本文選題：厚壁筒 + 自增強(qiáng)處理��； 參考：《長(zhǎng)江大學(xué)》2016年碩士論文

【摘要】：石油天然氣等底層資源日益匱乏,以及對(duì)油氣資源的開采難度逐漸增大,為穩(wěn)定現(xiàn)有油氣田開采量,提高新開發(fā)油氣井的采收率,超高壓容器設(shè)備在化工與石油行業(yè)中應(yīng)用逐漸廣泛。為了提高超高壓容器設(shè)備的承載能力及使用壽命,除了在材料屈服范圍內(nèi)提高容器設(shè)備的壁厚,采用自增強(qiáng)處理技術(shù)也是在對(duì)超高壓設(shè)備設(shè)計(jì)加工中不可或缺的一項(xiàng),通過對(duì)內(nèi)腔加壓處理,使內(nèi)層發(fā)生塑性變形,從而在設(shè)備內(nèi)腔處引入殘余應(yīng)力,以降低設(shè)備應(yīng)力水平,提高其疲勞強(qiáng)度。任何構(gòu)件在加工過程中不可避免出現(xiàn)因表面劃痕、金屬夾雜、腐蝕坑等加工缺陷而造成裂紋問題,在對(duì)超高壓設(shè)備采用自增強(qiáng)技術(shù)時(shí),裂紋尖端處會(huì)產(chǎn)生一定程度的應(yīng)力集中,影響尖端附近位置的殘余應(yīng)力分布,改變自增強(qiáng)處理效果。因此,在以斷裂力學(xué)為理論基礎(chǔ),假設(shè)構(gòu)件實(shí)際存在初始裂紋的條件下,定量研究殘余應(yīng)力下的裂紋尖端斷裂參數(shù)分布規(guī)律,并根據(jù)表征參量應(yīng)力強(qiáng)度因子評(píng)估在殘余應(yīng)力作用下裂紋的擴(kuò)展行為,開拓了自增強(qiáng)技術(shù)在對(duì)含裂紋超高壓設(shè)備應(yīng)用方面的研究領(lǐng)域。實(shí)際工程中裂紋的形式主要為三維裂紋問題,對(duì)于設(shè)備內(nèi)部型腔結(jié)構(gòu)通常較為復(fù)雜,用現(xiàn)有的斷裂力學(xué)理論無法進(jìn)行數(shù)值計(jì)算,且難以通過實(shí)驗(yàn)手段完成對(duì)理論的驗(yàn)證。根據(jù)對(duì)復(fù)雜內(nèi)部型腔裂紋產(chǎn)生位置分析,從研究的可行性角度考慮,把存在于復(fù)雜型腔內(nèi)裂紋最核心的位置進(jìn)行抽象簡(jiǎn)化成厚壁筒內(nèi)壁裂紋,為實(shí)際工程應(yīng)用中評(píng)判復(fù)雜內(nèi)腔裂紋對(duì)自增強(qiáng)處理效果提供理論指導(dǎo)。論文從彈塑性力學(xué)角度,基于理想化彈塑性模型以及雙線性隨動(dòng)強(qiáng)化模型兩種材料類型分別建立了自增強(qiáng)處理壓力卸載后殘余應(yīng)力計(jì)算公式。通過斷裂力學(xué)權(quán)函數(shù)理論,分析并驗(yàn)證了厚壁筒權(quán)函數(shù)式的準(zhǔn)確性,推導(dǎo)出了含裂紋厚壁筒自增強(qiáng)處理后殘余應(yīng)力的應(yīng)力強(qiáng)度因子計(jì)算公式。采用數(shù)值模擬方法,引用J積分來表征自增強(qiáng)處理下裂紋尖端斷裂特性,對(duì)不同裂紋形狀下厚壁筒的應(yīng)力分布以及裂紋尖端處的斷裂參數(shù)進(jìn)行數(shù)值計(jì)算,研究了穿透裂紋及橢圓裂紋的兩種含裂紋厚壁筒經(jīng)自增強(qiáng)處理后殘余應(yīng)力變化規(guī)律以及自增強(qiáng)處理引入的殘余應(yīng)力對(duì)裂紋尖端J積分值影響規(guī)律。對(duì)穿透型裂紋分析表明,自增強(qiáng)處理后厚壁筒裂紋的存在主要引起了裂紋尖端沿?cái)U(kuò)展方向上殘余壓應(yīng)力范圍內(nèi)的應(yīng)力變化,超高該范圍應(yīng)力狀態(tài)基本與不含裂紋的厚壁筒相近,其中最大殘余壓應(yīng)力出現(xiàn)在裂紋尖端沿?cái)U(kuò)展方向附近,而不是在裂紋應(yīng)力集中位置處,對(duì)降低裂紋尖端的的擴(kuò)展具有一定促進(jìn)作用；徑比K的變化影響裂紋前緣最大殘余切向應(yīng)力、裂紋尖端殘余切向應(yīng)力以及尖端沿?cái)U(kuò)展方向的殘余壓應(yīng)力區(qū)域范圍變化,徑比K小于1.6時(shí)自增強(qiáng)對(duì)降低裂紋尖端的起始擴(kuò)展效果不大,大于1.7時(shí)隨著K值的增大,自增強(qiáng)處理對(duì)降低裂紋尖端的擴(kuò)展速率逐漸顯著,但隨著自增強(qiáng)壓力的增大,K值的增大對(duì)裂紋擴(kuò)展速率影響較��；徑比K取較小值時(shí),選擇較小自增強(qiáng)壓力對(duì)抑制裂紋尖端起裂擴(kuò)展更明顯,而沿厚度方向經(jīng)自增強(qiáng)處理后,由殘余應(yīng)力場(chǎng)形成的J積分值在厚度小于40mm時(shí)為負(fù)值并呈現(xiàn)浴盆曲線形狀,在該范圍內(nèi)由殘余壓應(yīng)力場(chǎng)主導(dǎo)控制裂紋尖端,但靠近約束端位置處主要由殘余拉應(yīng)力場(chǎng)主導(dǎo)控制。對(duì)橢圓型裂紋分析表明,當(dāng)裂紋深度c與裂紋長(zhǎng)度的比值小于1時(shí),隨著比值的增大,裂紋尖端前緣最大殘余壓應(yīng)力逐漸增大,而當(dāng)比值大于1時(shí)反而呈逐漸減少的趨勢(shì)：橢圓長(zhǎng)短軸比例的變化對(duì)尖端前緣處的殘余切向應(yīng)力影響較小,變化幅度不大,而沿橢圓曲線方向上,在橢圓兩側(cè)端點(diǎn)以及中點(diǎn)位置處附近的殘余壓應(yīng)力明顯高于其它位置,這是由于在該三點(diǎn)位置裂紋尖端分別處于內(nèi)壁表面以及橢圓曲率半徑最大處；自增強(qiáng)處理對(duì)抑制軸向橢圓裂紋遠(yuǎn)離內(nèi)層壁面裂紋尖端的起裂擴(kuò)展相比裂紋其它位置效果更為顯著,同時(shí)當(dāng)裂紋深度與裂紋長(zhǎng)度比值為1.4時(shí),自增強(qiáng)處理對(duì)抑制裂紋尖端擴(kuò)展最為明顯；在相同裂紋形式下過大的增大厚壁筒徑比,自增強(qiáng)處理對(duì)抑制橢圓裂紋尖端的起裂擴(kuò)展效果越不明顯,而當(dāng)橢圓裂紋長(zhǎng)短軸比例較大時(shí),徑比K的增大對(duì)抑制表層裂紋尖端起裂擴(kuò)展影響較明顯,所以厚壁筒壁厚尺寸變化對(duì)裂紋尖端影響與裂紋結(jié)構(gòu)尺寸有較大關(guān)系。
