镗刀内置颗粒碰撞耗能分析

分别建立了两颗粒对心碰撞在弹性挤压、弹塑性挤压、弹性恢复三阶段下的力学模型。利用ABAQUS软件对两颗粒对心碰撞进行仿真,得出了耗能的主要形式,明确了阻尼颗粒材质的优选条件。通过切削试验验证了仿真的正确性,结果表明:在试验条件一致的情况下,填充铝青铜粉的镗刀具有更好的减振效果,镗刀在一阶固有频率下的功率谱密度值为2.464,相比填充铁粉降低了30.88%,颗粒的塑性越大,碰撞耗能越强。     

振动修整过程中三维介质运动离散模型的研究

振动修整过程中,系统中介质运动状态的变化受多方面因素的影响。因此,对振动修整系统中修整介质的动态运动情况进行预测具有重要意义。为此,基于离散元方法(DEM)建立振动修整三维有限元模型,用于计算介质粒子间的相互作用,如法向接触力和切向接触力;然后,基于Hertzian接触力学的DEM模型预测了单个粒子在机械振动容器内的动态运动;研究了接触刚度、摩擦、阻尼等接触参数对介质运动的影响,确定了振动修整过程的临界修整参数;最后,对仿真结果进行了实验验证。结论表明,振动修整三维离散有限元模型能准确预测介质流动和局部撞击颗粒的介质运动,通过参数设置调整颗粒运动模式和速度,能够获得最大限度地提高材料的去除率。     

胞元模型在骨组织建模中的应用及评价

针对去软组织骨生物力学建模问题,采用有限元仿真手段通过股骨CT体数据集三维几何重建、网格划分、股骨表观密度计算、有限元单元横观各项同性力学模型建立、力学参数确定等几个步骤实现对股骨的力学建模和解算。其中,最关键的工作是力学参数确定,尤其是弹性模量和表观密度关系式的建立。依据胞元理论建立了弹性模量和表观密度的分段函数关系,最终获得股骨力学模型并通过仿真计算得到载荷-轴向应变和载荷-横向应变数据。同时,也基于弹性模量和表观密度经验关系式建立力学模型并进行分析计算提取仿真结果,通过实施生物力学试验提取试验结果,将两种仿真结果与试验结果对比得出:同一块猪股骨,在相同力学环境下,胞元理论力学模型与试验结果轴向应变误差为25.92,横向应变误差为10.04,两种误差均小于经验公式力学模型仿真结果误差,因此,胞元理论力学模型在股骨建模中表现出模型更精确、适用范围更广泛的优势。     

颗粒间粘连力的散体元研究

考虑颗粒在接触时的表面粘连力,利用有限元软件对颗粒的功率谱进行模型仿真,从仿真效果可以看出计算结果与试验结果具有良好的一致性。说明考虑颗粒间粘连力的阻尼力学模型是可行的,能更加准确地模拟颗粒间的接触情况。     

带颗粒减振剂碰撞阻尼的减振特性

传统碰撞阻尼的工作原理大都建立在动量交换、摩擦耗能的范围内,动量交换并没有将振动能量永久地消耗掉,摩擦对于高频振动具有较好的减振效果,而对于低频振动效果较差。为此提出一种以微细颗粒塑性变形将振动能量永久消耗掉的新型的碰撞阻尼,称为带颗粒减振剂碰撞阻尼。分别对在传统单体碰撞阻尼和带颗粒减振剂碰撞阻尼作用下悬臂梁减振效果进行试验研究。试验结果表明：以微细颗粒塑性变形消耗振动能量的带颗粒减振剂碰撞阻尼具有优秀的减振效果,远远超过传统单体碰撞阻尼器。带颗粒减振剂碰撞阻尼在低频振动(低于50 Hz)中仍然具有良好减振性能,这是其他碰撞阻尼所缺乏的特性。机械振动多为低频振动,带颗粒减振剂碰撞阻尼具有广阔的应用前景。     

