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2015 Vol. 36, No. 3
Published: 2015-06-28
185
Extended Hellinger-Reissner Principle and Special Hybrid Stress Multilayer Elements
A new extended Hellinger-Reissner variational principle for non-homogeneous material has been developed which provides a convenient procedure for deriving the stiffness matrix of a non-homogeneous element that can be subdivided into regions of different material properties. In such case some of stress components along the interface and the displacement across the interface may become discontinuous. This formulation can also be used for thick laminated plates in which transverse shear stress of each layer is independent. One kind of new assumed stress hybrid multilayer element with a traction-free cylindrical surface is derived by the use of the extended principle. The stresses of each layer are interpolated by the natural coordinates and are obtained by the use of internal displacement as weight function to impose the equilibrium conditions in a variational sense. The stresses also satisfy the traction-free conditions over the cylindrical surface exactly. The continuous conditions of the displacement between the layers and the elements are relaxed by using Lagrange multipliers respectively. Numerical results show that the present elements are much more efficiency than the ordinary assumed stress hybrid elements and the conventional assumed displacement elements for analyzing stress distribution around difference types of cylindrical notches in thin to thick laminated composites when very coarse meshes are used.
2015 Vol. 36 (3): 185-196 [
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318
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197
Theoretical and Experimental Study on Debonding Mechanism of Steel Plate Strengthened with CFRP
The carbon fiber reinforced polymer (CFRP) always debond at the end from the steel plate, which is reinforced with CFRP. A finite element model of steel plate reinforced with CFRP is given out based on the cohesive force theory. Then the tensile experiment of steel plate reinforced by CFRP is studied, and that is used used to verify the finite element model. With the finite element model, it studies the mechanism of CFRP debonding from the steel plate. The results demonstrate that the cohesive method is suitable for the analysis of steel plate reinforced with CFRP, that the shear stress is the main factor of the stripping damage, that the whole process consists elasticity period ,soft period and debonding period, and that debonding begins from the end to the middle of CFRP until complete failure.
2015 Vol. 36 (3): 197-203 [
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253
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204
GEOMETRICALLY NONLINEAR MODEL AND NUMERICAL SIMULATION OF FUNCTIONALLY GRADED VARIABLE CURVATURE CURVED BEAM
Based on an exact geometrically nonlinear theory of planar elastic curved beams, the dimensionless governing equations and boundary conditions for functionally graded variable curvature curved beam subjected to mechanical loads and thermal loads were formulated, in which the basic unknown quantities were expressed as the functions of axial coordinates before the deformation. Then, taking an example of elliptic arc curved beam, two-point boundary value problem of nonlinear ordinary differential equations were solved by using shooting method, and thermal bending responses of transversely non-uniformly heated FGM elliptic arc curved beam with fixed-fixed ends were obtained. The influences of material gradient index, temperature parameter and structural geometric parameters on the internal force and deformation of curved beam were discussed in detail.
2015 Vol. 36 (3): 204-214 [
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196
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215
Warping Analysis of Medium Plate Based on Symplectic Elasticity Method
Warping Analysis of Medium Plate Based on Symplectic Elasticity Method
2015 Vol. 36 (3): 215-222 [
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209
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223
A novel approach for constructing master curves of rheological simple material
This study presents a novel approach for constructing master curves of rheological material. The approach conducts a calculation formula of the shift factor, which takes the area of the overlapping region between the shift curve and the reference curve as the determinant factor. The formula is succinct and clear. All the parameters come from the experimental data, that is to say, we can calculate the shift factor without interpolation or fitting. Thus, it makes the uniqueness and accuracy and escaping from the uncertainty of manual shifting subjective judgment and the error analysis of fitting of numerical shifting method. Meanwhile, because of the mathematical computing process of derivation, the formula is appropriate for all the materials satisfying the rheological simplicity. In addition, the applicability of the approach can be further strengthened by taking the significant peak value of the test curve into consideration. The effectiveness of the proposed approach is verified by an example of constructing dynamic mechanic property master curves of carbon-black rubber.
