电磁铆接过程铆钉动态塑性变形行为及组织性能研究

发布时间：2018-05-30 06:11

本文选题：电磁铆接 + 数值模拟　；参考：《哈尔滨工业大学》2016年博士论文

【摘要】：电磁铆接是一种高速冲击连接技术。相对于其他铆接技术,具有加载速度快、冲击力大、铆钉变形稳定等优点,可有效解决复合材料铆接时易被挤压破坏,以及难变形钛合金铆钉气动铆接加载力不足等技术瓶颈,该技术已应用于航空航天产品之中,势必将成为铆接工艺的重点发展方向。本文基于电磁铆接技术众多优点和航空航天领域需求,采用Φ10mm-2A10铝合金铆钉和Φ6mm-TA1钛合金铆钉,重点研究电磁铆接过程中铆钉动态塑性变形行为、高应变率下铆钉微观组织演化以及连接结构力学性能、成形质量。基于ANSYS/LS-DYNA有限元分析软件,建立电磁铆接过程电磁场-力场-温度场耦合数值模拟模型。以综合考虑应变强化、应变速率强化及温度软化对流变应力影响的Johnson-Cook模型为铆钉材料本构关系,实时考虑电磁场、力场以及温度场之间相互影响,对整个电磁铆接过程进行了系统分析。结果表明本文所建立的有限元模型与工艺试验结果相符,通过分析得到了很难实测的磁压力分布、应变速率变化和温度场分布等规律。磁压力时空分布表明磁压力以衰减正弦波形式变化,且在驱动片与线圈厚度中心相对位置处达到峰值。数值模拟发现沿着铆钉钉杆干涉量呈不均匀分布趋势。针对这一现象,本文结合弹塑性力学和应力波理论对铆钉动态塑性变形行为进行分析,建立了相对干涉量分布模型,通过试验实测干涉量验证了模型精度。沿着铆钉钉杆方向,越靠近镦头干涉量越大,并向半圆头一侧呈幂函数与指数函数乘积形式递减分布。干涉量大小直接决定了板材孔壁周围塑性变形区域大小,沿着板材厚度方向,塑性变形区域大小分布规律与干涉量分布相同。对于2A10铝合金铆钉电磁铆接,绝热剪切带是铆钉成形组织重要特征。绝热剪切带两侧金属较大的径向塑性流动速度差和绝热温升软化效应是绝热剪切带形成主要机制。另外,试验和数值模拟结果表明绝热剪切带优先萌生于镦头对角位置,随着变形量的增加而逐渐向镦头中心扩展,并在镦头中心相交。最终形成的绝热剪切带宽度约为80μm,狭窄的绝热剪切带内存在大量相互缠结的位错,位错滑移作用使其内部形成了宽度约0.8μm层片状亚结构。绝热剪切带内部微观组织及分布特征对铆钉镦头性能分布具有较大影响。大量Al2Cu强化相和较高位错密度使得绝热剪切带处硬度明显高于其他位置。绝热剪切带分布特征导致镦头径向压缩强度和高度方向拉伸强度分布不均,而铆接后镦头平均抗压缩屈服强度较原始铆钉强度提高了81%,这对铆接结构实际承载能力具有积极的影响。对于TA1钛合金铆钉电磁铆接,仅有镦头轴向变形量较大时才会出现绝热剪切带现象,绝热剪切带宽度约为10μm。钛合金绝热剪切带内部微观组织演化仍以位错滑移机制为主导,并且亚晶动态旋转机制导致绝热剪切带内部形成了尺寸在100~200nm之间的等轴状再结晶晶粒。整个铆接结构力学性能是评价其可靠性的重要标准,对于单个Φ10mm-2A10铝合金铆钉的电磁铆接结构,可承受最大剪切载荷和拉脱载荷分别为23.2kN和35kN,并且该铆接结构镦头高度在5~6mm之间时其力学性能最佳。而对于单个Φ6mm-TA1钛合金铆钉铆接结构,可承受最大剪切载荷和拉脱载荷分别可达9.9kN和12.3k N。为了探索电磁铆接技术工程化应用,本文对比分析了具有同等抗剪切承载能力的Φ10mm-2A10铝合金铆钉和Φ6mm-30CrMnSi钢制螺栓紧固件连接结构。相对于螺接结构,铆接结构抗剪切载荷和拉脱载荷分别高出3.1%和40%,而单纯从紧固件重量方面对比其总量轻15.8%。如果从比强度方面对比分析,铆接结构抗剪切和拉脱比强度分别高出22.6%和66.1%。因此,采用轻质的电磁铆接结构代替比强度较低的螺接结构,既可提高连接结构的可靠性,亦可实现明显的减重效果,对航空航天领域装配工艺具有重大的工程意义。
[Abstract]:Electromagnetic riveting is a high speed impact connection technology. Compared with other riveting technology, it has many advantages, such as fast loading speed, great impact force, and the stability of riveting. It can effectively solve the technical bottlenecks of the composite riveting, as well as the difficult deformation of the titanium alloy riveting, which has been applied to Aeronautics and Astronautics. In the product, it is bound to be the key development direction of riveting technology. Based on many advantages of the electromagnetic riveting technology and the needs of the aerospace field, the dynamic plastic deformation behavior of rivet in the electromagnetic riveting process and the microstructure evolution of rivet under the high strain rate are focused on by using the 10mm-2A10 aluminum alloy rivets and the 6mm-TA1 titanium alloy rivets. Based on the ANSYS/LS-DYNA finite element analysis software, a numerical simulation model of electromagnetic field force field temperature field coupling is established based on the finite element analysis software. The constitutive relationship of the rivet material with the strain hardening, the strain rate strengthening and the effect of temperature softening on the rheological stress is taken into consideration, and the real time examination of the rivet material is made. Considering the interaction between the electromagnetic field, the force field and the temperature field, the whole electromagnetic riveting process is systematically analyzed. The results show that the finite element model established in this paper is in agreement with the result of the process test. Through analysis, the distribution of magnetic pressure, the change of strain rate and the distribution of temperature field are obtained, and the time and space distribution table of magnetic pressure is also obtained. The magnetic pressure changes in the form of the attenuated sine wave and reaches the peak value at the relative position of the driving plate and the center of the coil thickness. The numerical simulation shows that the interference of the rivet rod is unevenly distributed. In this paper, the dynamic plastic deformation behavior of the rivet is analyzed with the elastoplastic mechanics and the stress wave theory, and the phase is established. The model accuracy of the interference quantity distribution model is verified by the measured interference measurements. The closer the