滚动轴承动态接触特性数值模拟中若干问题

滚动轴承运转过程中的动态接触特性与轴承使用寿命密切相关,目前主要是利用各种数值模拟技术开展轴承动态接触行为研究。通过在ANSYS/LS-DYNA研究平台上开展不同模型设计参数下滚动轴承动态接触特性的数值模拟研究,考察材料模型的设计、边界约束模式的选择和单元大小的定义等因素对数值模拟结果的影响情况。研究结果表明,由刚性体内外圈模型计算得到的滚子组最大应力仿真结果明显大于由弹性体内外圈模型得到的结果,且载荷方向上轴心位移变化起伏较大;采用外圈转动、内圈固定的边界约束模式时,轴承各组件上的最大动态接触应力值以及轴心在载荷方向的位移均高于采用内圈转动、外圈固定约束模式时的求解结果;单元大小也明显影响最终的动态模拟结果,较小单元尺寸下得到的应力结果明显大于较大单元尺寸下的模拟结果。研究结论可以为轴承动态接触特性数值模拟过程中模型构建方案的合理确定提供参考。     

Dynamic deformation under a modified split Hopkinson pressure bar experiment

This paper presents a modified split-Hopkinson pressure bar (SHPB) technique. The dynamic stress-strain behaviors were estimated at room temperature and subzero temperature to −75°C by using the conventional SHPB and compared with a modified SHPB technique. A computer simulation using a finite element algorithm is also performed to study the dynamic material responses. Furthermore, we attempt to find a proper material constitutive law by using the simulation process. It is suggested that the modified SHPB test used in this study can be successfully utilized to offer an experimental condition of a higher strain rate than that obtained from the conventional SHPB test.     

Damage and failure characterization of 7075 aluminum alloy hot stamping

7000 series high strength aluminum alloys are increasingly used in manufacturing automobile body parts to meet the more stringent demands for automobile lightweight. Hot stamping of 7000 series high strength aluminum alloys is a complex thermal-mechanical coupling process and precise simulation is needed to predict material fracture. To obtain damage model of 7075 aluminum alloy in hot stamping, five different stress triaxiality specimens were designed. The fracture strain, critical strain and average stress triaxiality of different specimens were obtained by the hybrid finite element simulation and experiment (FE-EXP) method. GISSMO model of 7075 aluminum alloy at 400 °C was established. Compared with the experimental results of U-shaped part hot stamping under different lubrication conditions, the calibrated GISSMO model was demonstrated to predict the damage behavior of 7075 aluminum alloy during high temperature deformation accurately.

     

Q345钢热变形奥氏体晶粒尺寸的数值模拟

用Gleeble1500型热模拟机进行了单道次压缩变形试验,分析了不同变形工艺参数对Q345钢奥氏体晶粒尺寸的影响规律,根据试验结果,建立了动态再结晶数学模型及其材料数据库,并写入Marc用户子程序,利用有限元软件Marc和热力耦合弹塑性有限元法模拟了试样的压缩过程,分析计算了采用不同再结晶模型得到的再结晶晶粒尺寸。结果表明：新建立的动态再结晶模型计算的奥氏体晶粒尺寸与实测值吻合很好。     

活塞环用异型截面型材轧制的显式动力学有限元分析

利用大型通用显式动力有限元分析软件ANSYS/LS_DYNA对活塞环用6Cr13Mo钢异型截面型材的轧制进行了有限元模拟,详细介绍了有限元模型的建立、材料模型的选择以及网格的划分,得到了各道次轧制金属的流动规律,对轧件的变形及轧制区内应力场的分布进行了深入的分析,为成型轧辊的设计以及优化生产工艺提供了参考.     

