本文選題：管材塑性失穩(wěn)　切入點：內(nèi)外壓復(fù)合作用　出處：《哈爾濱工業(yè)大學(xué)》2015年博士論文

【摘要】：輕量化是飛機、汽車等運輸工具節(jié)約燃料、減少廢氣排放的主要手段之一。內(nèi)高壓成形技術(shù)是在內(nèi)壓作用下使管材成為復(fù)雜形狀空心變截面輕量化構(gòu)件的先進技術(shù)。為了提高管材成形性,提出在管材內(nèi)外表面同時施加高壓液體的內(nèi)外復(fù)合加壓成形技術(shù)。本文研制了可實現(xiàn)管材內(nèi)外復(fù)合加壓的實驗裝置,結(jié)合實驗研究、數(shù)值模擬與力學(xué)分析,系統(tǒng)地研究了薄壁管材在內(nèi)外壓復(fù)合作用下的塑性變形行為、壓縮和拉伸失穩(wěn)行為以及起皺和開裂機制,探討該技術(shù)工業(yè)應(yīng)用的可行性。為測試三維應(yīng)力狀態(tài)下各向異性管材的力學(xué)性能,通過塑性增量理論,利用各向異性屈服準則推導(dǎo)了三維應(yīng)力狀態(tài)下管材脹形的等效應(yīng)力與應(yīng)變公式。研制了三維應(yīng)力狀態(tài)下管材力學(xué)性能測試裝置,提出了三維應(yīng)力狀態(tài)下管材力學(xué)性能測試方法。得到了5A02鋁合金管材在0、85MPa和127.5MPa三種外壓條件下的應(yīng)變硬化指數(shù)n值,發(fā)現(xiàn)隨著外壓增加,n值略有增加。研制出可實現(xiàn)管材內(nèi)外復(fù)合加壓的實驗裝置,該裝置實現(xiàn)了分體模具管材外壓密封,突破了外壓、內(nèi)壓和左右兩個沖頭位移的匹配加載與卸載關(guān)鍵技術(shù)。通過對薄壁管材進行內(nèi)壓作用下的起皺實驗研究,揭示了不同內(nèi)壓條件下管材起皺行為及展平過程皺紋的形狀變化規(guī)律。對于5A02鋁合金管材,內(nèi)壓低于1.0ps(初始屈服壓力)時,僅在兩端產(chǎn)生兩個非軸對稱皺紋,展平過程發(fā)生破裂;內(nèi)壓為1.2ps-1.8ps時,形成三個軸對稱皺紋,其中內(nèi)壓為1.2 ps-1.6ps時展平結(jié)束形成死皺,內(nèi)壓為1.8ps時皺紋被完全展平。對于彈性模量和屈服強度更高的不銹鋼管,內(nèi)壓在0.6ps-1.4ps時形成三個軸對稱皺紋,展平過程不易形成局部死皺。軸對稱皺紋形狀可以用高斯正態(tài)分布函數(shù)準確地描述,皺紋形狀和尺寸以及皺紋間距可以用高斯函數(shù)中的特征參數(shù)定量地表達。通過對5A02鋁合金管材進行內(nèi)外壓復(fù)合作用下的起皺實驗研究,揭示了外壓對5A02管材起皺行為的影響機理。壓差恒定時,外壓不改變管材的皺紋形狀,因為外壓不改變管材軸向的應(yīng)力分布規(guī)律以及管材等效應(yīng)力;內(nèi)壓恒定時,增加外壓使皺紋由三個軸對稱皺紋轉(zhuǎn)變?yōu)閮蓚�非軸對稱的端部皺紋,外壓抑制中間皺紋的形成;內(nèi)壓變化時,增壓外壓與內(nèi)壓比例也使皺紋數(shù)量發(fā)生變化,但中間皺紋是非軸對稱的。通過數(shù)值模擬和理論分析給出了皺紋形成過程應(yīng)力變化規(guī)律,揭示了內(nèi)外壓復(fù)合作用下管材皺紋發(fā)生與發(fā)展機理:管材端部由于邊緣彎曲效應(yīng)產(chǎn)生了兩個應(yīng)力峰值,在管材兩端先發(fā)生屈服及塑性失穩(wěn)而形成兩個皺紋,若壓差達到1.2ps,則逐漸形成中間皺紋。通過內(nèi)外壓自由脹形和圓角充填實驗研究了三種典型鋁合金管材的塑性變形與拉伸失穩(wěn)行為。最高外壓增加到212.5MPa時,自由脹形過程5A02、2A12及6063三種管材的脹形區(qū)輪廓、極限膨脹率、壁厚分布規(guī)律沒有發(fā)生改變,圓角充填過程5A02管材的極限圓角半徑?jīng)]有發(fā)生變化,表明外壓不會改變管材發(fā)生頸縮前的均勻變形能力。通過力學(xué)分析和數(shù)值模擬揭示了內(nèi)外壓復(fù)合作用下無法提高管材均勻塑性變形能力的機理:加載失穩(wěn)分析發(fā)現(xiàn)內(nèi)外壓復(fù)合作用下管材極限應(yīng)變與外壓無關(guān);外壓增加,環(huán)向、軸向和法向應(yīng)力降低,靜水壓力增加,但應(yīng)力偏張量并未改變,管材變形方式?jīng)]有發(fā)生改變。采用掃描電鏡研究了外壓對管材開裂行為的影響,發(fā)現(xiàn)隨著外壓增加,管材斷口上的等軸韌窩變扁平,韌窩方向發(fā)生偏轉(zhuǎn),韌窩數(shù)量、尺寸及所占比例都減少;外壓的增加可以提高管材斷裂極限:對于5A02鋁合金管材,外壓增加到212.5MPa時,自由脹形的等效斷裂應(yīng)變由1.022增加到2.466,提高了141.3%;圓角充填的等效斷裂應(yīng)變由0.860增加到3.054,提高了255.1%;外壓對2A12管材的影響規(guī)律與5A02管材相同。
[Abstract]:Lightweight aircraft, cars and other vehicles to save fuel, reduce exhaust emissions. One of the main means of hydroforming is under internal pressure of the pipe has become the advanced technology of complex shape hollow variable cross-section lightweight component. In order to improve the formability of composite pipe, inside and outside pressure forming technology applied in high pressure liquid pipe inside and outside at the same time the surface can be realized. This paper developed experimental device of pipe inside and outside composite pressure, combined with the experimental study, numerical simulation and mechanical analysis, systematic study of thin-walled tubes in the pressure inside and outside the plastic deformation behavior of the composite under the action of compression and tensile instability behavior and wrinkling and cracking mechanism, explore the feasibility of industrial application. In order to test the three-dimensional stress anisotropy of mechanical properties of pipe under the condition, the incremental theory of plasticity, yield criterion is derived by using the anisotropic shape of 3D stress Equivalent tube bulging under the state of stress and strain formula is developed. The three-dimensional stress state mechanical properties test device, test method should be put forward the three-dimensional mechanical properties of stress. The 5A02 Aluminum Alloy pipes in 0,85MPa and 127.5MPa three kinds of external pressure under the condition of strain hardening index n value found with the increase of external pressure, n value increased slightly. The developed experimental device can realize the pipe inside and outside composite pressure, the sealing device realizes split mold pipe breaks through the external pressure, external pressure, internal pressure and two punch displacement matching of loading and unloading of key technologies. Through the experimental study on the effect of thin