基于JKR模型的粗糙圆柱表面线黏着接触分析

利用粗糙平面接触模型,假定表面单个微凸体的接触采用JKR黏着接触模型,同时考虑圆柱体表面的整体变形,建立了粗糙圆柱表面线黏着接触模型,推导出表面等效压力分布方程。把压力方程量纲一化,采用修正Newton-Raphson法对方程进行迭代求解,计算出粗糙圆柱表面存在表面力作用下的等效压力分布曲线。结果表明外载荷不小于零时,接触中心压力为正,微凸体被压缩;而接触边缘处压力为负,微凸体被拉伸,表明黏着区域主要分布在接触边缘。同时计算出接触半宽随外载荷的变化曲线,当外载荷为拉伸力并大于某一临界值时,表面分开。并且与经典的接触模型进行了对比,发现低载时模型之间的差别较大,而载荷比较大时趋于一致。

基于JKR-Cohesion模型的湿颗粒松散堆积体滑坡模拟分析

为深入研究湿颗粒松散堆积体滑坡的运动特征,提出采用JKR-Cohesion模型模拟湿颗粒堆积体的运动行为。基于离散单元法(DEM)建立了三维松散堆积体滑坡水槽模型,模拟堆积体整个运移过程,并将计算结果与干燥颗粒堆积体运动结果进行对比。计算结果表明:湿颗粒松散堆积体的运动受水的粘附力影响很大,相对于干燥颗粒,运动速度最大值更小,运动时间更短,且大部分颗粒堆积在坡面上;湿颗粒堆积体在运动过程中解体为小团体单独运动,而干燥颗粒运动连续性好,运动距离更远。提出的方法对于含水堆土的滑坡模拟有一定借鉴作用。

基于JKR模型的湿式滚抛磨块离散元参数标定

目的确定湿式滚抛磨块在接触过程中各相关物理性能参数的取值。方法基于EDEM离散元仿真模拟,选取系统中"Hertz-Mindlin with JKR"接触模型,以休止角为评价指标,对湿式滚抛磨块离散元模拟的最优参数组合进行标定。首先运用Plackett-Burman试验选取对湿式滚抛磨块有显著影响的3个参数项(湿式滚抛磨块间的滚动摩擦系数、碰撞恢复系数和JKR表面能),然后用最陡爬坡试验确定出显著性参数的最优区间,最后通过响应曲面法(Box-Behnken)分别对休止角和相对误差与3个显著性参数的回归模型二次多项式进行方差分析,并寻找最优参数组合。结果得到了最优参数组合解:磨块间滚动摩擦系数为0.0597,碰撞恢复系数为0.7444,JKR表面能为0.1J/m2。运用最佳参数组合进行仿真分析,得到休止角的均值为27.17?,与实验的休止角相对误差为0.6%。结论使用该方法进行湿式滚抛磨块离散元物理性能参数的标定具有可行性,不仅可以为实现仿真模拟的参数确定提供依据,同时可为其他非规则形状散体的参数测定提供参考。

基于JKR模型的辣椒籽离散元参数标定

辣椒籽的物性参数是离散元仿真中重要的输入,为提高其数值模拟的可靠性与准确度,对辣椒籽的物性参数进行试验测量,主要包括三轴尺寸、密度、泊松比、摩擦系数、恢复系数等。结合EDEM中“Hertz-Mindlin with JKR”粘力模型,引入表面能参数,进行休止角试验。通过Plackett-Burman试验在各影响因子中筛选出最具显著性的3个影响参数(辣椒籽—籽滚动摩擦系数、辣椒籽表面能、辣椒籽—钢板滚动摩擦系数),建立3个显著影响参数与休止角的回归模型,研究显著因子在交互作用下对休止角的影响。将显著参数的区间按梯度平均分为5个水平进行爬坡试验得到最佳取值范围,运用响应面法(Box-Behnken)分析回归模型的二次多项式在休止角、相对误差和三个重要参数之间的方差,以相对误差最小值对模型进行优化,得到最优组合:辣椒籽间的滚动摩擦系数为0.75、JKR表面能为0.31 J/m^(2)、辣椒籽与钢板间滚动摩擦系数为0.60。用通过标定试验得到的最优参数组合进行模拟堆积试验,平均休止角为26.71°,相对误差为4.61%。

