發(fā)布時間：2018-08-02 14:04

【摘要】：隨著全球范圍內(nèi)能源緊張、環(huán)境惡化、氣候變暖等問題的日益突出,發(fā)展低能耗、低排放、低污染的低碳科技已經(jīng)成為人們的共識。超(超)臨界發(fā)電機(jī)組發(fā)電效率高、污染物排放低,是我國電力行業(yè)發(fā)展低碳科技的重要組成之一。然而,大容量、高參數(shù)的機(jī)組意味著電站部件的服役條件更為惡劣,由于幾何尺寸、載荷類型、所處環(huán)境等影響,實際構(gòu)件大多受到復(fù)雜應(yīng)力狀態(tài)作用。據(jù)統(tǒng)計,蠕變是過熱器、再熱器及其聯(lián)箱等部件發(fā)生失效的主要原因之一。而P92鋼以其優(yōu)良的焊接性、高溫強度和蠕變性能等,成為超(超)臨界燃煤發(fā)電機(jī)組高溫受熱面的常用鋼之一。研究復(fù)雜應(yīng)力狀態(tài)下P92鋼的蠕變損傷擴(kuò)展和微觀組織演變規(guī)律是對燃煤發(fā)電機(jī)組高溫部件進(jìn)行壽命預(yù)測的關(guān)鍵部分,對發(fā)電機(jī)組安全經(jīng)濟(jì)運行具有重要的意義。本文以高溫蠕變試驗、蠕變本構(gòu)模型和有限元數(shù)值模擬互為驗證為技術(shù)路線,開展對P92鋼復(fù)雜應(yīng)力狀態(tài)下高溫蠕變損傷擴(kuò)展及微觀組織演變的研究。論文的具體工作如下:首先,完成不同溫度、不同應(yīng)力水平下標(biāo)準(zhǔn)光滑試樣的單軸蠕變試驗,從微觀角度上分析光滑試樣的蠕變斷裂機(jī)制;建立Norton-Bailey and Kachanov-Robotnov蠕變本構(gòu)模型,明確模型的參數(shù)確定方法,并對其有效性進(jìn)行驗證,為后續(xù)研究提供基礎(chǔ)數(shù)據(jù)庫。其次,進(jìn)行多軸蠕變試驗及模型的研究。完成不同應(yīng)力、不同缺口銳度下的雙缺口蠕變試驗,從宏觀和微觀兩個尺度上對蠕變結(jié)果進(jìn)行分析;采用修正后的Kachanov-Robotnov模型預(yù)測P92鋼缺口試樣蠕變損傷的發(fā)展過程,得到試樣內(nèi)部應(yīng)力與損傷的分布及演變規(guī)律;基于應(yīng)變耗竭理論,引入延性耗竭的概念,將連續(xù)損傷力學(xué)與孔洞長大理論相結(jié)合,建立可以描述P92鋼蠕變行為的延性耗竭模型,并完成對延性耗竭模型的驗證;結(jié)合蠕變試驗微觀結(jié)果與有限元數(shù)值模擬結(jié)果,對比分析了多軸度對P92鋼斷裂韌性、微觀孔洞和硬度分布的影響。再次,基于P92鋼高溫蠕變的損傷機(jī)理,引入具有實際物理意義的損傷變量,建立基于微觀機(jī)制的多損傷變量蠕變本構(gòu)模型,確定出模型參數(shù),并對模型的有效性加以驗證;進(jìn)行P92鋼光滑試樣和雙缺口試樣的蠕變中斷試驗,對蠕變過程中的析出相、孔洞進(jìn)行定量化統(tǒng)計;采用該模型對P92鋼缺口試樣的蠕變損傷演變進(jìn)行預(yù)測,損傷值的預(yù)測結(jié)果與P92鋼中斷試驗結(jié)果吻合良好,進(jìn)一步證明了該模型的有效性。最后,設(shè)計全尺寸的管道彎頭蠕變試驗,現(xiàn)已完成大部分試驗開始前的準(zhǔn)備工作,如應(yīng)變、溫度的測量等;采用有限元數(shù)值計算軟件探究不等壁厚、初始橢圓度對管道彎頭蠕變損傷擴(kuò)展的影響規(guī)律,以期為后續(xù)的全尺寸管道彎頭的蠕變試驗提供數(shù)據(jù)基礎(chǔ)。
[Abstract]:With the global energy tension, environmental degradation, climate warming and other issues increasingly prominent, the development of low energy consumption, low emissions, low pollution low-carbon technology has become a consensus. Supercritical generating units have high generation efficiency and low pollutant emission, which is one of the important components in the development of low-carbon technology in China's power industry. However, the large capacity and high parameter units mean that the service conditions of the components of the power station are worse. Due to the influence of geometry, load type and environment, the actual components are mostly affected by the complex stress state. According to statistics, creep is one of the main reasons for the failure of superheater, reheater and its header. For its excellent weldability, high temperature strength and creep properties, P92 steel has become one of the most common steels for supercritical coal-fired generating sets. The study of creep damage propagation and microstructure evolution of P92 steel under complex stress is a key part in predicting the life of high temperature components of coal-fired generating units, which is of great significance to the safe and economical operation of generating units. In this paper, the creep damage propagation and microstructure evolution of P92 steel under complex stress state are studied by means of creep test at high temperature, creep constitutive model and finite element numerical simulation. The specific work of this paper is as follows: firstly, uniaxial creep tests of standard smooth specimens at different temperatures and different stress levels are completed, and creep fracture mechanism of smooth specimens is analyzed from a microscopic point of view, and Norton-Bailey and Kachanov-Robotnov creep constitutive model is established. The method of determining the parameters of the model is defined, and its validity is verified, which provides the basic database for further research. Secondly, the multiaxial creep test and model are studied. The creep test of two notches under different stress and notch acuity was completed, and the creep results were analyzed from macroscopic and microscopic scales, and the creep damage process of notched specimens of P92 steel was predicted by modified Kachanov-Robotnov model, and the creep damage of P92 steel notched specimens was predicted by using the modified Kachanov-Robotnov model. Based on strain exhaustion theory, the concept of ductility depletion is introduced to combine the theory of continuous damage mechanics with the theory of pore growth to establish a ductile depletion model which can describe the creep behavior of P92 steel. The effects of multiaxiality on fracture toughness, micropore and hardness distribution of P92 steel were compared and analyzed by combining the microscopic results of creep test and the results of finite element numerical simulation. Thirdly, based on the damage mechanism of high temperature creep of P92 steel, the creep constitutive model of multiple damage variables based on microscopic mechanism is established, and the validity of the model is verified. The creep interruption tests of smooth and double notched specimens of P92 steel were carried out, the precipitated phases and voids in creep process were quantitatively counted, and the creep damage evolution of notched specimens of P92 steel was predicted by the model. The predicted damage value is in good agreement with the test results of P92 steel, which further proves the validity of the model. Finally, the design of full-scale pipe bend creep test, has now completed most of the preparatory work before the start of the test, such as strain, temperature measurement, using finite element numerical calculation software to explore the unequal wall thickness, The influence of initial ellipticity on creep damage propagation of pipe elbows is expected to provide a data basis for subsequent creep tests of full-scale pipe bends.
【學(xué)位授予單位】：華北電力大學(xué)(北京)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TM621

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本文編號：2159673