本文選題：有限元模擬 + 非均勻殘余應(yīng)力分布��； 參考：《天津大學(xué)》2015年博士論文

【摘要】：超聲沖擊成形是一種新的適用于小曲率板件成形的無模冷加工成形方法。應(yīng)用該方法進(jìn)行材料成形,可以在成形構(gòu)件表面產(chǎn)生殘余壓應(yīng)力層,提高其機(jī)械性能。超聲沖擊成形方法適用于大尺寸薄板成形,在加工制造領(lǐng)域,特別是航天航空制造領(lǐng)域擁有廣闊的應(yīng)用前景。本文開展2024鋁合金試件自由和預(yù)應(yīng)力超聲沖擊成形過程數(shù)值分析研究,對(duì)于弄清超聲沖擊成形機(jī)理、促進(jìn)該方法的應(yīng)用具有重要的理論意義和實(shí)際應(yīng)用價(jià)值。根據(jù)超聲沖擊成形的物理過程,提出了分階段建立超聲沖擊成形子模型的方法,建立了三階段自由超聲沖擊成形數(shù)值分析模型(超聲沖擊子模型、數(shù)據(jù)擴(kuò)展子模型和試件成形子模型)和四階段預(yù)應(yīng)力超聲沖擊成形數(shù)學(xué)模型(預(yù)應(yīng)力施加子模型、超聲沖擊子模型、數(shù)據(jù)擴(kuò)展子模型和試件成形子模型),對(duì)各受控參數(shù)下的窄板和方板試件超聲沖擊成形過程進(jìn)行了數(shù)值分析。在超聲沖擊子模型中,分析了自由狀態(tài)下沖擊過程中能量的轉(zhuǎn)換、應(yīng)力波及等效塑性應(yīng)變傳遞等規(guī)律,探討了沖擊速度、沖擊針質(zhì)量及形狀、沖擊槍運(yùn)行速度和偏移距離等受控參數(shù)對(duì)殘余應(yīng)力的分布規(guī)律。指出試件內(nèi)部的殘余應(yīng)力分布是非均勻的,試件表層的平均殘余壓應(yīng)力在沖擊槍偏移方向上的值大于在沖擊槍運(yùn)行方向上的值,且沖擊速度和沖擊槍偏移距離對(duì)殘余應(yīng)力的影響較大。應(yīng)用數(shù)據(jù)擴(kuò)展模型,將超聲沖擊子模型獲得的應(yīng)力應(yīng)變數(shù)據(jù)進(jìn)行擴(kuò)展,并導(dǎo)入到試件成形子模型中進(jìn)行數(shù)值分析,獲得自由超聲沖擊下單曲率窄板試件變形和雙曲率方板試件變形,并分析各受控參數(shù)對(duì)試件成形量的影響規(guī)律,指出殘余應(yīng)力分布與試件變形量之間的關(guān)系。通過對(duì)比窄板和方板試件的變形量,探討試件表層殘余壓應(yīng)力對(duì)試件成形的促進(jìn)作用和試件內(nèi)部殘余拉應(yīng)力與試件剛度變化對(duì)試件成形的抑制作用,分析其在不同受控參數(shù)下的影響程度。應(yīng)用預(yù)應(yīng)力超聲沖擊成形模型進(jìn)行數(shù)值分析,探索了不同預(yù)應(yīng)力狀態(tài)對(duì)試件成形的影響規(guī)律,指出試件的預(yù)彎方向的變形隨著預(yù)彎半徑的降低逐漸增加,與預(yù)彎相垂直方向的變形逐漸降低;通過對(duì)比窄板和方板試件的預(yù)應(yīng)力超聲沖擊成形,明確了殘余應(yīng)力分布和試件剛度變化在成形過程中的作用,指出試件剛度變化對(duì)成形的影響較大。提出了復(fù)雜軌跡的超聲沖擊成形數(shù)值分析方法,進(jìn)行了“回”字形沖擊軌跡成形的數(shù)值模擬研究,證明了該方法能對(duì)較規(guī)則的超聲沖擊軌跡成形進(jìn)行數(shù)值模擬與成形預(yù)測。應(yīng)用該方法獲得的模擬試驗(yàn)結(jié)果表明,采用間隔區(qū)域沖擊的預(yù)應(yīng)力沖擊軌跡可以獲得單曲率柱面成形;采用圓形自由超聲沖擊軌跡可以獲得雙曲率球面成形。
[Abstract]:Ultrasonic impact forming is a new cold forming method without die for small curvature sheet forming. With this method, the residual compressive stress layer can be produced on the surface of the formed member, and its mechanical properties can be improved. Ultrasonic impact forming method is suitable for large scale sheet forming, and has a wide application prospect in the field of machining and manufacturing, especially in the field of aerospace manufacturing. In this paper, the numerical analysis of the free and prestressed ultrasonic impact forming process of 2024 aluminum alloy specimen is carried out, which has important theoretical significance and practical application value for clarifying the ultrasonic impact forming mechanism and promoting the application of this method. According to the physical process of ultrasonic impact forming, the method of establishing sub-model of ultrasonic impact forming in stages is put forward, and the numerical analysis model of three-stage free ultrasonic impact forming (ultrasonic percussive model) is established. Data extension sub-model and specimen forming sub-model, and four-stage pre-stressed ultrasonic impact forming mathematical model (prestressing force applied sub-model, ultrasonic impact sub-model), The ultrasonic impact forming process of narrow plate and square plate specimens under various controlled parameters was numerically analyzed by using the data extender