【摘要】：核能作為一種清潔能源,已得到許多國家的開發(fā)和利用。然而核能在使用過程中存在危險性,一旦出現(xiàn)事故便會造成很大損失。核反應(yīng)堆是核電站的核心,確保核反應(yīng)堆壓力容器安全服役是整個核電站的重中之重。斷裂韌度作為材料抵抗裂紋擴展的能力,是核反應(yīng)堆壓力容器在服役過程中需要重點關(guān)注的力學(xué)性能指標。如何實現(xiàn)無損測量在役核反應(yīng)堆壓力容器斷裂韌度成為近些年的研究熱點。自動球壓頭壓入試驗法可以實現(xiàn)對在役核容器斷裂韌度等力學(xué)性能的測算。作者對自動球壓頭壓入試驗法測算金屬材料斷裂韌度相關(guān)理論的起源和方法進行回溯和分析。利用有限元分析軟件ABAQUS對自動球壓頭壓入試驗和常規(guī)斷裂試驗過程進行模擬,分別對壓頭下方區(qū)域和裂尖區(qū)域材料的應(yīng)力應(yīng)變場進行了分析,分析發(fā)現(xiàn)雖然壓頭下方區(qū)域材料主要為壓應(yīng)力場,裂尖區(qū)域材料主要為拉應(yīng)力場,但是兩個區(qū)域材料所處的狀態(tài)仍然具有一定相似性,特別是壓頭下方與加載方向呈45°位置上的剪應(yīng)力與裂尖的剪應(yīng)力在數(shù)值和變化規(guī)律上都具有一定的相似性,剪應(yīng)力可以促進延性金屬材料發(fā)生韌窩斷裂。因此,在壓頭下方區(qū)域存在與裂尖區(qū)域應(yīng)力狀態(tài)相似的特征區(qū),為利用自動球壓頭壓入試驗法測算材料斷裂韌度提供一定支持。作者以核容器常用鋼SA508-3、SA516Gr70和SA533B為研究對象,分別進行常溫下的標準拉伸試驗、常規(guī)斷裂試驗和自動球壓頭壓入試驗,獲得材料的載荷-壓入深度曲線,分別利用 HFTM(Haggag Fracture Toughness Method,簡稱 HFTM)模型和 CIE(Critical Indentation Energy,簡稱C1E)模型對壓入試驗數(shù)據(jù)進行處理得到材料斷裂韌度。通過對比常規(guī)斷裂試驗和自動球壓頭壓入試驗結(jié)果發(fā)現(xiàn),對同種材料采用自動球壓頭壓入試驗法的測算結(jié)果與常規(guī)斷裂試驗結(jié)果存在偏差,自動球壓頭壓入試驗法測算斷裂韌度的理論仍需修正。利用掃描電鏡對自動球壓頭壓入試樣殘余凹坑截面進行觀察。觀察結(jié)果表明自動球壓頭壓入試驗過程會使壓頭下方材料產(chǎn)生孔洞損傷,隨著壓頭壓入深度的增加,截面中的孔洞數(shù)量和尺寸不斷增加,孔洞大多集中在與壓頭加載方向成45°的位置。對上述三種材料分別進行反復(fù)加卸載拉伸試驗,基于連續(xù)損傷力學(xué)相關(guān)理論,得出自動球壓頭壓入試驗CIE模型中對應(yīng)于壓頭臨界壓入深度的臨界孔洞率分別為f*=0.221、0.247和0.229。利用光學(xué)顯微鏡和掃描電鏡對自動球壓頭壓入試樣殘余凹坑邊緣進行觀察。觀察發(fā)現(xiàn)凹坑邊緣處發(fā)生明顯的塑性變形,存在明顯的"堆積"現(xiàn)象。利用有限元分析軟件ABAQUS研究了凹坑邊緣的"堆積"和"沉陷"現(xiàn)象,結(jié)合量綱分析理論,定性研究了壓頭壓入深度比h/D、材料應(yīng)變硬化指數(shù)n及屈服應(yīng)變ε0對堆積系數(shù)c~2的影響,總結(jié)出堆積系數(shù)c~2與三個變量間的關(guān)系式,為修正"堆積"和"沉陷"現(xiàn)象對于壓痕投影面積的影響提供支持�；谏鲜鲅芯�,對CI正模型進行了一定修正。利用有限元仿真得到的堆積系數(shù)的關(guān)系式修正"堆積"現(xiàn)象對于壓痕投影面積的影響;對臨界孔洞率的修正分別采用三種鋼各自臨界孔洞率f*=0.221、0.247和0.229及其平均值f*=0.232,將CIE模型修正前后測算得到的斷裂韌度值與常規(guī)斷裂試驗結(jié)果對比,發(fā)現(xiàn)CIE模型修正后的測算結(jié)果與常規(guī)斷裂試驗結(jié)果的偏差明顯小于修正前的偏差,其中采用各自臨界孔洞率修正后的CIE模型結(jié)果和常規(guī)試驗結(jié)果偏差在14%以內(nèi),而采用平均值f*=0.232修正后的結(jié)果和常規(guī)試驗偏差在22%以內(nèi)。通過比較發(fā)現(xiàn)采用各自臨界孔洞率修正后的CIE模型精度更高,但是使用平均臨界孔洞率f*=0.232代替三種鋼各自臨界孔洞率測算核容器鋼斷裂韌度的結(jié)果在其精度上也基本能滿足工程上的要求。而且如果直接使用平均臨界孔洞率f*=0.232測算核容器鋼斷裂韌度,便無需事先通過反復(fù)加卸載拉伸試驗獲得特定材料的臨界孔洞率,因此更方便在工程實際中使用。
文內(nèi)圖片：
圖片說明：圖１－１自動巧壓頭壓入試驗載荷－壓入深度曲線逡逑１．３．１壓入巧裂能模型逡逑
[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 擄 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.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TM623

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