Interface dynamics in bolted joint connections

螺栓连接是机械工程和钢结构中最常用、最重要的连接形式。但工程师在收紧过程中和操作中仍需处理故障。在拧紧过程中，失效通常表现为粘滑现象或与粘滑现象有关。在运行过程中，当螺栓连接受到冲击、振动或循环热载荷形式的动态载荷时，可能会松动。在这两种情况下，失效都是由微滑移运动引起的，因此是由粘滞到滑动的转变引起的。最近的发现，特别是来自物理学和地学的研究表明，波过程和类破裂动力学可能在接触伙伴的卡住和滑动之间的转变中起决定性作用。在这种背景下，静摩擦不再被认为是一个纯粹的材料常数。事实上，第一种建模方法将静态摩擦视为一个动态过程。尤其是界面粘滑转变的开始(微滑移)以及整个过程(完全破坏)是由界面的应力分布决定的。在这个项目中，这些研究成果应该被转移到螺栓联接的尺寸、紧固和操作行为上。通过建立适当的模型，考虑界面上的摩擦动力学，我们将获得关于螺栓联接的微小滑移和完全失效的力学知识。为了验证这些模型，程序中包括了四个实验部分。在第一部分中，我们将研究不对称性对界面应力分布的影响，从而影响盘-盘装置上的静摩擦系数。在第二部分中，我们将研究螺栓头的形状如何影响螺栓连接紧固过程中界面上的应力分布，从而影响粘滑运动。在第三部分中，我们将结合前两部分中最有希望的原理，设计新型的粘滑减径螺栓。在第四部分，也是最后一部分，我们将研究振动对螺栓连接在运行过程中自松的影响。作为理论和实验工作的结果，我们将得出第一套设计螺栓接头的指南，这些螺栓接头在紧固过程中具有很强的抗粘滑能力，并且不会因振动运动而在操作中发生故障。

Bolted joints are the most used and most important joints in mechanical engineering and steel construction. But engineers still have to deal with failures during the tightening process and in operation. During the tightening process, failures often manifest themselves in the form of or are related to stick-slip phenomena. During operation, bolted joints may turn loose when they are subjected to dynamic loads in form of shock, vibration, or cyclic thermal loadings. In both cases, failures are initiated by microslip motion and hence by a transition from sticking to sliding. Recent findings, especially from physics and the geosciences, have shown that wave processes and fracture-like dynamics may play a decisive role in the transitions between sticking and sliding of the contact partners. Against this background, static friction can be no longer considered as a pure material constant. In fact, first modeling approaches treat static friction as a dynamical process. Especially the beginning (microslip) of the sticking to sliding transition of the interface as well as the whole process (complete failure) is determined by the stress distribution in the interface. In this project, these findings should be transferred to the dimensioning, the tightening, and the operational behavior of bolted joint connections. By the development of appropriate models, taking the friction dynamics in the interface into account, we will gain knowledge on the mechanics of microslip and complete failure of bolted joint connections. For the validation of these models, four experimental parts are included in the program. In the first part, we will study asymmetries affecting the stress distribution in the interface and thus the static friction coefficient on a disc-on-disc setup. In the second part, we will investigate how the shape of the bolt head is affecting the stress distribution in the interface and thus stick-slip motion during the tightening process of bolted joints. In the third part, we will combine the most promising principles from the first two parts by designing new types of stick-slip reducing bolts. In the fourth and last part, we will study the effect of vibrations on the self-loosening of bolted joints during operation. As a consequence of the theoretical and experimental work, we will derive a first set of guidelines for designing bolted joints which are robust to stick-slip during tightening and will not suffer from failure in operation due to vibrational motion.