基于Abaqus的复合材料板冲击特性分析

基于Hashin准则,用Abaqus建立玻璃纤维/环氧树脂复合材料板的冲击仿真计算模型,分析材料在不同冲击能量、冲击质量与冲击速度影响下的初始损伤和损伤演化特性.通过对比发现仿真计算结果与试验结果吻合较好,表明该仿真计算模型对此材料的冲击预测有效.     

A new numerical approach for low velocity impact response of multiscale-reinforced nanocomposite plates

In this paper, the low velocity impact analysis of carbon nanotube (CNT)/carbon fiber (CF)-reinforced hybrid nanocomposite plates is presented using variational differential quadrature (VDQ) method due to its numerical essence and the framework of implementation. The hybrid nanocomposite plate deformation is formulated based on classical plate theory and the contact force between the plate and projectile is estimated using Hertzian contact law. Also, a new micromechanics approach is presented to calculate the effective mechanical properties of the CNT/CF polymer hybrid nanocomposites. Five important factors including, random orientation and random distribution of CNTs, CNT/polymer interphase region, waviness and transversely isotropic behavior of CNT are incorporated in the micromechanical analysis. The accuracy of the present approach is verified with the available open literature results showing a clear agreement. The effects of various factors such as volume fraction and non-straight shape of CNT, CNT/polymer interphase region, CF volume fraction, random and regular arrangement of CFs, plate geometrical parameters and impactor velocity on the low velocity impact behavior of the CNT/CF-reinforced hybrid nanocomposite plates are studied.

     

Estimation of low-velocity impact damage in laminated composite circular plates using nonlinear finite element analysis

Nonlinear finite element analysis is used for the estimation of damage due to low-velocity impact loading of laminated composite circular plates. The impact loading is treated as an equivalent static loading by assuming the impactor to be spherical and the contact to obey Hertzian law. The stresses in the laminate are calculated using a 48 d.o.f. laminated composite sector element. Subsequently, the Tsai-Wu criterion is used to detect the zones of failure and the maximum stress criterion is used to identify the mode of failure. Then the material properties of the laminate are degraded in the failed regions. The stress analysis is performed again using the degraded properties of the plies. The iterative process is repeated until no more failure is detected in the laminate. The problem of a typical T300/N5208 composite [45 °/0 °/ − 45 °/90 °]_s circular plate being impacted by a spherical impactor is solved and the results are compared with experimental and analytical results available in the literature. The method proposed and the computer code developed can handle symmetric, as well as unsymmetric, laminates. It can be easily extended to cover the impact of composite rectangular plates, shell panels and shells.     

Impact damage in composite laminates

A low velocity impact damage model for the quasi-symmetric graphite fiber composite plates is presented. The distribution of damage in each layer of the plate was calculated by employing Di Sciuva's composite laminate theory together with Hashin's failure criterion for fiber-reinforced composites. The dynamic deformation of the target plate was represented by the lower vibrational modes of the plate. The principle of virtual work was applied in the formulation of the problem. In the analysis, the material was regarded as ‘damaged’ when its designed strength was reduced by the failure of its constituents. The constituent failures consisted of matrix crackings, fiber breakages, and delamination between layers. According to damage modes, the moduli of material in the damaged zone were reduced according to the failure criteria. The interaction between layers and its role in damage propagation were also studied.     

An inverse solution for low-velocity impact in composite plates

An inverse model for estimating the mass and velocity of the impactor in low-velocity impact of composite plates is presented. In the model, a least-squares optimization technique is used to optimally reconstruct the force–time history by comparing direct model simulations of the impact response with experimental measurements. Guidelines for better initial guesses and faster direct models that are based on an impact characterization procedure are provided to the inverse algorithm. Three sets of experimental data covering a wide range of impact response are used to validate the model with excellent results.     

Natural frequency and buckling optimization of laminated hybrid composite plates using genetic algorithm and simulated annealing

In this study, genetic algorithm and simulated annealing are used to maximize natural frequency and buckling loads of simply supported hybrid composite plates. The aim of the study is to use two different techniques of optimization on the frequency and buckling optimization of composite plates, and compare the techniques for their effectiveness. The composite plate is made of carbon/epoxy and glass/epoxy hybrid plies, and assumed to be symmetric and balanced. The effect of hybridization is investigated using both techniques. The buckling problem has many maxima in the vicinity of local maxima. The best configurations are identified for different plate aspect ratios. The performance of both techniques is compared in terms of number of function evaluations as well as the capability of finding best configurations.     

