自动球压头压入试验法测算核容器钢断裂韧度的研究

发布时间：2019-07-05 16:41

【摘要】：核能作为一种清洁能源,已得到许多国家的开发和利用。然而核能在使用过程中存在危险性,一旦出现事故便会造成很大损失。核反应堆是核电站的核心,确保核反应堆压力容器安全服役是整个核电站的重中之重。断裂韧度作为材料抵抗裂纹扩展的能力,是核反应堆压力容器在服役过程中需要重点关注的力学性能指标。如何实现无损测量在役核反应堆压力容器断裂韧度成为近些年的研究热点。自动球压头压入试验法可以实现对在役核容器断裂韧度等力学性能的测算。作者对自动球压头压入试验法测算金属材料断裂韧度相关理论的起源和方法进行回溯和分析。利用有限元分析软件ABAQUS对自动球压头压入试验和常规断裂试验过程进行模拟,分别对压头下方区域和裂尖区域材料的应力应变场进行了分析,分析发现虽然压头下方区域材料主要为压应力场,裂尖区域材料主要为拉应力场,但是两个区域材料所处的状态仍然具有一定相似性,特别是压头下方与加载方向呈45°位置上的剪应力与裂尖的剪应力在数值和变化规律上都具有一定的相似性,剪应力可以促进延性金属材料发生韧窝断裂。因此,在压头下方区域存在与裂尖区域应力状态相似的特征区,为利用自动球压头压入试验法测算材料断裂韧度提供一定支持。作者以核容器常用钢SA508-3、SA516Gr70和SA533B为研究对象,分别进行常温下的标准拉伸试验、常规断裂试验和自动球压头压入试验,获得材料的载荷-压入深度曲线,分别利用 HFTM(Haggag Fracture Toughness Method,简称 HFTM)模型和 CIE(Critical Indentation Energy,简称C1E)模型对压入试验数据进行处理得到材料断裂韧度。通过对比常规断裂试验和自动球压头压入试验结果发现,对同种材料采用自动球压头压入试验法的测算结果与常规断裂试验结果存在偏差,自动球压头压入试验法测算断裂韧度的理论仍需修正。利用扫描电镜对自动球压头压入试样残余凹坑截面进行观察。观察结果表明自动球压头压入试验过程会使压头下方材料产生孔洞损伤,随着压头压入深度的增加,截面中的孔洞数量和尺寸不断增加,孔洞大多集中在与压头加载方向成45°的位置。对上述三种材料分别进行反复加卸载拉伸试验,基于连续损伤力学相关理论,得出自动球压头压入试验CIE模型中对应于压头临界压入深度的临界孔洞率分别为f*=0.221、0.247和0.229。利用光学显微镜和扫描电镜对自动球压头压入试样残余凹坑边缘进行观察。观察发现凹坑边缘处发生明显的塑性变形,存在明显的"堆积"现象。利用有限元分析软件ABAQUS研究了凹坑边缘的"堆积"和"沉陷"现象,结合量纲分析理论,定性研究了压头压入深度比h/D、材料应变硬化指数n及屈服应变ε0对堆积系数c~2的影响,总结出堆积系数c~2与三个变量间的关系式,为修正"堆积"和"沉陷"现象对于压痕投影面积的影响提供支持。基于上述研究,对CI正模型进行了一定修正。利用有限元仿真得到的堆积系数的关系式修正"堆积"现象对于压痕投影面积的影响;对临界孔洞率的修正分别采用三种钢各自临界孔洞率f*=0.221、0.247和0.229及其平均值f*=0.232,将CIE模型修正前后测算得到的断裂韧度值与常规断裂试验结果对比,发现CIE模型修正后的测算结果与常规断裂试验结果的偏差明显小于修正前的偏差,其中采用各自临界孔洞率修正后的CIE模型结果和常规试验结果偏差在14%以内,而采用平均值f*=0.232修正后的结果和常规试验偏差在22%以内。通过比较发现采用各自临界孔洞率修正后的CIE模型精度更高,但是使用平均临界孔洞率f*=0.232代替三种钢各自临界孔洞率测算核容器钢断裂韧度的结果在其精度上也基本能满足工程上的要求。而且如果直接使用平均临界孔洞率f*=0.232测算核容器钢断裂韧度,便无需事先通过反复加卸载拉伸试验获得特定材料的临界孔洞率,因此更方便在工程实际中使用。
文内图片：

