Nut Factor Studies in Bolted Joints

Shivaprasad, GK and Radhakrishna, M and Jana, S and Arunkumar, V (2006) Nut Factor Studies in Bolted Joints. In: 8th National Conference on Air Breathing Engines and Aerospace Propulsion, DIAT,Pune. (Submitted)

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In the design of rotating machinery it is often necessary to bolt components together with a known preload since the same controls the system dynamics considerably. Since a major percentage bolt tightening torque is resisted by frictional forces especially towards the end of tightening, and since the coefficient of friction in threads and under the bolt head to a large degree is indeterminate, the best method of ensuring desired clamping load is by measurement of bolt elongation, or by a load cell. However in large number of cases the incorporation of load cell is not practical and bolt elongation is insufficient to allow accurate measurement. ln such cases it becomes necessary to produce the desired end load by applying a specified torque to the bolt leading to the determination of nut factor .for each of the cases Here an attempt has been made to obtain the quantitative values of nut factors for bolted joints as a function of bolt diameter and tightening torque applied on bolted joints. A simple test rig 1 was designed and fabricated for the purpose in which the experiments were conducted. The instrumentation basically includes the monitoring of the bolt tightening torque through the torque wrench, and a load cell \vliich measures the clamping force developed in the joint. These experiments were conducted with thrust ball bearing and also without thrust ball bearing; resulting in possible analysis of the friction generated between nut and bolt threads and also between nut-washer surfaces. The results include generation of nut factors and coefficient of friction values developed for different torques and different bolt diameters, by using a mathematical relation which relates the bolt geometry, clamping force and the tightening torque applied. Also an effort has been made to develop a curve fit equation for nut factor values from experimental data leading to quantitative estimation of nut factors as a function of bolt diameter and tightening torque.

Item Type: Conference or Workshop Item (Lecture)
Uncontrolled Keywords: Bolted Joint, Nut Factor, Torque, Clamping force
Subjects: AERONAUTICS > Aeronautics (General)
AERONAUTICS > Aircraft Propulsion and Power
Depositing User: Dr. V Arun Kumar
Date Deposited: 02 Aug 2010 09:51
Last Modified: 02 Aug 2010 09:51

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