考虑不同库水耦合模式的拱坝振动特性分析

为探讨不同库水模型对拱坝结构动力特性的影响,结合拉西瓦工程实例,分别建立附加质量模型与流固耦合(fluid solid interaction,简称FSI)系统耦合模型进行动力特性分析,并将仿真结果与依据小波阈值-经验模态分解联合滤波的随机子空间(stochastic subspace identification,简称SSI)法辨识结果进行对比。结果表明:两种模型均可反映结构的振动特性,附加质量模型计算结果与辨识结果的频率误差为0.41%~7.55%;FSI系统耦合模型计算结果误差为0.09%~3.19%,且同阶次频率误差均比附加质量模型小,相邻阶次的频率间隔相对稳定,弥补了附加质量模型的模态缺失现象。FSI系统耦合模型在模拟阶数和精度方面都优于附加质量模型,能更全面、准确地反映坝体振动信息,可在拱坝结构动力特性分析中推广应用,亦可作为后续拱坝结构损伤诊断研究的基准有限元模型。     

NON-LINEAR VIBROISOLATION PADS DESIGN,NUMERICAL FEM ANALYSIS AND INTRODUCTORY EXPERIMENTAL INVESTIGATIONS

Design and theoretical and experimental investigation of vibroisolation pads with non-linear static and dynamic responses is the objective of the paper. The analytical investigations are based on non-linear finite element analysis where the load–deflection response is traced against the shape and material properties of the analysed model of the vibroisolation pad. A new model of vibroisolation pad of antisymmetrical type was designed and analysed by the finite element method based on the second-order theory (large displacements and strains) with the assumption of material's non-linearities (Mooney–Rivlin model). Stability loss phenomenon was used in the design of the vibroisolators, and it was proved that it would be possible to design a model of vibroisolator in the form of a continuous pad with non-linear static and dynamic response, typical to vibroisolation purposes. The materials used for the vibroisolator are those of rubber, elastomers, and similar ones. The results of theoretical investigations were examined experimentally. A series of models made of soft rubber were designed for the test purposes. The experimental investigations of the vibroisolation models, under static and dynamic loads, confirmed the results of the FEM analysis.     

A coupled finite element and meshfree analysis of erosive wear

Erosive wear is a kind of material degradation, which is largely involved in many industries, and caused a series of serious problems and economic loss. Many theoretical models and numerical models have been established to study the erosion phenomena. In this study, a coupled finite element and meshfree model was developed for the simulation and prediction of erosive wear. By utilizing the meshfree technique, the error due to mesh distortion and tangling at impacted area in the finite element analysis could be effectively avoided. The fundamental mechanisms of erosion by solid particle impact were investigated as well. Comparison against the results of analytical erosion models and finite element model are made. It is shown that the predicted results are in agreement with reported results. The present study could be very useful and efficient in studying erosive wear.     

立式捏合机桨叶转矩分析

建立了立式捏合机桨叶传动关系和转矩力学模型，应用ANSYS—CFX仿真软件，进行捏合机桨叶在混合高粘度流体时的受力数值模拟，得出了桨叶在捏合工作状态下，单输入多输出的各轴转矩分配定量结果，为捏合机桨叶和传动系统设计提供理论依据。     

电动汽车动力电池包结构设计分析研究进展

动力电池包是电动汽车的核心模块之一,有严格的安全性和轻量化的要求,必须通过规范的结构分析和优化来实现.简述动力电池包发展现状、总装结构设计要点以及结构设计流程,总结其结构动力学分析和温度场仿真模拟的研究进展,明确指出建立精细化有限元模型、进行温度场模拟的电池包动力学性能分析与结构优化是进一步提高电池包研发水平的重要方向...     

A Coupled Euler-Lagrange Model for More Realistic Simulation of Debris Denting in Rolling Element Bearings

Abstract

The objective of this study is to investigate the effects of the contamination of lubricants on denting in rolling element bearings. A dynamic, explicit finite element model (FEM) is developed to reproduce and analyse the elastic–plastic response of the surfaces when a spherical particle passes through a heavily loaded contact area. To cope with mesh distortion issues due to the high deformation of the debris along the process, a novel Eulerian approach is used to model the particle. A parametric study is conducted with the coupled Euler-Lagrange (CEL) model to determine the influence of the debris size, bearing loading, friction coefficient, material properties, and relative sliding between the surfaces on the indentation features. The FEM results emphasize the major role of the material properties of the three bodies on the dent geometry, pointing out that the softer surface undergoes more severe damage. In the same way, the protection of one of the surfaces by a specific heat treatment such as nitriding leads to more severe damage on the other one. The results exhibit a direct link between the particle and dent sizes. For large particles, a change in the dent geometry is observed when the deformed particle size overcomes the contact width because the particle is no longer enclosed in the contact and is therefore spread more easily. The model reproduces two important aspects of the indentation in rolling element bearings, which are the asymmetry of the dent and the residual stresses distribution, providing interesting prospects for future work on the fatigue failure caused by these defects.     

