含夹杂坯料镦粗的有限元分析

采用有限元数值模拟方法分析不同镦粗工艺对夹杂物的弥散作用.建立了常用的平砧镦粗、锥形砧镦粗和凹面砧镦粗等3种计算模型,通过对镦粗过程中夹杂物的应力应变集中程度、基体损伤值、夹杂物间距的结果分析,认为锥形砧镦粗工艺最好.     

Φ6 mm–2A10铝合金棒材电磁镦粗变形机理数值仿真研究

目的 针对块体材料在高应变速率成形过程中应力、应变结果等很难获得的情况,通过数值模拟方法揭示其变形机理。方法 将电磁成形技术和镦粗工艺相结合,建立电磁镦粗电磁场–力场数值耦合模型,同时进行相应的工艺试验,通过对比仿真和试验得到的鼓形特征验证模型的准确性,利用数值模型获得电磁镦粗的加载特性,分析电磁镦粗试样内部的应力和应变状态。结果 电磁镦粗试样的数值模拟结果与试验结果的最大径向相对误差为5.1%,平均径向相对误差为2.84%;驱动片上磁压力的峰值在时间上大致位于第1个周期的1/4处,在空间上大致位于驱动片半径的5/8处;冲头的最大冲击速度达13.9 m/s,在该冲击速度下电磁镦粗试样内部的应变速率达7 700 s⁻¹;电磁镦粗试样内部的金属塑性流动不均、不同区域的应力状态差异和绝热温升所导致的应力–应变分布与常规镦粗的类似。结论 证明了所建立的电磁镦粗电磁场–力场数值耦合模型的准确性和电磁镦粗工艺的可行性。     

轿车左转向节锻造工艺的模拟研究

针对轿车左转向节是带细杆的叉形件,同时兼有叉类、盘类和杆类零件的外形特点,分析其成形的工艺特点,进行工艺计算,确定工艺方案为头部镦粗—杆部拔长—预锻—终锻.利用有限元软件对成形过程进行模拟,得到飞边均匀的终锻成形件,并对模拟得到的应力场、应变场和载荷等信息进行分析.结果表明,各工序变形较为均匀,应力变化正常,没有出现破坏现象;最终锻件完全充满终锻模膛,没有出现缺料、折叠等缺陷,而且飞边均匀.     

基于比容测量对材料三维残余应力及其分布的测试分析

目的 判断比容差法是否可应用于材料内部残余应力分布状态的定量研究,旨在提供一种新的残余应力的测试方法。方法 通过对材料非切应变时的弹性力学进行讨论,推导体积应变,得出残余应力的计算公式。应用比容差法对一种工业纯铝的残余应力状态进行定量测量与表征,并进行钻孔法的定量验证。在此基础上,应用比容差法对纯铝镦粗变形后的三维平均残余应力的分布进行了测量研究。结果 比容差法对纯铝镦粗变形后的体积变化测量,可精确、定量表征材料的残余应力状态,与钻孔法实验结果相比,两者的误差在20%以内;镦粗变形后,残余压应力在坯料中心处取得最大值,且对称于中心沿高度方向逐渐减小,呈对称递减分布。结论 比容差法可用于材料三维残余应力分布的研究,为残余应力分布规律,提供了一种新的有效且精确的测试方法,具有实际应用的价值。     

Ti-6-2-4-2s钛合金热镦粗变形流变应力数学模型

采用最先进的热模拟机Gleeble-2000对Ti-6-2-4-2s钛合金在热镦粗时的流变应力进行了较为全面的研究.主要分析了在各变形温度、应变和应变速率下流变应力的变化情况,采用非线性数学回归的方法,回归出了Ti-6-2-4-2s钛合金在热镦粗变形时的流变应力数学模型.     

制动管一体式法兰接头热镦挤成形工艺仿真分析

目的 针对铁路货车空气管路制动系统中焊接法兰接头连接质量不佳的问题,提出一种制动管一体式法兰接头热镦挤工艺。方法 分析了制动管用AISI321不锈钢的高温变形行为并构建了本构方程,并通过DEFORM–2D软件对制动管件法兰接头热镦挤工艺进行了数值模拟。结果 应力–应变曲线在低应变速率时呈现稳态流动,但在高应变速率下会出现明显的波动。本构方程得到的应力计算值与试验真实值的相关系数为0.986,平均相对误差为6.7%。在热镦挤工艺成形法兰接头过程中,挤压阶段的最大应力位于制动管扩径的圆锥面处;镦粗阶段的最大应力位于法兰接头平面成形处,并最终转移至法兰接头的圆角处。结论 建立的本构方程能够反映AISI 321不锈钢真实应力–真实应变的关系,可用于描述该材料在热镦挤成形工艺中的塑性变形行为。在该制动管一体式法兰接头热镦挤成形过程的镦粗阶段,摩擦因数保持在0.3以下能够有效降低镦粗力。     

镍基合金材料塑性对应力腐蚀裂纹尖端应力应变场影响的研究

为了解材料塑性对高温水环境下核电关键结构材料应力腐蚀裂纹扩展的影响,利用大型非线性有限元软件,对镍基合金中由氧化膜和基体金属构成的应力腐蚀裂纹尖端应力应变场进行了分析,得出了材料屈服应力对应力腐蚀裂纹尖端应力应变场的影响规律.结果表明:在同样的外载条件下,随着材料屈服应力的增大,裂尖基体金属的应力增大而塑性应变减小;而...     

