【摘要】：旋壓成形技術(shù)作為制造大型薄壁回轉(zhuǎn)類零件最有效的工藝方法,已越來越多的應(yīng)用于純鈦及鈦合金的塑性成形過程。但是,純鈦及鈦合金屬于難變形金屬,在旋壓過程中容易產(chǎn)生韌性斷裂,嚴(yán)重制約了純鈦及鈦合金旋壓技術(shù)的應(yīng)用。本文針對純鈦及鈦合金強(qiáng)力旋壓成形過程中的韌性斷裂問題,研究了TA2純鈦在不同應(yīng)力狀態(tài)下的韌性斷裂行為,利用韌性斷裂準(zhǔn)則預(yù)測了TA2純鈦筒形件可旋性試驗和板材可旋性試驗的旋壓極限及損傷演化過程,揭示了筒形件和板材可旋性試驗中旋壓破裂的韌性斷裂機(jī)制。針對Ti-15-3鈦合金筒形件強(qiáng)旋過程中的表面開裂現(xiàn)象,研究了減薄率對筒形件內(nèi)外層損傷演化的影響,揭示了低塑性材料筒形件強(qiáng)旋的韌性斷裂機(jī)制。開展了TA2純鈦不同應(yīng)力狀態(tài)下的韌性斷裂實驗,分析了不同應(yīng)力狀態(tài)下塑性變形的特點,研究了應(yīng)力狀態(tài)改變對TA2純鈦韌性斷裂行為的影響。在高應(yīng)力三軸度下,隨著應(yīng)力三軸度的增加,材料的斷裂應(yīng)變逐漸減小。負(fù)應(yīng)力三軸度下壓縮試驗的斷裂應(yīng)變最大。低應(yīng)力三軸度下純剪切試驗的斷裂應(yīng)變較小,僅高于缺口半徑R2的圓棒拉伸試驗的斷裂應(yīng)變。將韌性斷裂準(zhǔn)則耦合到有限元軟件ABAQUS中,預(yù)測了TA2純鈦不同應(yīng)力狀態(tài)下韌性斷裂試驗的損傷分布,確定了各個韌性斷裂準(zhǔn)則的適用范圍,并獲得了各個韌性斷裂準(zhǔn)則在不同應(yīng)力狀態(tài)下的損傷極限。開展了TA2純鈦筒形件的可旋性試驗研究,確定了裂紋的萌生位置及其筒形件強(qiáng)力旋壓的可旋性。利用韌性斷裂準(zhǔn)則預(yù)測了TA2純鈦可旋性試驗的損傷分布。結(jié)果表明,除了Ayada準(zhǔn)則和Freudenthal準(zhǔn)則,其他準(zhǔn)則都可以預(yù)測TA2純鈦管材的外表面裂紋萌生。研究了應(yīng)變、應(yīng)力狀態(tài)等因素對TA2純鈦可旋性試驗韌性斷裂的影響。根據(jù)旋壓變形應(yīng)力應(yīng)變呈周期性變化的特點,提出了周期應(yīng)力三軸度和周期羅德系數(shù)概念,分析了斷裂位置內(nèi)外層金屬的應(yīng)力狀態(tài)隨旋壓過程的演化規(guī)律。研究結(jié)果表明,斷裂位置的最外層金屬由于高應(yīng)力三軸度和大塑性變形的影響在旋壓過程中最有可能首先開裂。研究了網(wǎng)格高寬比對韌性斷裂準(zhǔn)則預(yù)測精度和損傷累積的影響。在所有選用的準(zhǔn)則中,C-L準(zhǔn)則具有最高的預(yù)測精度并且受網(wǎng)格高寬比改變的影響較小,而網(wǎng)格高寬比對R-T準(zhǔn)則和MC準(zhǔn)則的預(yù)測精度有很大影響。此外,相比于壓縮試驗,拉伸試驗預(yù)測的筒形件可旋性數(shù)值更接近實驗值,相應(yīng)的預(yù)測精度也高于壓縮試驗。針對Ti-15-3鈦合金筒形件強(qiáng)旋中的破裂情況,進(jìn)行了不同減薄率下的損傷演化預(yù)測,研究了低塑性材料筒形件強(qiáng)旋過程中表面裂紋的產(chǎn)生機(jī)制。對于本文使用的韌性斷裂準(zhǔn)則,只有McClintock準(zhǔn)則的預(yù)測規(guī)律與試驗結(jié)果相符。由于同時考慮了第一主應(yīng)力和第二主應(yīng)力對損傷累積的影響,在中間減薄率下,McClintock準(zhǔn)則捕捉到了最內(nèi)層金屬第二主應(yīng)力在隆起變形階段和減薄變形階段的符號變化,從而預(yù)測了一個可以消除Ti-15-3表面裂紋的減薄率安全區(qū)域。進(jìn)行了TA2純鈦板材可旋性試驗研究和損傷預(yù)測研究。分析了應(yīng)力、應(yīng)力狀態(tài)等因素對TA2純鈦板材可旋性試驗韌性斷裂行為的影響。結(jié)果表明,最大剪切應(yīng)力對內(nèi)層金屬的韌性斷裂影響較小,但內(nèi)層金屬在整個成形過程中具有較高的應(yīng)力三軸度。雖然外層金屬的應(yīng)力三軸度低于內(nèi)層,但是外層金屬具有高于內(nèi)層的等效塑性應(yīng)變,并且最大剪切應(yīng)力對外層金屬的韌性斷裂影響顯著。因此,對于本文所選用的韌性斷裂準(zhǔn)則,主要考慮最大主應(yīng)力或應(yīng)力三軸度對韌性斷裂影響的模型,其預(yù)測的最大損傷值出現(xiàn)在旋壓板材的內(nèi)層,與實驗不符。只有Freudenthal,LeRoy以及Lou和Yoon提出的韌性斷裂準(zhǔn)則,可以預(yù)測TA2純鈦板材可旋性試驗中外層金屬的裂紋萌生。
[Abstract]:As the most effective technology for manufacturing large thin-walled rotating parts, spinning has been widely used in the plastic forming process of pure titanium and titanium alloys. However, pure titanium and titanium alloys are difficult to deform and are prone to ductile fracture during spinning, which seriously restricts the application of pure titanium and titanium alloy spinning technology. Aiming at the problem of ductile fracture of pure titanium and titanium alloy during high-strength spinning, the ductile fracture behavior of pure titanium TA2 under different stress states is studied. The spinning limit and damage evolution of TA2 barrel-shaped parts and sheet-metal spinnability tests are predicted by the ductile fracture criterion. The barrel-shaped parts and sheet-metal spinnability tests are revealed. Ductile fracture mechanism of spinning fracture in spinning test. Aiming at the surface cracking phenomenon of Ti-15-3 titanium alloy cylindrical parts during strong spinning, the effect of thinning rate on damage evolution of inner and outer layers of cylindrical parts was studied. The ductile fracture mechanism of low plastic material cylindrical parts