计算点接触碰撞恢复系数的一种理论模型

建立了一种计算点接触正碰撞恢复系数的理论模型.模型描述了弹塑性点正碰撞的接触力和变形量、变形量和接触半径的关系.理论计算结果与有限元(FEA)及实验结果吻合.研究结果为多体系统动力学计算提供了有益的参考.     

双柔性杆弹塑性碰撞动态子结构方法的研究

针对双柔性杆碰撞问题,考虑杆的弹塑性波传播,推导动力学控制方程,建立动态子结构模型,提出双柔性杆轴向碰撞的动态子结构方法。通过与三维弹塑性动力有限方法的对比表明,该方法的数值计算结果合理、精确,不仅能够计算复杂多变的碰撞力响应和变形响应,而且能够准确计算碰撞弹塑性波的传播,清晰刻画弹塑性波的传播、反射、相互作用等波传播规律。因此,可以作为一种研究多柔性杆弹塑性碰撞响应的有效的数值分析手段。     

双柔性杆弹塑性碰撞动态子结构方法的研究

针对双柔性杆碰撞问题,考虑杆的弹塑性波传播,推导动力学控制方程,建立动态子结构模型,提出双柔性杆轴向碰撞的动态子结构方法。通过与三维弹塑性动力有限方法的对比表明,该方法的数值计算结果合理、精确,不仅能够计算复杂多变的碰撞力响应和变形响应,而且能够准确计算碰撞弹塑性波的传播,清晰刻画弹塑性波的传播、反射、相互作用等波传播规律。因此,可以作为一种研究多柔性杆弹塑性碰撞响应的有效的数值分析手段。     

汽车座椅在低速后碰撞中的模拟研究

通过建立某汽车的安全座椅样件的CAD模型,利用FEA软件Hyperworks,建立了该座椅有限元模型并进行追尾碰撞座椅仿真模拟分析.针对Whiplash试验调整座椅设计参数,在产品尚未制造之前,解决可预见性的问题,大大节省了时间与成本.     

汽车碰撞中座椅转角数学建模

对汽车碰撞过程中,座椅产生的转角与能量问题进行分析与研究。为解决汽车被动安全中座椅转角难以预知的问题,通过对汽车碰撞时能量的传递与转移进行分析,提出一种预测座椅最大转角的方法,建立了相关数学模型,并以此模型的结果与FEA实验进行对比分析,证明了其可行性与正确性。该方法为研究汽车碰撞中座椅最大转角提供了一种预测手段,也为提高座椅被动安全的研究增加了一定的理论依据。     

两颗粒弹塑性正碰撞的耗散模型

为了快速地得到颗粒碰撞后的运动状态,从而实现颗粒碰撞阻尼系统的整体仿真研究,建立颗粒在单个碰撞周期中的分段力学模型.该模型将颗粒的单个碰撞周期分为三个阶段,通过三个阶段的力学分析得出颗粒在关键节点的运动状态,最终得到颗粒碰撞后的反弹速度、碰撞过程中的恢复系数和能量损耗的解析表达式.随后采用有限元方法对两颗粒的弹塑性碰撞过程进行模拟,有限元分析结果与分段力学模型的结果吻合较好,证明了分段力学模型的正确性.最后应用此分段力学模型对颗粒的碰撞速度、颗粒材料参数包括屈服点、弹性模量、密度和颗粒大小对耗能效果的影响进行定量的分析计算.计算结果表明,材料的屈服点和弹性模量之比越小,碰撞耗能效果越好;同时,质量密度越大的材料,耗能效果也越好;在设计颗粒阻尼器时可以以此为原则选用碰撞伙伴的材质.以上研究结果可以用于颗粒碰撞阻尼系统的阻尼特性分析和整体仿真研究.     

球-梁弹塑性次碰撞的试验研究和数值仿真*

次碰撞是柔性结构碰撞时特有的物理现象。为观测和深入研究这一现象,专门研制了一套柔性结构次碰撞试验平台。借助该试验平台,结合Hertz碰撞理论和动态子结构方法,对钢球坠落碰撞简支梁过程进行了详细的试验测试和数值仿真,观察到了复杂的次碰撞现象,深入探讨了次碰撞的碰撞接触时间规律和主要影响因素。研究结果表明,动态子结构方法可以作为球-梁弹塑性次碰撞行为分析的一种有效的数值计算手段。研究发现,在低速碰撞时Hertz碰撞理论所揭示的碰撞接触时间规律仍然适用于首个次碰撞过程,表明局部接触变形主导了首个次碰撞过程。次碰撞现象一旦发生,将导致简支梁碰撞端位移响应的前三阶振幅比和第一阶相位角均发生明显的变化。进一步的探讨则发现,次碰撞的发生与球-梁质量比、碰撞初速度和碰撞位置等因素密切相关,若用质量比来度量次碰撞的发生条件,发现存在一个质量比阈值,只有满足该质量比阈值,才会出现次碰撞。     