Optimal design of hybrid laminated composite plates with dynamic and static constraints

Optimization procedures are presented that consider the static and dynamic characteristic constraints for laminated composite plates and hybrid laminated composite plates subject to a concentrated load on the center of the plate. The design variables adopted are ply angle or ply thickness. Considered constraints are deflection, natural frequency and specific damping capacity. Using a recursive linear programming method, nonlinear optimization problems are solved, and by introducing the design scaling factor, the number of iterations is reduced significantly. Relating interactive optimization procedures with the finite element method analysis, various hybrid composite plates with arbitrary boundary conditions can be designed optimally. In the optimization procedure, verification of analysis and design of the laminated composite plates are compared with a previous paper. Various design results are presented on laminated composite plates and hybrid laminated composite plates.     

Numerical prediction of the flow field due to a confined laminar two-dimensional submerged jet

A confined laminar two-dimensional submerged jet impinging on a flat surface has been studied numerically. The transport equations were solved using hybrid differencing schemes (upsteam-weighted and upstream differencing schemes). The jet nozzle exit velocity profile was assumed to be fully developed. Effects of the length of the confinement plate, the jet Reynolds number and the jet-to-plate spacing on the flow characteristics were investigated. For long lengths of the confinement plate, the flow field is dominated by a recirculating vortex near the confinement plate together with a smaller vortex on the impingement plate. For short lengths of confinement plates, the recirculating vortices disappear and an inflow to the jet along the confinement plate becomes well established.     

Minimum cost design of a cellular plate loaded by uniaxial compression

Cellular plates are constructed from two base plates and an orthogonal grid of stiffeners welded between them. Halved rolled I-section stiffeners are used for fabrication aspects. The torsional stiffness of cells makes the plate very stiff. In the case of uniaxial compression the buckling constraint is formulated on the basis of the classic critical stress derived from the Huber’s equation for orthotropic plates. The cost function contains the cost of material, assembly and welding and is formulated according to the fabrication sequence. The unknown variables are the base plate thicknesses, height of stiffeners and numbers of stiffeners in both directions. The cellular plate is lighter and cheaper than the plate stiffened on one side. The Particle Swarm Optimization and the IOSO techniques are used to find the optimum. PSO contains crazy bird and dynamic inertia reduction criteria, IOSO is based on a response surface technology.     

碳纤维层合板冲击吸能有限元模拟

为预测复合材料结构的冲击吸能效果,用三维有限元法模拟金属圆柱体冲击碳纤维层合板的过程．层合板被简化为三维正交各向异性材料板;采用Abaqus提供的vumat等扩展编程接口,用FORTRAN编写程序表征材料的弹性、强度和累积失效,实现动态破坏过程仿真;计算结果与冲击试验结果具有可比性．Abaqus的显式分析方法结合编程接口可用于层合板的冲击吸能仿真,结果的准确性取决于用户建立的材料模型．对不同速度、质量和直径的金属圆柱体的冲击进行计算,结果表明在穿透情况下,随着圆柱体速度的增加,圆柱体的动能衰减增多,而系统动能的减少相对稳定,因此后者更适合于临界速度的计算．     

Experimental and numerical analysis of low velocity impact on a preloaded composite plate

An experimental and numerical study on the influence of biaxial preloading on the low velocity impact performance of E-glass/epoxy-laminated composite plates was conducted. For this aim, an experimental device was developed to apply the load in two perpendicular directions. Three preload cases, representative of actual structures were selected, biaxially tension, compression and, tension-compression (shear) loading cases. The samples were produced from unidirectional reinforced E-glass and epoxy, by using a hand lay-up technique. Laminated E-glass/epoxy with stacking sequence [0/90]_2s, dimensions were 140 × 140 mm² and a thickness of 2 mm for the samples used. Finite element analysis (FEA) was developed, using Hashin failure criteria for the composite material, and material models implemented by a User Material Subroutine into ABAQUS^®/explicit software, in order to simulate the failure mechanisms and force–time histories. Force–time and energy–time data were obtained by means of user material subroutine from the finite element model. The finite element results showed a good correlation to the experimental data in terms of force–time, energy–time graph or failure in composite plate, although these numerical results strongly depended on simulation parameters like mesh size or the number of element.     