under strong spinning was revealed. The characteristics of plastic deformation under different stress states are analyzed, and the effect of stress state change on the ductile fracture behavior of pure titanium TA2 is studied. At high stress triaxiality, the fracture strain decreases with the increase of stress triaxiality. The fracture strain of compression test under negative stress triaxiality is the largest. The ductile fracture criterion is coupled to the finite element software ABAQUS to predict the damage distribution in the ductile fracture test of pure titanium TA2 under different stress states. The applicable ranges of the ductile fracture criteria are determined and the ductile fracture criteria are obtained. Damage limits of TA2 titanium cylindrical parts under different stress states were studied. The location of crack initiation and the spinnability of TA2 titanium cylindrical parts under strong spinning were determined. The damage distribution of TA2 titanium cylindrical parts under spinnability test was predicted by using ductile fracture criterion. The results show that there are other criteria besides Ayada criterion and Freudenthal criterion. The effect of strain, stress state and other factors on the ductile fracture of TA2 titanium in spinning test was studied. According to the periodic variation of stress and strain during spinning, the concepts of periodic stress triaxiality and periodic Rhode coefficient were put forward, and the stress of inner and outer layers of metal at the fracture position was analyzed. The results show that the outermost metal in the fracture position is most likely to crack first in the spinning process due to the influence of high stress triaxiality and large plastic deformation. In addition, compared with the compression test, the predicted value of cylinder spinnability in tensile test is closer to the experimental value and the corresponding prediction accuracy is higher than that in compression test. The damage evolution of titanium alloy cylindrical parts under different thinning rates was predicted and the mechanism of surface crack formation during strong spinning was studied. For the ductile fracture criterion used in this paper, only McClintock criterion was found to be consistent with the experimental results. The McClintock criterion captures the symbolic changes of the second principal stress of the innermost metal during the uplift and the thinning stages at the intermediate thinning rate, thus predicting a safe thinning rate region for eliminating surface cracks on Ti-15-3. The results show that the maximum shear stress has little effect on the ductile fracture of the inner layer metal, but the inner layer metal has higher stress triaxiality in the whole forming process. The stress triaxiality is lower than the inner layer, but the outer layer metal has higher equivalent plastic strain than the inner layer, and the maximum shear stress has a significant effect on the ductile fracture of the outer layer metal. Only the ductile fracture criterion proposed by Freudenthal, LeRoy and Lou and Yoon can predict the crack initiation of the outer metal in the spinnability test of pure titanium TA2 plate.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TG306

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本文編號：2185927