Concepção, projeto e comissionamento de um sistema para análise da perda de pré-tensão em juntas aparafusadas

Abstract

Over the last decades, bolted joints have become indispensable and are currently the most used in engineering services. Thus, with technological development and the submission of these joints to increasingly complex efforts, a more efficient mechanical design is necessary so that failures in bolted joints become less frequent. This work aimed to conceive, design and commission an equipment that allows the analysis of prestress loss in bolted joints. For this purpose, an adaptation of an existing fatigue machine at the Laboratory of Technology in Friction and Wear (LTAD/UFU) was carried out. After analyzing the state of the art regarding the subject studied, the main parameters of the tests were defined and a pair of clamping jaws were designed to adapt the fatigue machine. Also, the calculations for verifying the capacity of the machine were presented in order to meet the test requirements, as well as the result of simulations via the Finite Element Method. In the construction of the equipment, problems such as misalignment of the test plates, rotation of the hydraulic cylinder and gaps present in the system were solved. Eleven pilot tests were carried out to obtain the pretension loss curves as a function of the number of loading cycles, varying the displacement amplitude, overtorque, retightening of the fastener set, among other factors. The characteristic curves obtained in the tests were consistent with those observed in the technical literature on the subject, making the equipment commissioning stage effective. Finally, the equipment's operating reliability was proven, for testing on M12 to M39 screws, with clamping lengths of up to 140 mm.