2015 Vol. 36 (3): 223-232 [
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187
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233
The approach to establishing a three-dimensional parameterized aggregate model for concrete simulation
In the numerical simulation of specimen of concretes in meso-level, to reduce the repellency and distances between aggregates as well as to improve the content of the aggregates and the computational speed of generating the specimen, the method of establishing a three-dimensional parametric aggregates model is developed. This method makes use of the parametric equation of the aggregates, presents a rule to determine whether a spatial point is inside the aggregates. Moreover, the fast algorithm for computing the distance between the spatial points and the generated aggregates is presented and the corresponding error analysis is given. Based on these facts, the space between aggregates can be controlled and therefore, the content of aggregates in the specimen can be improved. Numerical results show that this is an effective method, with which the concrete specimen with more than 55% irregular aggregates in volume can be generated according to two gradation. This is very close to content of aggregates in practical concrete. Therefore, an aggregate model of concretes in meso-level for further mechanical analysis is developed.
2015 Vol. 36 (3): 233-243 [
Abstract
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189
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243
Plastic Poisson's ratio of closed-cell aluminum foams
Of all the parameters that characterizing CCAF(closed-cell aluminum foam) mechanical properties, the plastic Poisson's ratio is a important one. In this study, based on Kelvin model, the three-dimensional mesoscopic models of CCAFs are established. The plastic Poisson's ratio of different relative densities three-dimensional mesoscopic models of CCAFs under uniaxial quasi-static compression is numerical analyzed. The calculation results show that Poisson's ratio of CCAF changes like a inverse S shape with the increase of axial strain. The average plastic Poisson's ratio of CCAF has a close relationship with its relative density. When the relative density is less than 0.1, the average plastic Poisson's ratio can be ignored; when the relative density is bigger than 0.1, the average plastic Poisson's ratio shows a linear increase with the enhancement of the relative density and grows from 0.17 to 0.5.
2015 Vol. 36 (3): 243-250 [
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573
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251
The Effect of Fractal Surface Topography on Stress Concentration Factor
A new method to build finite element model of complex surface topography was proposed. Based on linear elastic mechanics, the stress concentration factors induced by surface topographies simulated by W-M fractal function were investigated under various degrees of measurement. The relations between fractal parameters, profile moments and stress concentration factors were analyzed. The results show that the stress concentration factor of fractal surface topography depend strongly on the resolution of the roughness-measuring instrument, the second profile moment can reflect the degree of stress concentration induced by surface topography, the high frequency cut-off should be determined to evaluate the effect of surface topography on structural fatigue behavior.
2015 Vol. 36 (3): 251-257 [
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222
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258
Slip Characteristic Analysis Of Frictional Contact Interfaces in Piezoelectric Materials When It Inteacted With Elastic Waves
Abstract: A question was studied primary on propagation of elastic waves through a contact interface between two piezoelectric solids. When the incident wave is strong enough, the contact interface will separate or slip in local interface areas, the extent and location of the separation and slip regions will vary with the external mechanical-electrical loads and the incedent wave. The solution of the slip regions are given theoretically by using Fourier analysis and Matlab software, and a method is developed to determine the condition that the separation、slip and stick region will be generated, and more the factor influencing the slip and sepration location are analyzed through an example.
2015 Vol. 36 (3): 258-263 [
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361
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494
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264
OPTIMAL SOLUTION OF CAUGHEY DAMPING COEFFICIENTS IN SEISMIC RESPONSE ANALYSIS
When the Caughey damping matrix is constructed by traditional method, how to choose reasonable multi-reference frequencies and avoid negative modal damping ratios are challenges. Therefore, based on the seismic response spectral analysis, using the error of peak displacement as the objective function and making the modal damping ratios larger than zero as constraint condition, an optimal solution of Caughey damping coefficients is proposed by constraint quadratic programming. Then, a dome structure with 90m-diameter and 15m-height is analyzed to illustrate the necessity of Caughey damping when there are many significant contribution modes and the difference in natural frequencies of significant contribution modes for different response are great. Meanwhile, the traditional method and the optimal method are compared in the effects on structural seismic response errors. Numerical results show that the traditional method ignores the difference in different modal contributions to choose reference frequencies and cannot control the errors of dynamic responses effectively; the optimal method makes the damping ratios of significant contribution modes reasonable and the errors from the optimal method is smaller than that of the traditional method for more than 4 Caughey series.
2015 Vol. 36 (3): 264-276 [
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360
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