Vývoj metody předvídání povolování šroubů

Abstract

This thesis report of my 5-month internship explains the different possibilities I explored in order to reduce the loosening of the screws of a wheel by optimizing its design. Indeed, spontaneous loosening is a major issue in most bolted assemblies undergoing vibratory forces. These cyclic loadings can sometimes lead to spontaneous loosening of the bolts or screws, especially if the assembly was not correctly dimensioned. Despite all that, a lot of research has been done about screws loosening, but very few tackled the solving of this issue especially because many of these cases can be answered by using an additional system, which were not what we wanted. Therefore, to prevent this, the main points studied were the understanding and measuring of loosening in a general assembly, and the change of different design aspects to reduce the loosening previously measured. To understand and measure loosening, I compared a simple bolted assembly with that of Cobra software, which is able to detect loosening for small and simple assemblies. I also compared the results with Thomala’s method, a technique comparing the displacement of the screw with that of a theoretical beam. I also had to get a wheel model to optimize with OptiStruct, which I got by converting a previous Abaqus model given by Segula. Finally, I used my formerly acquired knowledge to change its design and improve the non-loosening of the four screws. To conclude, I modelled an optimized version of the wheel with a decreased loosening of the screws, and compared theses results with the initial version. I also conclude on the influence of the various parameters on loosening, in the specific case of the wheel, which could somewhat be extrapolated to other bolted assemblies.

This thesis report of my 5-month internship explains the different possibilities I explored in order to reduce the loosening of the screws of a wheel by optimizing its design. Indeed, spontaneous loosening is a major issue in most bolted assemblies undergoing vibratory forces. These cyclic loadings can sometimes lead to spontaneous loosening of the bolts or screws, especially if the assembly was not correctly dimensioned. Despite all that, a lot of research has been done about screws loosening, but very few tackled the solving of this issue especially because many of these cases can be answered by using an additional system, which were not what we wanted. Therefore, to prevent this, the main points studied were the understanding and measuring of loosening in a general assembly, and the change of different design aspects to reduce the loosening previously measured. To understand and measure loosening, I compared a simple bolted assembly with that of Cobra software, which is able to detect loosening for small and simple assemblies. I also compared the results with Thomala’s method, a technique comparing the displacement of the screw with that of a theoretical beam. I also had to get a wheel model to optimize with OptiStruct, which I got by converting a previous Abaqus model given by Segula. Finally, I used my formerly acquired knowledge to change its design and improve the non-loosening of the four screws. To conclude, I modelled an optimized version of the wheel with a decreased loosening of the screws, and compared theses results with the initial version. I also conclude on the influence of the various parameters on loosening, in the specific case of the wheel, which could somewhat be extrapolated to other bolted assemblies.