rivet rod direction is, the closer the interference amount to the upsetting head is, the smaller the distribution of the power function and the exponential function product of the half round head. The size of the circumference plastic deformation area of the plate hole wall is directly determined by the interference amount, along the thickness square of the plate. For 2A10 aluminum alloy rivet electromagnetic riveting, the adiabatic shear band is an important feature of rivet forming. The larger radial plastic flow velocity difference and adiabatic temperature rise softening effect on both sides of the adiabatic shear zone are the main mechanism of adiabatic shear band formation. The results of the value simulation show that the adiabatic shear band first occurs in the diagonal position of the upsetting head. With the increase of the deformation amount, it gradually extends to the center of the upsetting head and intersects at the center of upsetting head. The width of the adiabatic shear band is about 80 mu, and there is a large number of intertangled dislocation in the narrow adiabatic shear zone, and the dislocation slip action causes the internal formation of the adiabatic shear zone. The internal microstructure and distribution characteristics of the adiabatic shear zone have a great influence on the performance distribution of the rivet upsetting head. The hardness of the adiabatic shear band is obviously higher than that of the other positions. The adiabatic shear zone is characterized by the radial compressive strength and the high direction tension of the lead upsetting head. The distribution characteristics of the adiabatic shear band are obviously higher than that of the other positions. The tensile strength distribution is uneven, and the average compressive yield strength of the upsetting head after riveting is 81% higher than the original rivet strength, which has a positive effect on the actual bearing capacity of the riveted structure. For TA1 titanium alloy rivet electromagnetic riveting, only when the axial deformation of the upsetting head is large, an absolute heat shear zone will appear, and the width of the adiabatic shear band is about 10 mu. The internal microstructure evolution of the adiabatic shear zone of titanium alloy is still dominated by dislocation slip mechanism, and the dynamic rotation mechanism of the subcrystal leads to the formation of the equiaxed recrystallized grain between the adiabatic shear bands. The mechanical properties of the whole riveting structure is an important criterion for evaluating its reliability and for a single 10mm-2A10 aluminum alloy. The rivet riveting structure can bear the maximum shear load and the pull load of 23.2kN and 35kN respectively, and the mechanical performance of the riveting structure is the best when the upsetting height is between 5~6mm. The maximum shear load and the pull load can be reached to 9.9kN and 12.3k N. respectively for the exploration of the riveting structure of the riveting structure of the riveting structure. In the engineering application of electromagnetic riveting technology, this paper compares and analyzes the connection structure of the joint with the equal shear bearing capacity of the 10mm-2A10 aluminum alloy rivet and the bolt fastener of 6mm-30CrMnSi steel. Compared with the stud structure, the shear load and the pull load of the riveting structure are 3.1% and 40% higher respectively than the weight of the fasteners. If the total amount of light 15.8%. is compared and analyzed from the specific strength, the shear and the tensile strength of the riveting structure are higher than 22.6% and 66.1%., respectively. Therefore, the use of light electromagnetic riveting structure instead of the lower specific strength structure can not only improve the reliability of the connection structure, but also realize the obvious weight reduction effect, and the assembly process in the aerospace field It is of great engineering significance.
【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】：2016
【分类号】：TG391

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