[Abstract]:The underlying resources such as oil and gas are increasingly scarce and the difficulty in exploiting oil and gas resources is gradually increasing. In order to stabilize the production of existing oil and gas fields and improve the recovery rate of newly developed oil and gas wells, ultra high pressure vessel equipment is widely used in chemical and petroleum industries. In order to improve the carrying capacity and service life of UHP vessel equipment, In order to improve the wall thickness of the container equipment in the yield range of the material, the self reinforcing treatment technology is also an indispensable item in the design and processing of the ultra-high pressure equipment. Through the compression treatment of the inner cavity, the inner layer is plastic deformation, and the residual stress is introduced into the inner cavity of the equipment, so as to reduce the stress level of the equipment and improve its fatigue strength. In the process of processing, it is inevitable that cracks are caused by defects such as surface scratches, metal inclusions and corrosion craters. In the use of self reinforcement technology for ultra-high pressure equipment, a certain degree of stress concentration will be produced at the crack tip, which affects the distribution of residual stress in the position near the tip and changes the effect of self reinforcing treatment. On the basis of fracture mechanics, the distribution law of fracture parameters at the crack tip under the residual stress is quantitatively studied under the condition of the actual existence of the initial crack, and the propagation behavior of the crack under the residual stress is evaluated according to the stress intensity factor of the characterization parameter, and the self reinforcement technique should be developed for the ultra high pressure equipment with cracks. In the field of research, the form of cracks in practical engineering is mainly a three-dimensional crack problem. For the internal cavity of the equipment, the cavity structure is usually more complex. It is difficult to use the existing fracture mechanics theory to carry out numerical calculation, and it is difficult to verify the theory by experimental means. Considering the feasibility of the study, the most core position of the complex cavity crack is abstracted into the inner wall crack of the thick wall cylinder. It provides a theoretical guide for the evaluation of the effect of the complex inner cavity crack to the self reinforcing treatment in practical engineering application. The formula for calculating the residual stress after the pressure unloading of the two kinds of material is established respectively. Through the theory of the fracture mechanics weight function, the accuracy of the thick wall cylinder weight function is analyzed and verified, and the calculation formula of the stress intensity factor of the residual stress after the self reinforcing treatment of the thick wall cylinder with a crack is derived. The J integral is used to characterize the crack tip fracture characteristics under the self reinforcement treatment. The stress distribution and the fracture parameters at the crack tip in the thick wall under different crack shapes are numerically calculated. The changes of the residual stress and the self reinforcement of two kinds of cracked thick wall cylinders with crack and Elliptical Cracks are studied. The influence of residual stress introduced into the J integral value at the crack tip. The analysis of the penetrating crack shows that the existence of the crack in the thick wall tube after self reinforcement mainly causes the stress change