弹塑性微颗粒-钢球碰撞阻尼器衰减特性研究

弹塑性微颗粒-钢球碰撞阻尼器是在传统的碰撞阻尼器的基础上提出的,通过实验研究分析了弹塑性微颗粒-钢球碰撞阻尼器与其它阻尼器的实验结果对比以及在不同的颗粒减振剂、钢球直径和填充率条件下,悬臂梁振幅变化情况。实验结果表明,由于这种阻尼器结合了弹性变形和塑性变形的优势,具有更优异的减振性能,减振效果提高了29%;同时钢球直径和填充率均会对阻尼器的时间恢复系数产生较为明显的影响,直径越大减振效果有稍微的减弱,填充率在40%左右减振效果最佳。     

基于有限元方法的车架正面耐撞性分析

车架在非承载式车身结构中发挥了非常重要的碰撞吸能作用.采用有限元分析方法进行车架结构优化改进,改善了车架的刚度和变形,增强了车架对碰撞过程能量的吸收,降低了加速度峰值,延长了碰撞时间.分析结果为整车碰撞性能改善提供了很好的参考.     

汽车碰撞事故中乘员人体动力学分析

基于人机工程学的设计理念,应用汽车碰撞动力学原理,详细分析了汽车碰撞事故过程中,其乘员人体承受的加速度和碰撞的重要动力学参数,为研究汽车安全装置设计提供理论分析的依据,从而可获得最佳的乘员人体保护效果.     

On the Effect of Isotropic Hardening on the Coefficient of Restitution for Single or Repeated Impacts Using a Semi-Analytical Method

A semi-analytical method is proposed for the simulation of moderately high-speed impacts of a relatively hard particle on an elastic–plastic substrate. Potential applications of the current modeling approach include shot-peening and ultrasonic peening as well as impacts on functional surfaces such as mechanical seals or bearings. The coefficients of restitution for single impacts on an elastic–perfectly plastic semi-infinite body or one with isotropic hardening have been computed for various impact velocities. The current approach is three dimensional and numerically efficient in terms of CPU time and memory space required. Numerical results are in good agreement with those obtained by other authors for elastic–perfectly plastic behavior. Coefficients of restitution resulting from repeated impacts at a constant initial velocity are also studied. Finally, equations fitting these numerical results are proposed.     

In-plane elastic moduli and plastic collapse strength of regular hexagonal honeycombs with dual imperfections

The in-plane elastic modulus, Poisson's ratio and plastic collapse strength of regular hexagonal honeycombs with dual imperfections of non-straight and variable-thickness cell edges were theoretically derived from a model of curved cell edges with Plateau borders. Finite element analyses (FEA) on the stiffness and strength of regular hexagonal honeycombs with dual imperfections were also performed and then compared to the theoretical modeling. Both analytical and numerical results indicate that the in-plane elastic moduli and plastic collapse strength of regular hexagonal honeycombs with dual imperfections depend on their relative density, the solid distribution in cell edges and the curvature of cell edges. Meanwhile, the effects of dual imperfections on the in-plane elastic moduli and plastic collapse strength of regular hexagonal honeycombs are more drastic as compared to those of each single imperfection. Also, it is found that the normalized in-plane elastic modulus and plastic collapse strength of regular hexagonal honeycombs with dual imperfections are approximately equal to the products of those with each single imperfection.     

工作参数对接触式机械密封端面接触特性的影响

为研究和掌握接触式机械密封端面接触特性,通过模拟计算分析了工作参数对其特性的影响。结果表明,在密封端面间真实接触面积中,弹性变形微凸体接触面积所占比例最大,塑性变形微凸体接触面积所占比例最小;随着弹簧比压的增大,弹性接触面积比近似呈线性增大,弹塑性接触面积比和塑性接触面积比近似呈线性减小;随着密封介质压力的增大,弹性接触面积比增大,弹塑性接触面积比和塑性接触面积比减小;随着转速的增大,弹性接触面积比逐渐减小,弹塑性接触面积比和塑性接触面积比逐渐增大。     

弹塑性断裂随机分析的工程方法

为解决弹塑性断裂随机分析的参数计算问题，发展了前人的“弹塑性断裂力学工程方法”。以单边裂纹板为例，应用随机有限元进行全塑性无量纲断裂参数及其对基本随机变量变化率表值的计算，借助表值，通过插值进行断裂参数的计算和弹塑性断裂随机分析。结果表明工程估算方法与直接随机有限元方法所得结果较接近。     

Elastic moduli and plastic collapse strength of hexagonal honeycombs with plateau borders

The theoretical analysis for the elastic moduli and plastic collapse strength of hexagonal honeycombs with Plateau borders is proposed and presented here. The variation of cell edge thickness in real honeycombs is taken into account in deriving their elastic moduli and plastic collapse strengths. A repeating element, composed of three cell edges connected at a vertex with Plateau borders of constant radius of curvature and width, is employed to calculate the elastic moduli and plastic collapse strength of hexagonal honeycombs. Results suggest that both the elastic moduli and plastic collapse strength of hexagonal honeycombs with Plateau borders depend on their relative density and the volume fraction of solid contained in the Plateau border region. Meanwhile, effects of solid distribution on the elastic moduli and plastic collapse strength of hexagonal honeycombs are investigated, providing a guideline for the optimal microstructure design of honeycombs.     

