Limit analysis of space grids

The paper presents generalized, unique solutions for the limit design of pin-connected, double-layer space grids of regular construction, simply-supported along the sides of a rectangle and carrying a uniform concentration of normal nodal loading applied to the upper layer of the structure. The principal assumption upon which the foregoing results are obtained is that member forces increase monotonically with the applied loads, therefore insuring against the inducement of higher than ultimate loads in the compressive elements at anytime prior to structure failure. The virtual work method of the plastic analysis has been employed in conjunction with the techniques of the finite difference calculus to study the various collapse modes of the system. The work is concluded with an illustrative example to demonstrate the simplicity of the proposed solutions.     

Mechanical behavior of non-crimp fabric PEEK/C thermoplastic composites

The thermoplastic resin Poly-Ether-Ether-Ketone (PEEK) was used to develop four new NCF composite materials. They refer to two different principal concepts, while each concept was investigated for two different material modifications. The tensile and compression behavior of the newly developed NCF materials was experimentally investigated. For comparison, same tests were also performed on APC-2/AS4 reference material. Prior to the mechanical tests, the quality of the produced laminates was evaluated by means of non destructive investigation (C-Scan tests) and optical microscopy analyses to obtain defects such as delaminations, porosities, micro-cracks etc. The results of the mechanical tests were exploited to obtain the “optimal” NCF fabrication process; the mechanical properties of the material solution considered to be “optimal” compare well to the respective properties of the reference material thus providing evidence for improved cost efficiency by the production of thermoplastic composite components.     

2.5维自愈合C/SiC复合材料的压缩力学行为

试验研究了2.5维自愈合C/SiC复合材料的压缩力学行为,根据材料的细观结构特点,建立了压缩载荷下的损伤力学模型,得到了经纬向压缩的非线性应力应变关系,预测结果与试验值吻合较好。结果表明,经向和纬向的力学行为不同,纬向的压应力逐渐增大时,切线模量逐渐增大,压缩强度为270.05MPa,而经向压应力逐渐增大时,层间损伤逐渐发生,经纱承受的弯矩越来越大,切线模量逐渐降低,破坏强度为128.66MPa。     

Sensitivity analysis of composite laminated plates with bonding imperfection in Hamilton system

Sensitivity analysis of composite laminated plates with bonding imperfection is carried out based on the radial point interpolation method （RPIM） in a Hamilton system. A set of hybrid governing equations of response and sensitivity quantities is reduced using the spring-layer model and the modified Hellinger-Reissner （H-R） variational principle. The analytical method （AM）, the semi-analytical method （SAM）, and the finite difference method （FDM） are used for sensitivity analysis based on the reduced set of hybrid governing equations. A major advantage of the hybrid governing equations is that the convolution algorithm is avoided in sensitivity analysis. In addition, sensitivity analysis using this set of hybrid governing equations can obtain response values and sensitivity coefficients simultaneously, and accounts for bonding imperfection of composite laminated plates.     

Mechanical analysis of orbit tracking movement of feed system in large spherical radio-telescope

The curve equation and its mechanics analysis of suspended-cable under the condition of end load are given. Then on the basis of it, the mechanical analysis of suspended-cable system for large spherical radio-telescope is studied, and procedures of the control for the orbit tracking movement of the line feed in large spherical radiotelescope are given. The validity of the results mentioned above is confirmed by means of computer simulations.     

Mechanical and optical characterization of cellulose acetate

To obtain the basic relations for photo-viscoelastoplastic stress analysis using cellulose acetate, the effect of strain rate as well as room temperature on mechanical and optical properties was precisely investigated by the uniaxial tension test. As a result, the nonlinear stress-strain, the non-linear-stress-fringe order and the nonlinear-fringe-order strain relations were uniquely reoresented in their nondimensional forms regardless of strain rate and room temperature. Young's modulus, yield stress and the yield fringe order were linearly related both to room temperature and to logarithm of strain rate. The effect of strain rate on these relations has caused great difficulties in experimental stress analysis with respect to photoplasticity. However, it was found in this work that the value of the strain rate at any points in the model can be determined by the fringe-order rate measured. Therefore, it is possible to estimate not only the distribution of strain rate but that of stress or strain in the photo-viscoelastoplastic model with cellulose acetate.     

