基于FEM-DEM的压气机叶片喷丸强化数值模拟研究

基于有限元与离散元(FEM-DEM)相耦合的方法,建立了喷丸强化过程仿真模型,获得了表面覆盖率与丸粒数目之间的关系曲线,基于规则钛合金局部模型,研究了喷丸强化过程中主要工艺参数(丸粒直径、喷丸速度和表面覆盖率)对残余应力场及表面粗糙度的影响规律。针对实际叶片结构,根据不同特征区域和局部表面曲率特征,分析了残余应力场的分布及变化规律。结果表明,在一定范围内,通过增大工艺参数可以获得更好的残余应力分布。然而,当工艺参数过大时,喷丸强化效果会被削弱,表面粗糙度增加,导致残余应力松弛现象出现。此外,在相同喷丸工艺参数下,不同压气机叶片区域的表面曲率特征对喷丸效果影响较大,曲率较大时产生的残余应力场分布较浅,而曲率较为平滑的区域可以获得更佳的喷丸强化效果。

基于FEM-DEM耦合法的转载溜槽磨损研究

考虑到颗粒物料在输送时冲击力对转载溜槽的影响,运用离散元与有限元耦合方法对颗粒物料转运过程进行了研究,以期揭示颗粒物料对转载溜槽磨损的影响规律。此研究采用Herz-Mindlin无滑动接触模型和Archard磨损模型进行仿真计算,分析了不同颗粒物料和不同工况条件下转载溜槽的磨损与应力应变的变化情况。结果表明:溜槽所受的磨损和应力应变与皮带输送机带速、溜槽倾斜角及颗粒类型度密切相关,矿石颗粒相对于大豆颗粒对溜槽造成的磨损更为严重;当皮带速度为4.5 m/s时,颗粒对溜槽的冲击力和压力最大,皮带速度的增加导致颗粒之间的碰撞及颗粒对溜槽碰撞的剧烈程度更为复杂,当皮带速度增加0.5 m/s时,转载溜槽的磨损量增加55%、形变量增加40%;溜槽倾斜角度增大会导致颗粒与溜槽的接触面积增加,从而导致切向摩擦力及溜槽磨损面积增加,当溜槽倾角在45°~50°时溜槽的形变量、磨损面积最小。

基于FEM-DEM的齿轮钢随机喷丸模型及残余应力仿真研究

以20CrMnTi材料制造的齿轮钢为受喷目标,基于对Abaqus有限元软件,应用P3D3离散单元的DEM模型模拟弹丸喷射,建立了随机喷丸的"FEM-DEM"模型。研究了不同沙漏刚度对模型结果的影响,获得了有效控制沙漏模式的沙漏刚度。建立了基于"FEM-DEM"喷丸模型求解的覆盖率表征模型,得出了满足100%覆盖率时所需的弹丸数。同时研究了不同覆盖率对齿轮钢残余应力的影响,当覆盖率小于100%时,喷丸强化应力效果显著,超过200%应力强化作用减弱。

颗粒驱动软体驱动器设计及FEM-DEM运动分析

颗粒物质具有流动传压和阻塞刚化的双相特性,是变刚度软体机器人的理想驱动介质.由于颗粒物质复杂的力学特性,颗粒驱动软体机器人运动预测极具挑战性.综合考虑颗粒物质的离散性和超弹软体型腔的连续性,本文提出了一种基于FEM-DEM耦合计算的软体驱动器运动分析方法.为降低颗粒充入软体型腔时的局部径向膨胀,设计了具有径向增强约束的弯曲驱动器软体型腔结构.利用FEM-DEM耦合计算方法对此驱动器的运动变形规律进行了分析,同时采用基于颗粒物质Mohr⁃Coulomb连续介质模型的FEM开展了对比计算.利用3D打印和硅胶浇注技术制造驱动器样机,测试了软体驱动器的运动特性及变刚度能力.研究结果表明:与基于Mohr-Coulomb模型的FEM相比,利用FEM-DEM耦合计算方法,可使驱动器弯曲角度的预测精度提高约14.3%;使用较小直径的颗粒介质可以提高机器人的变形能力;与前期研究中的原始方案相比,本文提出的径向增强约束驱动器在不削弱刚度调节能力的前提下,最大弯曲角度从48.9°提升至了72.7°.