单个薄壁多孔金属空心球体力学行为研究

金属空心球多胞材料结构是一种新型的多孔金属材料,它是由多个金属空心球组合而成,对于单个金属空心球的力学行为研究是整体材料力学性能的基础。通过对外径2 mm～3 mm,且壁厚不等厚(壁厚10μm～40μm)的单个超薄壁多孔空心球体进行纳米压痕试验、准静态单轴压缩试验以及纯弹性阶段的压缩试验,进而得到该金属空心球体材料和整个球体的弹性模量等相关力学参数,以及金属空心球体压缩变形过程和特征,并对金属空心球体弹性阶段采用有限元软件Abaqus进行模拟,分析孔隙率对于球体弹性模量的影响,结果表明,随着球壁孔隙率的增大,球体的弹性模量减小,且呈非线性分布,并可以描述成与球壁孔隙率与球壁材料的力学性能关系相同的幂函数形式。     

颗粒阻尼器配置对齿轮传动系统动特性影响

齿轮传动正朝着高速、重载和高精度方向发展,对其动态性能要求越来越高。颗粒阻尼通过颗粒间、颗粒与阻尼器壁间的非弹性碰撞和摩擦作用耗能,具有减振效果显著、耐高温、各向同性、对原结构改动小等优点。利用有限元法对齿轮进行了有预应力的模态分析,通过齿轮系统动力学分析,研究单双齿啮合激励对齿轮传动的影响;同时建立齿轮传动离心场中颗粒系统耗能模型,将离散元法计算颗粒系统耗能和试验测试对比,分析阻尼器配置对齿轮传动系统动特性的影响。结果显示,阻尼器配置方案是影响齿轮传动系统动特性的一个重要因素,在阻尼孔中填充一定数量的颗粒,当阻尼器总体积相同且齿轮结构静刚度相差不大时,阻尼器个数越多颗粒系统能耗越大;当阻尼孔直径相同时,阻尼孔个数越多颗粒系统总能耗越小;当阻尼孔个数相同时,阻尼孔直径越大颗粒系统能耗越小。通过试验和仿真对比验证了模型的正确性,为颗粒阻尼在离心场中的应用提供重要的理论依据。     

基于DEM算法的多颗粒碰撞耗能机理分析与振动抑制研究

针对机械构件主系的封闭空间中填充微小颗粒,进行振动抑制问题,对填充颗粒的尺寸、数量以及材料特性因素对振动抑制效果的影响开展了研究。通过采用离散单元法(discrete element method,DEM),分析了颗粒与颗粒以及颗粒与主系统之间的运动学特性,建立了能够充分表达颗粒在相互碰撞摩擦过程中的受力、变形关系以及耗能计算模型,分析了多个颗粒之间的碰撞与耗能机理,确定了碰撞过程中颗粒的状态、受力及耗能大小的计算求解算法。在Matlab环境下,针对不同颗粒材质、数量及大小对系统振动抑制性能进行了仿真分析,得出了颗粒材质大小以及数量对减振性能的影响规律,并通过搭建的试验台,进行了试验数据采集和分析。试验结果与仿真结果相吻合,验证了算法的有效性,该算法为提高机械构件的减振性能设计提供了重要参考。     

基于离散单元法颗粒阻尼的耗能研究

提出了用于颗粒阻尼耗能研究的新算法,建立了颗粒阻尼软球耗能模型,并通过研究颗粒层之间的滑移和竖直压力来计算颗粒层之间的耗能情况,通过迭代法得到颗粒阻尼中摩擦耗能情况,并由此推导出颗粒阻尼摩擦耗能的理论计算公式。在简谐激励条件下,对圆柱形钢制容器内的颗粒体耗能情况进行测试,系统地研究了颗粒层深度对阻尼性能的影响,试验结果对理论计算给予了有效验证,同时得出随着颗粒填充高度的增加,阻尼效果明显加强。     

橡胶阻尼材料分数微分模型研究

推导了橡胶阻尼材料的Zener四参数分数微分模型以及五参数分数微分模型,并分析了微分阶数对于各模型的影响。通过动态力学热分析实验,拟合出两种分数微分模型的参数值,并与实验值进行对比分析,发现五参数分数微分模型能够较好地描述耗能模量关于频率对数非对称的橡胶阻尼材料的频率特性,而Zener四参数分数微分模型则仅仅适用于耗能模量关于频率对数光滑对称的橡胶阻尼材料。     

Material deformation and removal due to single particle impacts on ductile materials using smoothed particle hydrodynamics

