Finite element modeling of erosive wear

Material damage caused by the attack of particles entrained in a fluid system impacting a surface at high speed is called ‘Erosion’. Erosion is a phenomenon that takes place in several engineering applications. It also can be used in several manufacturing process such as abrasive waterjet machining. Erosion is a complex process dependent on particle speed, size, angle of attack as well as the behavior of the eroded material. Extensive experimental results have been reported in the literature on the erosion of different materials. Simulating the erosion process through finite element enables the prediction of erosion behavior of materials under different conditions, which will substitute the need of experimentation, and will enable the identification of constants required for existing analytical models.In this paper, an elasto-plastic finite element (FE) model is presented to simulate the erosion process in 3D configuration. The FE model takes into account numerical and material damping, thermal elastic–plastic material behavior and the effect of multiple particle impacts as well as material removal. The workpiece material modeled was Ti–6Al–4V. The effects of strain hardening, strain rate and temperature were considered in the non-linear material model. Comparison against results reported in literature and erosion models by Finnie, Bitter and Hashish are made. It is shown that the predicted results are in agreement with published results obtained experimentally and from analytical erosion models.     

碳纤维复合材料的磨削热分配比仿真研究

碳纤维增强树脂基复合材料是一种比模量高、比强度高、比刚度高的复合材料,在航空航天领域具有较大的应用前景。磨削由碳纤维和树脂组成的碳纤维增强树脂复合材料时,当磨削温度超过树脂的玻璃化转变温度就会产生树脂烧毁等缺陷。为了研究此问题,利用碳纤维复合材料-康铜丝半人工热电偶在线测量磨削过程中的温度,通过试验与仿真相结合的方法计算出传入工件的热分配比为2.0%～3.5%。      

Finite element modeling of creep deformation in cellular metals

The creep of reticulated metallic foams is studied through the finite element method using three-dimensional, periodic unit cells with four different architectures characterized by struts which deform primarily by: (i) simple bending, (ii) compression, (iii) a combination of simple bending and compression and (iv) double bending (for Kelvin space-filling tetrakaidecahedra). The creep behavior of each of these models is examined with respect to temperature, stress and foam relative density. Calculated creep rates for both bending and compression models are below those predicted from simplified analytical models and bracket those of the combination model. The simple and double bending models predict nearly identical strain rates despite very different geometries, because in both cases the deflection rates of the fastest deforming struts are similar. Both analytical and numerical predictions are compared to published creep data for metallic foams.     

Finite element modeling of ultrasonic surface rolling process

Ultrasonic surface rolling (USRP) is a newly developed process in which ultrasonic vibration and static force are applied on work-piece surface through the USRP operator to generate a nanostructured surface layer with mechanical behaviors highly improved. Compared with other surface severe plastic deformation (S²PD) methods, it can realize mechanized machining and be directly used for preparing final product. Notwithstanding the excellent performance of USRP, elaborate relation between process parameters and surface layer characteristics is still inadequacy due to inconvenient and costly experimental evaluation. Therefore, in this paper a three-dimensional finite element model (FEM) has been developed to predict the treatment conditions that lead to surface nanocrystallization. Simulated results of surface deformation, stress and strain are investigated to assess the formation of nanostructured layer. The numerical results from the FEM corresponds well with the values measured experimentally, indicating that this dynamic explicit FEM is a useful tool to predict the processing effects and to relate the treating parameters with the surface layer in terms of the size of nanostructured layer, residual stress and work hardening.     

碾压强化有限元建模及分析研究

碾压是强化金属表层的一种重要且很有发展潜力的强化方法,工件表层经碾压变形强化后会表层留有应力,能提高表层硬度和强度,同时还能改善工件表面粗糙度.对装备构件进行碾压模拟,模拟结果显示工件表层经碾压后产生较高应力且内部状态无明显变化,强化效果明显.接着改变下压量进行模拟,发现在一定范围内,随下压量增大,碾压强化效果愈好.     

