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2011 Vol. 32, No. 4
Published:
论文
325
Critical conditions and optimal design of closed-celled aluminum foam protection under low velocity impact
A one-dimensional collision model for a large-mass structure protected by high porosity, close-celled aluminum foam subjected to low velocity impact is established and validated with drop hammer tests. Based on the proposed model, the concept of critical impact velocity is introduced, which is dependent upon the mass ratio of the collision system as well as foam porosity. Both the minimum acceleration and critical acceleration of the protected structure are obtained under different impact conditions. It is demonstrated that closed-celled aluminum foams are suitable for protecting large-mass structures subjected to low velocity impact. When the initial impact velocity is lower than the critical one, the stress imposed by the foam on the structure will not exceed the plateau stress of the foam, with the corresponding acceleration of the structure significantly reduced if the foam porosity is relatively high. On the other hand, when the initial velocity exceeds the critical one, due to foam densification, the imposed stress increases sharply (about 5~15 times of foam plateau stress): correspondingly, the acceleration of the structure increases rapidly (even up to 1000g). The influence of impact mass ratio, porosity and geometrical dimensions of foam protection on the critical velocity and acceleration is systematically explored.
2011 Vol. 32 (4): 325-328 [
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523
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534
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339
Free vibration analysis of all-composite tetrahedral lattice truss core sandwich beam
Lattice sandwich structure，which is characterized by two thin face sheets and a lattice core sandwiched between them, is a novel kind of structure with the features of lightweight and multifunction. Due to its own structural form, the analysis of mechanical behavior of lattice sandwich structure is relatively complex. Converted discrete core to continuum homogenized material, the free vibration of all-composite tetrahedral lattice truss core sandwich beam is studied in this paper. Considering the bending deformation of face sheets and shearing deformation of the core, the governing equation for free vibration of sandwich beam is derived using Hamilton’s principle. Tetrahedral lattice truss core sandwich beam under simply supported condition is taken as an example to calculate the natural frequencies. Theoretical results are compared with those obtained from numerical simulation, and good agreements are observed. Further, the effects of laminate stacking sequence, truss radius, truss inclination angle, core height and beam length on the natural frequencies of sandwich beams are discussed. The results are valuable for understanding the frequency characteristic of all-composite tetrahedral lattice truss core sandwich beam.
2011 Vol. 32 (4): 339-345 [
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839
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346
Tensile performance analysis of combined adhesive and bolted joints for plain woven composites
Experimental work was carried out on the tensile performance of combined adhesively bonded and bolted (a single row) joints for woven composites. The failure forms of the joint were analyzed with 4mm and 6mm diameter bolt hole respectively. A 3-D damage propagation model was established including non-linear touch problem to simulate the mechanical performance of the joints and the FEM results were matched well with the experimental results. It is shown that the adhesive joint can be reinforced with mechanical joint by the shared distribution of applied load to the bolts. The larger the bolt diameter, the more effective is the reinforcement. The analysis of tensile properties of adhesively bonded joint with more than one row of bolts in mechanical joint poses great difficulty and more precautions must be taken for its application. The study results and the analysis method in this paper can provide some relevant reference and technological support for combined adhesive and bolted joint design.
2011 Vol. 32 (4): 346-352 [
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490
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353
Dynamical Behavior and Constitutive Model of Superelasticity NiTi Shape Memory Alloy wire: Experiment and Theory
Shape memory alloys (SMA) are a class of novel functional materials, used as both actuators and sensors, possessing unique thermomechanical behaviors such as shape memory effect (SME), superelasticity and high damping property, et al, which make them become perfect candidates for structural vibration control in civil engineering. This paper presents a study of the dynamic behavior and strain-rate-dependent constitutive model of superelastic NiTi SMA wires. Cyclic tensile tests on NiTi SMA wires with different stain rates were carried out to assess their dynamic properties. The equations that were used to describe the relationship between the stress increments and the strain rates were proposed. Base on the experimental data, an improved SMA constitutive model that can capture the strain-rate-dependent property was presented. To certify the validity and suitability of the improved SMA model, the comparisons between the numerical results and experimental data were made. The results show that the mechanical behaviors of NiTi SMA wires, including energy dissipation per cycle, secant stiffness and equivalent damping rate, initially increase with an increasing of the strain rate, but tend to be stable when strain rate is greater than 1.0×10-3/s. The numerical results and the experimental data are in good agreement, which indicate that the improve model, to a certain extent, can describe the strain rate dependent property of NiTi SMA wires.
