Delamination behavior of L-shaped composite beam with manufacturing defects

Journal of Mechanical Science and Technology - Composite structures are more susceptible to manufacturing defects than conventional materials. Fiber misalignment, cracks, and voids are typical...     

Dynamic behavior of composite joints in hydrodynamic ram simulator

The fracture behavior of carbon/epoxy composite joint structures under highly dynamic pressure loading was studied experimentally and numerically. The considered dynamic pressure loading, called hydrodynamic ram (HRAM), potentially causes fractures in structures filled with fluid. First, experiments using the HRAM simulator method were carried out to monitor the fracture behavior of the composite joint structure. In the experiment, highly dynamic pressure loading was generated which propagated and initiated the fracture of the composite joint. Next, numerical simulation was performed through finite element analysis using LS-DYNA. The dynamic pressure loading inside the fluid was predicted using the arbitrary Eulerian Lagrangian (ALE) method and the fracture behavior of the composite joint structure was simulated using cohesive zone modeling (CZM). The analysis was validated by comparing the predicted results with those from the experiment. The predicted pressure loadings were well-matched with the experimentally measured ones. The strain histories and failure strain values obtained by the analysis also agreed reasonably well compared to those in the experiment for selected points in the composite structure. Finally, the effects of impact velocity and the stiffness of the joint structure on the fracture behavior were examined.

     

Dynamic response of composite panels under thermo-mechanical loading

In this communication, large amplitude flexural vibration behavior of composite curved and doubly curved panels has been studied using the finite element method. Here nonlinear governing equations of motion has been derived based on first order shear deformation theory with von Karman's kinematics, and these governing equations are solved by employing second-order time integration scheme proposed by Bathe. The efficacy of the method for the nonlinear static and dynamic response of curved panels is validated with the published results. Thereafter, the nonlinear dynamic response of cylindrical and spherical panels under thermal shock loading with and without radial pressure is investigated; the parametric study is also being carried out. This study will be valuable for the scientific community.

     

Dynamic condition assessment of a cracked beam with the composite element model

Existing models of local damage in a beam element are usually formulated as a damage in a single element, and the coupling effect between adjacent damages is simply ignored. This coupling effect is larger in the case of a fine mesh of finite elements or when there is a high density of damage in the structure. This paper studies such effect from multiple cracks in a finite element in the dynamic analysis and local damage identification. The finite beam element is formulated using the composite element method [P. Zeng, Composite element method for vibration analysis of structure, Journal of Sound and Vibration 218 (1998) 619–696] with a one-member–one-element configuration with cracks where the interaction effect between cracks in the same element is automatically included. The accuracy and convergence speed of the proposed model in computation are compared with existing models and experimental results. The parameter of the Christides and Barr [One dimensional theory of cracked Bernoulli–Euler beams, International Journal of Mechanical Science 26 (1984) 639–648] crack model is found needing adjustment with the use of the proposed model. The response sensitivity-based approach of damage identification is then applied in the identification of single and multiple crack damages with both simulated and experimental data. Results obtained are found very accurate even under noisy environment.     

Vibration and reliability of a rotating beam with random properties under random excitation

In this paper, vibration and reliability of a rotating beam with random properties under random excitations are studied. The rotating beam is under a stochastic load modeled as a stationary white noise. The cross-sectional area, elasticity modulus, moment of inertia, shear modulus, damping coefficient, mass density and rotational speed are modeled as random variables. To develop the equations of motion, the finite element method and space state analysis are applied. In order to consider the randomness of properties, a second order perturbation method is used. The effects of rotational speed, setting angle, hub radius, variances of random properties, correlation of random variables and damping matrix forms on the vibration and reliability of rotating beams, are studied completely.     