7075铝板弹性模量退化行为研究及回弹预测

金属板材的弹性模量随塑性变形发生衰退,这一现象对板材成形中的回弹预测影响巨大。为研究7075高强铝板的弹性模量衰退规律,采用传统的循环加载试验进行弹性模量测试,同时借助DIC应变测量系统设计弯曲卸载试验进行测试。试验结果表明：弹性模量随塑性变形发生明显退化且衰退规律受材料变形所处的应力状态影响。将两种试验所得衰退规律用于C形梁成形过程中的有限元回弹仿真,仿真与试验的对比结果表明：弯曲卸载试验所得弹性模量衰退规律对C形梁回弹分析的结果明显优于循环加载试验所得规律的结果,四个回弹角的预测精度分别提高了42%、7%、40%和200%。     

Elastic recovery of a scratch in a polymeric surface: experiments and analysis

A scratch may be regarded as a tangential indentation. Hence standard indentation laws can be used to analyse the geometry of the scratches left by a moving tip on the surface of a viscoelastic viscoplastic body such as a commercial grade of cast polymethylmethacrylate (PMMA). This paper presents experimental results and an analysis of the elastic recovery of a scratch after contact with a tip. The experimental data were obtained with a new scratch apparatus fitted with a built-in microscope, which allows in situ analysis of the contact area and the groove left on the surface. The elastic plastic total penetration depth h_ep is split into its plastic part h_p and elastic part h_e. In the case of full plasticity around the tip during scratching, which for an elastic plastic material implies a sufficiently high value of the contact strain, the elastic law describes the depth relaxation and experimental data agree with the analysis. In the case of a purely elastic response of the material, corresponding to low values of the contact strain, the rear contact radius is equal to the front contact radius. At intermediate levels of strain, an analysis of the elastic recovery must take into account the contribution of the plastic term to the elastic plastic response of the material.     

弹性模量对塑料瓦推力轴承润滑性能的影响

弹性金属塑料瓦(EMP瓦)压缩弹性模量是一复合弹性模量,并不像金属材料那样是一个常数,而是随压力增大而逐渐增大。结合"三峡推力轴承方案"中EMP瓦推力轴承数据,从理论上计算了EMP瓦压缩弹性模量的变化对推力轴承润滑性能的影响,从而对EMP瓦压缩弹性模量允许的变化范围有所了解。计算结果表明:压缩弹性模量的变化对最小油膜厚度、最高油膜温度和最大压力有一定的影响,而对功耗影响不大。     

A finite-element analysis of the indentation of an elastic-work hardening layered half-space by an elastic sphere

An elastic–plastic contact problem in elastic-work hardening layered half-space indented by an elastic sphere was solved numerically using the finite element method. The case of a surface layer stiffer than the substrate is considered, and general solutions for the subsurface stresses and deformation fields are presented for a relatively thin elastic layer. Differences between the elastic and elastic–plastic solutions for the contact pressure distribution have been investigated for various layer thicknesses. Crack initiation and decohesion of the layer was also discussed with reference to the growth of the plastic zone.     

Elastic and elastic-perfectly plastic analysis of an axisymmetric sinusoidal surface asperity contact

ABSTRACT

Closed-form finite-element empirical models are available for elastic and elastic–plastic spherical and sinusoidal contact. However, some of these models do not consider the effect of interaction with adjacent asperities or require extensive numerical resources because they employ a full 3-D model. Therefore this work has analysed and quantified the behaviour of an elastic and elastic- perfectly plastic axisymmetric sinusoidal surface in contact with a rigid flat for a wide range of material properties and different values of the amplitude to wavelength ratio from initial to complete contact (high load). The numerical results agreed well with the Hertz model and the Jackson–Green elastic–plastic spherical contact model at low loads. Empirical equations for elastic and also elastic-perfectly plastic cases are formulated for the contact pressure, contact area and surface separation. From the current analysis, it is found that it is not any single parameter, but different combinations of material properties and surface roughness that govern the whole contact behaviour. The critical value of the amplitude of the sinusoidal asperity below which it will deform completely elastically from initial to complete contact is established. At low values of amplitude normalized by the critical amplitude, it was found that the contact behaved similar to a spherical contact, with the average pressure (hardness) always remaining lower than three times the yield strength. However, at higher values the average pressure increased toward a value as high as six times the yield strength at complete contact. All of these equations should be useful in rough surface contact modelling, lubrication analysis, electrical contact modelling and in many other applications.