2011 Vol. 32 (4): 353-359 [
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466
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480
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360
Frequency Domain Analysis of Supercritical Nonlinear Vibration of Axially Moving Beams
In the present paper, the first two supercritical natural frequencies of nonlinear transverse free vibration of axially moving beams are numerically investigated. In the supercritical transport speed regime, the nonlinear integro-partial-differential equation is cast in the standard form of continuous gyroscopic systems via introducing a coordinate transform for the non-trivial equilibrium configuration. Numerical schemes are presented for the governing equations via the finite difference method under the simple support boundary condition. Time series of the discrete Fourier transform is defined as numerically solutions of three nonlinear governing equations for the first two natural frequencies of nonlinear transverse vibration. The numerical results illustrate the tendencies of the first two natural frequencies with the changing system parameters.
2011 Vol. 32 (4): 360-364 [
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479
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525
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365
ANALYSIS ON COUPLING MAGNETO-ELASTIC CHARACTERISTIC OF THE GIANT MAGNETOSTRICTIVE TRANSDUCTER
For the purpose of application to non-circular turning processing, the coupling magneto-elastic dynamics model and complex coefficient dynamics differential equation of the giant magnetostrictive transducer are established. Furthermore, based on the function among the current, the axis-direction position of giant magnetostrictive material and magnetic fields intensity which comes from experiment, the magneto-elastic analytical solution among the magnetic fields, force and displacement of the giant magnetostrictive transducer is derived. Then the relationship between current and displacement at different frequency is studied, and the theoretical formula between current and magnetic fields intensity of hollow column solenoid is amended, and the effects on frequency-response relation in different bias magnetic field are discussed, and the numerical solutions are compared with analytical solutions. The results indicate that the relationship between output displacement and the input excitation current forms hysteresis loop, and the excitation frequency has distinct effect on its area and the loop swing trend position, and the conclusions of amend formula and experiment are perfectly matched. The frequency response of the transducer appears as resonance and anti-resonance characteristics, and the sign of frequency response decides the loop swing trend position and the size of absolute displacement decides the area of loop. Simultaneity, the area and lean of loop are increased following by the bias magnetic field increased. The results lay a foundation for the control and optimization of giant magnetostrictive transducer.
2011 Vol. 32 (4): 365-371 [
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518
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630
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372
Symplectic Method for Energy Bands and Surface States of 1D Periodic Structure with Defects
In this paper, based on the symplectic method, the eigen-equations for one dimensional periodic structure, semi-infinite periodic structure and semi-infinite periodic structure with defects are derived. By analysis based on symplectic method, the eigen-problem for semi-infinite periodic structure is transformed into an eigen-problem on a unit cell which simplifies the problem. Based on symplectic method and W-W algorithm, an accurate, stable and efficient method for solving eigen-problem of semi-infinite periodic structure with defects is proposed. Numerical examples are also presented to validate the methods proposed in this paper.
2011 Vol. 32 (4): 372-381 [
Abstract
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488
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474
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382
Quasi-static Bending of Saturated Poroelastic Timoshenko Cantilever Beam
Based on the three dimensional theory of incompressible saturated porous media, first, a one-dimensional mathematical model for quasi-static bending of the transversely isotropic saturated poroelastic Timoshenko cantilever beam is established with assumptions of deformation of the classical single phase Timoshenko beam and the movement of pore fluid only in the axial direction of the poroelastic beam, and the corresponding boundary conditions are presented. Secondly, the quasi-static bending of the saturated poroelastic Timoshenko cantilever beams with different end permeability conditions, subjected to a step load at its free end, is analyzed by the Laplace transform and its numerical inverse transform. The variations of the deflections, bending moments of the poroelastic beam and the equivalent couples of the pore fluid pressure against the time are shown in figures and are compared with those of the saturated poroelastic Euler-Bernoulli cantilever beam. The effect of the slenderness ratio of the beam is examined. It is shown that the interaction coefficient between the solid skeleton and pore fluid plays a role as viscidity, and the quasi-static deflections of the saturated poroelastic beams possess the creep behavior. Furthermore, the influence of the end permeability conditions on the bending behavior is great, and the Mandel-Cryer phenomenon also occurs in the quasi-static deformations of the saturated poroelastic Timoshenko cantilever beam.