An improved lattice Boltzmann model for high gas and liquid density ratio in composite grids

Lattice Boltzmann method is one of the widely used in multiphase fluid flow.However,the two main disadvantages of this method are the instability of numerical calculations due to the large density ratio of two phases and impossibility of the temperature distribution to be fed back into the velocity distribution function when the temperature is simulated.Based on the combination prescribed by Inamuro,the large density ratio two-phase flow model and thermal model makes the density ratio of the model simulation to be increased to 2778:1 by optimizing the interface distribution function of two-phase which improves the accuracy of differential format.The phase transition term is added as source term into the distribution function controlling two phase order parameters to describe the temperature effect on the gas-liquid phase transition.The latent heat generated from the phase change is also added as a source term into the temperature distribution function which simulates the movement of the flow under the common coupling of density,velocity,pressure and temperature.The density and the temperature distribution of single bubble are simulated.Comparison of the simulation results with experimental results indicates a good agreement pointing out the effectiveness of the improved model.     

Thermal stress analysis of a silicon carbide/aluminum composite

Thermal deformations and stresses were studied in a silicon-carbide/aluminum filamentary composite at temperatures up to 370°C (700°F). Longitudinal and transverse thermal strains were measured with strain gages and a dilatometer. An elastoplastic micromechanical analysis based on a one-dimensional rule-of-mixtures model and an axisymmetric two-material composite cylinder model was performed. It was established that beyond a critical temperature thermal strains become nonlinear with decreasing longitudinal and increasing transverse thermal-expansion coefficients. This behavior was attributed to the plastic stresses in the aluminum matrix above the critical temperature. An elastoplastic analysis of both micromechanical models was performed to determine the stress distributions and thermal deformation in the fiber and matrix of the composite. While only axial stresses can be determined by the rule-of-mixtures model, the complete triaxial state of stress is established by the composite cylinder model. Theoretical predictions for the two thermal-expansion coefficients were in satisfactory agreement with experimental results.     

Mechanical and optical viscoelastic characterization of Hysol 4290

Mechanical and optical characterization of Hysol 4290 as a function of time and temperature is presented. The kinetic theory of polymers, the Williams, Landel and Ferry equation and the time-temperature superposition principle, is discussed. Rubber-like elasticity is used as a simple experimental method to ascertain if the time-temperature superposition should be expected to apply. Finally, the glass-transition temperature of Hysol 4290 is established and its importance in correctly assessing experimental data is discussed.     

基于非结构网格的高效求解方法研究

非结构网格的求解效率一直是计算流体力学工作者十分关注的问题。本文从一个新的角度分析了N-S(Euler/Navier-Stokes)方程求解效率的高低,表明计算效率不仅涉及时间离散的效率,空间离散和程序算法都与之息息相关。采用不同的计算状态,对目前非结构网格上广泛应用的LU-SGS、对称Gauss-Seidel和GMRES方法进行较详细地比较和分析,考查了空间离散的耗时对方程求解效率的影响。结果表明,LU-SGS方法的计算效率在所给的算例中均是最低的;在不考虑大量内存消耗时,GMRES算法求解Euler方程的效率较高,松耦合求解N-S方程时效率会有所降低;在大规模计算中,多次对称的Gauss-Seidel迭代方法应是较好的选择,特别是N-S方程的求解。     

平纹编织C/SiC复合材料低速冲击数值模拟

首先,基于空气炮装置进行了2D-C/SiC薄板在冲击速度为79~219 m/s范围内的低速冲击实验,对碎片云团发展过程进行高速摄影记录;其次,基于Autodyn软件正交各向异性复合材料模型,推导2D-C/SiC材料相关参数;选取SPH求解器建立二维计算模型,对实验工况进行数值模拟,并基于碎片云结构、B扫描检测结果和碎片云轴向发展速度验证了该模型可以很好地描述C/SiC材料在冲击载荷作用下的脆性特征和软化行为。最后,基于数值模拟结果推导得出了钢弹丸冲击C/SiC材料的极限侵彻深度预测公式。     

