球墨铸铁QT600在不同应力状态下断裂的试验与数值研究
发布时间：2019-05-27 10:37
【摘要】：针对球墨铸铁QT600,设计了一系列不同尺寸和几何形状的圆棒、薄壁圆管、板状及缺口试样,对光滑实心圆棒、缺口实心圆棒、缺口平板和中心孔板试样进行单轴拉伸试验以及对薄壁圆管试样进行扭转试验,获得了试样的荷载-位移曲线,并测试了材料在不同应力状态下的断裂应变;通过对试样变形过程的观测,用光学显微镜确定了试样的启裂位置。结合观测球墨铸铁金相组织,采用Matlab编写程序对球墨铸铁金相进行了定量金相分析,针对球墨铸铁金相组织的不同因素讨论其球墨铸铁力学性能的影响;使用光学显微镜和扫描电镜系统对试样断口形貌进行观测,根据试样宏微观断口讨论不同试样的断裂形式,为研究材料在复杂应力状态下破坏提供依据。然后采用ABAQUS有限元分析软件进行弹塑性大变形数值模拟计算分析,结合数值模拟与显微观测结果,确定了不同试样启裂点位置的应力状态参数,进一步探讨了断裂应变与应力三轴度之间的关系。通过研究,得到的主要结论有:(1)根据拉伸和扭转试验与数值模拟分析,拉伸和扭转的等效应力应变曲线基本相同。(2)根据本文的试验与数值模拟结果可知,缺口实心圆棒试样断裂应变随着应力三轴度的升高而降低,与GTN模型描述由孔洞模型韧性材料破坏规律相符合,而缺口平板试样和中心孔板试样的破坏规律与GTN模型描述的断裂应变与应力三轴度的规律不相符。(3)对断裂应变相同而应力三轴度不同的情形,发现Lode参数相差较大,可判定Lode参数是影响材料断裂的重要因素。
[Abstract]:A series of round rods, thin-wall tubes, plates and notched specimens with different sizes and geometric shapes are designed for nodular cast iron QT600,. For smooth solid round rods and notched solid round rods, The load-displacement curves of notched plate and central orifice plate were obtained by uniaxial tensile test and torsional test of thin-wall circular tube specimen, and the fracture strain of the material under different stress conditions was tested. Through the observation of the deformation process of the sample, the crack opening position of the sample is determined by optical microscope. Combined with the observation of the metallographic structure of nodular cast iron, the metallographic analysis of nodular cast iron was carried out by Matlab program, and the influence of the mechanical properties of nodular cast iron was discussed according to the different factors of the metallographic structure of nodular cast iron. The fracture morphology of the sample was observed by optical microscope and scanning electron microscope system. According to the macro and micro fracture of the sample, the fracture forms of different samples were discussed, which provided the basis for the study of the failure of the material under complex stress state. Then the elastic-plastic large deformation numerical simulation analysis is carried out by using ABAQUS finite element analysis software. Combined with the numerical simulation and microscopic observation results, the stress state parameters of different crack opening points of the specimen are determined. The relationship between fracture strain and stress triaxiality is further discussed. Through the study, the main conclusions are as follows: (1) according to the tensile and torsional tests and numerical simulation analysis, the equivalent stress-strain curves of tensile and torsional are basically the same. (2) according to the experimental and numerical simulation results of this paper, The fracture strain of notched solid rod decreases with the increase of stress triaxiality, which is consistent with the failure law of ductile material described by GTN model. However, the failure law of notched plate specimen and central orifice plate specimen is not consistent with the law of fracture strain and stress triaxiality described by GTN model. (3) for the case of the same fracture strain and different stress triaxiality, it is found that the Lode parameters are quite different. It can be determined that Lode parameters are an important factor affecting the fracture of materials.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG143.5
本文编号：2486077
[Abstract]:A series of round rods, thin-wall tubes, plates and notched specimens with different sizes and geometric shapes are designed for nodular cast iron QT600,. For smooth solid round rods and notched solid round rods, The load-displacement curves of notched plate and central orifice plate were obtained by uniaxial tensile test and torsional test of thin-wall circular tube specimen, and the fracture strain of the material under different stress conditions was tested. Through the observation of the deformation process of the sample, the crack opening position of the sample is determined by optical microscope. Combined with the observation of the metallographic structure of nodular cast iron, the metallographic analysis of nodular cast iron was carried out by Matlab program, and the influence of the mechanical properties of nodular cast iron was discussed according to the different factors of the metallographic structure of nodular cast iron. The fracture morphology of the sample was observed by optical microscope and scanning electron microscope system. According to the macro and micro fracture of the sample, the fracture forms of different samples were discussed, which provided the basis for the study of the failure of the material under complex stress state. Then the elastic-plastic large deformation numerical simulation analysis is carried out by using ABAQUS finite element analysis software. Combined with the numerical simulation and microscopic observation results, the stress state parameters of different crack opening points of the specimen are determined. The relationship between fracture strain and stress triaxiality is further discussed. Through the study, the main conclusions are as follows: (1) according to the tensile and torsional tests and numerical simulation analysis, the equivalent stress-strain curves of tensile and torsional are basically the same. (2) according to the experimental and numerical simulation results of this paper, The fracture strain of notched solid rod decreases with the increase of stress triaxiality, which is consistent with the failure law of ductile material described by GTN model. However, the failure law of notched plate specimen and central orifice plate specimen is not consistent with the law of fracture strain and stress triaxiality described by GTN model. (3) for the case of the same fracture strain and different stress triaxiality, it is found that the Lode parameters are quite different. It can be determined that Lode parameters are an important factor affecting the fracture of materials.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG143.5
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