Optimal design of sandwich and laminated composite plates based on the planning of experiments

Optimal design problems of sandwich plates with soft core and laminated composite face layers, and multilayered composite plates are investigated. The optimal design problems are solved by using the method of the planning of experiments. The optimization procedure is divided into the following stages: choice of control parameters and establishment of the domain of search, elaboration of plans of experiment for the chosen number of reference points, execution of the experiment, determination of simple mathematical models from the experimental data, design of the structure on the basis of the mathematical models discovered, and finally verification experiments at the point of the optimal solution. Vibration and damping analysis is performed by using a sandwich plate finite elements based on a broken line model. Damping properties of the core and face layers of the plate are taken into account in the optimal design. Modal loss factors are computed using the method of complex eigenvalues or the energy method. Frequencies and modal loss factors of the plate are constraints in the optimal design problem. There are also constraints on geometrical parameters and the bending stiffness of the plate. The mass of the plate is the objective function. Design parameters are the thickness of the plate layers. In the points of experiments computer simulation using FEM is carried out. Using this information, simple mathematical models for frequencies and modal loss factors for the plate are determined. These simple mathematical functions are used as constraints in the nonlinear programming problem, which is solved by random search and the penalty function method. Numerical examples of the optimal design of clamped sandwich and simply supported laminated composite plates are presented. A significant improvement of damping properties of a sandwich plate is observed in comparison with a simple plate of equal natural frequencies.     

Process for design optimization of honeycomb core sandwich panels for blast load mitigation

A general process for optimization of a sandwich panel to minimize the effects of air blast loading is presented here. The panel geometry consists of two metal face plates with a crushable honeycomb or other type of core. Optimization is necessary as there is strong coupling between the several variables and the physics, which makes parametric studies relatively ineffective. Virtual testing is used to develop a homogenized model for the stress–strain curve of the honeycomb core, which can be readily applied to other types of cellular core. The homogenized model has been validated by comparison to existing results as well as to results from detailed finite element (FE) models. A design of experiments (DOE) based response surface optimization method in combination with LS-DYNA is used to minimize dynamic deflection or acceleration of the back face plate. Constraints on total mass and on plastic strain in the face plates are imposed. The mechanism of lowering the backface deflection is by increasing front face plate thickness which effectively distributes the blast load to a larger area of the core and avoids local concave deformation of the front face plate. Further, core depth is increased which increases panel stiffness. For acceleration minimization, results again produce a stiffer front face plate, but accompanied by a sufficiently soft core. The mechanism of lowering the backface acceleration is by absorbing energy with low transmitted stress. A clear cut comparison between monolithic metal plates and sandwich plates, for the same loading and failure criteria, is presented here.     

A quadrilateral finite difference plate element for nonlinear transient analysis of panels

A quadrilateral plate element for the analysis of nonlinear transient response of panels has been developed based on the variational finite difference method for an irregular mesh. Due to the superior computational characteristics of the variational finite difference method with a lesser degree of continuity constraint on the interpolation functions and the use of lower-order polynomials allowing faster numerical integration methods to be implemented, this plate element is quite competitive or perhaps even superior when compared with the conforming finite elements. Three illustrative problems have been solved using this plate element to demonstrate its capability and accuracy in analyzing the large deformation response of panels subject to dynamic loadings.Very favorable correlation was observed between analysis and experiment on large deformations of elasticplastic rectangular plates subject to intensive impulsive loadings. Similar correlation was also observed for circular plates modeled with this quadrilateral plate element under impulsive loadings. Finally, the large dynamic deformations of composite rectangular panels of graphite-epoxy, boron-epoxy, glass-epoxy, and isotropic material were analyzed and found in good agreement with other analytical results.     

等面密度钢/铝组合靶的抗侵彻性能研究

金属靶板的抗侵彻性能一直以来都是被重点关注的研究领域。为明确结构参数对钢/铝组合结构抗步枪弹垂直侵彻性能的影响,建立了步枪弹侵彻钢板和铝板的数值计算模型,并通过弹道冲击实验进行了验证;进而基于数值计算模型分析了相同厚度下钢-铝、铝-钢的组合形式、靶板间距对组合靶板抗侵彻性能的影响。仿真结果表明：相同厚度下,钢板在前的组合形式优于铝板在前的靶板,但不同组合形式的层板间距对其抗侵彻性能影响较小;另外,比较了不同初速度下钢-铝厚度比的变化对组合靶板的抗侵彻性能影响,均呈现出随厚度比增加,抗侵彻性能先降低后增加的趋势,最终趋于一个稳定值。变化过程中存在一个抗侵彻性能最差的低点,在结构设计中应尽可能避开。最后,依据R-I公式拟合了仿真数据,得到了步枪弹侵彻钢-铝组合结构的弹道极限公式。研究结果可为组合靶板的抗侵彻性能设计和人员、物资防护提供参考。     