基于JKR黏结模型的混凝土离散元参数标定

为获取装配式建筑用混凝土的仿真模型和接触力学参数,采用颗粒离散单元法,基于对此种混凝土的坍落度试验结果,实现对浇筑预制构件的新拌混凝土进行模拟与接触力学参数的标定。在对混凝土建模的过程中考虑到混凝土颗粒之间的黏结力,用JKR黏结模型对混凝土颗粒进行建模,以JKR表面能的大小表征混凝土间的黏度效果,以影响混凝土坍落时形态和坍落后物料堆积高度为结果变量,以预制构件用混凝土坍落度试验的真实测量值为目标建立三维离散元分析模型。选取砂浆-砂浆、砂浆-石灰石、石灰石-石灰石、砂浆-壁面、石灰石-壁面之间的静摩擦因数、滚动摩擦因数和JKR表面能的15个参数作为研究对象,采用控制变量法改变单一参数的大小,确定影响此种混凝土坍落度试验中混凝土形态的显著参数,并采用响应曲面法确定显著参数的最佳组合值。以本研究标定参数模拟的混凝土与实际预制构件混凝土之间的坍落度试验数据相对误差在允许范围内,该研究标定的混凝土离散元模型和接触力学参数对混凝土布料设备及预制构件研究具有重要意义。

The relation between a microscopic threshold-force model and macroscopic models of adhesion

This paper continues our recent work on the relationship between discrete contact interactions at the microscopic scale and continuum contact interactions at the macroscopic scale (Hulikal et al., J. Mech. Phys. Solids 76, 144-161, 2015). The focus of this work is on adhesion. We show that a collection of a large number of discrete elements governed by a threshold-force based model at the microscopic scale collectively gives rise to continuum fracture mechanics at the macroscopic scale. A key step is the introduction of an efficient numerical method that enables the computation of a large number of discrete contacts. Finally, while this work focuses on scaling laws, the methodology introduced in this paper can also be used to study rough-surface adhesion.

方形管道内无气离心喷涂涂料液滴流动特性的数值模拟

采用Fluent-EDEM软件数值模拟了方形管道内无气离心喷涂涂料液滴流动过程。采用RNG k-ε模型模拟了方形管道内喷枪旋转引发的气体流动和JKR接触模型追踪涂料液滴的运动。采用堆积角虚拟仿真试验预测了涂料液滴与水平壁面接触表面能。数值模拟结果表明,随着喷枪旋转速度的增大,涂料液滴速度和碰撞作用力增大,沿方形管道壁面长度方向涂料液滴数呈现中部高、两端低的变化趋势。提出了基于沿壁面长度液滴数分布的无因次均匀度系数。研究结果表明,随着喷枪旋转速度的降低,液滴无因次均匀度系数减小;喷枪Ⅱ增加了射流小孔数,有助于降低壁面液滴无因次均匀度系数,改善液滴分布的均匀性。

基于离散元方法的型砂流动性仿真研究

铸造用型砂预固化阶段的流动性是影响砂型固化后均实性的决定性因素。为了准确预测型砂预固化阶段的流动性,用型砂休止角表示其流动性,并提出一种基于DEM中JKR模型的方法准确仿真型砂休止角。通过建立JKR物理模型对原砂、碱性酚醛树脂和固化剂不同质量配比型砂的预固化阶段休止角进行仿真实验,并运用EDEM软件Protractor功能测得休止角数值,与试验休止角平均值相比误差在3%范围内。研究结果表明:基于DEM的JKR模型能够准确预测型砂预固化阶段的流动性,仿真结果为砂型数字化柔性挤压成形技术中型砂填充砂箱和砂型3D打印的工艺设计提供依据,对准确预测型砂成形能力和砂型固化后的紧实均匀度有重要意义。

基于计算流体力学-离散元法耦合方法的海底黏性滑坡体运动行为模拟

海底滑坡是海洋中常见的一种灾害地质现象,一旦发生将会对水下基础设施造成破坏,而目前很少有有关海底黏性滑坡体运动演化行为方面的模拟研究。采用计算流体动力学(computational fluid dynamics,简称CFD)和离散元法(discrete element method,简称DEM)建立了描述水与颗粒相互作用的流固耦合模型,通过引入颗粒间黏聚力模型,发展海底黏性滑体运动演化过程的CFD-DEM耦合分析方法,并开展了多个典型算例的验证分析。在此基础上,考虑滑体黏性作用和初始速度,系统地模拟了海底滑坡体的运动学特征(运动速度和距离)和形态特征(滑体长度、宽度、形状等),并深入探究了滑体运动及演化过程的影响机制。结果表明:该耦合方法可以较好地模拟再现海底滑坡体的小尺度运动行为,滑坡体的黏性作用对其运动学特征和形态特征具有显著影响,初始速度也明显影响了滑体各部位在运动过程中的颗粒流场演化及分布特征。这一成果可为真实海底滑坡的运动演化过程模拟和有效预测提供重要的科学依据。