Dynamic response and damage of composite shell under impact

The dynamic response and damage of laminated composite cylindrical shell subjected to impact load is numerically investigated using the finite element method. A nine-node isoparametric quadrilateral element based on Sander's shell theory is developed, in which the transverse shear deformation is considered. A semi-empirical contact law that accounts for the permanent indentation is incorporated into the finite element program to evaluate the contact force. The Newmark time ingegration algorithm is used for solving the time dependent equations of the shell and the impactor. The Tsai-Wu failure criterion is used to estimate the failure of the laminated shell. Numerical results, including the contact force history, interlaminate damage zone, and failure indices in the shell are presented. Effects of curvature, impact velocity and mass of impactor on the composite shell behaviors are discussed.     

Dynamic characteristics of rotating pretwisted clamped-clamped beam under thermal stress

Effects of thermal stress on the vibration characteristics, buckling limit and critical speed of a rotating pretwisted beam clamped to rigid hub at a stagger angle were investigated. By considering the work done by thermal stress, the thermal influence on stiffness matrix was introduced in the dynamic model. The motion equations were derived based on Lagrange equation by employing three pure Cartesian deformation variables combined with nonlinear von Karman strain formula. Numerical investigations studied the modal characteristics of the beam. Numerical results calculated from a commercial finite element code and obtained with the present modeling method were in good agreement with the previous results reported in the literature. The combined softening effects due to the thermal stress and the rotation motion were observed. Furthermore, it is shown that the inclusion of thermal stress is necessary for blades operating under a high temperature field. Buckling thermal loads and the critical rotating speed were calculated through solving the corresponding nonlinear equations numerically, and some pertinent conclusions are outlined. It is also found that the peak value position of the first mode shape approaches to the tip of blade with the increment of rotating speed and hub radius. However, the variation in the environment temperature causes only a slight alteration in the mode shape.     

斗轮堆取料机在头部激振下的动态响应

分析斗轮堆取料机的实际工程特点,对其进行有限元建模并进行模态和谐响应分析,以了解斗轮堆取料机轮斗头部在滚筒或斗轮激振力作用下垂直方向的动态特性。     

碳纤维复合材料低速冲击特性及损伤分析研究

针对碳纤维复合材料汽车保险杠的低速耐冲击性能问题,利用真空辅助树脂扩散成型工艺制备了不同铺层比例与铺层顺序的碳纤维复合材料试样,对其进行了简支梁低速冲击性能试验,根据低速冲击响应特性曲线及损伤模式探究了复合材料能量吸收机理;同时基于ABAQUS/Explicit对典型铺层试样建立了简支梁冲击仿真模型,利用Hashin失效准则进行失效判断,研究了低速冲击响应应力变化及损伤过程并将模拟结果与实验值进行了比较。研究结果表明:碳纤维复合材料简支梁低速冲击主要损伤模式为纤维断裂,通过增加(0,90)铺层能够提高接触力载荷与冲击韧性强度,通过在试样冲击表面铺设(±45)铺层能够缓解结构剧烈破坏。峰值载荷误差为5.1%,峰值位移误差为3.2%,证明了模型的有效性,为碳纤维复合材料保险杠提供了设计基础。     

Plastic deformation behavior of a uniaxial metal matrix composite under transverse compression

Plastic deformation behavior of a stainless-steel/Sn−Bi composite was examined using transverse compression tests on rectangular specimens under plane strain loadings. Based on the anisotropic yield criterion proposed by Hill, a theoretical analysis on the relationship between the yield strength of the matrix material and the yield strength of the composite was developed and compared to experimental results. Experiments were carried out to investigate the effects of the forming parameters such as yield strength of the matrix material, fiber packing patterns, fiber volume fraction, and lubrication of the compression platens, on the plastic deformation behavior of the metal matrix composite. Failure modes of the composite included shear band formation and eye formation at the fiber-matrix interface. Low deformability in the transverse directions was found for the metal matrix composite specimen. The theoretical and experimental results on the effects of the forming parameters provide basic information for further research on the transverse compression of metal matrix composite materials.     