陶瓷/液舱复合结构抗侵彻数值分析

为研究陶瓷/液舱复合结构抗侵彻机理,在前期弹道冲击实验结果基础上,运用LS-DYNA进行了数值模拟,再现了陶瓷/液舱复合结构在弹体冲击下的破坏过程和破坏模式,得到与实验一致的结果。结果表明:弹体撞击结构后,结构内产生的冲击波以撞击处为圆心、以球形向前传播,并在结构内来回反射振荡;弹体在水中运动时,水中形成空泡且不断扩展,弹体头部水域形成高压区域;弹体发生墩粗和侵蚀破坏,在低速冲击下,弹体破坏主要发生在穿透陶瓷和前面板过程中,在高速冲击下,弹体破坏主要发生在水中运动阶段,最终形成类似“饼状”的严重变形;前、后面板发生局部破坏和整体变形,在高速弹体撞击下,后面板将发生花瓣开裂。     

陶瓷/金属复合装甲冲击响应的三维SPH法分析

采用自编三维SPH程序对弹体侵彻陶瓷/金属复合装甲问题进行了数值模拟.为了描述金属和陶瓷材料非线性变形及损伤特性,在程序中嵌入Johnson-Cook和Johnson-Holmquist Ⅱ本构模型及Mie-Gruneisen状态方程.SPH计算得到的典型位移随时间变化曲线与实验结果吻合较好.通过数值模拟合理再现了弹体...     

Modal analysis of lightweight graphite reinforced silica/polymer matrix composite plates

In this paper we describe how finite element and experimental modal analyses can be used to characterize the dynamic behavior of plates made from a new class of graphite reinforced silica/polymer matrix composite (GRSPMC) materials. An agreement is obtained between both methods, and the results show that GRSPMC materials can be modeled and tested using tools similar to those applied to the study of classical composite laminates.     

Mechanical characteristics of composite honeycomb sandwich structures under oblique impact

Carbon fiber reinforced polymer (CFRP) and CFRP-based composite honeycomb sandwich structures are particularly sensitive to impact. The mechanical characteristics of composite honeycomb sandwich structures under oblique impact are studied by numerical simulation and experiment. The oblique impact model is established, and the reliability of the model is verified by the oblique impact test. To further analyze the influence of structural parameters on energy absorption under oblique impact, the influence of impact angle, face sheet thickness and wall thickness of the honeycomb is numerically studied. The results show that the impact angle has an important effect on energy distribution. The structural parameters also have an effect on the peak contact force, contact time, and energy absorption, and the effect is different from normal impact due to the presence of frictional dissipation energy. Compared with normal impact, the debonding of oblique impact will be reduced, but the buckling range of the honeycomb core will be expanded.     

正交正放类网架结构分析的分解刚度法

把正交正放类网架结构简化为构造上正交异性的夹层板,采用考虑剪切变形的具有三个广义位移的平板弯曲理论进行分析。基于分解刚度思想对三类屋面网架(正放四角锥网架、两向正交正放网架和正放抽空四角锥网架)进行了静力分析和固有振动分析,对三类竖向承重网架墙体进行了稳定性分析,给出了简便实用的计算公式。通过与有限元法分析结果的对比,表明了本文提出的方法作为一种简化的计算方法,其精度是比较高的,绝大多数的误差都小于5%,可以应用于工程结构的初步设计。此外,与其他的简化计算方法相比它的精度比较高而且计算过程大大简化了。     

含三角对称分布共晶团复合陶瓷力学性能研究

从Al2O3/ZrO2(4Y)自生复合陶瓷棒状共晶团的生长机理出发,研究了三角对称分布棒状共晶团的力学性能。基于相互作用直推法,先求得三角对称分布棒状共晶团每一组分的力学性能,然后通过坐标变换求得了整个棒状共晶团的力学性能。对棒状共晶团进行了随机均匀化处理,在考虑Al2O3块晶和ZrO2颗粒夹杂的情况下,求解了复合陶瓷的力学性能。计算中将Al2O3块晶视为椭球,通过三主轴比值的变化近似地模拟了任意形状的Al2O3块晶夹杂;计算了三个主轴的长度比变化时对复合陶瓷材料弹性性质的影响,并与实验结果进行了比较。研究表明:三角对称分布棒状共晶团每一组分呈横观各向同性,其弹性模量与ZrO2纤维的体积含量呈线性关系;三角对称分布棒状共晶团亦为横观各向同性,其在垂直[0001]晶向的平面内力学性质是完全对称的,与平面内坐标选取无关;随Al2O3块晶三个主轴长度比的变化,弹性模量的最大值与最小值相差3.1%。