锻造对30CrNi2MoV钢在亚温淬火下组织与性能的影响

30CrNi2MoV钢是一种中碳合金钢,常用于制造高强韧性的大型锻件,广泛用于制造火电、核电等电站装备和大型冶金、矿山和运输装备中的承力和传动结构部件.为提高30CrNi2MoV钢的低温冲击韧性和室温强度,本文采用金相显微镜、扫描电子显微镜、拉伸机和硬度仪等方法对其进行组织观测、断口形貌分析和力学性能测试,研究了不同锻造方式对30CrNi2MoV钢的组织与力学性能的影响.结果表明:经过2次镦粗的30CrNi2MoV钢再经1次镦粗或1次镦粗+1次拔长两种锻造方式后能够有效细化且均匀晶粒,提高晶粒等轴性;与2次镦拔工艺的30CrNi2MoV钢相比,再经过1次镦粗或1次镦粗+1次拔长后其抗拉强度、延伸率和冲击韧性分别由1 043.6 MPa、35.65%和40.33 J提高至1 161.6和1 157.4 MPa、37.80%和36.13%、103和87 J.数据表明,30CrNi2MoV钢经过2次镦拔+1次镦粗工艺后,其组织与力学性能达到最好状态.     

高碳钢冷轧辊拔长过程内 部孔洞演变模拟分析

目的研究拔长锻造过程中,不同的工艺参数对锻件内部孔洞闭合效果的影响。方法采用数值模拟的方法,研究了高碳钢冷轧辊拔锻坯在拔长锻造过程中,下砧宽、压下量、送进量等关键工艺参数对锻坯内部孔洞闭合效果及应力应变分布状态的影响。结果 3个工艺参数都对锻件心部质量及内部应力应变状态有影响。结论有效压实心部疏松缺陷的最佳砧宽为200 mm;采用每次压下量基本一致的工艺方案,即每次压下率保持在17%左右,可保证锻件变形均匀,从而获得较好的心部质量;相对送进量为0.8时,有利于心部孔洞的锻合。     

轴承环毛坯塔锻工艺的编制

详细阐述了轴承环毛坯塔锻成形工艺的编制方法;介绍了塔锻件公差、余量的选取,锻件图的制定、塔锻件、预成形件、镦粗件和坯料形状和尺寸的设计和计算.     

Analysis of laminated crack defect in the upsetting process of heavy disk-shaped forgings

Using nonlinear finite element method, a thermo-mechanical coupled simulation model for the formation mechanism of the laminated crack defect has been established in the upsetting of heavy disk-shaped forgings. Through numerical simulation, the distributions of stress, equivalent strain and strain rate were analysed. Meanwhile the distribution diagram of stress state evolution was obtained, and the uncoordinated deformation, under tri-lateral compression, is determined as the main reason leading to laminated crack defect. To reveal the characteristics of the uncoordinated deformation, the variations of each variable and its gradient in numerical simulation were presented, and a combined prediction model of laminated crack defect were proposed based on degree of deformation and gradient of deformation speed. Subsequently, the morphology and distribution of laminated crack were obtained in the centre of forging using the prediction model. Comparison of calculation results and experimental data indicates that both of them match well. In addition, the effect of friction coefficient on the deformation is also presented. The results show that the decreasing of friction coefficient is an effective measure to restrain the laminated crack defect.     

脆性材料在双向应力下的断裂和失效研究

采用热力学方法对脆性薄片试样成功地进行了双向和单向平面拉伸试验,通过观察和记录试片中心的直通裂纹的扩展和断裂过程,测试出玻璃和陶瓷薄片的断裂韧性在双向和单向拉伸载荷时的差别．结果表明双向拉伸使裂纹阻力增强,平行于裂纹的应力对裂纹扩展有影响．该研究表明,对线弹性材料在双向载荷作用下,传统的应力强度因子准则不适用．裂纹张开的应变依赖性被证实在双向应力的断裂评价中．     

Characterization of interlaminar shear failures of graphite/epoxy composite materials

Research undertaken to develop a more fundamental understanding of interlaminar shear failure in laminated graphite/epoxy composites is described. A test method capable of producing a state of pure interlaminar shear stress within a specified region of a composite test specimen was devised. The test method consisted of the four-point flexural testing of a unique test sample constructed of a coupon of Hercules AS4/3501-6, unidirectional, graphite/epoxy material bonded between two strips of steel using a room-temperature-curing epoxy adhesive. The major advantage of the test method is that the interlaminar shear failure of the composite coupon results from an induced state of pure shear stress, rather than from damage resulting from a complex stress state affecting the region of loading as typically occurs in the case of conventional flexural-type shear tests. The resulting shear failures were characterized with respect to fracture surface appearance, mode of failure, and stress state on the failure plane. A specially designed crack detection device was used to determine the site of fracture initiation and the direction of crack propagation.     