FEM-DEM coupled modeling of cone penetration tests in lunar soil

Cone penetration test(CPT)is an appropriate technique for quickly determining the geotechnical properties of lunar soil,which is valuable for in situ lunar exploration.Utilizing a typical coupling method recently developed by the authors,a finite element method(FEM)-discrete element method(DEM)coupled model of CPTs is obtained.A series of CPTs in lunar soil are simulated to qualitatively reveal the flow of particles and the development of resistance throughout the penetration process.In addition,the effects of major factors,such as penetration velocity,penetration depth,cone tip angle,and the low gravity on the Moon surface are investigated.

Numerical investigation of rock dynamic fragmentation during rockslides using a coupled 3D FEM-DEM method

Rockslides are one of the most common geological hazards in mountainous areas and can pose significant threats to the safety of human lives and infrastructures. Studying the dynamic fragmentation process, and fragment characteristics of rock blocks during rockslides is of great significance. In this study,the influences of the slope angle on the dynamic fragmentation process, damage and energy evolution,and the fragments’ flying velocity and flying angle were systematically investigated using a coupled 3D FEM-DEM method. An improved fragment search algorithm was first proposed to more effectively extract the information of the fragments after impacting. The input parameters in the numerical modeling were carefully calibrated based on the quasi-static uniaxial compression tests and the rockimpact tests. The complex fragmentation process of rock block sliding along an inclined slope was simulated. The results indicate that the fragmentation intensity gradually increases with increasing the slope angle, and the fragmentation intensity of the front region of the rock block is always higher than that of the rear region. Additionally, the slope angle can significantly affect the damage ratio, energy dissipation, and the ratio of tensile crack to shear crack during the rockslides. The number of the fragments having higher flying velocities and larger flying angles increases with increasing the slope angle,which contributes to a larger spreading distance and a wider deposition area.

基于FEM-DEM的粗糙表面喷丸数值模拟与试验研究

考虑试件喷丸前粗糙度的影响,提出了粗糙表面喷丸的有限元与离散元(FEM-DEM)耦合模型。制备喷丸与未喷丸两类45#钢试件,测量了试件喷丸前后表面与亚表面的残余应力。根据测量结果验证耦合模型,研究了喷丸工艺参数对试件亚表面残余应力的影响规律。结果表明,提高表面覆盖率和喷丸强度,均可增大残余压应力峰值,其中,喷丸强度的影响更为显著;相同表面覆盖率和喷丸强度下,小直径弹丸可增大残余压应力峰值,大直径弹丸则有利于增大残余压应力层厚;若喷丸前试件粗糙度过大,可通过提高表面覆盖率来增强喷丸强化效果。研究为粗糙表面喷丸强化工艺优化提供了一定的理论依据。

抛物线壳体软模成形FEM-DEM耦合仿真研究

针对一些形状复杂、具有局部特征的难变形薄壁构件的成形问题,提出固体颗粒介质成形(Solid granules medium forming,SGMF)技术。并以薄壁的抛物线壳体零件为例,分析零件的特征及成形难点;基于ABAQUS平台,自行编制程序对抛物线壳体SGMF成形过程进行有限元法(Finite element method,FEM)和离散元法(Discrete element method,DEM)耦合仿真分析,探究不同摩擦因数对工件SGMF的影响。研究表明,FEM-DEM耦合分析技术兼顾离散颗粒介质与连续体板材各自的变形特点,能较准确模拟金属板材SGMF成形过程,并采用该耦合分析技术确定该抛物线壳体零件的最佳成形工艺参数;最后在模拟结果的基础上,开展抛物线壳体零件的颗粒介质成形试验研究,并成功试制出合格工件,试验结果与FEM-DEM耦合模拟结果基本吻合。

