different strength in tension and compression，the elasto-plastic bearing capacity of double and multilayer thick wall cylinder is analyzed based on unified strength theory. The separate radius, assemblage pressure and shrinkrange fundamental solutions are derived based on the yield condition for unified strength theory. The unified solutions for combined thick wall cylinder are also deduced. Parametric studies are carried out to evaluate the effects of unified strength theory parameter, tension-compression ratio, radius ratio and combined cylinder layer numbers on the unified solutions. The results are versatile in the theory of combined thick wall cylinder and pressure vessel. It makes full use of the strength potentialities for combined cylinder due to considering the intermediate principal stress. The solution has an important practical value for the optimum design and engineering application of combined thick wall cylinder.
2014 Vol. 35 (1): 63-70 [
Abstract
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357
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511
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71
Spectral stochastic element-free Galerkin method for laminated composite plates
A spectral stochastic element-free Galerkin method is proposed to solve the stochastic structural problems with parameters having big changes, which can not be solved by the methods based on the perturbation theory. Based on the orthogonal decomposition theory of random fields, this method applied the Karhunen-Loève series to expand a random field into a series of uncorrelated random variables. A spectral expansion with use of polynomial chaos is employed to represent the stochastic nodal displacements in terms of standard normal random variables. The spectral stochastic element-free Galerkin method of the composite laminated plates with random variables was derived, with the computational formulas of the statistical characteristics of structural responses being given. This method will not be subject to the size constraints of the coefficient of variation and have an advantage of the element-free Galerkin method. Numerical results show that the method is correct and effective.
2014 Vol. 35 (1): 71-76 [
Abstract
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174
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478
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77
Compressive behavior of 2.5D self-healing C/SiC composite
The compressive behavior of 2.5D C/SiC composite was studied by means of experiment. According to the micro-structure of composite, a new mechanical model was established，the nonlinear stress-strain curves in weft and warp directions were gained. The result shows that, the mechanical behavior in weft direction is different from that in warp direction. As the compressive stress in weft direction increases, the modulus increases, and the compressive strength in weft direction is 270.05MPa. As the compressive stress in warp direction increases, the interlaminar damage occurs, the bending moment caused by compressive stress increases, modulus decreases, and the compressive strength in warp direction is 128.66MPa.
2014 Vol. 35 (1): 77-84 [
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355
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85
Complex variable solutions for elliptical hole involving time-dependent boundary in viscoelastic infinite plane
The structures involving time-dependent boundary regions are commonly encountered in engineering, i.e. structures under construction in civil engineering. For tunnel excavations in rheological rock mass, this paper presents the analytical solutions of problem with elliptical hole in viscoelastic infinite plane by using the complex variable method and corresponding principle of time-dependent boundary problem in combination. First, basic formulations of complex variable method are established for general viscoelastic problems involving time-dependent boundary regions. Then, based on the derived potentials with respect to ? in the reference, the potentials in z-plane are obtained by introducing the inverse mapping function, and therefore the variable t used in Laplace transformation is decoupled with the t which comes from mapping function. At last, the expressions of displacement and stress are derived for the general cases of viscoelasticity. In addition, the Boltzmann viscoelastic model is chosen as an example to obtain the exact solutions of stress and displacement in integral form by substituting the material parameters into the general expressions. The comparison between the specific analytical and FEM solutions is made to validate the correctness of the derivation and further analyses are performed to illustrate the influence of boundary varying process on the relationship between stress (displacement) and time. The results show that the variations of displacement and stress are correlated with boundary varying speeds. The solutions can be used in mechanical analysis and preliminary design of underground elliptical tunnel excavation. Furthermore, the method in this paper is also suitable for the analysis of the underground excavation problems in arbitrary sharp.
2014 Vol. 35 (1): 85-94 [
Abstract
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216
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431
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95
Study on the interaction of tip fields between periodic cracks and periodic rigid line inclusions
The problem of a doubly periodic array of cracks and rigid line inclusions in an infinite medium under far-field antiplane shear is investigated. By employing the conformal mapping technique and the elliptical function theory, an exact solution of the whole-field stress is obtained. The closed form formulae for the stress intensity factor at the tips of cracks and rigid line inclusions are presented. The interaction of the tip fields between cracks and rigid line inclusions is discussed. The major results are: (a) the tip fields of cracks and rigid line inclusions show different laws with the change of horizontal and vertical distribution periods; (b) with the increase of the length of cracks 2a (0≤a/ω1≤0.5), the stress intensity factor of cracks increases monotonously, whereas the tip field of rigid line inclusions show almost unchanged; (c) when the length of rigid line inclusions 2d (0≤d/ω2≤1) increases, the stress intensity factor of rigid line inclusions gradually decreases from 1 to 0, whereas the tip field of cracks is only slightly increased.
2014 Vol. 35 (1): 95-100 [
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182
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493
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101
Study on Keys Influencing Optimization Effect of Rational Criterion Methods of Structural Optimization
Keys influencing optimization effect of rational criterion methods of structural optimization are correctness of criteria equation groups and astringency of iterative algorithm, these keys are dissectionally lucubrated. It is firstly pointed out that structural weight plays two ambivalent roles in structural optimization: As design resource, weight can improve structural performances; On the other hand, as structural load, weight may make structural performances bad. Criteria equation group of virtual work method has ignored derivatives of structural load to design variables, can not consider the other hand of ambivalent roles of structural weight, this ignoring can not be treated as a rational approximation. For aircraft, spacecraft, high-precision antenna, high-speed train, vehicle and machine etc., their structural main load is structural weight or inertial load, the result obtained through Virtual Work method is far away from the optimum solution. In Guide-weight method, the criteria equation groups of are strictly deduced, the limitation of Virtual Work method has been overcome, and its optimization result is improved greatly. Rational criteria methods come down to directly iterative solution of nonlinear criteria equation group, which is a fixed point mapping problem with strict convergence condition. The step factor method is often used to ensure iteration convergence. It can be proved that the step factors making iteration convergence must be existent. And theoretic value range and practical selection methods of step factors making iteration convergence has been educed and proposed. Optimization examples of a truss with 10 bars and two antenna structures can validate above contention.
2014 Vol. 35 (1): 101-107 [
Abstract
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198
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522
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