Smoothed particle hydrodynamics (SPH) was used to simulate the impact of single angular particles on Al6061-T6 targets, and the implications for solid particle erosion were discussed. The results of the simulations were verified by comparison to measurements obtained from impact experiments performed using a gas gun which was specifically designed to accelerate angular particles without disturbing their orientation with respect to the target. Both the simulations and the experiments showed that an increase in impact angle and initial orientation of the particle altered the deformation mechanism of the target material, as noted by other investigators. For impact angles close to normal, a significant amount of target material was extruded and piled up at the edge of the impact craters, due to the limited strain hardening of Al6061-T6. However, for certain combinations of incident parameters, the particle machined the surface and a chip was removed. With appropriate constitutive and failure parameters, SPH was demonstrated to be suitable for simulating all of the relevant damage phenomena, including crater formation, material pile-up and chip separation.     

Model of a single-row flow of cars: Derivation and integration of equations

A chain of cars moving one after another in a single traffic lane is considered. It is assumed that the cars are point particles and these particles interact with adjacent ones according to the safe distance law. The differential functional equations of the particle flow are derived, and their solution is obtained. Boundary conditions at sections of particle input and output from a piece of a traffic lane are added to the equations. It is shown that models of a single-row flow of particles can be constructed as a chain of a finite number of mass points in a friction-free channel with pulse control as well as a finite-state automation model.     

Erosion of 304 stainless steel

Erosion rate measurements and scanning electron microscopy observations were made for the steady state erosion of 304 stainless steel eroded by sharp alumina particles. Both the velocity and the particle size dependence of the erosion rates were similar at all angles of impact between 10° and 90°. Micrographic observations of the steady state erosion surfaces disclosed similar overall features at low and high angles of impact. Results reported in the literature for aluminum tend to confirm these observations. It was concluded that a single erosion mechanism can be operative at all impact angles 7in ductile metals such as stainless steel, rather than a superposition of different mechanisms for the low angle and high angle range. The physical basis for a single mechanism of erosion by sharp particles was discussed.     

Numerical simulation of solid particle impacts on Al6061-T6 Part II: Materials removal mechanisms for impact of multiple angular particles

In the accompanying paper (M. Takaffoli, M. Papini, Numerical simulation of solid particle impacts on Al6061-T6 Part I: Three dimensional representation of angular particles), it was demonstrated that realistic 3D models of angular particles could be generated and used with a smoothed particle hydrodynamics model to simulate the damage done to an Al6061-T6 target due to many non-overlapping particle impacts. In this paper, the same methodology was used to simulate overlapping impacts, and thus the material removal mechanisms associated with the solid particle erosion of this material. The evolution of the topography of the blasted surface was simulated, and the surface ripple patterns that typically form during the erosion of aluminum alloys were observed. The predicted volumetric erosion rates at different impact angles were, on average, within 7% of those measured in erosion experiments. An investigation of the simulated trajectory of the impacting particles revealed the cooperative contribution of overlapping impacts to material loss, and solid particle erosion mechanisms such as the micromachining of chips, the ploughing of craters, and the formation, forging and knocking off of crater lips. The results indicate that numerical simulation of the solid particle erosion of ductile metals by realistic angular particles is possible.     

Experimental verification of a model of erosion due to the impact of rigid single angular particles on fully plastic targets

A previously described rigid-plastic model of the erosion of ductile targets by the impact of single angular particles was experimentally verified over a wide range of particle angularities, incident angles of attack, and incident orientation angles. The model assumes that the particle is perfectly rigid and thus is non-deforming, while the target material response is fully plastic, so that elastic rebound effects are neglected.Measurements of particle rebound kinematics, crater volume, and crater shape revealed generally good agreement with those predicted by the rigid-plastic model, and erosion mechanisms resulting from particles tumbling either forwards or backwards, were identified. For highly angular particles, target material removal sometimes occurred due to tunnelling of the particles below the target surface, leading to early break-off of a machined chip, behaviour that could not be predicted by the rigid-plastic model. Besides providing insights into fundamental erosion mechanisms, the results of the present study can be used to predict particle rebound kinematics, crucial for simulations of erosive streams which take into account interference between incident and rebounding particles.     

