Article

Comparative study on loosening of anti-loosening bolt and standard bolt system

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Abstract

In general, bolted connections are exposed to vibrations or repeated over-loads that could lead to self-loosening due to loss of preload. Pre-tensioned bolts in ring flanges are critical parts in Offshore Floating Wind Power Systems, and normally a certain percentage of the installed bolt connections are checked and re-tightened every year. This re-tightening is often done at a high cost and a short weather window due to strong winds and high waves. In this paper, three bolt dimensions (M20, M30 and M42) of the anti-loosening bolt system have been tested. The M30 and M42 bolt systems were preloaded and exposed to transverse oscillating loading, and the loss of preload as a function of load amplitude and number of cycles were measured and compared to standard bolts of HV type, exposed identically. The tested novel bolt system has shown superior capacities to withstand self-loosening, compared to standard bolts.

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... The main source of excitation force for fixed structures is the alternating electromagnetic force between leads [20], [21], as shown in Fig. 11. In order to be close to the actual situation, the setting of exciting force in the test process refers to the electromagnetic exciting force of a single cleat when the unit is running. ...
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... However, no quantitative results were provided for the verification of the models. Following Junker's basic assumptions [2], Sakai [3] proceeded to conduct a theoretical analysis, trying to derive the conditions necessary for a bolt to loosen by selfrotation. It was concluded that unless the friction coefficient was less than 0.03, the bolt would not rotate loosely. ...
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This paper presents a numerical model that maps the evolution of fretting fatigue life of Hertzian rough contacting bodies in fretting wear. Effect of surface roughness parameters (i.e. root mean square, skewness and orientation) on fretting fatigue life is reported. Fretting fatigue life is calculated as the crack initiation period predicted by the Smith Watson Topper multiaxial fatigue theory. Fretting wear is also accommodated in the analysis and is calculated by local application of Archard's wear law. The results from this investigation indicate that wear initially improves resistance to fatigue cracking, and reduces fatigue life as it becomes dominant. The approach developed in this study allows for implementation of real rough surfaces and study the effects of various statistical surface properties on fretting fatigue life. The presence of surface roughness in the analytical model reduces predicted fatigue life significantly. Other statistical surface parameters such as skewness and orientation also have a major impact on fretting fatigue life calculations.
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The two most widespread causes of failure of threaded fasteners subjected to dynamic loads are fatigue and vibration induced loosening. This paper presents results of a study on failure of threaded fasteners by vibration induced loosening caused due to dynamic shear loads. Previous experimental work has revealed that fastener loosening occurs as a result of complete or localized slip at the thread and head contact surfaces. A three-dimensional finite element (FE) model is used to study details of four different loosening processes that are characterized by either complete or localized slip at the head and thread contacts. The FE model is found to be capable of adequately modeling factors that influence slip and predicting the different loosening processes. Primary factors that influence slip at fastener contacts are discussed. The results show that loosening can occur at relatively low shear loads due to the process of localized slip.
Article
This paper presents a study on loosening of threaded fasteners subjected to dynamic shear loads. A fundamental analysis of loosening reveals that a fastener can loosen at lower loads than previously expected due to localized slip at the contact surfaces. Four different loosening processes of a screw under different conditions of slip at the head and thread contact regions are identified. Experimental results illustrating these loosening processes are presented. In addition, the minimum dynamic shear force required to initiate loosening is determined experimentally.
On modelling techniques for mechanical joints: Literature study. Int. Workshop of Advanced Manufacturing and Automation (IWAMA
  • Ø Karlsen
  • H G Lemu
Ø. Karlsen, H.G. Lemu, On modelling techniques for mechanical joints: Literature study. Int. Workshop of Advanced Manufacturing and Automation (IWAMA 2019). Springer, Singapore, 634 (2020) 116-125. https://doi.org/10.1007/978-981-15-2341-0_15.