本文選題：7055鋁合金厚板 + 有限元模擬　； 參考：《北京有色金屬研究總院》2017年博士論文

【摘要】：7xxx系鋁合金具有高強(qiáng)、高韌及綜合性能優(yōu)異等特點,被廣泛應(yīng)用于航空航天領(lǐng)域。隨著大規(guī)格整體結(jié)構(gòu)件的發(fā)展與應(yīng)用,高性能7xxx系鋁合金厚板的需求日益迫切。鋁合金厚板殘余應(yīng)力的控制是該領(lǐng)域的研究難點之一。本文以航空用超高強(qiáng)7055鋁合金大規(guī)格厚板為研究對象,結(jié)合有限元模擬和實驗測試,系統(tǒng)研究了殘余應(yīng)力分布與演變規(guī)律及其影響因素,研究了厚板殘余應(yīng)力表征方法,建立了厚板淬火殘余應(yīng)力分布預(yù)測綜合方法,探索了不均勻淬火對殘余應(yīng)力的影響規(guī)律,為工廠大規(guī)格7055鋁合金厚板淬火-預(yù)拉伸過程中殘余應(yīng)力控制提供可靠的參考。利用ANSYS有限元軟件建立了 7055鋁合金厚板淬火-預(yù)拉伸殘余應(yīng)力有限元模型。通過實驗測試確定了 7055鋁合金厚板的熱物性參數(shù),利用實驗和反算法獲得了淬火過程中的換熱邊界條件。研究了淬火殘余應(yīng)力分布及演變規(guī)律,淬火殘余應(yīng)力為"外壓內(nèi)拉"分布,拉壓轉(zhuǎn)換點位于四分之一厚度位置,厚板內(nèi)為平面均勻應(yīng)力狀態(tài),僅在厚度方向存在應(yīng)力梯度。研究了預(yù)拉伸對殘余應(yīng)力分布的影響規(guī)律,應(yīng)力消減率隨著預(yù)拉伸量的增大呈先迅速增大后緩慢增大的趨勢。7055鋁合金厚板殘余應(yīng)力實驗測試與數(shù)值模擬綜合研究表明:對不同寬度厚板表面應(yīng)力的測試結(jié)果顯示出,采用鉆孔法與X射線衍射法均具有較好的穩(wěn)定性和準(zhǔn)確性;X射線衍射法表面應(yīng)力測試結(jié)果與有限元模擬結(jié)果吻合較好,中子衍射法內(nèi)應(yīng)力測試結(jié)果與有限元模擬結(jié)果基本吻合,驗證了有限元模型的準(zhǔn)確性;對不同淬火介質(zhì)參數(shù)的厚板進(jìn)行殘余應(yīng)力表征,采用鉆孔法和裂紋柔度法測得的表面應(yīng)力水平吻合較好,裂紋柔度法內(nèi)應(yīng)力測試結(jié)果與有限元模擬基本吻合,驗證了裂紋柔度法測試的準(zhǔn)確性。由此,提出了表面應(yīng)力測試方法優(yōu)選原則,建立了基于鉆孔法、X射線衍射法和裂紋柔度法的7055鋁合金厚板小規(guī)格試樣殘余應(yīng)力綜合表征方法。研究了淬火介質(zhì)參數(shù)對換熱系數(shù)的影響規(guī)律:隨著水溫或PAG濃度的升高,換熱系數(shù)水平逐漸降低;隨著噴淋水流量的升高,換熱系數(shù)水平逐漸升高;各淬火介質(zhì)的換熱能力順序為1 0%NaCl+KNO3溶液20℃水13.76L/min噴淋15%PAG溶液。研究了淬火介質(zhì)參數(shù)對7055鋁合金厚板淬火殘余應(yīng)力的影響規(guī)律:隨著水溫的升高,淬火殘余應(yīng)力逐漸降低;隨著PAG濃度的升高,淬火殘余應(yīng)力逐漸降低;在各淬火介質(zhì)參數(shù)下7055鋁合金厚板淬火殘余應(yīng)力水平為10%NaCl+KNO3溶液20℃水5%PAG溶液。系統(tǒng)研究了尺寸因素對7055鋁合金厚板淬火殘余應(yīng)力的影響規(guī)律。尺寸因素對應(yīng)力水平的影響規(guī)律為:當(dāng)長度和寬度較小時應(yīng)力水平存在峰值,當(dāng)長厚比和寬厚比均6時,應(yīng)力水平趨于穩(wěn)定。尺寸因素對應(yīng)力分布的影響規(guī)律為:應(yīng)力水平隨著長度的增大基本不變,但波動區(qū)域比例逐漸減小;隨著寬度的增大,應(yīng)力水平與波動區(qū)域比例均逐漸減小;隨著厚度的增大,應(yīng)力水平與波動區(qū)域比例均逐漸增大。提出了長向和寬向殘余應(yīng)力分布預(yù)測方法,通過該方法和5×5×1模型的長向和寬向淬火殘余應(yīng)力分布,可預(yù)測x×y×1模型的長向和寬向淬火殘余應(yīng)力分布,其中x≥y≥5。通過對不同寬度7055鋁合金厚板表面淬火殘余應(yīng)力的測試與模擬研究,驗證了長向和寬向應(yīng)力分布預(yù)測方法是可行的。通過研究不同厚度和不同淬火介質(zhì)參數(shù)厚板的厚向應(yīng)力分布函數(shù)和心部應(yīng)力水平預(yù)測模型,建立了厚向淬火殘余應(yīng)力分布預(yù)測模型。結(jié)合長向和寬向應(yīng)力分布預(yù)測方法以及厚向應(yīng)力分布預(yù)測模型,建立了 7055鋁合金厚板淬火殘余應(yīng)力分布預(yù)測綜合方法,利用小規(guī)格試樣淬火殘余應(yīng)力分布和大規(guī)格厚板表面中心點應(yīng)力水平可預(yù)測大規(guī)格7055鋁合金厚板淬火殘余應(yīng)力分布。研究了不均勻淬火對7055鋁合金厚板殘余應(yīng)力分布的影響規(guī)律:當(dāng)厚板上下表面不對稱淬火時,厚向應(yīng)力分布介于上、下表面平均換熱系數(shù)對應(yīng)應(yīng)力分布之間,中心兩側(cè)不對稱,應(yīng)力水平相當(dāng)于上表面與下表面平均換熱系數(shù)對應(yīng)應(yīng)力水平的平均值;同一表面不均勻淬火時,表面應(yīng)力分布與不均勻換熱系數(shù)分布類似,應(yīng)力水平相當(dāng)于平均換熱系數(shù)對應(yīng)的應(yīng)力水平,而心部應(yīng)力分布近似為均勻應(yīng)力分布狀態(tài),應(yīng)力水平相當(dāng)于線性分布兩極值的心部應(yīng)力水平的平均值。大規(guī)格7055鋁合金厚板表面淬火殘余應(yīng)力實測結(jié)果的分布線型與多段線性不均勻淬火殘余應(yīng)力分布線型相似。同時研究了預(yù)拉伸對不均勻淬火殘余應(yīng)力分布的影響規(guī)律,預(yù)拉伸對不均勻淬火的心部應(yīng)力不均勻性具有調(diào)控作用,但對表面應(yīng)力不均勻性無調(diào)控作用。
[Abstract]:7xxx aluminum alloy has been widely used in aerospace field because of its high strength, high toughness and excellent comprehensive performance. With the development and application of large size integral parts, the demand for high performance 7xxx system aluminum alloy thick plate is increasingly urgent. The control of residual stress of aluminum alloy thick plate is one of the difficult problems in this field. The large thickness plate of strong 7055 aluminum alloy is studied. Combined with the finite element simulation and experimental test, the residual stress distribution and evolution law and its influencing factors are systematically studied. The residual stress characterization method of the thick plate is studied. The comprehensive method for predicting the residual stress distribution of the thick plate quenching is established, and the influence of the uneven quenching on the residual stress is explored. A reliable reference is provided for the residual stress control in the process of quenching and predrawing of large size 