【作者】 刘冰；

【导师】 董兴建；

【作者基本信息】 上海交通大学 ， 机械工程， 2019， 硕士

【摘要】 螺栓连接结构装配和拆卸方便、预紧力易于控制、成本低廉并且连接可靠,因此广泛应用在各种装配结构中。但螺栓连接结构也破坏了结构和材料的连续性,引入接触非线性,结合面复杂的接触机理导致结合面的非线性特性。用接触有限元算法建立装配体接触模型,自由度多、计算效率低、收敛困难,占用内存空间大,接触模型动态响应计算时间成本高。针对复杂装配体线性部分可以用模态综合法进行简化,而针对接触非线性部分进行简化的方法尚不成熟。本文针对螺栓连接结合面的非线性特性的表征、滞回曲线离散化方法、接触非线性简化等效模型建立、静态、动态响应以及建立复杂结构的简化等效模型几个方面,展开了以下工作:基于Weierstrass-Mandbrot函数模拟相互接触的粗糙表面微观形貌,研究分形维数和特征尺度对于结合面表面形貌的影响,根据表面形貌、变形和黏滑摩擦行为推导结合面的恢复力和位移的关系,定性的揭示了结合面随着切向载荷增大的刚度软化现象以及恢复力与位移的滞回特性。建立搭接结构的接触有限元模型,有限元仿真结果表明预紧力增大、摩擦系数增大、位移幅值增大,滞回曲线包围的面积增大,能量耗散增大,同时结合面存在剩余刚度,且剩余刚度主要受摩擦系数的影响,并使用MTS疲劳试验机和螺栓搭接结构进行实验,滞回曲线和接触模型滞回曲线吻合,表明接触模型的有效性。连续Iwan模型(C-Iwan模型)恢复力与位移的滞回特性与螺栓连接结合面特性比较吻合,但C-Iwan模型缺少剩余刚度,因此在C-Iwan模型中并联一个常系数的弹簧构成修正的连续Iwan模型(MC-Iwan模型)。由于MC-Iwan模型只能揭示结合面的滞回特性和能量耗散现象,并不适合求解结合面的动态响应。因此采用化曲为直的思想,用几个Jenkins单元和一个常系数的弹簧组成的修正离散Iwan模型(MD-Iwan模型)来代替MC-Iwan模型,求MD-Iwan模型动力学方程分段线性解析解得到动态响应,并且用ANSYS中的COMBIN40、COMBIN14、MASS21单元建立MD-Iwan模型求解得到的动态响应与分段线性解析解吻合。MD-Iwan模型和螺栓连接结合面的滞回特性吻合,基于MD-Iwan模型提出了一种滞回曲线离散化方法,对搭接结构接触模型仿真滞回曲线和实验滞回曲线分别离散化得MD-Iwan参数,在ANSYS中建立搭接结构简化等效模型求解动态响应,与接触模型静态滞回特性以及动态响应吻合,计算效率提高,表明离散化方法建立等效模型有效。针对复杂螺栓连接结构,首先用接触模型分析得到法向拉压双线性、以及切向的滞回特性;使用固定界面模态综合法对非接触部分进行模态缩聚建立复杂结构的模态综合模型;针对复杂结构的拉压双线性用带有间隙的COMBIN40和COMBIN14单元等效,切向采用本文建立的离散化方法,对三个方向进行耦合,建立复杂结构的等效模型。对等效模型进行法向和切向特性验证,结果吻合很好;对三种模型进行模态分析,模态综合模型和接触模型结果完全一致,等效模型吻合较好,仅绕轴线扭转固有频率有一定误差;针对三种模型分别进行切向和法向的动态简谐激励和冲击响应计算,结果表明模态综合模型和接触模型结果完全一致,等效模型切向、法向简谐激励响应、法向冲击响应、切向的冲击响应吻合较好,表明针对复杂结构建立的简化模型有效,并且简化模型和接触模型相比计算效率大大提高且占用内存空间减小,可扩展性好。更多还原

