大型复杂机械结构的安定性分析方法及其应用

发布时间：2018-03-09 10:05

本文选题：大型结构　切入点：复杂机械　出处：《燕山大学》2016年博士论文　论文类型：学位论文

【摘要】：在大型液压机本体结构中,往往会在一些重要的复杂零部件上出现因局部高应力而导致的局部塑性变形问题。这是一类通过建立在弹性力学基础上的结构分析方法无法解决的强度分析问题。基于安定理论的结构分析方法,因允许承载结构的局部区域在其整体结构安全服役的前提条件下发生一定程度的塑性变形,所以可以用来解决此类问题。为此,本文针对大型液压机本体结构的弹塑性强度分析问题,应用安定理论,建立了一种适用于大型复杂机械结构安定性分析的有限元方法。该方法不仅考虑了常用结构钢随动硬化特性对结构安定性的影响,而且还适用于结构在同时承受恒定载荷和循环载荷作用的情况。针对由随动硬化材料构成的机械结构,应用考虑材料随动硬化特性的下限安定定理,通过构造时间无关的自平衡应力场,采用解析方法推导出了结构安定极限载荷的一般表达式,并且给出了结构在对称循环加载和非对称循环加载时安定极限载荷的表达式。应用这些结果对考虑材料随动硬化特性的薄壁管受对称循环扭转及非对称循环拉伸作用、法兰管受非对称轴向载荷及非对称压力作用和带中心圆孔方板受非对称拉伸载荷作用时的问题进行安定性分析,结果表明,本文的结果与文献中的结果相吻合。针对机械结构同时承受恒定和循环载荷作用的情况,根据Polizzotto下限安定定理构造了与恒定载荷相平衡的应力场,推导出了与该应力场相对应的结构安定条件。在此基础上分析了结构在恒定和循环载荷共同作用下的安定性,求得了结构在同时承受恒定和循环载荷作用时安定极限载荷的一般表达式。应用上述一般解析解,对同时受恒定拉伸和对称循环扭转作用的薄壁管,进行了安定性分析,结果显示,其安定解与相关文献给出的安定解相一致。考虑到工程实际中大型复杂机械结构的常用材料特性和所承受载荷的特点,通过构造时间无关、且与恒定载荷相平衡的应力场及时间无关的背应力场,推导了由随动硬化材料构成的结构,在同时承受恒定与循环载荷作用时的结构安定条件。并提出了特定的加载路径,利用增量弹塑性有限元技术,根据上述安定条件,建立了一种适合于大型复杂机械结构安定性分析的弹塑性有限元方法。该方法的有效性得到了Q235带中心圆孔方板安定性实验的验证。通过对某大型锻造液压机主液压缸及某大型锻造液压机上横梁的安定性分析,分别确定了其安定极限载荷及弹塑性强度安全裕度。
[Abstract]:In the structure of large hydraulic press body, The problem of local plastic deformation caused by local high stress is often found in some important complicated parts. This is a kind of strength analysis problem which can not be solved by means of structural analysis based on elastic mechanics. Structure analysis method based on shakedown theory, This kind of problem can be solved by allowing a certain degree of plastic deformation to occur in the local area of the bearing structure under the precondition of safe service of the whole structure. In this paper, the stability theory is applied to the elastoplastic strength analysis of the bulk structure of a large hydraulic press. A finite element method for structural shakedown analysis of large and complex mechanical structures is established, which not only considers the influence of the following hardening characteristics of common structural steels on the structural stability. It is also applicable to the case that the structure is subjected to constant load and cyclic load at the same time. The lower bound shakedown theorem, which considers the characteristics of the material, is applied to the mechanical structure composed of the following hardening material. By constructing a time-independent self-equilibrium stress field, a general expression of the limit load of structural shakedown is derived by means of analytical method. The expressions of the shakedown limit load of the structure under symmetric cyclic loading and asymmetric cyclic loading are given, and the results are applied to the symmetrical cyclic torsion and asymmetric cyclic tension of thin-walled tubes which take into account the following hardening characteristics of materials. The stability analysis of flange pipe subjected to asymmetric axial load and asymmetric pressure and asymmetric tensile load on the square plate with a central circular hole shows that, The results in this paper are consistent with those in the literature. According to the Polizzotto lower bound shakedown theorem, the stress field in equilibrium with the constant load is constructed according to the condition that the mechanical structure is subjected to both constant and cyclic loads at the same time. The structural shakedown condition corresponding to the stress field is derived, and the stability of the structure under the combined action of constant and cyclic loads is analyzed. The general expression of the shakedown limit load of the structure subjected to constant and cyclic loads at the same time is obtained. Using the above general analytical solution, the shakedown of thin-walled tubes subjected to both constant tension and symmetrical cyclic torsion is analyzed. The results show that the shakedown solution is consistent with the shakedown solution given in relevant literature. Considering the characteristics of materials and loads of large and complex mechanical structures in engineering practice, the construction time is independent. The stress field in equilibrium with the constant load and the time-independent back stress field are derived, and the structural stability conditions of the structure, which is composed of the following hardening materials and subjected to constant and cyclic loads at the same time, are derived, and the specific loading path is proposed. Using the incremental elastoplastic finite element technique, according to the above shakedown condition, An elastoplastic finite element method suitable for shakedown analysis of large and complex mechanical structures is established. The effectiveness of this method has been verified by the stability experiment of Q235 square plate with a central circular hole. Stability analysis of the upper beam of hydraulic cylinder and a large forging hydraulic press, The stability limit load and the safety margin of elastoplastic strength are determined respectively.
【学位授予单位】：燕山大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG305

【相似文献】