本文選題：力場(chǎng)-化學(xué)場(chǎng)耦合 + 電解質(zhì)GDC　； 參考：《哈爾濱工業(yè)大學(xué)》2017年碩士論文

【摘要】：固體氧化物燃料電池(SOFC)中最重要的組成部分是固體電解質(zhì),固體電解質(zhì)的離子電導(dǎo)率和機(jī)械強(qiáng)度是現(xiàn)今科研人員關(guān)注和研究SOFC的重點(diǎn)。固體電解質(zhì)具有離子導(dǎo)電性的原因是氧空位的存在為氧離子的擴(kuò)散傳遞提供了途徑,而氧空位作為一種點(diǎn)缺陷來(lái)考慮時(shí),其存在必然會(huì)對(duì)材料的機(jī)械性能產(chǎn)生影響。尤其是當(dāng)電解質(zhì)中存在裂紋時(shí),裂紋尖端應(yīng)力場(chǎng)會(huì)發(fā)生巨大的改變,這必然會(huì)影響到氧空位的重新分布,導(dǎo)致電池系統(tǒng)受到影響。因此,本文首先利用宏觀有限元方法對(duì)力場(chǎng)-化學(xué)場(chǎng)耦合作用下電解質(zhì)GDC(氧化釓摻雜的氧化鈰)中裂紋尖端應(yīng)力場(chǎng)和氧空位的關(guān)系進(jìn)行了研究分析,然后采用微觀分子動(dòng)力學(xué)方法對(duì)不同條件下的電解質(zhì)GDC斷裂韌度進(jìn)行了計(jì)算分析,為固體氧化物燃料電池中的固體電解質(zhì)的安全設(shè)計(jì)與壽命評(píng)估提供了參考價(jià)值。本文首先從宏觀連續(xù)介質(zhì)力學(xué)角度,推導(dǎo)了力場(chǎng)-化學(xué)場(chǎng)耦合方程,并利用有限元思想對(duì)方程進(jìn)行離散處理。通過(guò)數(shù)值模擬計(jì)算發(fā)現(xiàn)當(dāng)電解質(zhì)材料中有微裂紋存在時(shí),裂紋尖端應(yīng)力場(chǎng)對(duì)氧空位的分布具有吸引誘導(dǎo)作用,且這種吸引誘導(dǎo)作用會(huì)隨裂紋尖端應(yīng)力場(chǎng)的增大而增強(qiáng)。然后從微觀分子動(dòng)力學(xué)(MD)角度對(duì)電解質(zhì)GDC中氧離子的擴(kuò)散進(jìn)行了MD模擬,分別以摻雜濃度、溫度和載荷作為變量,對(duì)GDC中氧離子的均方位移進(jìn)行模擬,通過(guò)理論計(jì)算獲得擴(kuò)散系數(shù),得到不同條件下氧離子擴(kuò)散的情況并進(jìn)行了相應(yīng)的分析。最后應(yīng)用MD方法建立了CeO_2和GDC的模型并對(duì)其進(jìn)行了單軸拉伸模擬,通過(guò)對(duì)應(yīng)力-應(yīng)變曲線的分析得到楊氏模量,并對(duì)不同條件下CeO2和GDC的楊氏模量變化規(guī)律進(jìn)行了總結(jié)�；跅钍夏Ａ康那蠼�,根據(jù)斷裂力學(xué)基本理論計(jì)算了CeO_2宏觀各向同性時(shí)的斷裂韌度。接下來(lái)對(duì)CeO_2與GDC的表面能進(jìn)行了模擬計(jì)算,給出了考慮晶體各向異性時(shí)的斷裂韌度的變化規(guī)律,并將二者的斷裂韌度進(jìn)行比較,發(fā)現(xiàn)GDC斷裂韌度明顯小于CeO_2的斷裂韌度,且這種差異與摻雜濃度、溫度和晶向都有關(guān)系。
[Abstract]:Solid electrolyte is the most important component of solid oxide fuel cell (SOFC). The ionic conductivity and mechanical strength of solid electrolyte are the focus of researchers' attention and research on SOFC.The reason for the ionic conductivity of solid electrolytes is that the existence of oxygen vacancies provides a way for the diffusion and transfer of oxygen ions, and when oxygen vacancies are considered as a point defect, the existence of oxygen vacancies will inevitably affect the mechanical properties of the materials.Especially when there is a crack in the electrolyte, the stress field at the crack tip will change greatly, which will inevitably affect the redistribution of oxygen vacancies, which will affect the battery system.Therefore, the relationship between the stress field at crack tip and oxygen vacancy in GDCelectrolyte under the coupling of force field and chemical field is studied by means of the macroscopic finite element method (FEM), and the relationship between the stress field at the crack tip and the oxygen vacancy in the electrolyte GDC (gadolinium oxide doped cerium oxide) is studied.Then the fracture toughness of electrolyte GDC under different conditions is calculated and analyzed by micromolecular dynamics method, which provides a reference value for the safe design and life evaluation of solid electrolyte in solid oxide fuel cell (SOFC).In this paper, the coupling equations of force field and chemical field are derived from the viewpoint of macroscopic continuum mechanics, and the equations are discretized by finite element method.The numerical simulation results show that the stress field at the crack tip has an attractive effect on the distribution of oxygen vacancies when there are microcracks in the electrolyte material, and this attraction inducement will increase with the increase of the stress field at the crack tip.Then the MD simulation of oxygen ion diffusion in electrolyte GDC was carried out from the viewpoint of micro molecular dynamics (MD). The mean square displacement of oxygen ion in GDC was simulated by using doping concentration, temperature and load as variables, respectively.The diffusion coefficient is obtained by theoretical calculation, and the diffusion of oxygen ions under different conditions is obtained and analyzed accordingly.Finally, the models of CeO_2 and GDC are established by using MD method, and the uniaxial tensile simulation is carried out. The Young's modulus is obtained by analyzing the stress-strain curves, and the variation law of Young's modulus of CeO2 and GDC under different conditions is summarized.Based on the solution of Young's modulus, the fracture toughness of CeO_2 macroscopic isotropy is calculated according to the basic theory of fracture mechanics.Then, the surface energy of CeO_2 and GDC is simulated and calculated, and the variation law of fracture toughness considering crystal anisotropy is given. It is found that the fracture toughness of GDC is obviously smaller than that of CeO_2, and the fracture toughness of GDC is obviously smaller than that of CeO_2.The difference is related to the doping concentration, temperature and crystal direction.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：O346.1;TM911.4

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