内外压复合作用下管材塑性失稳行为研究

发布时间：2018-03-31 12:52

本文选题：管材塑性失稳　切入点：内外压复合作用　出处：《哈尔滨工业大学》2015年博士论文

【摘要】：轻量化是飞机、汽车等运输工具节约燃料、减少废气排放的主要手段之一。内高压成形技术是在内压作用下使管材成为复杂形状空心变截面轻量化构件的先进技术。为了提高管材成形性,提出在管材内外表面同时施加高压液体的内外复合加压成形技术。本文研制了可实现管材内外复合加压的实验装置,结合实验研究、数值模拟与力学分析,系统地研究了薄壁管材在内外压复合作用下的塑性变形行为、压缩和拉伸失稳行为以及起皱和开裂机制,探讨该技术工业应用的可行性。为测试三维应力状态下各向异性管材的力学性能,通过塑性增量理论,利用各向异性屈服准则推导了三维应力状态下管材胀形的等效应力与应变公式。研制了三维应力状态下管材力学性能测试装置,提出了三维应力状态下管材力学性能测试方法。得到了5A02铝合金管材在0、85MPa和127.5MPa三种外压条件下的应变硬化指数n值,发现随着外压增加,n值略有增加。研制出可实现管材内外复合加压的实验装置,该装置实现了分体模具管材外压密封,突破了外压、内压和左右两个冲头位移的匹配加载与卸载关键技术。通过对薄壁管材进行内压作用下的起皱实验研究,揭示了不同内压条件下管材起皱行为及展平过程皱纹的形状变化规律。对于5A02铝合金管材,内压低于1.0ps(初始屈服压力)时,仅在两端产生两个非轴对称皱纹,展平过程发生破裂;内压为1.2ps-1.8ps时,形成三个轴对称皱纹,其中内压为1.2 ps-1.6ps时展平结束形成死皱,内压为1.8ps时皱纹被完全展平。对于弹性模量和屈服强度更高的不锈钢管,内压在0.6ps-1.4ps时形成三个轴对称皱纹,展平过程不易形成局部死皱。轴对称皱纹形状可以用高斯正态分布函数准确地描述,皱纹形状和尺寸以及皱纹间距可以用高斯函数中的特征参数定量地表达。通过对5A02铝合金管材进行内外压复合作用下的起皱实验研究,揭示了外压对5A02管材起皱行为的影响机理。压差恒定时,外压不改变管材的皱纹形状,因为外压不改变管材轴向的应力分布规律以及管材等效应力;内压恒定时,增加外压使皱纹由三个轴对称皱纹转变为两个非轴对称的端部皱纹,外压抑制中间皱纹的形成;内压变化时,增压外压与内压比例也使皱纹数量发生变化,但中间皱纹是非轴对称的。通过数值模拟和理论分析给出了皱纹形成过程应力变化规律,揭示了内外压复合作用下管材皱纹发生与发展机理:管材端部由于边缘弯曲效应产生了两个应力峰值,在管材两端先发生屈服及塑性失稳而形成两个皱纹,若压差达到1.2ps,则逐渐形成中间皱纹。通过内外压自由胀形和圆角充填实验研究了三种典型铝合金管材的塑性变形与拉伸失稳行为。最高外压增加到212.5MPa时,自由胀形过程5A02、2A12及6063三种管材的胀形区轮廓、极限膨胀率、壁厚分布规律没有发生改变,圆角充填过程5A02管材的极限圆角半径没有发生变化,表明外压不会改变管材发生颈缩前的均匀变形能力。通过力学分析和数值模拟揭示了内外压复合作用下无法提高管材均匀塑性变形能力的机理:加载失稳分析发现内外压复合作用下管材极限应变与外压无关;外压增加,环向、轴向和法向应力降低,静水压力增加,但应力偏张量并未改变,管材变形方式没有发生改变。采用扫描电镜研究了外压对管材开裂行为的影响,发现随着外压增加,管材断口上的等轴韧窝变扁平,韧窝方向发生偏转,韧窝数量、尺寸及所占比例都减少;外压的增加可以提高管材断裂极限:对于5A02铝合金管材,外压增加到212.5MPa时,自由胀形的等效断裂应变由1.022增加到2.466,提高了141.3%;圆角充填的等效断裂应变由0.860增加到3.054,提高了255.1%;外压对2A12管材的影响规律与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.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG115.5

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