基于虚拟激励法的三维随机路面仿真

通过改进的虚拟激励法原理,在现有二维路面谱的基础上,从空间路面频率谱出发,将之拓展到三维空间内的路面谱,给出模拟随机路面谱的方法。同时,为了给虚拟样机仿真分析提供较为复杂三维仿真路面环境,基于单点FFT路面不平度时域模型,建立了三维FFT随机路面数学模型,并实现了其在Matlab中的仿真;依据改进的虚拟激励法理论,建立了生成三维路面文件的通用模型,包括节点的生成和单元生成算法,并导入Adams形成所需的三维路面仿真环境。应用上述方法生成C级路面.对所选择的车辆样机进行了行驶平顺性仿真,与GB/T 13441—92标准对比分析得到了该车行驶平顺舒适性的合理时间。     

Weak beam under convergent beam illumination

The weak beam technique is now used widely for the determination of stacking fault energies, in particular for intermetallic alloys, and the accuracy of the approach is critically dependent upon the reliability of the relationship between the image and the actual position of the dissociated dislocations. Examining as a model case a dislocation dissociated into two Shockley partial dislocations in Cu at 100 kV for orientations ranging through the g(3g) weak beam condition, image simulations are used to explore the accuracy to which the true spacing between the partial dislocations can be determined from the spacing measured on the image as a function of the dislocation character, the foil thickness, the dislocation depth in the foil, the diffraction condition and the beam convergence. It appears that for image simulations and for the given conditions a beam convergence of about 5 mrad allows to greatly improve the accuracy, and that beam convergence must be taken into account quantitatively when deducing the true partial dislocation spacing as it is the principal parameter controlling the precision in this type of measurement.     

Dynamic behavior of cracked pipe conveying fluid with moving mass based on timoshenko beam theory

In this paper we studied about the effect of the open crack and the moving mass on the dynamic behavior of simply supported pipe conveying fluid. The equation of motion is derived by using Lagrange’s equation and analyzed by numerical method. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments i.e. the crack is modeled as a rotational spring. The influences of the crack severity, the position of the crack, the moving mass and its velocity, the velocity of fluid, and the coupling of these factors on the vibration mode, the frequency, and the mid-span displacement of the simply supported pipe are depicted.     

Dynamic plastic behavior of a free–free beam striking the mid-span of a clamped beam with shear and membrane effects considered

Recently Yu et al. (Int. J. Solids Struct. 38 (2001) 261) made a study on the dynamic behavior of a flying free–free beam striking the tip of a cantilever beam using the rigid, perfectly plastic (r-p-p) material model. Later, also based on the r-p-p material model Yang and Yu (Mech. Struct. Mach. 29 (2001) 391) analyzed another impact problem of a free rotating hinge beam striking a cantilever beam. Both of these studies ignored the finite deflection effects on the plastic behavior of the colliding beams. However if the free–free beam strikes a clamped beam, the influence of finite-deflections, or, geometric changes, must be retained in the governing equation if the maximum permanent transverse displacement of the clamped beam exceeds the corresponding beam thickness. The problem becomes more interesting since the deformation mechanisms of the beam system and the partitioning of energy dissipation in the beams are significantly different from those predicted by ignoring the influence of membrane forces. Accordingly the failure modes of the structure are different.In the present paper, a theoretical model based on the r-p-p material idealization is proposed to simulate the dynamic behavior when the mid-point of a translating free–free beam impinging on the mid-span of a clamped beam with the beam axes perpendicular to each other. The plastic behavior of the beam system is explored with shear sliding and finite deflection effects taken into account. The final deflection, the dissipation of energy within the two beams after impact and the influence of the structural and material parameters are discussed. It is shown that membrane force plays an important role during the response process, especially when the deflection is of the same order as the thickness of the clamped beam.     

An experimental study on inelastic behavior for exposed-type steel column bases under three-dimensional loadings

Considerable damage occurred to steel structures during the Kobe earthquake in Japan. Numerous exposed-type column bases failed in several consistent patterns caused by brittle base plate fracture, excessive anchor bolt elongation, unexpected early anchor bolt failure, and inferior construction work. An exposed-type column base receives axial force and biaxial bending when receiving an arbitrary multidirectional earthquake motion. Up to now, numerous researchers have examined methods to identify their stiffness and strength, but those studies have heretofore been restricted to in-plane behaviors. Therefore, it is necessary to clarify the inelastic behavior of exposed type steel column bases under biaxial lateral loading and axially compressive-tensile loading, which is a closer simulation of the real seismic excitation. In this study, exposed type steel column bases with different failure types, anchor bolt yielding and base plate yielding, are tested under different loading programs, then moment resisting mechanisms and failure modes are investigated.     

