爆炸载荷下中空夹层玻璃的动力响应影响因素

利用LS-DYNA有限元软件,基于多物质ALE算法,模拟中空夹层玻璃在爆炸载荷下的动力学响应,通过变化PVB夹层属性和中空气体层厚度分析了其改变对玻璃板板心最大挠度的影响。结果表明:(1)随气体层厚度的增加,中空钢化夹层玻璃上层玻璃板挠度减小而下层玻璃板挠度增加; (2)一定气体层厚度下,随夹层杨氏模量的增加,上、下玻璃板的挠度减小。     

Scaling of structures subject to impact loads when using a power law constitutive equation

It is well known that structures subjected to dynamic loads do not follow the usual similarity laws when the material is strain rate sensitive. As a consequence, it is not possible to use a scaled model to predict the prototype behaviour. In the present study, this problem is overcome by changing the impact velocity so that the model behaves exactly as the prototype. This exact solution is generated thanks to the use of an exponential constitutive law to infer the dynamic flow stress. Furthermore, it is shown that the adopted procedure does not rely on any previous knowledge of the structure response. Three analytical models are used to analyze the performance of the technique. It is shown that perfect similarity is achieved, regardless of the magnitude of the scaling factor. For the class of material used, the solution outlined has long been sought, inasmuch as it allows perfect similarity for strain rate sensitive structures subject to impact loads.     

Differential-algebraic approach to large deformation analysis of frame structures subjected to dynamic loads

A nonlinear mathematical model for the analysis of large deformation of frame structures with discontinuity conditions and initial displacements, subject to dynamic loads is formulated with arc-coordinates. The differential quadrature element method （DQEM） is then applied to discretize the nonlinear mathematical model in the spatial domain, An effective method is presented to deal with discontinuity conditions of multivariables in the application of DQEM. A set of DQEM discretization equations are obtained, which are a set of nonlinear differential-algebraic equations with singularity in the time domain. This paper also presents a method to solve nonlinear differential-algebra equations. As application, static and dynamical analyses of large deformation of frames and combined frame structures, subjected to concentrated and distributed forces, are presented. The obtained results are compared with those in the literatures. Numerical results show that the proposed method is general, and effective in dealing with disconti- nuity conditions of multi-variables and solving differential-algebraic equations. It requires only a small number of nodes and has low computation complexity with high precision and a good convergence property.     

Analysis of dynamic reliability of structures subjected to a set of stochastic loads

In this paper addressing how to predict structural reliability and based upon thorough research, the four most common types of load stresses are integrated into three related models, using Turkstra’s rule. Predictions of the combined loads are calculated, both with and without strength degeneration, using Turkstra’s method and the stress-strength interference theory. An illustration is provided, demonstrating that the predictive models are practical, feasible, and consistent with standard engineering practices.     

Bifurcation of equilibrium of flexible bars subject to eccentric loads

The multiple equilibrium shapes, i. e., bifurcation behavior of the flexible bars subject to axial eccentric force are analyzed by the large deflection theory. Three types of elastica of equilibrium shape are discussed, and the method for determining the various classes of bifurcation of equilibrium due to given loads is presented.     

Transient analysis of viscoelastic helical rods subject to time-dependent loads

The transient analysis of viscoelastic helical rods subject to time-dependent loads are examined in the Laplace domain. The governing equations for naturally twisted and curved spatial rods obtained using the Timoshenko beam theory are rewritten for cylindrical helical rods. The curvature of the rod axis, effect of rotary inertia and, shear and axial deformations are considered in the formulation. The material of the rod is assumed to be homogeneous, isotropic and linear viscoelastic. The viscoelastic constitutive equations are written in the Boltzmann–Volterra form. Ordinary differential equations in canonical form obtained in the Laplace domain are solved numerically using the complementary functions method to calculate the dynamic stiffness matrix of the problem. The solutions obtained are transformed to the real space using an appropriate numerical inverse Laplace transform method. Numerical results for quasi-static and dynamic response of viscoelastic models are presented in the form of graphics.     

Refined theory of orthotropic plates subject to tangential surface loads

The existence of two correction coefficients traditionally introduced to account for the effect of the distribution of tangential stresses over the thickness of a plate is discussed. The virtual-work principle is used to generalize the expressions for the coefficients to the case of arbitrary loading. These expressions and hypotheses for displacements help to derive equations for orthotropic rectangular plates subject to tangential surface loads. These equations account for the effect of the distribution of tangential stresses over the thickness of the plate. Numerical examples are given. The results obtained are compared with those produced by other theories __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 4, pp. 107–119, April 2008.     