A coupled fluid FEM-DEM technique for predicting blasting operations in tunnels

We present recent developments in the coupling of the finite element method(FEM)and the discrete element method(DEM)for the analysis of rock blasting operations in tunnels.The coupled FEM-DEM technique has been proven to be an efficient procedure for pre-dicting the multiple fractures of rock induced by the loads generated in blasting.The coupled FEM-DEM procedure is applied in tunnel construction,as well as to gas pressure blasting pyrotechnics to break rocks for the excavation of the tunnel front.In the latter case,the effect of gas explosion is modeled by solving the equations of gas dynamics in the analysis domain using FEM.The effect of gas forces in the underlying rock mass is modeled via an embedded fluid-structure interaction method.The efficiency of the coupled FEM-DEM tech-nique is demonstrated in several examples of fracture tests and rock blasting problems related to tunnel engineering.The examples pre-sented indicate that the combination of the DEM with simple three-node linear triangular elements(for two-dimensional problems)captures the onset of fractures and their evolution accurately,accounting for the penetration of gas in the failure domain(Zarate&Onate,2015;Zarate,Cornejo,&Onate,2018).

Multi-layer perceptron-based data-driven multiscale modelling of granular materials with a novel Frobenius norm-based internal variable

One objective of developing machine learning(ML)-based material models is to integrate them with well-established numerical methods to solve boundary value problems(BVPs).In the family of ML models,recurrent neural networks(RNNs)have been extensively applied to capture history-dependent constitutive responses of granular materials,but these multiple-step-based neural networks are neither sufficiently efficient nor aligned with the standard finite element method(FEM).Single-step-based neural networks like the multi-layer perceptron(MLP)are an alternative to bypass the above issues but have to introduce some internal variables to encode complex loading histories.In this work,one novel Frobenius norm-based internal variable,together with the Fourier layer and residual architectureenhanced MLP model,is crafted to replicate the history-dependent constitutive features of representative volume element(RVE)for granular materials.The obtained ML models are then seamlessly embedded into the FEM to solve the BVP of a biaxial compression case and a rigid strip footing case.The obtained solutions are comparable to results from the FEM-DEM multiscale modelling but achieve significantly improved efficiency.The results demonstrate the applicability of the proposed internal variable in enabling MLP to capture highly nonlinear constitutive responses of granular materials.

Effect of dry-wet cycles on dynamic properties and microstructures of sandstone:Experiments and modelling

Underground pumped storage power plant(UPSP)is an innovative concept for space recycling of abandoned mines.Its realization requires better understanding of the dynamic performance and durability of reservoir rock.This paper conducted ultrasonic detection,split Hopkinson pressure bar(SHPB)impact,mercury intrusion porosimetry(MIP),and backscatter electron observation(BSE)tests to investigate the dynamical behaviour and microstructure of sandstone with cyclical dry-wet damage.A coupling FEM-DEM model was constructed for reappearing mesoscopic structure damage.The results show that dry-wet cycles decrease the dynamic compressive strength(DCS)with a maximum reduction of 39.40%,the elastic limit strength is reduced from 41.75 to 25.62 MPa.The sieved fragments obtain the highest crack growth rate during the 23rd dry-wet cycle with a predictable life of 25 cycles for each rock particle.The pore fractal features of the macropores and micro-meso pores show great differences between the early and late cycles,which verifies the computational statistics analysis of particle deterioration.The numerical results show that the failure patterns are governed by the strain in pre-peak stage and the shear cracks are dominant.The dry-wet cycles reduce the energy transfer efficiency and lead to the discretization of force chain and crack fields.

基于DEM-FEM耦合方法的碎屑流对桥墩最大冲击力的影响因素研究

碎屑流是我国山区最危险的地质灾害之一,山区桥墩常受到碎屑流冲击而开裂、倾斜甚至倒塌,给山区桥梁建设、运营带来严重的安全隐患。采用离散元方法(discrete element method,DEM)和有限元方法(finite element method,FEM)耦合的三维数值模拟方法模拟了碎屑流对双柱式桥墩的冲击效应,并结合斜槽试验,验证了耦合方法的准确性,进一步分析了碎屑流冲击坡度、距离和体积密度对桥墩冲击力的影响规律。结果表明,最大冲击力与碎屑流冲击坡度、距离和体积密度分别呈幂函数(指数大于1)、幂函数(指数小于1)和线性正相关。冲击坡度、距离和体积密度对最大冲击力的敏感度值分别为3.012、0.202、0.804,在桥梁碎屑流灾害防治时需重视冲击坡度和体积密度的影响。将冲击力的数值模拟值与流体动力学模型预测值对比分析表明,流体动力学模型理论公式能较好地预测桥墩所受的最大冲击力,最大预测误差低于23.6%。相关研究结果可为山区桥梁碎屑流灾害防治与设计提供一定的参考依据。