7055 aluminum alloy thick plate of the factory. The finite element model of quenching and prestretching residual stress of 7055 aluminum alloy thick plate is established by ANSYS finite element software. The thermal physical parameters of the 7055 aluminum alloy thick plate are determined by experimental test, and the experiment and inverse algorithm are used. The heat transfer boundary conditions in the quenching process are obtained. The distribution and evolution of the residual stress of quenching are studied. The residual stress of quenching is "external pressure internal pull" distribution, the transition point of tension and pressure is located in the 1/4 thickness position, the thick plate is a plane uniform stress state, and the stress gradient only exists in the direction of thickness. The distribution of residual stress in pretension is studied. The stress reduction rate increases rapidly and then increases slowly with the increase of pretension, the experimental test and numerical simulation of the residual stress of.7055 aluminum alloy thick plate show that the test results of the stress on the surface of thick plates with different width show that both the drilling method and the X ray diffraction method have good stability and good stability. The results of the surface stress test of X ray diffraction method are in good agreement with the finite element simulation results. The results of the stress test in the neutron diffraction method agree with the finite element simulation results basically. The accuracy of the finite element model is verified. The residual stress of the thick plate with different quenching medium parameters is characterized by the drilling method and the crack flexibility method. The surface stress level is in good agreement. The test results of the internal stress of the crack flexibility method are basically consistent with the finite element simulation, and the accuracy of the test of the crack flexibility method is verified. Therefore, the optimization principle of the surface stress testing method is put forward, and the remnants of the small size sample of 7055 aluminum alloy thick plate based on the drilling method, the X ray diffraction method and the split pattern flexibility method are established. The influence of the quenching medium parameters on the heat transfer coefficient is studied. With the increase of water temperature or PAG concentration, the heat transfer coefficient level gradually decreases. With the increase of the flow rate of spray water, the heat transfer coefficient level increases gradually; the heat transfer capacity of each quenching medium is 1 0%NaCl+KNO3 solution at 20 C 13.76L/min spray 15%PAG The influence of quenching medium parameters on the residual stress of 7055 aluminum alloy thick plate quenching is studied. With the increase of water temperature, the residual stress of quenching gradually decreases. With the increase of PAG concentration, the residual stress of quenching gradually decreases, and the residual stress level of 7055 aluminum alloy thick plate quenched under the parameters of each quenching medium is 10%NaCl+KNO3 solution 20 C 5 water. The influence law of size factors on the residual stress of 7055 aluminum alloy thick plate quenching is studied systematically. The influence law of dimension factors on the stress level is that when the stress level of length and width is at the peak value, when the length to thickness ratio and the width to thickness ratio are 6, the stress level tends to be stable. The influence law of size factors on the stress distribution is that: the stress distribution is the following: the effect of the size factor on the force distribution is: the stress distribution is the following: the effect of the size factor on the force distribution is: the stress distribution