AISI-1045、1025钢的冲裁模拟

介绍了负间隙冲裁的基本原理,对不同材料刚塑性力学模型进行了分类,采用塑性分析软件DEFORM模拟金属塑性无飞边冲裁过程,基于刚塑性有限元理论建立了负间隙冲裁的几何模型.采用与实验条件完全一致的模拟参数,对金属塑性变形区域的平均应力、损伤、等效应力、等效应变等进行了仿真,得到冲裁变形区域的应力场和应变场,对等值线云图进行了一定的分析.结果表明,负间隙冲裁推迟了裂纹的发生,冲裁质量较好.     

精冲工艺的大变形弹塑性有限元分析

精冲成形是一个复杂的力学过程,涉及弹性变形、塑性变形、损伤软化和韧性断裂等现象.本文使用DEFORM 2D软件对AISI-1035钢精冲工艺进行了弹塑性大变形有限元数值模拟,将McClintock断裂准则应用于精冲韧性断裂的预测中,预测了材料变形过程中静水应力、等效应力和等效应变的分布以及发展趋势、精冲最后阶段微裂纹产生发展和最终断裂.     

考虑材料韧性损伤的中厚板半冲孔成形过程分析

为研究半冲孔成形过程中韧性损伤的演化以及部分工艺参数对成形质量的影响规律,本文在ABAQUS有限元模拟软件中建立了半冲孔轴对称有限元模型,并通过VUMAT用户子程序引入GTN(Gurson-Tvergaard-Needle-man)损伤模型,结合同时考虑空穴形状与体积变化影响的韧性断裂准则,进行弹塑性大变形有限元分析.基于该有限元模犁,预测了半冲孔工艺中静水压力、等效应力、等效应变、应力三轴度以及损伤断裂的产生和发展趋势,分析了反顶力、压边力和冲裁间隙对零件的影响规律,并与实验结果进行对比分析,验证了数值模拟的准确性.     

韧性断裂准则及损伤模型在冲裁有限元模拟中的应用研究

在冲裁有限元模拟中,韧性断裂准则的选择会对冲裁件断面质量与尺寸精度产生很大影响。为了获得符合实际的模拟结果,进而优化冲裁工艺,重点研究了一些常用的韧性断裂判定依据,并从物理学角度阐述了韧性断裂机制。基于试验的韧性断裂准则,考虑了变形历史中的应力应变关系,使用由反求法确定的临界值来判定韧性断裂的发生与否。基于连续损伤力学建立的损伤模型,考虑了变形过程中损伤累积对材料本构关系的影响,能够更准确地描述断裂过程。此外,还分析了冲裁有限元模拟中的关键技术,如采用任意拉格朗日欧拉方法来解决网格畸变问题,使用单元分裂、单元分离与单元删除等技术来处理裂纹的萌发与扩展。探讨了目前韧性断裂模拟中存在问题以及未来发展方向。     

精密冲裁成形仿真技术研究进展

精密冲裁是在普通冲裁基础上发展起来的一种先进的金属精密塑性成形工艺,是一个局部剧烈塑性大变形的过程.材料在狭小的凸凹模间隙附近形成塑性剪切带,发生剧烈的剪切流动,使成形过程的数值模拟存在许多难点.本文从延性损伤、韧性断裂准则及裂纹萌生与扩展仿真3个方面回顾了相关技术在精密冲裁成形过程数值模拟中的研究进展.     

精冲压边与间隙的有限元模拟优化研究

运用DEFORM2D软件对板料精冲过程中压边与间隙进行了数值模拟分析。将NormalC＆．L断裂准则应用于预测精冲韧性断裂,分析了不同压边力、压边方式、反顶力以及冲裁间隙对材料涡流流动特性、冲裁断面圆角和撕裂带的影响;根据模拟结果提出了新的工艺建议。     

AISI-1035钢精冲成形与断裂的数值模拟

使用DEFORM2D软件对AISI-1035钢的落料、冲孔精冲工艺进行了弹塑性大变形有限元数值模拟,将McClintock断裂准则应用于精冲韧性断裂的预测中,预测了材料变形过程中静水应力、等效应力和等效应变的分布以及发展趋势、精冲最后阶段微裂纹产生发展和最终断裂。     