Finite element modeling of segmental chip formation in high-speed orthogonal cutting

An explicit, Lagrangian, elastic-plastic, finite element code has been modified to accommodate chip separation, segmentation, and interaction in modeling of continuous and segmented chip formation in highspeed orthogonal metal cutting process. A fracture algorithm has been implemented that simulates the separation of the chip from the workpiece and the simultaneous breakage of the chip into multiple segments. The path of chip separation and breakage is not assigned in advance but rather is controlled by the state of stress and strain induced by tool penetration. A special contact algorithm has been developed that automatically updates newly created surfaces as a result of chip separation and breakage and flags them as contact surfaces. This allows for simulation of contact between tool and newly created surfaces as well as contact between simulated chip segments. The work material is modeled as elastic/perfectly plastic, and the entire cutting process from initial tool workpiece contact to final separation of chip from workpiece is simulated. In this paper, the results of the numerical simulation of continuous and segmented chip formation in orthogonal metal cutting of material are presented in the form of chip geometry, stress, and strain contours in the critical regions.     

SiCp/Al复合材料磨削加工去除机理的有限元分析

本文建立了SiCp/Al复合材料的二维实体模型,基于压痕断裂力学的方法,研究了压痕深度的变化对SiCp/Al复合材料磨削加工去除机理的影响。结果表明:随着压痕深度的增加,压头下方SiC颗粒的第一主应力逐渐变大,Al基体的von Mises等效应力也逐渐变大。当压痕深度大于等于0.15μm时,压头下方会形成塑形变形区;压痕深度大于等于0.292μm时,SiC颗粒会由于拉应力的作用而产生径向裂纹;当压痕深度超过0.34μm时,Al基体由于局部被压溃而影响SiCp/Al复合材料延性去除机理。     

Finite element analysis for grinding of wire-sawn silicon wafers: a designed experiment

Silicon is the primary semiconductor material used to fabricate microchips. The quality of microchips depends directly on the quality of starting silicon wafers. A series of processes are required to manufacture high quality silicon wafers. Surface grinding is one of the processes used to flatten the wire-sawn wafers. A major issue in grinding of wire-sawn wafers is the reduction and elimination of wire-sawing induced waviness. This paper presents the results of a finite element analysis for grinding of wire-sawn silicon wafers. In this investigation, a four-factor two-level full factorial design is employed to reveal the main effects as well as the interaction effects of four factors (wafer thickness, waviness wavelength, waviness height and grinding force) on effectiveness of waviness reduction. The implications of this study to manufacturing are also discussed.     

基于拉格朗日公式的冷轧有限元分析

根据材料形变过程,在网格移动和空间形变中,金属形变过程的有限元分析可以用校正的拉格朗日公式准确的表达,然而,一些金属的形变过程有稳定变形的特性,如挤压、拉深和轧制,需要用合并欧拉-拉格朗日公式进行分析.文中分别用这两种公式对棒材的冷轧过程进行了分析,分别讨论用这两种公式所得的数据结果,并与实际棒材冷轧试验结果的数据进行了比较.挤压弯曲载荷的分析结果显示,用合并欧拉-拉格朗日有限元公式能够更准确的预测金属的形变过程.     

Sm-Fe系薄膜悬臂板磁致伸缩行为的有限元模拟分析

以离子束溅射沉积(IBSD)法制备的Sm-Fe系超磁致伸缩薄膜悬臂板为研究对象,通过ANSYS有限元分析法,对超磁致伸缩薄膜/盖玻片衬底悬臂板自由端挠度值的大小进行模拟计算,并模拟Sm-Fe薄膜、Sm-Fe/Fe复合膜的内部磁化状态.结果表明:在薄膜与衬底厚度比较小的情况下,悬臂板端点挠度值随薄膜厚度的增加而线性增加,且与衬底厚度近似成二次抛物线关系,有限元分析结果与实测情况吻合较好;Sm-Fe单层膜内部磁力线分布较均匀;在Sm-Fe/Fe复合膜中,由于Fe膜的负磁场效应,使Sm-Fe膜内的磁力线分布出现不均匀的现象,且磁感应强度比Sm-Fe单层膜小.     