in the range of the residual compressive stress in the direction of the crack, and the maximum stress state in this range is similar to the thick wall cylinder without crack. The residual compressive stress occurs near the crack tip in the direction of the crack tip, not at the stress concentration in the crack, and has a certain effect on reducing the expansion of the crack tip. The variation of the diameter ratio K affects the maximum residual shear stress in the front of the crack, the residual shear stress at the crack tip and the residual compressive stress zone along the direction of the crack tip. When the diameter ratio is less than 1.6, the effect of self reinforcement on the initiation and expansion of the crack tip is not significant. When the K value increases, the expansion rate of the crack tip decreases with the increase of the K value. But with the increase of the self reinforcing pressure, the increase of the K value has little effect on the crack spreading rate; when the diameter ratio is smaller, the selection of the diameter ratio is smaller. The smaller self reinforcing pressure is more obvious to restrain the crack propagation in the crack tip, and the J integral value formed by the residual stress field is negative and presents the bathtub curve shape when the thickness is less than 40mm, and the residual stress field dominates the crack tip in this range, but the position near the confinement end is mainly controlled by the residual stress field. The residual tensile stress field dominated control. The analysis of elliptical crack shows that when the ratio of crack depth C and crack length is less than 1, the maximum residual compressive stress at the front edge of crack tip increases with the ratio increasing, but when the ratio is greater than 1, it decreases gradually: the change of the ratio of elliptical long and short axis to the remnants at the front edge of the tip The shear stress has little influence on the shear stress, but the residual compressive stress near the elliptical direction is obviously higher than that in other positions near the ellipse and the middle point. This is because the crack tip at the three points is at the surface of the inner wall and the maximum radius of the elliptical curvature, and the autofrettage treatment can restrain the axial ellipsoid. The crack propagation of a circular crack far away from the crack tip of the inner wall is more significant than that of other cracks. At the same time, when the ratio of the crack depth to the crack length is 1.4, the self reinforcement treatment is most obvious for the growth of the crack tip. The increase of the thickness of the thick wall and the diameter ratio of the thick wall under the same crack form, and the self reinforcement treatment for the suppression of the elliptical crack When the ratio of the long and short axis of the elliptical crack is larger, the increase of the diameter ratio K is more obvious to the crack growth of the surface crack tip. Therefore, the influence of the thickness of the wall thickness on the crack tip is closely related to the crack structure size.
【學(xué)位授予單位】：長(zhǎng)江大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2016
【分類號(hào)】：TH49

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