wall wrinkling the pipe under internal pressure, reveals the shape variation of pipe wrinkling behavior and flattening process of wrinkles in different pressure conditions. For the 5A02 Aluminum Alloy pipe, 1.0ps internal pressure (lower than the initial yield pressure), only two at both ends The non axisymmetric wrinkles, flattening process of rupture; internal pressure is 1.2ps-1.8ps, the formation of three axisymmetric wrinkles, the internal pressure of 1.2 ps-1.6ps flat end forming die wrinkle, when internal pressure is 1.8ps was completely flattened wrinkles. For the elastic modulus and yield strength of higher stainless steel pipe, internal pressure forming three axisymmetric wrinkles in the 0.6ps-1.4ps, the flattening process is not easy to form local dead wrinkles. The axisymmetric wrinkles shape can be described accurately by using Gauss normal distribution function, shape and size and spacing wrinkles wrinkles can be used in surface quantitative characteristic parameters in the Gauss function. Based on the 5A02 Aluminum Alloy pipe experimental study on composite wrinkling under the action of internal and external pressure, reveals the effect of external pressure on 5A02 pipe wrinkling behavior mechanism. The constant pressure, external pressure does not change the pipe wrinkles shape, because the external pressure does not change the tube axial stress distribution and tube The effects of material force; internal pressure is constant, increasing external pressure to change from the three axisymmetric wrinkles wrinkles for two non axisymmetric end of the formation of wrinkles, wrinkles in the middle pressure suppression; internal pressure changes, and the internal pressure ratio so that wrinkles quantity changes of external pressure booster, but the middle is wrinkles non axisymmetric. Through numerical simulation and theoretical analysis are given wrinkles formation process of stress variation, reveals the internal and external pressure under the action of composite pipe wrinkle occurrence and development mechanism of the pipe end because of the edge bending effect produced two stress peak value, yield and plastic instability and the formation of two occurred in the first wrinkles the pipe ends, if the pressure reached 1.2ps, is gradually formed by the internal and external pressure. The middle wrinkle free bulging and corner filling experiment on the plastic instability and tensile deformation behavior of three kinds of typical Aluminum Alloy pipes. The highest pressure increased to 212.5MPa, free The bulging contour bulging process of 6063 5A02,2A12 and three pipes, limit the expansion ratio, thickness distribution did not change, the limit radius of fillet filling process of 5A02 pipe has not changed, that does not change the external pressure pipe before Necking Deformation. Through the mechanical analysis and numerical simulation of inside and outside under the action of pressure composite can improve pipe mechanism of uniform plastic deformation ability: stability analysis of composite pipe under the action of internal and external pressure that limit strain and external pressure to increase external pressure, load loss; circumferential, axial and normal stress decreases, the hydrostatic pressure increases, but the deviatoric stress tensor has not changed, no pipe deformation change. To study the influence of external pressure on the pipe cracking behavior by using scanning electron microscope, we found that with the increase of external pressure, pipe on the fracture surface dimple becomes flat, dimple deflect, dimple number, The size and the proportion are reduced; increase external pressure can improve the pipe fracture limit for 5A02 Aluminum Alloy pipe, the external pressure increased to 212.5MPa, the equivalent fracture strain free bulging increased from 1.022 to 2.466, increased by 141.3%; equivalent fracture strain corner filling increased from 0.860 to 3.054, increased by 255.1%; influence of external pressure pipe with 5A02 of 2A12 pipes.

【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】：2015
【分類號】：TG115.5

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