冲裁间隙对多层薄铜板成形的影响

以单层0.3 mm厚的薄铜板叠6层进行冲裁,研究冲裁间隙对多层薄铜板成形的影响。对多层薄铜板在冲裁成形中的受力与应力状态进行分析,利用ABAQUS软件对多层薄铜板在不同冲裁间隙下的冲裁质量进行有限元仿真。研究表明:冲裁初期最大等效应力出现在凸凹模刃口处,导致最上层与最下层薄铜板先行断裂,中间层薄铜板受相邻层挤压,最大等效应力出现在软质凸凹模刃口处,最后出现在中间层薄铜板缩紧截面内;随着冲裁间隙的增加,各层薄铜板拉伸变形明显,导致冲孔直径增大、毛刺高度增加。前3层薄铜板的冲孔直径变化较为稳定,与凸模直径接近;后3层薄铜板的冲孔直径变化幅度较大,与各自凹模直径接近。最后,通过试验验证,冲裁精度符合国标要求,在实际生产过程中选择合理的、尽可能小的冲裁间隙能提高冲裁件的冲裁质量。     

高强度钢板热冲裁成形工艺研究

冲裁间隙、凸凹模圆角半径对高强度钢板热冲裁模具寿命有很大的影响。运用有限元模拟研究了不同参数对等效应力应变的影响。结果表明,随着间隙增大,最大等效应力和应变都逐渐减小;随圆角半径增大,最大等效应力和应变呈现波动的规律。该研究结果可以进一步向实际生产中推广。     

负间隙精密冲裁最佳负间隙的合理取值

基于相似理论基础建立了刚塑性有限元仿真几何模型,采用金属塑性有限元分析软件DEFORM-2D对AISI-1045钢进行了不同负间隙冲裁的模拟与分析,获得了不同负间隙值与塌角、剪切带、冲裁力的关系曲线.并依据模拟的结果对3.8 mm厚的45钢进行了不同负间隙值的冲裁实验,获得了剪口质量好且无毛刺的冲裁件,总结出负间隙值c取-0.1～-0.15 mm时可以实现无毛刺精密冲裁.     

Analytical model to determine the critical feed per edge for ductile-brittle transition in milling process of brittle materials

Brittle materials like glass are considered difficult-to-machine because of their high tendency towards brittle fracture during machining. The technological challenge in machining such brittle materials is to achieve material removal by plastic deformation rather than characteristic brittle fracture. In ductile mode machining, the material is removed predominantly by plastic deformation and any cracks produced due to possible fracture in the cutting zone are prevented from extending into the machined surface. This is achieved by selecting an appropriate cutting tool and suitable machining parameters. In ductile machining by milling process, fracture induced cracks are diverted away from final machined surface by selecting a suitable feed per edge less than a critical threshold value. Hence determination of critical feed per edge is of paramount importance to achieve ductile mode machining by milling process. This paper presents an analytical model based on fracture mechanics principles to predict the critical feed per edge in milling process of glass. The size and orientation of cracks originating from brittle fracture during machining have been quantified by using indentation test results and the critical value of feed per edge has been determined analytically as a function of intrinsic materials properties governing brittle fracture and plastic deformation. Furthermore, an equivalent tool included angle has been suggested for machining operation as against the indenter included angle to correlate the indentation and machining test results with improved degree of accuracy. Experimental results validated the proposed model fairly accurately. It has been established that if the longest cracks oriented in radial direction to the cutting edge trajectory are prevented from reaching the final machined surface by selecting a feed per edge less than or equal to a critical value, a crack-free machined surface can be achieved.     

7075铝合金的变化型临界损伤因子(英文)

韧性断裂作为一种主要的失效形式制约了成形工艺开发。Cockcroft-Latham损伤准则适用于多数合金韧性断裂失效的数值计算。对于应变软化型7075铝合金,确立临界损伤因子并揭示其与变形条件间的内在联系具有重要意义。通过压缩试验与数值模拟相互佐证的途径获得了7075铝合金临界损伤因子及其分布规律。结果表明:温度一定时,最大累积损伤值随着应变速率的增大而单调减小;7075铝合金的临界损伤因子不是常数,而是为在0.255～0.453范围内变化的变量;可由应变速率和温度为自变量表征临界损伤因子的变化规律。根据临界损伤因子规律分布图,可以精确地预测材料加工中发生断裂的时刻和位置,此外,还可识别出稳健的加工工艺参数区间。     

铝合金板在循环塑性变形下的韧性断裂行为模拟(英文)