随机载荷作用下货车车轴的疲劳应力计算

对货车车轴进行了随机载荷下的应力——应变状态模拟计算。在建立C64A型货车动力学计算模型的基础上，考虑轨道不平顺的影响，通过动力学仿真得到了施加在轮对上的随机载荷，将统计分析后的载荷谱作为边界条件，利用ANSYS软件所建立的轮对有限元计算模型，将LZ50车轴材料考虑成弹塑循环非线性本构关系，得到了典型工况下车轴各部位的应力分布情况。     

[动力电池]基于模型的动力电池系统多尺度热安全设计

针对锂离子动力电池系统的热安全问题,从电池材料、电池单体、电池系统三个尺度,提出了基于模型的电池系统热安全设计开发总体思路。总结了电池材料热稳定性、电池单体热失控特性、电池系统热失控蔓延特性等的测试表征方法。探讨了建立电池热失控的化学反应动力学模型、单体热失控温度与压力预测模型、电池模组热失控蔓延模型过程中需要考虑的因素。利用模型进行仿真分析,可以得到影响电池系统热安全性的主要因素,并指导多尺度热安全设计。     

Prediction of wear in dumper truck body by coupling SPH-FEM

Abstract

Abrasive wear is largely involved in many industries processes, and can cause serious problems and economic loss. A number of theoretical models and numerical models have been established to study wear phenomena. However, simulation and prediction of wear at large scale are seldom presented. Sliding abrasive wear of steel plates from interaction with granular material is here studied with numerical simulations. Abrasive wear of unloading of two different dumper body geometries are studied with the smoothed particle hydrodynamics method coupled to the finite element method. These numerical tools are of interest as they can reproduce interaction between solid and granular material. Wear pattern on the dumper bodies obtained from numerical simulation shows a reasonably good correspondence to experimental measurements. An advanced analysis tool that takes into account both the actual material flows, coupled with wear calculation model would be a new tool to design and optimise handling equipment against wear.     

Structural safety assessment of bowstring type RC arch bridges using ambient vibration testing and finite element model calibration

The structural safety evaluation of a bowstring type reinforced concrete (RC) arch bridge was investigated by ambient vibration testing and finite element model calibration in this study. The bridge named as Ali Çetinkaya Bridge in Samsun, Turkey, was selected for this investigation. The bridge constructed in 1937 consists of the seven discrete arches and its total length is approximately 250 m. The bridge damaged by environmental effects and it was closed to the traffic loads. The presented study consists of four main parts: ambient vibration test, initial finite element modeling, finite element model calibration and structural analysis of the calibrated finite element model. The ambient vibration tests were performed using Operational Modal Analysis Method under the wind, human and water flow loads to identify the actual natural dynamic parameters, such as the natural frequencies and mode shapes, modal damping ratios. Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification methods were used to extract the experimental dynamic characteristics. The initial finite element model was developed by including the soil effects in SAP2000 program to obtain the analytical dynamic characteristics. In the initial finite element model, the beam, plane and solid elements were used. After that, the initial finite element model was calibrated according to the ambient vibration test results considering the material properties and boundary sections as variable parameters. The calibrated model assumed to reflect the current state of the bowstring bridge was analyzed under dead, moving, traffic, water and earthquake loads. The maximum displacements, tensile stress, compressive stress and shear stress were attained each case and compared with each other.     