Z型折叠机翼的非线性动力学与模态分析研究

针对Z型折叠机翼这种复杂多体结构,运用多种不同的方法得到了结构的前4阶振动模态.将Z型折叠机翼假设为由三块碳纤维复合材料板组成,两板之间均以刚性铰链相连接.其中内翼左侧是固定端,并与机身相连接;中间翼以对边简支形式连接在内外翼之间;外翼的外端是自由端.在第一个铰链上施加驱动力矩M1为机翼提供折叠角速度,使中间翼进行转动;同时施加力矩M2于第二个铰链处,使外翼与内翼始终保持平行.本文首先利用Hamilton原理与von Karman大变形理论建立Z型折叠机翼的动力学模型,然后通过ANSYS软件设置合理的边界条件进行模态分析与谐响应分析,其次根据ANSYS模拟的Z型折叠机翼的振动形式,假设合适的模态函数,通过结构边界条件和系统动力学方程求出来的边界条件,求出三个板的横向振动模态函数,最后通过Maple验证得出的模态函数与ANSYS模拟的振动形式相符合.该研究不仅是Z型机翼的受迫振动响应分析的前提,而且对于Z型机翼的设计与实验也具有参考价值.     

Nonlinear transient responses of initially stressed composite plates

The nonlinear transient response of initially stressed composite plates is investigated using the finite element method. A nine-node isoparametric quadrilateral element is developed to model laminated plates under initial deformation and initial stress according to the Mindlin plate theory and von Karman large deflection assumptions. In the time integration, the Newmark constant acceleration method in conjunction with an efficient and accurate iteration scheme is used. Numerical results for deflections and bending moments for isotropic and laminated plates are obtained.     

Reduced basis technique for evaluating the sensitivity of the nonlinear vibrational response of composite plates

A reduced basis technique and a computational procedure are presented for generating the nonlinear vibrational response, and evaluating the first-order sensitivity coefficients of composite plates (derivatives of the nonlinear frequency with respect to material and geometric parameters of the plate). The analytical formulation is based on a form of the geometrically nonlinear shallow shell theory with the effects of transverse shear deformation, rotatory inertia and anisotropic material behavior included. The plate is discretized by using mixed finite element models with the fundamental unknowns consisting of both the nodal displacements and the stress-resultant parameters of the plate. The computational procedure can be conveniently divided into three distinct steps. The first step involves the generation of various-order perturbation vectors, and their derivatives with respect to the material and lamination parameters of the plate, using Linstedt-Poincaré perturbation technique. The second step consists of using the perturbation vectors as basis vectors, computing the amplitudes of these vectors and the nonlinear frequency of vibration, via a direct variational procedure. The third step consists of using the perturbation vectors, and their derivatives, as basis vectors and computing the sensitivity coefficients of the nonlinear frequency via a second application of the direct variational procedure. The effectiveness of the proposed technique is demonstrated by means of numerical examples of composite plates.     

An analytical solution for static stability of multi-scale hybrid nanocomposite plates

An analytical answer to the buckling problem of a composite plate consisted of multi-scale hybrid nanocomposites is presented here for the first time. In other words, the constituent material of the structure is made of an epoxy matrix which is reinforced by both macro- and nanosize reinforcements, namely, carbon fiber (CF) and carbon nanotube (CNT). The effective material properties such as Young’s modulus or density are derived utilizing a micromechanical scheme incorporated with the Halpin–Tsai model. To present a more realistic problem, the plate is placed on a two-parameter elastic substrate. Then, on the basis of an energy-based Hamiltonian approach, the equations of motion are derived using the classical theory of plates. Finally, the governing equations are solved analytically to obtain the critical buckling load of the system. Afterward, the normalized form of the results is presented to emphasize the impact of each parameter on the dimensionless buckling load of composite plates. It is worth mentioning that the effects of various boundary conditions are covered, too. To show the efficiency of presented modeling, the results of this article are compared to those of former attempts.

     

Experimental evaluation of MEMS strain sensors embedded incomposites

Micromechanical in-plane strain sensors were fabricated and embedded in fiber-reinforced laminated composite plates. Three different strain sensor designs were evaluated: a piezoresistive filament fabricated directly on the wafer; a rectangular cantilever beam; and a curved cantilever beam. The cantilever beam designs were off surface structures, attached to the wafer at the root of the beam. The composite plate with embedded sensor was loaded in uniaxial tension and bending. Sensor designs were compared for repeatability, sensitivity and reliability. The effects of wafer geometry and composite plate stiffness were also studied. Typical sensor sensitivity to a uniaxial tensile strain of 0.001 (1000 με) ranged from 1.2 to 1.5% of the nominal resistance (dR/R). All sensors responded repeatably to uniaxial tension loading. However, for compressive bending loads imposed on a 2-3-mm-thick composite plate, sensor response varied significantly for all sensor designs. This additional sensitivity can be attributed to local buckling and subsequent out of plane motion in compressive loading. The curved cantilever design, constructed with a hoop geometry, showed the least variation in response to compressive bending loads. All devices survived and yielded repeatable responses to uniaxial tension loads applied over 10 000 cycles