The Experimental Determination of the Coefficients of Friction in Bolted Joints

Coefficients of friction in bolted joints affect their strength, assembly time and labor intensity. Determining the coefficient of friction in the thread is complicated by a variety of factors that change its value. Most of them are subject to random variations that cannot be calculated analytically. The authors propose an experimental method to solve this problem. It is based on over-twisting of the bolt when it is tightened due to the excess torque in the thread compared to the friction torque at the bolt end. A laboratory unit for measuring the tightening force is used for the experiments. As the nut is tightened, the torques are measured using a torque wrench. To improve the efficiency of the research, the Statgraphic Plus software package is used for the experiment design and statistical analysis of the results. The statistical data shows the absence of systematic errors in the experimental measurements. The values obtained for the coefficients of friction are in good agreement with reference data.

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