model and the specimen forming sub-model. In the ultrasonic percussive model, the laws of energy conversion, stress and equivalent plastic strain transfer in the free state are analyzed, and the impact velocity, the quality and shape of the impact needle are discussed. Distribution of residual stress by controlled parameters such as velocity and offset distance of impact gun. It is pointed out that the distribution of residual stress inside the specimen is non-uniform, and the average residual compressive stress in the surface layer of the specimen is larger in the direction of deviation of the impact gun than in the direction of movement of the impact gun. The impact velocity and the offset distance of the impact gun have great influence on the residual stress. Using the data expansion model, the stress and strain data obtained from the ultrasonic percussive submodel are extended and introduced into the specimen forming sub-model for numerical analysis. The deformation of single curved narrow plate specimen and double curvature square plate specimen under free ultrasonic impact is obtained. The effect of controlled parameters on specimen forming quantity is analyzed and the relationship between residual stress distribution and specimen deformation is pointed out. By comparing the deformation of narrow plate and square plate, the paper discusses the promoting effect of the surface residual compressive stress on the forming of the specimen and the restraining effect of the residual tensile stress inside the specimen and the change of the stiffness of the specimen on the forming of the specimen. The degree of its influence under different controlled parameters is analyzed. By using the pre-stress ultrasonic impact forming model, the influence of different prestressing states on the specimen forming is studied. It is pointed out that the deformation of the pre-bending direction of the specimen increases with the decrease of the pre-bending radius. The vertical deformation decreases gradually with the prebending phase, and the effect of residual stress distribution and specimen stiffness change in the forming process is clarified by comparing the prestressed ultrasonic impact forming of narrow plate and square plate specimen. It is pointed out that the stiffness change of the specimen has a great influence on the forming. In this paper, a numerical analysis method of ultrasonic impact trajectory with complex trajectory is proposed, and the numerical simulation of "return" shaped impact trajectory forming is carried out. It is proved that this method can be used to simulate and predict the formation of regular ultrasonic impact trajectory forming. The simulation results obtained by this method show that the single curvature rate cylindrical forming can be obtained by using the prestress impact trajectory in the spacer zone and the double curvature spherical forming can be obtained by using the circular free ultrasonic impact trajectory.
【學(xué)位授予單位】：天津大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG663

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