液动压悬浮抛光中磨粒与工件表面作用的数值模拟研究

针对液动压悬浮抛光固-液两相流中固相磨粒与工件表面撞击的过程中,对磨粒以不同的速度和不同的角度撞击工件表面后残余应力沿工件深度方向的分布规律进行了研究,利用ABAQUS软件建立了单颗磨粒撞击工件表面的三维有限元模型。对磨粒流撞击工件表面时的速度场进行了输出,利用PFC/3D软件建立了磨粒流撞击工件表面的三维离散元模型。研究结果表明:随着撞击角度和速度的增大,在工件表层形成的压应力场会增大,沿深度方向残余应力值急剧下降,磨粒流中磨粒间的撞击对磨粒撞击工件表面的速度场影响不大。     

Calculation of water droplet impingement using the coupled method of rigid body dynamics and the moving particle semi-implicit method

When a liquid droplet impacts on a solid surface, it recoils to the center of that surface after reaching its maximum spreading diameter. The mechanism of droplet recoiling is not fully understood. To simulate this recoiling of a droplet, a particle method is a good choice because it does not require grids for simulating fluid motions, and can easily handle a large deformation of fluid. In this study, the coupled method of rigid body dynamics and the moving particle semi-implicit (MPS) method (Park and Jeun, 2011) was used to calculate three-dimensional droplet impingement. Also, the previous surface tension model for MPS (Nomura et al., 2001) was revised to get a more realistic surface tension force. A two-step calculation was performed. In the first step, a MPS calculation was performed with particles that were considered to have no mass or volume. In the second step, rigid body dynamics came into the calculation and considered the diameters of particles being slightly lesser than the initial distance between particles. In this study, the calculated results were compared with the measured data (Kim and Chun, 2000) and the recoiling lengths of droplets for the various initial impingement speeds were estimated.     

基于离散单元法的铝粉冲击加载过程三维数值模拟

基于离散单元法原理,应用三维离散元软件PFC3D对金属粉末的冲击加载过程进行了模拟,利用分离式霍普金森压杆实验验证了模拟结果。对压制过程中颗粒的运动情况进行了初步研究分析,发现颗粒的速度分布形状为不规则弧形,并存在分布梯度。刚受到冲击时,颗粒以横向移动为主进行重排,随着颗粒速度的增加,颗粒的运动方向逐渐向下偏移,以此规律,逐步传递。上部颗粒的垂直下移与下部颗粒的横向重排是颗粒间产生剪切的主要原因。     

Numerical Study of Impact Behaviors of Angular Particles on Metallic Surface Using Smoothed Particle Hydrodynamics

Modeling and studying the impact behaviors of angular particles is critical in understanding the mechanisms of erosive wear on solid surfaces. This article focuses on effective mesh-free model based on the smoothed particle hydrodynamics (SPH) method to simulate impacts of angular particles on metallic surfaces. The predicted results are compared with the available experimental data, and good agreement has been achieved. Our simulations under different incident conditions successfully reproduce the general impact behaviors of angular particles, including rotating behavior and rebound behavior, which enables detailed examinations of erosion mechanisms. We find that the rotating behaviors are mainly determined by initial orientation and impact angle, whereas impact velocity has little effect. For backward impact involving a prying-off action, there generally exsits a critical impact velocity below which the cutting process would never be finished, which may result in a rebound angle greater than 90°. Further, multiple and overlapping impacts are simulated to reveal the effect of a pre-created crater on the subsequent impact. The results demonstrate the ability of the present model to handle the extremely deformed surface by overlapping impacts. The proposed SPH model and the present study could be useful in the study of erosive wear on the surface of metal devices that carry granular substances.     

基于有限元法催化剂颗粒撞击壁面的数值模拟

为解决催化裂化装置中的许多构件因为催化剂颗粒长期不断冲击而导致失效等的问题,将有限元法应用到其模拟仿真中,分析了单颗催化剂颗粒参数(角度、速度、材料)对不同壁面材料的撞击而造成壁面磨损的影响,建立了催化剂颗粒撞击壁面的数值分析模型,研究了催化剂颗粒以不同的速度、撞击角度,以及不同的催化剂颗粒的材料撞击不同材料的壁面对壁面造成的影响,并分析了催化剂颗粒变形对壁面磨损的影响,根据计算的结果,对催化剂颗粒参数进行了优化控制,提出了减少催化剂颗粒变形和构件磨损的技术措施.研究结果表明,该方法能够使催化裂化装置长期安全稳定地运行.