本文選題：多軸疲勞 + 比例與非比例加載　； 參考：《南京航空航天大學(xué)》2014年博士論文

【摘要】：工程實際中的許多結(jié)構(gòu)和構(gòu)件,如航空發(fā)動機葉片、機匣以及主軸等常常處于多軸應(yīng)力狀態(tài),一方面是由于這些結(jié)構(gòu)本身的幾何形狀比較復(fù)雜,其結(jié)構(gòu)上往往具有小孔、凸臺、溝槽、焊縫等,即使僅承受單一疲勞載荷作用,結(jié)構(gòu)局部應(yīng)力應(yīng)變分布實際為多軸應(yīng)力狀態(tài);另一方面這些結(jié)構(gòu)在工作時往往承受多種載荷的循環(huán)作用,各載荷之間可能為比例加載,也可能為非比例加載,甚至是隨機加載。因此,發(fā)展相應(yīng)于多軸的疲勞理論和疲勞試驗方法對于更好地解決實際問題有著十分重要的意義。本文選取航空發(fā)動機結(jié)構(gòu)典型材料TC4鈦合金,對其開展多軸疲勞試驗與理論研究,論文的主要內(nèi)容包括以下四個方面:針對航空發(fā)動機結(jié)構(gòu)典型材料TC4鈦合金開展了單軸、多軸疲勞試驗研究,試驗包括準靜態(tài)拉伸、單向拉壓疲勞、純扭轉(zhuǎn)疲勞、比例與非比例常幅多軸、變幅多軸、缺口常幅多軸及缺口變幅多軸疲勞試驗。試驗研究表明,TC4鈦合金在循環(huán)載荷作用下呈現(xiàn)循環(huán)軟化現(xiàn)象。采用位移控制模式對光滑薄壁圓筒進行常幅多軸疲勞試驗的結(jié)果表明,45o和90o非比例載荷下,TC4鈦合金非比例硬化現(xiàn)象明顯,在低壽命區(qū),非比例載荷路徑下的疲勞損傷更大,疲勞壽命降低。采用載荷控制模式對兩種類型的缺口件進行缺口多軸疲勞試驗的結(jié)果表明,45o和90o非比例載荷下的疲勞損傷比比例載荷下的小,疲勞壽命較長。驗證和評估了幾種常用的多軸疲勞壽命模型對TC4鈦合金多軸常幅疲勞壽命的預(yù)測能力,并在此基礎(chǔ)上基于臨界平面理論,提出了一種新的多軸疲勞壽命預(yù)測模型,該模型以最大剪應(yīng)變幅平面為臨界平面,考慮了臨界平面上的正應(yīng)力和正應(yīng)變對疲勞損傷的貢獻,可以同時適用于比例和非比例加載下的多軸疲勞問題,能夠描述平均應(yīng)力對材料多軸疲勞壽命的影響。采用TC4鈦合金及其他5種金屬材料的多軸常幅疲勞試驗數(shù)據(jù)對該模型的壽命預(yù)測能力進行驗證和評估,結(jié)果表明提出的多軸疲勞壽命模型具有較高的預(yù)測精度。基于本文提出的多軸疲勞壽命模型,針對變幅多軸載荷下的疲勞壽命問題,提出了一種變幅多軸載荷下的疲勞壽命預(yù)測方法。采用TC4鈦合金及其他三種金屬材料的多軸變幅疲勞試驗數(shù)據(jù)對該方法的壽命預(yù)測能力進行了驗證和評估,對幾種材料的多軸變幅疲勞壽命預(yù)測結(jié)果均在試驗結(jié)果的2倍分散帶內(nèi)。提出了缺口件在多軸載荷下疲勞危險點的確定方法。將臨界距離理論應(yīng)用于缺口件多軸疲勞壽命預(yù)測中,給出了多軸載荷作用下缺口件缺口根部損傷梯度修正的點法和線法的臨界距離的計算方法。采用TC4鈦合金缺口件的多軸疲勞試驗數(shù)據(jù)對點法和線法的疲勞損傷梯度修正能力進行了評估,結(jié)果表明這兩種方法具有良好的損傷梯度修正能力,并且修正能力相當。
[Abstract]:In engineering practice, many structures and components, such as aeroengine blades, casing and spindle, are often in a multi-axial stress state.Even if the groove, weld, etc., are subjected to single fatigue load, the local stress and strain distribution of the structure is actually a multiaxial stress state; on the other hand, these structures are often subjected to the cyclic action of many kinds of loads.The load may be proportional, non-proportional, or even random.Therefore, it is very important to develop fatigue theory and fatigue test method corresponding to multi-axis for solving practical problems better.In this paper, the typical material of aero-engine structure, TC4 titanium alloy, is selected to carry out multiaxial fatigue test and theoretical research. The main contents of this paper include the following four aspects: single axis is developed for TC4 titanium alloy, a typical material of aero-engine structure.The multiaxial fatigue tests include quasi-static tension, uniaxial tension and compression fatigue, pure torsional fatigue, proportional and non-proportional constant amplitude multiaxial, variable amplitude multiaxial, notched constant multiaxial and notch variable multiaxial fatigue test.The experimental results show that TC4 alloy shows cyclic softening under cyclic loading.The results of constant amplitude multiaxial fatigue test on smooth thin-walled cylinder by displacement control mode show that the non-proportional hardening phenomenon of TC4 titanium alloy is obvious under non-proportional load of 45o and 90o, and the fatigue damage of TC4 titanium alloy under non-proportional load path is more serious in low life region.The fatigue life is reduced.The results of multiaxial fatigue tests on two types of notched parts by load control mode show that the fatigue damage under non-proportional load is smaller and the fatigue life is longer than that under proportional load.The ability of several commonly used multiaxial fatigue life models to predict the multiaxial fatigue life of TC4 titanium alloy is verified and evaluated. Based on the critical plane theory, a new multiaxial fatigue life prediction model is proposed.The model takes the maximum shear strain amplitude plane as the critical plane and considers the contribution of normal stress and normal strain on the critical plane to fatigue damage. It can be applied to the multiaxial fatigue problem under both proportional and non-proportional loading.The effect of average stress on multiaxial fatigue life of materials can be described.The multiaxial constant amplitude fatigue test data of TC4 titanium alloy and other five kinds of metal materials are used to verify and evaluate the prediction ability of the model. The results show that the proposed multiaxial fatigue life model has higher prediction accuracy.Based on the multiaxial fatigue life model proposed in this paper, a prediction method for fatigue life under variable amplitude multiaxial loading is proposed.The life prediction ability of TC4 titanium alloy and other three kinds of metal materials is verified and evaluated by using the multiaxial variable amplitude fatigue test data.The prediction results of multiaxial variable amplitude fatigue life of several kinds of materials are in the dispersion band of 2 times of the experimental results.A method for determining fatigue hazard point of notched parts under multi-axial load is presented.The critical distance theory is applied to the prediction of multiaxial fatigue life of notched parts. The point method and the critical distance calculation method of notch root damage gradient correction under multiaxial loading are given.The multiaxial fatigue test data of TC4 titanium alloy notches are used to evaluate the fatigue damage gradient correction ability of point method and line method. The results show that the two methods have good damage gradient correction ability and the correction ability is equivalent.
【學(xué)位授予單位】：南京航空航天大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TH133.2

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