基于JKR模型的饲料调质器特性与仿真分析

为研究草鱼养殖饲料颗粒在调质过程中的运动规律和黏结状况,并优化饲料调质条件,开展了基于Hertz-Mindlin with JKR模型的草鱼养殖饲料颗粒EDEM仿真分析。首先,进行了草鱼饲料颗粒的离散元理论研究,并建立了调质颗粒的湿黏模型;其次,通过建立调质轴转速和桨叶安装角度两因素仿真对照组,分析了调质轴转速和桨叶安装角对饲料调质效果的影响;根据饲料调质特性需求,进行了转轴转速和桨叶安装角的最优搭配;并通过理论计算与仿真分析。结果显示,当调质器转轴转速n=250 r/min、桨叶安装角θ=30°时,草鱼饲料颗粒不易黏附腔体内壁,物料混合均匀,可获得最佳调质效果。研究表明,饲料调质器调质效果与桨叶安装角度和转轴转速密切相关。本研究可为饲料厂家生产不同种类饲料优化调质效果提供理论依据和参考。

任意轴对称弹性体吸附接触的广义Maugis模型

通过线性叠加Sneddon方法和Lowengrub-Sneddon方法分别给出的解,得到了一个弹性半空间轴对称混合边值问题的一般解,进而研究了两个一般轴对称弹性体的正向无摩擦吸附接触问题．考虑任意有效的表面形状(要求中心部分首先进入接触)和任意的表面吸附作用,推广得到了广义Maugis模型．该模型是一个半解析的模型,它可以分解成表面形状和表面吸附作用的分别独立影响的两部分,以及一个关联变形和吸附作用的式子．利用Dugdale模型近似表面吸附作用,得到了具有任意有效的表面形状的广义M-D模型．它在强吸附或软材料条件下的极限形式是广义JKR模型,而在弱吸附或硬材料下的另一个极限形式是广义DMT模型．

热固性聚氨酯粉末物性参数的测定及应用

为获取热固性聚氨酯粉末离散元接触模型的关键物性参数,应用于废旧热固性塑料粉末混合再生制备的精确模拟计算。以120目的聚氨酯超细粉末为例,融合了Johnson-Kendall-Roberts(JKR)模型及其尺度变换准则,借助 MATLAB图像处理技术,利用 Minitab软件对关键物性参数:碰撞恢复系数、静摩擦因数、JKR表面能,进行了Box-Behnken试验设计,得到仿真试验的堆积角回归模型,以多次真实试验测定的堆积角均值38.45°为响应值,对回归模型进行接触参数寻优,获得关键接触参数的最佳组合为:碰撞恢复系数0.25,静摩擦因数0.69,JKR表面能 6.97 J/m 2 ,最后将仿真得到的堆积角与真实试验值进行对比验证,误差在5%以内,无显著性差异。结果表明,以堆积角为参照虚拟标定的热固性聚氨酯粉末接触参数是可行的;同时探究了接触参数应用于混合搅拌再生试验的混合效率可达到80.34%,研究成果为废旧热固性塑料再生材料的制备提供了理论依据。

Discrete element method for adhesion properties evaluation of deep-sea sediment from macro and micro perspectives

The adhesion between the mining machine and the deep-sea sediments will significantly affect the driving performance of the mining machine in the deep-sea environment.When the mining machine and the deep-sea sediment interaction simulation was carried out,the accuracy of the particle interaction parameters will directly affect the simulation results.This study proposed a method to systematically calibrate the interaction parameters between deep-sea sediment and grouser through the combination of experiment and simulation.The uniaxial compression test and macro adhesion test and corresponding discrete element numerical simulation were carried out,modifying the contact parameters until the simulation results are close to the experimental results.Then the micro-parameters of the JKR adhesion contact model were back calibrated with the test results,and the contact parameters between soil particle-soil particle and soil particle-metal are calibrated.Besides,the adhesion test shows that the adhesion forces were ranked in the order of 5052<STi80<TA2<TC4 under the same surface roughness,which indicates the aluminum alloy 5052 has the best anti-adhesion performance.The relationship between surface adhesion force and microscopic contact parameters was studied by discrete element numerical simulation,and the result shows that the coefficient of static friction and the coefficient of rolling friction has little effect on adhesion force.While it is mainly affected by the coefficient of restitution and surface energy,the surface adhesion force tends to decrease with the increase of the coefficient of restitution and increase with the growth of surface energy.The obtained parameters of soil particle to soil particle and soil particle to metal affecting the adhesion can contribute to the design optimization for the grouser of mining machines to decrease surface adhesion and enhance its movability and mining efficiency.