冷浸田起垄平整装置设计与试验

针对冷浸田终年积水、水土温度低及排水不良,需进行垄作栽培水稻的生产要求及目前缺乏相关机具的生产现状,设计了一种适宜于冷浸田作业的起垄平整装置,该装置主要由起垄辊、微垄开沟器及平整部件组成,实现大垄排水、微垄蓄水作业,利于冷浸田排水及水稻种子生长发育。根据《冷浸田机械起垄水稻栽培技术规程》,对起垄辊、微垄开沟器及平整部件关键参数进行了设计,确定起垄辊回转半径为560 mm、锥形面倒角为28°,微垄开沟器宽度为50 mm、高度为40 mm及平整部件可调节角度为5°。基于DEM-FEM耦合仿真分析确定了装置较优运行参数,当机具前进速度为0.6 m/s、旋耕刀辊转速为230 r/min、起垄辊转速为120 r/min时,土壤回流率为3.51%,并进行了起垄辊应力应变分析。田间试验结果表明,平均垄沟沟深为160.03 mm、沟顶宽为174.84 mm,平均垄顶宽为1888.89 mm,平均厢面平整度为11.26 mm,平均微垄沟沟宽为60.16 mm、沟深为36.48 mm,各项指标均满足冷浸田机械化起垄作业要求。

盾构切桩弧形撕裂刀几何构型优化研究

该研究利用有限元与离散元的方法构建弧形撕裂刀切削钢筋混凝土耦合模型,并开展参数分析,探明弧形撕裂刀刃宽与刃角对刀具切削性能与损伤的影响,给出弧形撕裂刀在切削钢筋混凝土时的推荐结构设计方案。研究结果表明,刃宽与刃角对弧形撕裂刀的切削性能有显著影响,刃宽越小,刃角越小,弧形撕裂刀的刀刃越锋利,有助于提高破桩能力。但是,这样的设计带来的缺点是容易出现局部应力集中现象,导致弧形撕裂刀断裂失效和损坏。因此,刀刃宽度不应过大或过小,综合考虑有效应力和切削力,实际工程中设计弧形撕裂刀时,建议刀刃宽度控制在4~5 mm之间,刃角建议控制在80~90°之间。研究结论可为未来盾构切桩的弧形撕裂刀选型优化提供参考和借鉴。

影响盾构贝壳刀对钢筋混凝土切削性能的参数研究

本研究利用有限元与离散元耦合的分析方法,构建了贝壳刀切削钢筋混凝土桩基三维细观模型,探明了刀具与钢筋混凝土桩基的相互作用机理,分析了贝壳刀结构形式对刀具切削性能的影响,给出了贝壳刀在切削钢筋混凝土时的优化几何构型。研究结果表明,刃宽、刃角与刃前角均对贝壳刀的切削性能有显著影响,刃宽、刃角与刃前角均不应过大或过小,综合考虑应力和切向力,在实际工程中,建议刀刃宽度控制在4mm~5mm之间,刀刃角度控制在80°~90°之间,刀刃前角小于55°。研究结论可为未来盾构切桩的贝壳刀选型优化提供参考与借鉴。

基于DEM-FEM耦合的环锤式破碎机反击板可靠性分析

由于环锤式破碎机破碎物料的过程是一个极其复杂多变的过程,且与反击板所受的碰撞力是不连续、无规则的,因此,无法使用公式推导或使用单一软件对反击板受力进行计算,为了能够更好地确定破碎机破碎过程中反击板的载荷大小、分布和寿命,文中提出了一种基于离散元(DEM)和有限元(FEM)耦合计算的环锤式破碎机反击板可靠性分析方法,通过EDEM建立环锤式破碎机破碎物料仿真过程,并提取出破碎过程中反击板的载荷分布,与ANSYS Workbench建立耦合计算通道,计算得到在正常工作参数下反击板的受力大小和位置,在此基础上采用n Code Design Life疲劳分析软件对反击板进行寿命分析,得到反击板的受力云图和损伤云图,研究转子转速、反击板倾角、转子与筛板距离等不同因素下对反击板可靠性的影响,结果表明:转子转速为1000 r∕min时反击板的最大受力值为247.9 MPa、反击板角度为60°时应力最大值为206.48 MPa、转子与筛板距离为530 mm时受力最大值为268.37 MPa。

