共查询到17条相似文献,搜索用时 484 毫秒
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目的 研究拉伸冲击载荷作用下螺栓预紧力对应力波的影响.方法 针对螺栓弹性变形、塑性变形和冲击破坏3种情形,对螺栓未施加预紧力及施加不同预紧力下的连接结构进行冲击数值模拟,对比分析连接结构的测点应变及螺栓响应,并与霍普金森拉伸实验结果进行对比.结果 螺栓达到断裂或塑性变形时,预紧力对测点应变及螺栓最大应力影响较小;螺栓弹性变形时,预紧力对测点应变及螺栓最大应力影响较大.结论 螺栓达到断裂或塑性变形时,螺栓拉伸变形远大于预紧力变形,此时预紧力影响可忽略;螺栓在弹性变形时,螺栓拉伸变形与预紧力变形程度接近,此时预紧力影响不可忽略,且预紧力越高,螺栓变形越大. 相似文献
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应用上限法建立了由矩形毛坯正挤压矩形截面工件的等挤压比流动模型 ,推导出了三次多项式表示的流线方程 ,给出了变形区的动可容速度场、应变速率场及上限功率的表达式 ,获得了挤压力的上限数值解 ;分析了变形程度、工件截面形状等参数对挤压力的影响 ,并获得了相对挤压应力与截面形状系数之间的近似关系式。研究证明采用流线速度场进行上限分析比其他方法更符合实际情况 ,根据流线设计的凹模优于常规凹模 ,如平底模。 相似文献
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轴对称两出口轴向挤压金属流动规律的研究 总被引:1,自引:0,他引:1
本文在实验的基础上,通过分析比较,提出了塑性变形材料的“等应变分配原理”,并通过对轴对称两出口轴向挤压金属流动规律的研究,对这一原理进行了验证。同时也赋予了平面应变复合挤压分流层几何确定的物理意义。 相似文献
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介绍了变形温度、应变速率、润滑剂的使用对LDll等温挤压的影响,在240活塞铝裙等温挤压生产中对上述工艺参数进行了选用及控制;同时就该件等温挤压工艺的特点与热模锻工艺进行了初步比较. 相似文献
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1967年E.R.Lambert和S.Kobayashi等人对稳定状态成形过程引用了流函数法来确定上限流动模式。这种方法可用之于平面应变问题,也可处理轴对称流动问题。Lambert首先对平面应变状态的挤压过程进行了动可容速度场的研究。以后C.T.Chen与F.F.Ling用流函数法研究了金属经过曲线轮廓凹模的棒料挤压问题,V.Nagpal对通过任何轮廓凹模的平面应变挤压过程进行过分析。他们对不可压缩材料用估计的流线形状来选择动可容速度场族,要求动可容场要满足流线的预定形状以求得与真实变形模型接近一致。本文以通过余弦曲线轮廓凹模的平面应变挤压为例,阐述流函数法在上限流动模式中的应用。 相似文献
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H.-J. Hu 《Journal of Manufacturing Processes》2012,14(3):181-187
It is important to research the effect of die structures parameters for equal channel angular extrusion (ECAE) on the deformation behavior, strain distribution and loads requirement. ECAE is an extrusion process widely researched for its potential to produce ultra-fine grained microstructures in magnesium alloys. In this paper some three-dimensional (3D) geometric models with different corner angles 90° and 135° and with fillets or not in the bottom die were designed by UG software. Some important isothermal process parameters were regarded as basal conditions used in DEFORM?-3D software such as temperatures, the friction coefficient, and extrusion speed. The deformation heterogeneity of ECAE was analyzed from the simulation and experimental results. The deformation homogeneity caused by the EACE die with fillets was improved comparing with the die without fillets. But the cumulative maximum strains decreased. The requirement extrusion force decreased with the fillets and channel angle increase in ECAE die. From the simulation and experimental results the smaller channel angle can obtain the higher cumulative strains and produce tinier subgrains. The loads of top die decrease mainly with fillets. The ECAE die with the channel angle 90° and fillets is good to improve the plasticity and deformation homogeneity of the billets if the extrusion force is enough. It was demonstrated that the simulation results were in good agreement with experimental results and the theoretical calculation. 相似文献
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《Journal of Manufacturing Processes》2014,16(2):233-240
A thermo-mechanical model has been developed for modeling of hot extrusion processes. Accordingly, an admissible velocity field was first proposed by means of stream function method and then, extrusion pressure as well as temperature variations within the metal and the die were predicted employing a combined upper bound and Petrov–Galerkin finite element analysis. In order to evaluate the model predictions, hot extrusion of AA6061-10%SiCp was considered under both isothermal and non-isothermal conditions and the predicted force–displacement diagrams under various extrusion conditions were compared with the experimental ones and reasonable consistency was found between the two sets of results. 相似文献
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H.-J. Hu 《Journal of Manufacturing Processes》2010,12(2):67-72
Extrusion of magnesium billets is associated with large deformations, high strain rates and high temperatures, which results in computationally challenging problems in process simulation. A series of experiments were done to obtain the simulation parameters: stress–strain curves, friction factors and heat transfer coefficient etc. Three-dimensional, thermo-mechanically coupled finite element simulations of extruding a wrought magnesium alloy AZ31 into a small bar at certain ram speeds were performed. The computed model was rotational symmetric and built up by meshing. Computed parameters including workpiece material characteristics and process conditions (billet temperature, reduction ratio, and ram speed) were taken into consideration. The distributions of temperature were different comparing the transient-state extrusion with steady-state extrusion. The extrusion simulation was the reliable predictions of strain rate, effective strains, effective stresses and metal flow velocity in an AZ31 billet during direct extrusion. 相似文献