Exact analysis of the orientation-adjusted adhesive full stick contact of layered structures with the asymmetric bipolar coordinates

The adhesion failure has become one dominant factor in determining the reliability and service life of miniaturized devices subject to loadings with arbitrary orientations.This article establishes an adhesive full stick contact model between an elastic half-space and a rigid cylinder loaded in any direction.Using the Papkovich-Neuber functions,the Fourier integral transform,and the asymmetric bipolar coordinates,the exact solution is obtained.Unlike the Johnson-Kendall-Roberts(JKR)model,the present adhesive contact model takes into account the effects of the load direction as well as the coupling of the normal and tangential contact stresses.Besides,it considers the full stick contact which has large values of the friction coefficient between contacting surfaces,contrary to the frictionless contact supposed in the JKR model.The result shows that suitable angles can be found,which makes the contact surfaces difficult to be peeled off or easy to be pressed into.

角膜变形的三维球对称模型分析

为研究完整角膜对生理眼压的形变响应,用球形探针对完整角膜进行压痕实验,并用接触力学的JKR(Johnson-Kendall-Roberts)模型分析角膜在响应眼内压的等效弹性模量。在此基础上,将角膜简化为球对称模型,用弹性理论计算了完整角膜对生理眼压的三维应变,探讨了厚度、泊松比对角膜的三维应变的影响。结果表明,在眼内压作用下,完整角膜在周向和径向分别产生拉、压的应变响应;角膜周向和径向应变均随角膜厚度增加而增加;随着泊松比的增加,周向应变呈减小、径向应变呈增大的趋势。结果提示角膜周向-径向应变间存在拮抗作用,使完整角膜以均匀的体积形变响应眼压的变化。结果有助于定量分析角膜在不同眼内压下的生物力学特性,可为角膜力学的数值建模、模型仿真提供参考。

不同土质下耕刀工作的离散元受力仿真分析

通过DEM法,赋予土壤颗粒模型不同粘结能量,分别建立了不同类型粘结度的土壤模型,通过仿真得到适于模拟的土壤参数;然后,通过DEM法与多体动力学耦合的计算方式,得到了耕刀在3种情形下的角速度、角加速度及扭矩输出等动力学参数。同时,利用统计土壤中粘结键数量方式得出当土壤粘结能量在10~20J时,仿真效果最好。此外,发现耕刀受力与土壤粘结度不成正比关系,土壤粘结度增大,耕刀受力条件急剧恶化。

Adhesion Performances Between Two Orthotropic Solids Influenced by Temperature Increment

The classical adhesive contact models belong to isothermal adhesion theories,where the effect of temperature on adhesion was neglected.However,a number of experimental results indicated that the adhesion behaviors can be significantly affected by temperature.In this paper,the two-dimensional non-slipping anisothermal adhesion behaviors between two orthotropic elastic cylinders are investigated within the framework of the Johnson-Kendall-Roberts theory.The stated problem is reduced to the coupled singular integral equations by virtue of the Fourier integral transform,which are solved analytically with the analytical function theory.The closed-form solutions for the stress fields in the presence of thermoelastic effect are obtained.The stable equilibrium state of contact system is determined by virtue of the Griffith energy balance.The effect of temperature difference on adhesion behaviors between orthotropic solids is discussed.It is found that the difference between the oscillatory and non-oscillatory solutions increases with increasing the degree of anisotropy of orthotropic materials.The oscillatory solution cannot be well approximated by the non-oscillatory solution for the orthotropic materials with relatively high anisotropy.

Influence of interparticle interactions on the kinetics of self-assembly and mechanical strength of nanoparticulate aggregates

Computer simulations based on Discrete Element Method have been performed in order to investigate the influence of interparticle interactions on the kinetics of self-assembly and the mechanical strength of nanoparticle aggregates. Three different systems have been considered. In the first system the interaction between particles has been simulated using the JKR （Johnson, Kendall and Roberts） contact theory, while in the second and third systems the interaction between particles has been simulated using van der Waals and electrostatic forces respectively. In order to compare the mechanical behaviour of the three systems, the magnitude of the maximum attractive force between particles has been kept the same in all cases. However, the relationship between force and separation distance differs from case to case and thus, the range of the interparticle force. The results clearly indicate that as the range of the interparticle force increases, the self-assembly process is faster and the work required to produce the mechanical failure of the assemblies increases by more than one order of magnitude.

Adhesive contact of a rigid sphere to finitely stretched substrates

Exemplified by adhesive contact of a rigid sphere with equiaxially stretched elastomeric substrates, the effect of finite pre-strain on adhesion behavior is studied based on the JKR model. The analysis indi-cates that the pre-strain reduces the contact area between the sphere and the substrate, but does not alter the adhesion strength.