is the following: the effect of the size factor on the force distribution is: the stress distribution is the following: the effect of the size factor on the force distribution is: the stress distribution is the following: the effect of the size factor on the force distribution is: the stress distribution is the following: the effect of the size factor on the force distribution is: the stress distribution is the following: the effect of the size factor on the force distribution is: the stress distribution is the following With the increase of the width, the ratio of stress level and fluctuating region gradually decreases with the increase of the width. With the increase of thickness, the ratio of stress level and fluctuation region gradually increases. The prediction method of long direction and wide residual stress distribution is put forward, through this method and 5 x 5 x 1. The distribution of the residual stress in the long direction and wide direction quenching of the model can be used to predict the residual stress distribution in the long direction and wide direction quenching of the x x y x 1 model. In the test and Simulation of the surface quenching residual stress of the 7055 aluminum alloy thick plate with different width, the prediction method of the long direction and wide stress distribution is proved to be feasible by the study of the difference between the long direction and the wide direction quenching of the model. The method of the prediction of the long and wide stress distribution is proved to be feasible. The thick direction stress distribution function of thick plate with different quenching medium parameters and the prediction model of the stress level of the heart are established. The prediction model of the residual stress distribution in the thick quenching is set up. The prediction of the residual stress distribution of the 7055 aluminum alloy thick plate quenching is established by combining the prediction method of the long and wide stress distribution and the prediction model of the thick stress distribution. The residual stress distribution of the large size 7055 aluminum alloy thick plate can be predicted by the residual stress distribution and the center point stress level of the large size plate surface. The influence of the uneven quenching on the residual stress distribution of the 7055 aluminum alloy thick plate is studied. The distribution of the thick stress distribution when the upper and lower surface of the thick plate is quenched asymmetrically. On the upper surface, the average heat transfer coefficient of the lower surface corresponds to the stress distribution, and the stress level is equal to the average stress level corresponding to the average heat transfer coefficient between the upper and the lower surfaces. The surface stress distribution is similar to that of the non uniform heat transfer system when the same surface is unevenly quenched, and the stress level is equivalent to the average heat transfer system. The stress level of the center is approximately equal to the uniform stress distribution, and the stress level is equal to the average of the two extremes of the linear distribution. The distribution line of the measured results of the surface quenching residual stress of the large size 7055 aluminum alloy thick plate is similar to that of the multi segment linear unevenly quenched residual stress distribution line. The effect of pretension on the distribution of residual stress in non uniform quenching is studied. The pretension has a control effect on the stress inhomogeneity of the unevenly quenched heart, but it has no control effect on the surface stress inhomogeneity.
【學(xué)位授予單位】：北京有色金屬研究總院
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TG146.21;TG166.3

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