Interface dynamics in bolted joint connections

螺栓连接是机械工程和钢结构中应用最多、最重要的连接形式。但工程师们仍然需要处理拧紧过程和操作中的故障。在拧紧过程中，破坏往往表现为粘滑现象或与粘滑现象有关。在运行过程中，螺栓连接受到冲击、振动或循环热载荷等动态载荷时，可能会发生松动。在这两种情况下，破坏都是由微滑移运动引起的，因此是由粘着过渡到滑动。最近的研究结果，特别是来自物理学和地球科学的研究结果表明，波动过程和类似裂缝的动力学可能在接触伙伴的粘着和滑动之间的转变中起决定性作用。在这种背景下，静摩擦不能再被视为纯粹的材料常数。事实上，第一种建模方法将静摩擦视为动态过程。特别是界面粘滑过渡的开始（微滑移）和整个过程（完全破坏）是由界面内的应力分布决定的。在本项目中，这些发现应转移到螺栓连接的尺寸，拧紧和操作行为。通过建立适当的模型，考虑到界面中的摩擦动力学，我们将获得关于螺栓连接微滑移和完全破坏的力学知识。为了验证这些模型，程序中包括四个实验部分。在第一部分中，我们将研究影响界面应力分布的不对称性，从而影响盘面上的静摩擦系数。在第二部分中，我们将研究螺栓头的形状如何影响界面中的应力分布，从而在螺栓连接拧紧过程中产生粘滑运动。在第三部分中，我们将结合前两部分中最有前途的原理，设计出新型的粘滑减速螺栓。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的自松动的影响。作为理论和实验工作的结果，我们将得出第一套设计螺栓连接的指导方针，这些螺栓连接在拧紧过程中对粘滑具有鲁棒性，并且不会因振动运动而导致操作失败。

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.