共查询到19条相似文献,搜索用时 953 毫秒
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为了精确计算粘性介质压力成形过程中粘性介质/板材界面粘性附着作用,分析了压力、剪切速率、温度等因素对粘着应力的影响,提出了粘着应力计算模型.将提出的粘着应力模型引入有限元分析软件中,对粘着应力拉伸过程进行了数值模拟,并将计算结果与试验结果进行对比,验证提出模型的可靠性.结果表明:采用建立的模型预测的试样伸长量及应变分布与实验测量结果具有较好的一致性.说明建立的粘着应力模型可以准确反映板材/粘性介质界面粘着应力大小,为精确模拟粘性介质压力成形过程提供了模型. 相似文献
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控制厚度分布的正反向超塑胀形的有限元分析 总被引:4,自引:1,他引:4
为研究正反向超塑胀形工艺对厚度分布的影响,应用商业有限元软件MARC对带有凹槽的深盒形7475合金零件正反向超塑胀形过程进行了有限元模拟,并对不同工艺条件下成形后零件的壁厚分布结果进行了分析.研究表明:正反向超塑胀形工艺是控制成形零件壁厚的有效途径,通过优化压力-时间曲线和反向胀形模具形状,明显改善了零件的厚度分布,达到了零件的设计要求;后处理直观地显示了该零件正反向超塑胀形的全过程,为成形提供了合理的方案;零件变形各阶段的应变速率控制在7475合金的应变速率范围内,证明压力-时间曲线设计合理. 相似文献
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This paper describes the joint properties and their improvement in thin walled circular pipe friction welded joint for an AISI 310S austenitic stainless steel. Pipes were welded with the combination of the same thickness and outer diameter by a continuous drive friction welding machine that has an electromagnetic clutch. Then, when the clutch was released, the relative speed between both specimens instantly decreased to zero. When the joint with a pipe thickness of 1.50 mm was made at a friction pressure of 120 MPa, the joining could be successfully achieved and that had 100% efficiency with the base metal fracture. However, the joining became difficult with decreasing pipe thickness, and it was not successful at a pipe thickness of 0.50 mm. On the other hand, when the joint with a pipe thickness of 0.50 mm was made at a friction pressure of 30 MPa, the joining could be successfully achieved, although that did not have 100% efficiency. Then, when the joint was made under a friction time of 0.6 s, i.e. the friction torque reached just after the initial peak, and a forge pressure of 60 MPa, it had 100% efficiency with the base metal fracture. However, when that was made with high forge pressure such as 120 MPa, the joining could not be achieved because the adjacent region of the weld interface had heavy buckling. To obtain the successful joining and 100% joint efficiency with the base metal fracture for the thin walled circular pipe, the joint should be made with opportune friction welding condition as follows: low friction pressure, a friction time of just after the initial peak of the friction torque, and a forge pressure of double value of a friction pressure. 相似文献
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Numerical study on the deformation behaviors of the flexible die forming by using viscoplastic pressure-carrying medium 总被引:1,自引:0,他引:1
The flexible die forming (FDF) of sheet metal with the aid of viscoplastic pressure-carrying medium (VPCM) is one of the advanced forming technologies for forming complex sheet metal components with large plastic deformation. The technology has been used in industries by employing different VPCMs, the epistemological understanding of the deformation and process behaviors of this process, however, has not yet been fully addressed. In this paper, numerical study is conducted to look into the deformation behaviors of this process by explicit 3D-FE simulation under the ABAQUS platform, in which the counter pressure variations of VPCM is applied via user subroutine VDLOAD and the ductile fracture criterion is implemented by using VUMAT. Three case study parts, viz., barrel, conic and parabolic parts with large Limit Drawing Ratio (LDR) are studied. The comparison between the conventional deep drawing (CDD) and VPCM-based FDF is conducted in terms of wall-thickness reduction, hydrostatic pressure, principal stress distribution and damage factor. The uniqueness and the deformation behaviors of the VPCM-based FDF are then highlighted. The simulation results show that the higher VPCM pressure could result in the higher hydrostatic pressure throughout the process and further resist wall thinning and prevent fracture of the sheet metal. The formability is thus increased significantly. 相似文献
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The fully plastic fracture of a metal sheet subjected to a small transverse gradient of tensile strain near a reinforcement is modeled as mode I fracture under transverse plane strain (TPS). Necking and fracture were analyzed by assuming that they were set by prior uniform strains and then necking displacements. Equations for the spreading of TPS necking and fracture were thus derived for a sheet with strain gradient. Experiments on tapered specimens confirmed the expected fracture displacements within 12 percent, but Moiré studies suggest the agreement may be fortuitous. In any event, in-plane transverse displacements and normal strains in the crack growth direction, as well as shear strains, were negligible. This should simplify any future numerical analysis. 相似文献