2011 Vol. 32 (4): 382-389 [
Abstract
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500
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450
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简报
390
Analysis on Mechanical Properties of Asphalt Mixture with 3D Random Model
Asphalt mixtures are described as a two-phase composite material consisting of asphalt sand and coarse aggregates in the paper. A three-dimensional random model can be generated by packing randomly aggregates from the aggregate base created in accordance with an actual grading curve. The constitutive relationship of asphalt sand can be obtained by extending the generalized Maxwell model into three-dimension and the material model parameters are calculated by fitting the axial relaxation experiment data with nonlinear fitting method. The proposed model is validated by comparing the creep simulation and test results of asphalt mixture with a particular gradation. With the method, the finite models of asphalt mixtures with different aggregate volume fraction and gradations are created, and then the nonlinear numerical simulations are conducted on them. The result shows that the instantaneous elastic modulus increases with the increasing volume fraction of aggregate and ranges from Paul’s bottom to top bound. Within certain bound of aggregate size, the resisting ability of asphalt mixture increases with the increasing aggregate size.
2011 Vol. 32 (4): 390-397 [
Abstract
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465
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465
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398
LOCATION OPTIMAL OF PIEZOELECTRIC PATCH USING GENETIC ALGORITHM
Active control equations are derived from the dynamic equation of linear elastic piezoelectric laminated structure. Piezoelectric actuator/sensor are modeled by the three-dimension eight-node coupled element. The finite element model of piezoelectric smart structure has been developed by use of ANSYS/APDL parameter language, modal analysis has been also performed. The optimal actuator/sensor location problem is formulated in the framework of a zero-one optimization problem which is solved using genetic algorithms (GA). Taking piezoelectric smart cantilever beam structure as numerical samples, the direct proportional feedback control performance of smart structure under transient load collocated actuator/sensor at optimal and general locations is studied. To verify the correctness of the method, further studied the effect control system under harmonic load.
2011 Vol. 32 (4): 398-404 [
Abstract
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558
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558
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405
Identification of hydrodynamic coefficients on offshore platform and precision analysis of its results
2011 Vol. 32 (4): 405-410 [
Abstract
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425
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476
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411
ENERGY-VARIATIONAL METHOD OF LATERAL STATIC ANALYSIS OF THIN-WALLED CURVED BOX GIRDERS
Gan Ya-nan
Based on the energy variation principle, this paper proposes an approach of analyzing the effect of shear lag, shear deformation on the lateral static characteristic of curved thin-walled box girders generally used in engineering, the minimum potential principle is applied to establish the lateral governing differential equations and the corresponding natural boundary conditions, thus closed-form solutions of generalized displacements are obtained. The variations of shear lag effects of curved box girders, caused by the change of factors such as span-height ratio, types of loading and natural boundary conditions are discussed, the thin-walled curved box girders theory is enriched and developed. This study compares the finite shell element solutions with the analytical solutions of this paper and verify the validity of the proposed approach. The formulas obtained in this study develop the existing shear lag theory.
2011 Vol. 32 (4): 411-418 [
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456
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529
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419
Simulation of Fragmentation Process of Charge Bed Under Impact Load
Compress and fracture of gun propellant charge is one the fundamental reason of breach blow, the fracture dynamics of charge bed is one of the theoretical foundations in the research field of launch safety. Based on discrete element method, the packing process of propellant bed under gravity is simulated, and the close-grained structure of propellant bed was acquired; then the propellant grains were divided into spring-spheres system, applying Mohr-Coulomb failure rule, the compress and fracture process of propellant grains under impact load was simulated. In addition, the dynamic display was displayed by post processing, which reproduced the compress and fracture process of propellant grains in simulation chamber, and the computation mode provides a kind of important theoretical foundation and computation method for the study of fracture law of charge bed.
2011 Vol. 32 (4): 419-425 [
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481
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435
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426
Plane crack problem for functionally graded strip with arbitrarily distributed properties
In this paper the plane elasticity problem for a functionally graded coating containing a crack bonded to homogeneous material substrate has been considered. A multi-layered model is employed to model arbitrary variations of material properties based on two linear-distributed material compliance parameters. By utilizing the Fourier transformation technique and the transfer matrix method, the mixed boundary problem is reduced to a system of singular integral equations that are solved numerically. The influences of the graded variation of material parameters, geometric parameters and graded parameter on the stress intensity factors are investigated. The numerical results show that the geometric parameters, graded variation of material parameters and graded parameters have significant effects on the stress intensity factors.
2011 Vol. 32 (4): 426-432 [
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449
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498
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