Determination of Fracture Parameters for Multiple Cracks of Laminated Composite Finite Plate

A predictive method for estimation of stress state at zone of crack tip and assessment of remaining component lifetime depend on the stress intensity factor (SIF). This paper discusses the numerical approach for prediction of first ply failure load (F_L), progressive failure load, SIF and critical SIF for multiple cracks configurations of laminated composite finite plate using finite element method (FEM). The Hashin and Chang failure criterion are incorporated in ABAQUS using subroutine approach user defined field variables (USDFLD) for prediction of progressive fracture response of laminated composite finite plate, which is not directly available in the software. A tensile experiment on laminated composite finite plate with stress concentration is performed to validate the numerically predicted subroutine results, shows excellent agreement. The typical results are presented to examine effect of changing the crack tip distance (S), crack offset distance (H), and stacking fiber angle (θ) on F_L, and SIF .     

Semi-analytical method of wedge-shaped interface transition layer model in laminated composites

The wedge-shaped interface transition layer model is proposed for determining the crack growing directions in laminated composites. The Navier equations are given with the material parameters varying with the angle in the polar coordinate system. The singularity of the order of −1/2 is proved. An effective solver of the ordinary differential equations is adopted, and the continuous eigenfunctions of the stress, strain and displacement fields near the crack tip are obtained. The crack growing directions can be determined rapidly and accurately based on the obtained results and the relevant fracture criterion. Therefore, a highly effective approach is provided for solving the complicated problem of crack growing directions in the laminated composites.     

Complex variable method for problems of a laminate composed of multiple isotropic layers

A new method of the analysis of a plate composed of thin layers of isotropic linear elastic material is developed. A general solution for displacement, resultant stress and resultant moment fields is obtained by using the complex function theory. It is proved that the complete solutions of the laminated plate subjected to tractions prescribed on its boundary can be obtained from the sum of solutions for uncoupled plates. Particular attention is devoted to the crack tip field and energy release rate for the laminated plate. A closed form solution for singular fields near the crack tip and the relation between the J-integral and the intensity factors are derived through the complex potential formula. Complete forms of the complex potentials for a crack in an infinite laminate as well as for the singularities such as a point force, a point moment and a dislocation are also obtained. This revised version was published online in August 2006 with corrections to the Cover Date.     

用光塑性方法求解锻(轧)件应变场的初步研究

本文建立了光塑性方法模拟热锻 (轧) 件的相似关系,研究了圆柱镦粗和轴楔横轧时的三维应变场。     

A hybrid finite element analysis of interface cracks

A versatile hybrid finite element scheme consisting of special crack-tip elements and crack face contact elements is developed to analyse a partially closed interface crack between two dissimilar anisotropic elastic materials. The crack-tip element incorporates higher-order asymptotic solutions for an interfacial crack tip. These solutions are obtained from complex variable methods in Stroh formalism. For a closed interfacial crack tip, a generalized contact model in which the crack-tip oscillation is eliminated is adopted in the calculation. The hybrid finite element modelling allows the stress singularity at an open and closed crack tip to be accurately treated. The accuracy and convergence of the developed scheme are tested with respect to the known interface crack solutions. Utilizing this numerical scheme, the stress intensity factors and contact zone are calculated for a finite interface crack between a laminated composite material.     

轴对称件扭压成形的粘塑性有限元分析

运用体积微可压缩法的三维刚粘塑性有限元方法.对轴对称体的扭压成形变形规律进行了模拟分析.结果表明:与一般镦粗成形相比,扭压成形具有可促使变形均匀、增加变形量等优点.     

Some engineering property comparisons for 7050 and AZ 74.61 die forgings

A comparison of some of the engineering properties of 7050-T736 and AZ 74.61 die forgings is made. The properties investigated were strength, fracture toughness, stress corrosion resistance and fatigue life and crack propagation resistance. Some of the properties of these alloys are also compared with those of 7079 and DTD 5024 die forgings. It is concluded that 7050 possessed a superior combination of properties. However, the susceptibility of 7050 to general corrosion warrants extra consideration of corrosion protection systems applied to this alloy.