电流输入电动汽车电池等效电路模型的比较

基于电动汽车系统仿真的研究需要,提出两个非线性等效电路电池模型：GNL模型和CR模型。为了评价两个模型的性能,以320单体串联的80 Ah镍氢电池组为研究对象,基于同一组复合脉冲试验数据,应用多元线性回归方法同时辨识Rint模型、Thevenin模型、PNGV模型、GNL模型和CR模型的参数,进而建立各等效电路模型基于MATLAB/Simulink的电流输入仿真模型,使用26.67 A恒流放电和FUDS工况试验数据来验证模型精 度。模型计算结果与试验数据的误差表明,电流输入等效电路模型中,PNGV模型和GNL模型更适用于电动汽车仿真,GNL模型具有更好的精度。     

Trajectory analyses of uncontrolled circular parachutes in random spatial wind fields

The present paper explores the trajectories of two uncontrolled circular parachute models which differ in size and mass in random spatial wind fields. The wind velocity components were generated through three-dimensional inverse fast Fourier transforms; and the correlations of the simulation data compared with the theoretical functions to confirm the accuracy of the wind model. The parachute systems are modelled as six-degrees-of-freedom rigid bodies, on which the aerodynamic forces and moments are applied. The dynamics model was validated before being used to study the drop trajectories of the parachute systems in spatial wind fields. Analyzing the drop trajectories and the impact point dispersion characteristics of the two parachute systems, the paper shows that the smaller one oscillates at a higher frequency and is affected more strongly by the wind. While descending at low altitude, there could be resonance between the dynamics of the larger parachute model and the wind turbulence. Moreover, it is found that the use of simplified vertical wind profiles, which include only the variation of the wind velocity against the altitude, may cause significant error in the simulation results.

     

Finite element analysis of a subtrochanteric fractured femur with dynamic hip screw, dynamic condylar screw, and proximal femur nail implants--a comparative study

Selection of the correct type of implant for fracture fixation has become a very interesting problem in the orthopaedic community. The present work studies the biomechanical behaviour of the femur with three different implant configurations for simple transverse subtrochanteric fracture and the intact femur using finite element analysis. The implants considered in this study are as follows: dynamic hip screw (DHS), dynamic condylar screw (DCS), and proximal femur nail (PFN). The modelling software Unigraphics and finite element simulation software ANSYS are used for the present analysis. The three implants are compared for deflection, stress, and strains. The simulation also includes modelling of the cortical defect near the fracture. An estimation of the critical depth of the cortical defect based on the von Mises stress is obtained using this study on the DHS implant. The displacement and principal stress on the proximal femur have been compared for all the implant models. The stresses on the cortical screws for DCS and DHS implants have also been compared. The result shows that the DHS and DCS implants behave in a similar way to the intact femur compared with the PFN implant.     

Failure mechanism for metal cylinder under explosive loading

This paper presents the numerical study of dynamic fracture for metal cylinder under internal explosive loading. Also, the effects of fracture models and groove designs on fracture behavior are investigated. For the dynamic hardening behavior, the Lim-Huh model including the thermal softening effect is adopted [1, 2]. Also, the Lou-Huh fracture model considering the strain rate dependency is used for fracture prediction [3]. The tensile fracture occurs first at the outer surface, and the shear fracture is observed near the inner surface. In addition, finite element analyses are performed to study the effect of various groove designs on dynamic fracture; single U-groove and V-groove at the outer surface. The tensile and shear fracture lines are predicted near the groove tip and inner surface, respectively. It is concluded that the stress triaxiality parameter is one of the critical factors in the dynamic fracture prediction of the metal cylinder.

     

单晶硅力学性能及尺寸效应的离散元模拟

通过建立紧密连接且随机分布在指定区域内的圆盘形颗粒离散单元的力学模型来研究单晶硅的力学性能,并采用不同尺寸的离散元模型研究力学性能尺寸效应。结果表明:泊松比、单轴抗压强度、弹性模量以及断裂韧性的尺寸效应不明显,弯曲强度则随着模型尺寸的增大而减小。建立了连续体经典断裂力学有限宽板条单边直裂纹的离散元力学模型,改变初始裂纹长度进行模拟得到的结果与单边切口梁模拟结果及文献报道的试验值一致。