摘要：机械结构都是由许多零部件以一定的方式联接而成的，螺纹联接是最常用的一种联接方式。在以高速、精密、重载为重要发展标志之一的现代机械中，螺纹联接件的松动、松脱将造成设备工作可靠性的降低。螺纹联接一旦失效，会造成严重的后果。传统的螺纹联接方法其中有些固然可靠，但结构有时很复杂，或者是重复使用性不好，防松性能不可靠，经不起高速运转、强烈振动的冲击。为了有效地解决螺纹联接的松动、松脱和断裂问题，国外的科学家提出了一种新型的螺母--变螺距螺母。随着变螺距螺旋结构在国内外的广泛应用，变螺距螺母的防松性能和防松机理的研究变得非常重要。
　　根据螺纹出现松动的原因得知，螺母的防松性能主要取决于螺纹牙的受力与变形。通过对螺纹联接的受力和变形的理论分析可知，改变螺母的螺距，能够改善螺纹牙的受力分布与变形，可以提高螺母的防松性能。与传统的普通螺纹结构相比，变螺距螺纹结构改善了螺纹间载荷分布不均的现象，减小了螺纹牙间的变形量，提高了螺纹联接的防松性能。
　　从理论上分析螺纹联接的受力与变形，只能够定性地得出变螺距螺母具有更好的防松性能。在正确处理建模、复杂边界条件及多步骤复合载荷的施加的有限元技术问题基础上，可进一步利用先进的有限元软件对变螺距螺母的防松性能进行量化分析。
　　基于ANSYS Workbench有限元分析软件，以M16 A级1型六角螺母为例，对变螺距螺母的防松性能进一步研究，分别分析变螺距螺母与标准螺母的螺纹牙的应力分布、变形分布与啮合螺纹间微滑移的变化趋势，了解了变螺距螺母各圈螺纹承载能力更加平均，大大减小第一圈螺纹的应力，使变螺距螺母强度更高；变螺距螺母的初始变形较小，比标准螺母具有更好的变形协调性，并且具有更强的恢复性；微滑移的积累量小，说明变螺距螺母螺纹的紧固能力更强。
　　从数值分析上定量地得出了变螺距螺母具有更好的防松能力，改变螺母的螺距，提高螺纹联接的防松性能，能够改善机械设备的可靠性，对工程实践上具有重要的意义。
　　关键词：变螺距螺纹，防松性能，螺纹联接

　　Abstract:Mechanical structure is composed of many components which are connected together in a certain way, and thread connection is the most common kind of joint. Nowadays, with the development of modern mechanical equipment which feature is high-speed, heavy-load and precise, thread loosen will reduce the reliability of mechanical equipment. Once thread connection looses, it will cause serious consequences. There are so many traditional threaded connection methods, some of which are reliable, but sometimes, are very complicated, or re-use is bad, or the anti-looseness properties is not reliable, or the structure can not withstand high-speed operation and the strong impact. In order to effectively solve loosen and fracture problems of the thread connection, foreign scientists proposed a new type of nut which is called variable thread nut. With the wide application of the variable pitch of helical structure at home and abroad, studies on the variable thread nut about properties and principles of anti-looseness become more and more important.
　　According to loosening reasons of the thread, we can conclude that the anti-looseness properties of the nut mainly depend on the force and deformation of the threads. What's more, the anti-looseness properties of the nut can be improved by changing the pitch of the nut. And by analyzing the force and elastic deformation of thread connection in theory, changing the pitch of the nut can also improve the stress distribution and deformation of thread. Compared with the traditional common thread structure, variable pitch thread can be achieved by cutting the single side of the nut thread teeth, which could improve the load distribution between the threads, and reduce the amount of deformation between the threads, in order to improve the anti-looseness properties.
　　Analysis the force and deformation of thread connection in theory can only qualitatively reach the better anti-looseness properties of variable thread nut. Dealing with the finite element technique about modeling, complex boundary conditions and applying multi-step composite loads in proper, can quantitatively analyze the anti-looseness properties of variable thread nut based on ANSYS Workbench.
　　Using the advanced finite element software, and a M16 with 1 type of hexagon nut as an example, we can make further study about the anti-looseness properties of variable thread nut. Through anglicizing the stress distribution, the deformation distribution and the micro slip of the thread, and comparing the data with the standard nut, we can summed up that each thread pitch of the variable thread nut bears loads more average, and stress can greatly reduce on the first thread, proving that variable thread nut has higher strength; the variable thread nut's initial deformation is smaller, and the deformation compatibility of the variable thread nut is better than the standard nut's, proving that the variable thread nut has better recovery; the micro slip's accumulation of the variable thread thread is less than the standard nut's, proving that the thread of the variable thread nut fastens stronger.
　　The anti-looseness properties of the variable thread nut is superior to standard nut's from the numerical analysis, and variable thread nut has many advantages. Improving the anti-looseness properties of the thread connection and the reliability of mechanical equipment by changing the pitch of the thread, it makes a great significance to engineering practice.
　　Key words:anti-looseness properties, variable thread, thread connection
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