Elasticity solutions for functionally graded annular plates subject to biharmonic loads

Based on England’s expansion formula for displacements, the elastic field in a transversely isotropic functionally graded annular plate subjected to biharmonic transverse forces on its top surface is investigated using the complex variables method. The material parameters are assumed to vary along the thickness direction in an arbitrary fashion. The problem is converted to determine the expressions of four analytic functions α (ζ), β (ζ), ? (ζ) and ψ (ζ) under certain boundary conditions. A series of simple and practical biharmonic loads are presented. The four analytic functions are constructed carefully in a biconnected annular region corresponding to the presented loads, which guarantee the single-valuedness of the mid-plane displacements of the plate. The unknown constants contained in the analytic functions can be determined from the boundary conditions that are similar to those in the plane elasticity as well as those in the classical plate theory. Numerical examples show that the material gradient index and boundary conditions have a significant influence on the elastic field.     

Creep life predictions for structures subject to variable loading

Previous work which established upper and lower bounds on the creep life of steadily loaded structures is extended to cater for load and temperature variations in non-homogeneous structures. The investigation is limited to the range where short term plasticity and fatigue damage can be ignored. For proportional loading, the upper bound which is based on limit analysis, is similar in form to that for constant loading. In the more general case, the upper bound is less stringent and is based on the mean load and temperature distribution over the lifetime. A lower bound on life is taken as the time for the first part of the structure to fail.The bounds are applied to three simple structures. For proportional loading the upper bound predicts the lifetime with the same accuracy as for constant loading except for extreme load variations. The presence of a temperature distribution alters the accuracy of the upper bound prediction but in most cases the change is small. In contrast, the lower bound is very sensitive to the temperature gradient.The authors use these results to develop approximate techniques for estimating the creep life of components subjected to variable loads and temperature distributions. Simplified design procedures based on the upper bound are examined and suitable amendments are proposed.     

动载荷的识别方法

大多数情况下, 作用在工程结构上的动载荷, 如高性能战斗机在大攻角机动飞行时作用在垂尾结构上的抖振载荷, 是无法直接测量的, 只能通过测试结构在动载荷作用下的动态响应来识别出结构的动载荷. 首先阐述了动载荷识别的基本原理, 然后根据结构模型的特点, 将动载荷识别方法分为确定性结构的动载荷识别方法和不确定性结构的动载荷识别两大类, 对近些年国内外学者在这两方面的研究进展进行述评, 最后针对目前动载荷识别方法研究中所存在的问题, 提出有待深入探讨的课题.      

Dynamic ice loads on conical structures

Two series of model tests were performed to observe the dynamic ice loads on conical structures. The variable testing parameters include the water line diameter of the model cone and ice parameters. During small water line diameter tests, two-time breaking is found to be the typical failure of ice on steep conical structure, and also be controlled by other factors, such as ice speed and the cone angle. During big water line diameter tests, the ice sheet failed nonsimultaneously around the cone. Several independent zones of bending were found in the nonsimultaneous failure process of ice. With the increase of the ratio of D/h and the number of independent zones, the total ice force was found being gradually reduced.     

Stabilization of a wheeled robotic vehicle subject to dynamic effects

The paper addresses the problem of designing a stabilization system for a wheeled robotic vehicle with one steering wheel subject to dynamic effects. A solution of the problem is given for the case of coasting. The admissible error of the robot speed in generating a feedback signal is estimated. The general problem of stabilization with allowance for dynamic effects is considered __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 9, pp. 116–126, September 2006.     