图片说明：图１－１自动巧压头压入试验载荷－压入深度曲线逡逑１．３．１压入巧裂能模型逡逑
[Abstract]:As a clean energy source, nuclear energy has been developed and used by many countries. However, nuclear energy is dangerous in the process of use, and once an accident occurs, a great deal of loss is caused. The nuclear reactor is the core of the nuclear power plant, ensuring that the safety service of the nuclear reactor pressure vessel is the top priority of the whole nuclear power plant. The fracture toughness, as the material's ability to resist the crack growth, is the mechanical property index that the nuclear reactor pressure vessel needs to pay attention to during the service. How to realize the non-destructive measurement of the fracture toughness of the pressure vessel of the in-service nuclear reactor has become a hot spot in recent years. The calculation of the fracture toughness and other mechanical properties of the in-service nuclear container can be realized by the press-in test of the automatic ball head. In this paper, the origin and method of the theory of fracture toughness of metal material are reviewed and analyzed by means of the press-in test of the automatic ball head. The stress and strain field of the material in the lower area and the crack tip area of the pressure head were analyzed by using the finite element analysis software ABAQUS, and the stress and strain fields of the material in the lower area and the crack tip area under the pressure head were analyzed. the material of the crack tip region is mainly a tensile stress field, but the state of the two regional materials still has certain similarity, in particular, the shear stress and the shear stress at the 45-degree position below the pressure head and the loading direction have certain similarity with the numerical value and the change rule, The shear stress can promote the ductile fracture of the ductile metallic material. Therefore, a characteristic region similar to the stress state of the crack tip region exists in the lower region of the pressure head, and a certain support is provided for measuring the fracture toughness of the material by using the automatic ball head press-in test method. The authors used the common steel SA508-3, SA516Gr70 and SA533B of the nuclear container as the research object. The standard tensile test, the normal fracture test and the automatic ball head press-in test at normal temperature were carried out to obtain the load-press-in depth curve of the material. And the C1E model is used for processing the press-in test data to obtain the fracture toughness of the material. Through the comparison of the conventional fracture test and the automatic ball head press-in test, it is found that the calculation result of the self-ball-head press-in test method for the same type of material is different from the conventional fracture test result, and the theory of the automatic ball-head press-in test method to calculate the fracture toughness is still to be corrected. The residual pit cross-section of the specimen was observed by scanning electron microscope. The results show that the hole damage of the material under the pressure head can be caused by the press-in test of the automatic ball pressing head. With the increase of the press-in depth, the number and size of the holes in the cross-section are increasing, and the holes are mostly concentrated in the position of 45 掳 with the loading direction of the pressure head. Based on the theory of continuous damage mechanics, the critical hole rate corresponding to the critical pressure inlet depth of the pressure head is f * = 0.221, 0.247 and 0.229, respectively, based on the theory of continuous damage mechanics. The automatic ball indenter was pressed into the edge of the residual pit of the sample by means of an optical microscope and a scanning electron microscope. It was found that there was a significant "build up" of plastic deformation at the edge of the pit. The "build up" and "subsidence" of the edge of the pit are studied by using the finite element analysis software ABAQUS, and the effect of the pressure head pressure-in depth ratio h/ D, the strain hardening index n of the material and the yield strain rate 0 on the accumulation coefficient c-2 is studied by means of the dimensional analysis theory. The relationship between the accumulation factor c ~ 2 and the three variables is summarized, and the support for correcting the effect of the "build up" and the "subsidence" on the projection area of the indentation is provided. Based on the above research, the positive model of CI is modified. The influence of the "build up" phenomenon on the projection area of the indentation is corrected by using the relation of the accumulation coefficient obtained by the finite element simulation, and the critical hole ratio of the three steels is respectively f * = 0.221, 0.247 and 0.229 and the average value f * = 0.232 for the correction of the critical hole rate, and comparing the measured fracture toughness value measured before and after the correction of the CIE model with the conventional fracture test result, and finding that the deviation of the measurement result after the correction of the CIE model and the conventional fracture test result is obviously smaller than the deviation before the correction, The results of the CIE model and the deviation of the conventional test results are within 14%, and the average value of f * = 0.232 and the deviation of the routine test are within 22%. The results of using the average critical hole ratio f * = 0.232 to measure the fracture toughness of the nuclear container steel can also meet the requirements of the engineering. And if the average critical hole rate f * = 0.232 is directly used to calculate the fracture toughness of the nuclear container steel, the critical hole rate of the specific material is not required to be obtained in advance by the repeated loading and unloading tensile test, and therefore, the method is more convenient to use in the engineering practice.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM623

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