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Magnesium alloys have poor formability at room temperature. The formability can be improved through hot forming at the cost of deterioration in strength and other mechanical properties. Improvements in texture and grain refinement are the alternate ways for formability improvement. The economically viable process for such applications is alloying or grain refinement technologies like equal channel angular pressing (ECAP), friction stir processing (FSP), and accumulative roll bonding (ARB), etc. Friction stir processing is an emerging solid state microstructure modification technique that can produce homogeneous microstructure with fine-grains in a single pass. The desirable characteristics for sheet formability are the maximum limiting dome height under plane and biaxial strain deformation conditions and the major fracture strain limits through forming limit diagrams (FLDs). Equiaxed homogeneous microstructure with fine grains through FSP results in the enhancement of formability of the material. The objective of the present work is to establish the methodology for viable sheet metal forming practices by altering the process conditions. This needs a clear understanding of the friction stir processed Mg alloy under different strain conditions to get optimized process parameters. 相似文献
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P. G. Tracy T. P. Rich R. Bowser L. R. Tramontozzi 《International Journal of Fracture》1982,18(4):253-277
This paper explores the statistical nature of the mechanisms of fracture in structural materials and the loads that initiate them. The result of employing either a weak link or bundle model in the application of statistics to problems of fracture is examined. Experimental data is presented for the fracture of metal chains and the fracture of sheet aluminum containing machined cut-outs and cracks. The scatter in fracture loads for the chains and fracture toughness for the sheet specimens is statistically analyzed utilizing four statistical distributions: normal, lognormal, extreme value, and two-parameter Weibull functions. Based upon this work there appears to be no general a priori justification to utilize either the weak link or the bundle model in the statistical assessment of the fracture of typical engineering structural components. 相似文献
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为减少极端工况下因密封环摩擦磨损导致的疲劳断裂,保证马达的容积效率和可靠性。以法向正压力和剪切应力线性表示密封环摩擦力,并通过模态分析法和有限体积法分别研究系统多体动力学与缸孔内流体动力学,计算不同主轴转角、不同宽径比和弧面锥角下密封环的法向正压力和壁面剪切应力。研究结果表明:改变主轴转角引起的排量变化对摩擦力的影响较小;而密封环结构参数的变化影响明显,当宽径比小于0.3和弧面锥角小于1.8°时,摩擦力随宽径比和锥角增大而减小,在宽径比为0.3,弧面锥角为1.8°时摩擦力达到最小,最大缩减率分别为28%和25%;但当宽径比大于0.3和弧面锥角大于1.8°时,摩擦力随宽径比和锥角增大而增大;另剪切应力随着宽径比增大而增大;而受弧面锥角影响较小。研究结果为柱塞马达密封环减摩设计提供理论基础和依据。 相似文献
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目的 研究铝/钢薄板无铆连接过程中接头形貌的影响因素。方法 采用有限元模拟方法分析了铝/钢薄板在平底模具下接头形貌的成形过程。结合变形区域的金属流动情况,解释了互锁结构的形成机理,并分析了不同工艺参数对接头形貌的影响。结果 接头互锁结构主要是依靠铝板填充钢板的凹陷部位而形成的,抑制钢板与模具接触一侧的金属流动有助于接头底部和侧壁的钢板拉薄,进而形成内部凹陷,促进互锁结构的形成。摩擦因数对接头形貌参数影响较大,增大摩擦因数可显著提高接头的互锁量。结论 冲头半径、冲头圆角、凹模深度以及摩擦因数对颈厚值和互锁量均有显著影响。通过控制这些影响因素,可以得到良好的接头。此外,接头的失效形式以铝板颈厚较薄处的剪断失效为主,因此对于采用铝上钢下的无铆连接,保证颈厚值相对于互锁量更加重要。 相似文献
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In automotive industry, significant efforts are being put forth to replace steel sheets with aluminum sheets for various applications. Besides its higher cost, there are several technical hurdles for wide usage of aluminum sheets in forming. Major problems in aluminum sheet metal forming operations are deformation errors and spring back effect. These problems are dependent on the number of parameters such as die and tool geometry, friction condition, loading condition and anisotropic properties of the metal.To predict the exact shape, the geometry based punch contact program must be used. The shape changes once the punch is withdrawn, because of the materials elasticity. Prediction of such a spring back effect is a major challenging problem in industry involving sheet metal forming operations. It also needs applying appropriate back tension during the forming complex shapes. Slight deformation of the metal leads to non-axisymmetric loading. One can predict the residual stress by determining plastic and elastic deformation. Thus appropriate spring back effect can be investigated.The present investigation was carried out to determine the spring back and thinning effect of aluminum sheet metal during L-bending operation. Number of specimens with thickness varying from 0.5 mm to 3.5 mm were prepared. The experiments were conducted for different clearances between punch and die. It is observed that, beyond a particular clearance for each thickness of the sheet metal, the spring back and thinning effects were linearly increasing. However, below the critical clearance, scratches on the surface of the sheet metal were seen due to wear. The scratches were analyzed through Scanning Electron micrographs. As the clearance between punch and die reduces further, more wear on the punching surface was observed. And, as the clearance increases it leads to increase the spring back effect and fracture propagation. 相似文献