基于数值模拟的方法研究在循环塑性变形下铝合金板的力学行为。首先,通过Cockcroft-Latham韧性断裂准则得到材料的断裂极限应力图,并通过实验对成形极限应力图进行验证。数值模拟结果表明:滚边时弯曲中心的应变路径可以认为是平面应变状态;采用绳式滚边方法可以改善在弯曲中心线上的应力集中现象。从滚边断口的扫描电镜照片可以发现,循环塑性变形对铝合金板的韧性断裂行为有影响。     

Investigation on ductile fracture in fine-blanking process by finite element method

In order to continuously analyze the whole fine-blanking process.from the geginning of the operation up to the total rupture of the sheet-metal,without computational divergence, a 3-D rigid visco-plastic finite-element method based on Gurson void model was developed.The void volume fraction was introduced into the finite element method to document the ductile fracture of the sheet-metal.A formulation of variation of the rigid visco-plastic material was presented according to the virtual work theory in which both the effects of equivalent stress and hydrostatic pressure in the deformation process were considered.The crack initiation of the sheet was predicted and the crack propagation was geometrically fulfilled in the simulation by separating the nodes according to the stress state.Furthermore.the influences of different state-variables on the deformation process were also studied.     

Low cyclic fatigue behavior of electron-beam-welded Ti–6Al–4V titanium joint

The low cycle fatigue(LCF) tests were carried out using symmetrical cyclic loading under total strain amplitude control conditions.The present paper is devoted to investigating the cyclic deformation response of Ti–6Al–4V titanium and the electron-beam-welded(EBW) joint in the following aspects,i.e.,cyclic deformation behavior,fatigue life and fatigue fracture behavior.The results show that the softening of the joint is significant at larger strain ranges,while not obvious at smaller strain ranges.The joint shows shorter fatigue life at larger strain ranges and equivalent fatigue life at smaller strain ranges compared with Ti–6Al–4V base metal.A fatigue crack of the joint not only originates at the surface or subsurface,but also at defects in the fusion zone(FZ).The crack propagation zone of Ti–6Al–4V base metal shows ductile fracture mechanism,while the joint shows brittle fracture mechanism.In all the fatigue fracture zones many dimples appear,showing the typical ductile fracture.     

Fracture behaviour and numerical study of resistance spot welded joints in high-strength steel sheet

Cross tension tests of resistance spot welded joints with varying nugget diameter were carried out using 980 MPa high strength steel sheet of 1.6 mm thickness. In proportion, as nugget diameter increased from 3√t to 5√t (where t is thickness), cross tension strength (CTS) increased while fracture morphology simultaneously transferred from interface fracture to full plug fracture. In cases of interface fracture, circumferential crack initiation due to separation of the corona bond arose at an early stage of loading. The crack opening process without propagation was recognized until just before fracture and then the crack propagated to the nugget immediately in a brittle manner around CTS. In full plug fracture, main ductile crack initiation from the notch-like part at the end of sheet separation occurred with the sub-crack initiated at an early stage. The ductile crack propagated toward the HAZ and base material to form full plug fracture. The mode I stress intensity factor was considered as a suitable fracture parameter because the circumferential crack behaved pre-crack for brittle fracture in the nugget region at the final stage. Based on the FE analysis, the mode I stress intensity factor was calculated as 116 MPa √m at CTS as fracture toughness for the nugget. With respect to full plug fracture, ductile crack initiation behaviour from the notch-like part was expressed by concentration of equivalent plastic strain. On the assumption that the ductile crack arose in critical value of equivalent plastic strain, the value was calculated as 0.34 by FE analysis. Reasonable interpretation for interface fracture and full plug fracture in the resistance spot welded joint was proposed due to first crack initiation by stress concentration, brittle fracture by using mode I stress intensity factor, and ductile crack initiation by using equivalent plastic strain.     

延性金属材料损伤变量的实验表征方法研究

基于微观损伤的宏观表征,采用各种实验方法对延性金属塑性变形过程中的宏观损伤变量进行表征。通过预拉伸变形的方法制备了6种不同真应变条件下的拉伸试样,并基于微小材料压缩试验机(MCT-W501)对不同预变形试样的压缩试验结果,分别采用显微硬度、弹性模量、韧性指标和电阻率等指标归一化表征了金属材料的韧性损伤,并就损伤变量的变化规律及所代表的物理含义进行分析讨论。结果表明:综合应用上述各损伤表征量并构造等效损伤曲线,能真实反映与解释延性金属材料的实际损伤过程。