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Prevailing Torque Locking in Threaded Fasteners

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Abstract

This paper presents analyses of prevailing torque locking features common in locknuts, inserts and bolts. Existing manufacturing specifications for these components quantify required minimum and maximum locking torque values for a wide range of thread sizes. The self-loosening moment inherent to threaded fasteners and dependent on joint preload and thread pitch is computed and compared to the specification locking torque values. The self-loosening moment alone, i.e., not including loosening from external loads, is found to exceed the minimum locking torque manufacturing specification values for all fastener sizes at typical preload and for some large thread sizes is found to exceed the maximum locking torque specification. Calculations are provided for SAE and AN fasteners. Sample prevailing torque measurements from locknuts are presented which are well above the minimum specification. Analysis for the loosening moment from an external axial load is developed and presented with example calculations. Fastener locking requirements are defined.

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Acknowledgment

The author gratefully acknowledges the support of Dr. Michael Dube and the NASA NESC.

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Authors and Affiliations

  1. Department of Mechanical Engineering, University of South Florida, 4202 E. Fowler Avenue, ENB 118, Tampa, FL, 33620, USA

    D. P. Hess

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  1. D. P. Hess
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Correspondence to D. P. Hess.

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Hess, D.P. Prevailing Torque Locking in Threaded Fasteners. J Fail. Anal. and Preven. 18, 1562–1572 (2018). https://doi.org/10.1007/s11668-018-0555-9

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  • DOI: https://doi.org/10.1007/s11668-018-0555-9

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