Thermal beam of metastable krypton atoms produced by optical excitation

A room-temperature beam of krypton atoms in the metastable 5s[3/2]2 level is demonstrated via an optical excitation method. A Kr-discharge lamp is used to produce vacuum ultraviolet photons at 124 nm for the first-step excitation from the ground level 4p6 1S0 to the 5s[3/2]1 level. An 819 nm Ti:sapphire laser is used for the second-step excitation from 5s[3/2]1 to 5s[3/2]2 followed by a spontaneous decay to the 5s[3/2]2 metastable level. A metastable atomic beam with an angular flux density of 3 x 10(14) s(-1) sr(-1) is achieved at the total gas flow rate of 0.01 cm3/s at STP (or 3 x 10(17) at./s). The dependences of the flux on the gas flow rate, laser power, and lamp parameters are investigated.     

Effects of a one-way clutch on the nonlinear dynamic behavior of spur gear pairs under periodic excitation

Nonlinear behavior analysis was used to verify whether a one-way clutch is effective for reducing the torsional vibration of a paired spur gear system under periodic excitation. The dynamic responses were studied over a wide frequency range by speed sweeping to check the nonlinear behavior using numerical integration. The gear system with a one-way clutch showed typical nonlinear behavior. The oscillating component of the dynamic transmission error was reduced over the entire frequency range compared to a system without a one-way clutch. The one-way clutch also eliminated unsteady continuous jump phenomena over multiple solution bands, and prevented double-side contact, even with very small backlash. Installing a one-way clutch on both sides of the gear system was more effective at mitigating the negative effects of external periodic excitation and various parameter changes than a conventional gear system without a one-way clutch.     

Dynamic behavior of lifting pipe with equivalent model under mining vessel heave motion

The lifting pipe is a key component of deep sea mining whose dynamic response directly affects the safety of the lifting operation. The objective of this paper was to investigate the effects of heave motion and sailing velocity of mining vessel and the buffer mass on the dynamic response of lifting pipe. First, an equivalent model of the lifting pipe was established, and the natural frequency and dynamic response of the lifting pipe equivalent model were determined with consideration of the wave action by the method of separated variables. Secondly, the reliability of the equivalent model was verified by simulating a 5000 m stepped pipe with OrcaFlex software. Then the dynamic displacement, axial tension, axial stress of the lifting pipe under different sea conditions and sailing velocities were studied, and the main factors affecting the dynamic response of the pipe described. By comparing the simulation results of actual and equivalent models, the equivalent model can be used to analyze the longitudinal vibration characteristics of the lifting pipe. The sailing velocity of the mining vessel has little effect on the dynamic response of the lifting pipe, but the surface wave has a significant effect.

     

Dynamic characteristics of a beam angular-rate sensor

This paper gives a bandwidth and sensitivity analysis for a vibrating square beam angular-rate sensor. A skew-symmetric gyroscopic inertia matrix results from rotating about an axis orthogonal to the plane of a forced-vibration elastic system giving unique characteristics permitting measurement of its rotation rate. The quality factor has a huge influence on the forced response at the resonant frequencies governing the dynamic operating range in its use as an angular-rate sensor. Fourier-type solution for the cantilever beam with electrostatic excitation reveals characteristics analogous to those occurring for more complex systems. The deflection-dependent nature of the electrostatic excitation induces the parametric excitation into the system, yielding a Hill-type equation. Although it causes the behavior to be more complex, linear sensitivity curves can be obtained, provided that the displacement of the beam is small compared with the gap in static equilibrium. Finally, it is seen that the system provides the applicability of the rotating beam for use as an angular-rate sensor within a certain small range of parametric excitation. Design rules are suggested by observing that sensor sensitivity decreases with increasing sensor bandwidth.