【Abstract】 The bolted connection structure is easy to assemble and disassemble,the preloading force is easy to control,the cost is low,and the connection is reliable,therefore,it is widely used in various assembly structures.However,the bolted joint structure also lead to discontinuity in structure and materials,introduces contact nonlinearity,and the complex contact mechanism of the joint interface leads to the nonlinear characteristics of the bolted interface.The contact finite element algorithm is used to establish the assembly contact model,which has many degrees of freedom,low computational efficiency,difficulty in convergence,large memory space,and high time-consuming calculation of dynamic response of the contact model.The linear part of the complex assembly can be simplified by the modal synthesis method,and the method of simplifying the contact part is not mature.In this paper,the following work is carried out on the characterization of the nonlinear characteristics of the bolted joint surface,the hysteresis curve discretization method,the contact nonlinear simplified equivalent model establishment,the static and dynamic response,and the simplified equivalent model for building complex structures.:Based on Weierstrass-Mandbrot function,the micro-morphology of rough surfaces in contact is simulated,and the influence of fractal dimension and characteristic scale on the surface morphology of the interface is studied,the relationship between restoring force and displacement of the interface is deduced according to the surface morphology,deformation and stick-slip friction behavior,which is qualitatively revealed that the interface increases with tangential load,the stiffness softening phenomenon and hysteretic characteristics of restoring force and displacement are also discussed.The contact finite element model of overlap structure is established,the hysteretic curve of finite element simulation shows that the pre-tightening force,friction coefficient and displacement amplitude increase,the area surrounded by hysteretic curve increases,and the energy dissipation increases.At the same time,the residual stiffness of the joint surface exists,and the residual stiffness is mainly affected by friction coefficient,and MTS fatigue test machine is used and bolt overlap structure were tested,and the hysteretic curves of the contact model and the hysteretic curves of the contact model coincided,which indicated the validity of the contact model.The continuous Iwan model(C-Iwan model)has a hysteresis characteristic of restoring force and displacement,and the relationship between hysteresis characteristics and displacement amplitude is consistent with the bolted joint interface.But the C-Iwan model lacks residual stiffness,so paralleling a constant-coefficient spring in the C-Iwan model constitutes a modified continuous Iwan model(MC-Iwan model).Since the MC-Iwan model can only reveal the hysteresis characteristics and energy dissipation of the joint interface,it is not suitable for solving the dynamics response of the joint interface.Therefore,using the idea of turning the curve into a straight line,a modified discrete Iwan model(MD-Iwan model)composed of several Jenkins elements and a constant coefficient spring is used instead of the MC-Iwan model to solve piecewise linear analytical solution of the MD-Iwan model dynamic equation.The dynamic response is obtained by the analytical solution,and the dynamic response obtained by solving the MD-Iwan model with the COMBIN40,COMBIN14,and MASS21 elements in ANSYS is consistent with the analytical solution.The hysteresis characteristics of the MD-Iwan model and the bolted joint interface are consistent,based on the MD-Iwan model,a hysteresis curve discretization method is proposed.The hysteretic curve and the experimental hysteresis curve of the lap joint contact model are respectively discrete.The MD-Iwan parameters are obtained,and simplified equivalent model of overlap structure is established in ANSYS to solve the dynamic response,which is consistent with the static hysteresis characteristics and dynamic response of the contact model,and the computational efficiency is greatly improved,indicating that the discretization method is established and the equivalent model is valid.Finally,for the complex bolted joint structure,the contact model is firstly used to obtain the normal tension and compression bilinear and tangential hysteresis characteristics of the structure;the non-contact part is fixed by the fixed interface modal synthesis method.Perform modal polycondensation to establish a modal synthesis model of complex structures;for the complex structure of the tension and compression bilinear COMBIN40 with a gap and a COMBIN14 are used to replace,tangentially using the discretization method,coupling in three directions,to establish an equivalent model of complex structures.The axial and tangential characteristics of the equivalent model are verified,and the results are in good agreement.The modal analysis is carried out on the three models,the modal comprehensive model and the contact model are completely consistent,the equivalent model agrees well and only there are some difference in the mode of axial torsion.The tangential and normal dynamic harmonic excitation and impact response calculations are performed for the three models,the results show that the modal comprehensive model and the contact model are completely consistent,and the equivalent model tangential and normal harmonic excitation response and the tangential and normal shock response agree well,it shows that the simplified model is effective,and equivalent model improves computational efficiency and occupies less memory space,the equivalent model scalability is good.更多还原