基于平均应力三轴度的304不锈钢断裂准则建立及应用

发布时间：2018-08-12 18:21

【摘要】：金属材料在其加工过程中的塑性变形达到一定程度时,会出现韧性断裂和承载能力的损失。韧性断裂是影响金属材料可加工性和工程构件安全的重要因素。在产品的设计和优化过程中,对材料韧性断裂的准确预测起着至关重要的作用。工艺过程中,选用一种适用可靠的断裂准则显得很有必要。从目前的研究来看,众多韧性断裂准则和极限断裂准则被提出用于预测材料变形过程中裂纹的启裂位置和时刻。不锈钢作为一种绿色环保且综合性能优异的材料,已广泛地应用于各领域。近年来,对不锈钢的力学性能、耐腐蚀等问题进行了大量的研究,但对于不锈钢成形过程中断裂准则的研究却鲜有提及。本文以304不锈钢为对象,研究了其成形过程中的断裂准则,并将该准则应用于精冲领域,用以评价304不锈钢的精冲性能。文中设计了7组不同高径比的304不锈钢圆柱试样,对其进行平板镦粗破裂实验。对实验过程中测量的数据进行计算,建立了304不锈钢在其变形过程中的断裂准则,即“平均应力三轴度-等效应变”断裂准则。结果表明,平均应力三轴度存在一个极限值-1/3。在ABAQUS/Explicit平台上建立304不锈钢圆柱平板镦粗有限元模型,基于实验建立的断裂准则应用于有限元模拟中。将有限元模型中失效断裂点的应力、应变变量提取出来并计算,通过曲线拟合的方法建立校准后的断裂准则。结果表明,第4次校准的模拟结果能够较好地符合平板镦粗实验现象。通过对3组不同尺寸系列的圆环试样进行压缩实验,将测量的实验数据应用于圆环压缩有限元模拟中。有限元模拟结果和圆环压缩实验中试样的破裂情况进行对比,来验证校准建立的断裂准则的适用性和可靠性。结果表明,基于第4次校准建立的断裂准则能够较好的预测圆环压缩实验中试样的破裂情况。为了研究304不锈钢的精冲性能,设计开发了一种材料精冲性能实验装置,同时给出了一种材料精冲性能评价方法。将建立的304不锈钢断裂准则引入到精冲有限元模拟中,来预测精冲过程中裂纹的出现。通过对精冲模拟结果中试样光洁带l和毛刺高度t的测量,依据给出的标准评价了304不锈钢的精冲性能。评价结果表明,304不锈钢的精冲性能不好。
[Abstract]:When the plastic deformation of metal material reaches a certain degree, ductile fracture and loss of bearing capacity will occur. Ductile fracture is an important factor affecting the machinability of metal materials and the safety of engineering components. In the process of product design and optimization, it is very important to predict ductile fracture accurately. In the process, it is necessary to select a reliable fracture criterion. From the current research, many ductile fracture criteria and limit fracture criteria have been proposed to predict the location and time of crack initiation in the process of deformation of materials. Stainless steel has been widely used in various fields as a kind of green and comprehensive performance material. In recent years, the mechanical properties and corrosion resistance of stainless steel have been studied extensively, but the study of fracture criterion in the forming process of stainless steel is seldom mentioned. In this paper, the fracture criterion of 304 stainless steel during forming process was studied and applied to fine blanking field to evaluate the fine punching performance of 304 stainless steel. In this paper, seven groups of 304 stainless steel cylinder specimens with different aspect ratio were designed and the upsetting fracture test was carried out. The fracture criterion of 304 stainless steel during deformation is established by calculating the measured data during the experiment, that is, "average stress triaxial-equivalent strain" fracture criterion. The results show that the average stress triaxiality has a limit value of -1 / 3. The finite element model of 304 stainless steel column upsetting was established on ABAQUS/Explicit platform. The fracture criterion based on experiment was applied to finite element simulation. The stress and strain variables of the failure fracture point in the finite element model are extracted and calculated, and the calibrated fracture criterion is established by curve fitting method. The results show that the simulated results of the fourth calibration are in good agreement with the plate upsetting experiment. Three groups of annular specimens with different sizes were tested and the measured data were applied to the finite element simulation of ring compression. In order to verify the applicability and reliability of the proposed fracture criterion, the finite element simulation results are compared with the fracture conditions of the specimen in the annular compression test. The results show that the fracture criterion based on the fourth calibration can predict the fracture of the specimen in the annular compression test. In order to study the precision punching performance of 304 stainless steel, a material precision punching performance experimental device was designed and developed. At the same time, an evaluation method of material precision punching performance was given. The fracture criterion of 304 stainless steel is introduced into the finite-blanking finite element simulation to predict the crack occurrence in the fine blanking process. The fine punching properties of 304 stainless steel were evaluated according to the standard given by the measurement of the smooth strip l and the burr height t of the sample in the simulation results of fine blanking. The evaluation results show that the fine punching performance of stainless steel is not good.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG142.71

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