高聚物粘结炸药模压成型的数值模拟研究进展

为给高聚物粘结炸药(polymer bonded Explosive,PBX)实际生产工艺参数制定和品质调控提供精确指导,梳理基于连续介质假设和微粒学观点2种方法的PBX压制成型数值模拟研究进展,介绍炸药晶体颗粒与粘结剂的物性模型、微结构损伤表征与演化,以及PBX在机械载荷作用下力学行为的相关理论;从PBX的材料特性以及散粒组合复合材料的特殊几何结构等角度,分析PBX压制理论研究的难点,提出基于统计学概念的PBX压制变形与损伤分析的设想。结果表明:数值模拟可克服物理实验的限制,从而得到PBX在热-力耦合作用下的重要信息。

基于离散元与有限元耦合的料斗衬板磨损分析

针对转运系统转载物料过程中料斗衬板的磨损影响运输效率的问题,改用新型钢基陶瓷复合衬板来代替传统耐磨钢,采用离散元法(distinct element method,DEM)描述颗粒物料运动过程,通过Archard磨损模型分析预测不同工况条件下衬板磨损规律,并通过磨损规律和磨损特征验证了磨损模型的合理性。基于DEM的有限元法(finite element method,FEM)耦合方法分析了衬板应力与变形特性。研究结果表明:料斗衬板的最大磨损深度随颗粒度增大而减小,随传送带带速、衬板安装高度、衬板安装倾角的增大而增大。结合实际来看,衬板在粒径25mm、带速2.8m/s、高度3000mm、角度60°的工况下磨损最小。铁矿石散料对衬板的摩擦和冲击作用造成的应力较大的位置主要集中在衬板连接的螺栓孔周围,磨损最严重的位置多为颗粒与衬板优先接触区域,因此,为了降低应力集中,应该在衬板连接处加强螺栓孔的强度并进行圆角设计。

基于DEM-FEM耦合模型的质量流量对喷丸强化效果的影响

目的提出一种将有限元(FEM)与离散元(DEM)相耦合的新方法,即通过定义关键字的方式在ABAQUS软件内实现DEM-FEM耦合功能,并应用此方法建立喷丸强化模型。方法将弹丸视为等直径刚体,利用刚体动力学模拟弹丸-弹丸和弹丸-靶材之间相互作用以及整个弹丸流。通过建立的DEM-FEM耦合喷丸强化模型研究质量流量对残余应力场和表面粗糙度的影响。结果质量流量对喷丸强化效果有显著影响,最大残余应力随质量流量的增加而减小,由2 kg/min时的–596.77 MPa下降到6 kg/min时的–581.91 MPa;表面残余应力随质量流量的增加先增大后减小,由2 kg/min时的–420.86 MPa增大到4 kg/min时的472.06 MPa,随后减小到6 kg/min时的–450.50 MPa;表面粗糙度Ra随质量流量的增加减小,由2 kg/min时的11.21μm减小到6 kg/min时的9.82μm。设计了喷丸强化实验,对质量流量2 kg/min的结果进行了验证。结论实测值与模拟值吻合较好,所建立的模型可以准确反映实际喷丸强化过程。质量流量对喷丸强化效果具有显著影响。

水平振动式滚磨光整加工残余应力离散元有限元耦合仿真与实验研究

为探究水平振动式滚磨光整加工对零件表面残余应力的影响,提出一种适用于动态零件的离散元有限元(DEM-FEM)耦合仿真方法。分析了振动周期内颗粒运动状态以及颗粒间平均接触力的变化,构建了颗粒与零件间的随机接触模型,开展了不同振动参数下的残余应力仿真,并进行了实验验证。研究结果表明:随着振动强度的增大,容器内颗粒运动更加剧烈,颗粒与零件间有效法向接触力发生概率及均值增大,导致零件表面残余压应力呈增大趋势。残余应力仿真值与实验值对振动参数的响应趋势一致,误差在3.6%~11.3%之间。