Finite element modeling of the uniaxial compression behavior of carbon microballoons

Recent interest in syntactic foams has led to a multitude of new research efforts into these materials and their constituents. Our contribution includes a uniaxial compression technique to obtain mechanical properties of single microballoons (MBs). We have used finite element modeling, with ANSYS 8.0, to simulate the uniaxial compression of individual carbon microballoons (CMBs), obtaining deformed shapes and stress states under experimentally determined CMB failure conditions. Previously published data on CMBs, namely failure load, displacement at failure, wall thickness and Young’s modulus, were used for linear elastic analysis. Boundary conditions were chosen to achieve axisymmetry and compression was displacement controlled. When modeling the average conditions for three CMB populations, predicted maximum first principal stresses at failure ranged from 637 to 835 MPa. Compression of CMBs with various radius-to-thickness ratios (R/t) was also simulated and a transition of failure mode, from fracture in flexure to buckling, was observed at critical R/t values. Given that real CMBs have imperfections, two common experimentally observed defects, non-concentricity of the internal cavity and through-thickness holes, have also been considered. The two flaws were modeled in different locations relative to the location of load application and their effects on the stress state in CMBs were evaluated. Through-thickness holes in CMB walls were more detrimental to the compressive properties of the CMBs, despite the fact that thin regions in a CMB’s wall could cause buckling in a situation where the CMB’s average radius and thickness would otherwise predict failure to occur in flexure.     

联轴器螺栓紧固件的有限元建模仿真和试验分析

研究了联轴器螺栓紧固件在复杂载荷作用下的应力状态,对分析联轴器螺纹螺栓的失效具有重要价值。采用精确几何形状螺纹建模方法对联轴器的螺纹进行了建模,并将其嵌入ANSYS软件对螺纹螺栓的预紧力、联轴器受载后的等效应力和联轴器螺纹螺栓的结构应力进行了仿真分析,并进行了试验对比研究。结果表明：所建立的模型能很好地仿真螺栓自松弛现象,可以认为螺栓松弛乃至结构的疲劳强度对扭转载荷的大小更敏感,能为深入研究联轴器螺纹螺栓的失效提供参考。     

Ni-Cr/陶瓷连接界面残余应力有限元分析

采用有限元法分析Ni-Cr合金与陶瓷连接冷却过程中界面残余应力形成的大小和分布特征.结果表明,Ni-Cr合金与陶瓷存在较大的线膨胀系数差,在界面间会产生较大的残余应力,并因为边缘效应在拐角处产生应力集中,残余应力最大值出现在Ni-Cr/陶瓷界面的近瓷侧,可达131 MPa.Ni-Cr/陶瓷界面残余应力σz较大值出现在Ni-Cr/陶瓷界面近瓷侧的狭小区域内,剪应力τzx的较大值出现在金/瓷界面,向合金和陶瓷两侧递减.采用钛中间层缓解了Ni-Cr/陶瓷界面残余应力,使残余应力向钛中间层转移,残余应力σz较大值出现在钛中间层,剪应力τzx最大值出现在Ni-Cr/Ti界面;随着钛中间层厚度增加,界面残余应力σz增大,剪应力τzx变化不大.     

Finite element modeling of fixture–workpiece contacts: single contact modeling and experimental verification

Knowledge of workpiece elastic deformation and reaction forces are essential for machining surface error prediction and stability analysis of the fixture–workpiece system. A finite element (FE) model of the fixture–workpiece system is well-suited for predicting workpiece elastic deformation and reaction forces as it can easily account for all sources of compliance in the system. However, the reaction forces and workpiece elastic deformations predicted by the FE model are known to be very sensitive to the boundary conditions used to model the fixture–workpiece contact interface. In this paper, the effects of different FE boundary conditions on the deformation and reaction force predictions for a single fixture–workpiece contact are analyzed. Specifically, frictional contact elements, and nodal force and displacement boundary conditions applied to spherical–planar and planar–planar locator and clamp contact geometries are considered. The effects of workpiece compliance on the prediction accuracy are also evaluated. Based on this study, specific guidelines for FE modeling of locator–workpiece/clamp–workpiece contacts are developed and verified through experiments.     