随机车辆冲击作用下简支梁桥疲劳可靠度评估

为了研究考虑随机车辆冲击效应的简支梁桥疲劳安全水平,提出了基于车-桥耦合振动与随机车流的桥梁疲劳应力谱模拟方法,并应用于疲劳可靠度评估。基于某高速公路桥梁动态称重数据建立随机车流模型,采用小样本车辆数据拟合桥梁等效疲劳应力范围的插值响应函数,最后由高斯混合模型拟合大样本随机车流作用于桥梁构件的疲劳应力谱。分析了25 m标准跨径简支T梁桥底部普通钢筋的疲劳应力谱,评估了考虑路面劣化与交通量增长的桥梁疲劳可靠度。数值分析结果表明,基于随机车流模拟的疲劳应力谱具有典型的多峰分布特征,包含了超载车辆产生的疲劳应力;车辆对桥梁的冲击效应致使等效疲劳应力放大系数略大于冲击系数,当路面等级为一般时,采用规范冲击系数将低估车辆冲击效应的疲劳损伤;路面劣化与交通量增长均会导致桥梁运营期内的疲劳可靠指标显著降低,由路面劣化导致车辆对简支梁桥的冲击效应不可忽略。     

The dynamic mechanical response of fiber-reinforced beams to large transverse loads

The paper describes the results of experiments on fiber-reinforced metal beams which have been subjected to dynamic transverse loading. The beams were fabricated by embedding sets of parallel steel wires in a matrix of lead-tin alloy, and were clamped at one end. The transverse dynamic loading was applied to the tip of the beam so that the problem was one of the transverse deformation of a composite cantilever. Two separate techniques were employed to load the specimens, one being to hit the end with a fast moving hammer in a “Hyge” Shock Testing Machine; the other was to detonate an explosive charge in contact with a small projectile close to the tip. The deformations were monitored by a number of different experimental techniques and the final plastic transverse deflection of the tip as well as the final position of the plastic wave front were compared with the theoretical predictions of Spencer, Jones and their co-workers. The agreement was found to be very satisfactory. In making these comparisons strain rate effects in the lead-tin matrix metal had to be allowed for and this was done with the help of a separate set of tests.     

Performances of dynamic vibration absorbers for beams subjected to moving loads

The goal of this work is a general assessment regarding the performances of linear and nonlinear dynamic vibration absorbers (DVAs) applied to the specific problem of moving loads or vehicles. The problem consists of a simply supported linear Euler–Bernoulli beam excited with a moving load/vehicle; a DVA is connected to the beam in order to reduce the vibrations. The moving vehicle is modeled by a single degree of freedom mass spring system. The partial differential equations governing the beam dynamics is reduced to a set of ordinary differential equations by means of the Bubnov–Galerkin method. A parametric analysis is carried out to find the optimal parameters of the DVA that minimize the maximum vibration amplitude of the beam. For the case of a moving vehicle, the energy absorbed by the DVA is evaluated. Comparisons among the performances of different types of linear and DVAs are carried out. The goal is to clarify if the use of nonlinearities in the DVAs can effectively improve their performances. The study shows that the most effective type of DVA for the test cases considered is the piecewise linear elastic restoring force.     

On the stress concentration around a hole in a half-plane subject to moving contact loads

We study the stress concentration due to a pore in an elastic half-plane, subject to moving contact loading, in the entire range of possible geometrical parameters (contact area/hole diameter, hole depth/hole diameter). Since the number of cases is very large to study with FEM even with modern machines, the use of a recent simple approximate formula due to Greenwood based on the stress field in the absence of the hole is first attempted, and compared with a full FEM analysis in sample cases. To further distillate the effects of the hole distance from the free surface and of the contact area size, the limiting cases are studied of: (i) concentrated load perpendicular to the surface and aligned with the hole centre; (ii) constant unit pressure on the top surface of the half-plane and (iii) hydrostatic load. A full investigation is then conduced for the case of Hertzian load on the surface, and it is seen that the tensile stress concentration is significantly reduced with respect to that of the concentrated load, when the contact area size is of the same order of the hole radius. Results obtained with the approximate Greenwood formula are generally accurate however only if the hole distance from the surface is greater than two times the hole radius.     

Vortex-induced dynamic loads on a non-spinning volleyball

An experiment on vortex-induced dynamic loads on a non-spinning Volleyball was conducted in a wind tunnel. The flow past the Volleyball was visualized, and the aerodynamic load was measured by use of a strain gauge balance. The separation on the Volleyball was measured with hot-film. The experimental results suggest that under the action of an unstable tail vortex system the separation region is changeable, and that the fluctuation of drag and lateral forces is the same order of magnitude as the mean drag, no matter whether the seam of the Volleyball is symmetric or asymmetric, with regard to the flow. Based on the experimental data a numerical simulation of Volleyball swerve motion was made.