连铸大方坯自然热收缩行为的有限元模拟分析

结合国内某钢厂360 mm×450 mm大方坯连铸的实际生产工艺,利用商用有限元软件MSC.MARC对连铸大方坯自然热收缩行为进行三维热力耦合模拟。本次有限元模拟采用热弹塑性模型,研究不同拉速下铸坯温度场与凝固收缩规律。研究结果表明：拉速越高,温度变化越慢,铸坯总收缩量越小;拉速越小,温度变化越快,铸坯总收缩量越大;铸坯在宽度方向和厚度方向表现出不同规律的自然热收缩行为。     

Predictive modeling of surface roughness in grinding

The surface roughness is a variable often used to describe the quality of ground surfaces as well as to evaluate the competitiveness of the overall grinding system. This paper presents the prediction of the arithmetic mean surface roughness based on a probabilistic undeformed chip thickness model. The model expresses the ground finish as a function of the wheel microstructure, the process kinematic conditions, and the material properties. The analysis includes a geometrical analysis of the grooves left on the surface by ideal conic grains. The material properties and the wheel microstructure are considered in the surface roughness prediction through the chip thickness model. A simple expression that relates the surface roughness with the chip thickness was found, which was verified using experimental data from cylindrical grinding.     

Finite element modeling of power spinning of thin-walled shell with hoop inner rib

A 3D elasto-plastic finite element（FE） model of power spinning of thin-walled aluminum alloy shell with hoop inner rib was established under software ABAQUS. Key technologies were dealt with reasonably. The reliability of the FE model was verified theoretically and experimentally. The forming process was simulated and studied. The distribution of the thickness and stress, and the variations of spinning force were obtained. The workpiece springback was analyzed with ABAQUS/Standard. The results show that the FE model considering elastic deformation can not only be used to analyze the workpiece springback in the complex spinning process, but also serve as a significant guide to study the local deformation mechanism and choose the reasonable parameters.     

Finite element modeling and optimization of superplastic forming using variable strain rate approach

Detailed finite element simulations were carried out to model and optimize the superplastic blow forming process using a microstructure-based constitutive model and a multiscale deformation stability criterion that accounts for both geometrical instabilities and microstructural features. Optimum strain rate forming paths were derived from the multiscale stability analysis and used to develop a variable strain rate forming control scheme. It is shown that the proposed optimization approach captures the characteristics of deformation and failure during superplastic forming and is capable of significantly reducing the forming time without compromising the uniformity of deformation. In addition, the effects of grain evolution and cavitation on the superplastic forming process were investigated, and the results clearly highlight the importance of accounting for these features to prevent premature failure. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

Finite element modeling of friction stir welding—thermal and thermomechanical analysis

Friction stir welding (FSW) is a relatively new welding process that may have significant advantages compared to the fusion processes as follow: joining of conventionally non-fusion weldable alloys, reduced distortion and improved mechanical properties of weldable alloys joints due to the pure solid-state joining of metals. In this paper, a three-dimensional model based on finite element analysis is used to study the thermal history and thermomechanical process in the butt-welding of aluminum alloy 6061-T6. The model incorporates the mechanical reaction of the tool and thermomechanical process of the welded material. The heat source incorporated in the model involves the friction between the material and the probe and the shoulder. In order to provide a quantitative framework for understanding the dynamics of the FSW thermomechanical process, the thermal history and the evolution of longitudinal, lateral, and through-thickness stress in the friction stirred weld are simulated numerically. The X-ray diffraction (XRD) technique is used to measure the residual stress of the welded plate, and the measured results are used to validate the efficiency of the proposed model. The relationship between the calculated residual stresses of the weld and the process parameters such as tool traverse speed is presented. It is anticipated that the model can be extended to optimize the FSW process in order to minimize the residual stress of the weld.     

钢轨焊接接头的静弯试验有限元建模及受力分析

钢轨焊接接头的静弯试验是评定焊接工艺和接头性能的重要方法。基于静弯试验系统的结构特征,建立了包含双接触对的钢轨焊接接头静弯接触有限元模型,分析了单元尺寸和接触刚度等接触对参数对计算时间及计算结果精度的影响,优化确定出合适的单元尺寸和接触对模型参数,并通过对比已有文献数据,证明了模型的适用性。然后根据钢轨闪光焊接头的静弯检验标准,对钢轨轨头受压(正弯)和轨头受拉(反弯)时的应力分布进行了模拟计算,获得了钢轨静弯时的应力分布特征、最大等效应力及其位置。通过对计算结果进行分析,对钢轨窄间隙电弧焊接头的强度、残余应力等提出了控制要求,可为后续钢轨窄间隙电弧焊接的工艺改进、接头质量控制和性能改善提供有价值的参考。