Graduation Year


Document Type




Degree Granting Department

Mechanical Engineering

Major Professor

Daniel P. Hess, Ph.D.

Committee Member

Craig Lusk, Ph.D.

Committee Member

Nathan Crane, Ph.D.


Heli-Coil, bolt, transverse vibration, prevailing torque, Loctite


This thesis presents a study of the dependency of loosening parameters on secondary locking features of threaded inserts subjected to dynamic shear loads. Secondary locking is used to assist and/or provide redundancy to the primary locking feature (threads) in preventing preload loss in almost any mechanical applications. Two different secondary locking features are studied: the Locking Heli-Coil insert and the Loctite Threadlocker (R) applied before assembly to a Standard Heli-Coil insert. Five parameters are studied in this thesis: percentage loss of initial preload, initial rate of preload loss, secondary rate of preload loss, steady-state value, and the final preload value.

Statistical analysis was used to quantify the dependencies between locking levels. Results show that the loss of initial preload is dependent on secondary locking features, the initial and secondary rate of preload loss are dependent on secondary locking features, the steady-state value and the final preload value are dependent on secondary locking features. Also, due to secondary locking features, 83% of the "Locking Heli-Coil with Braycote" tests reached steady-state while only 16% of the "Standard Heli-Coil with Loctite" tests reached steady-state even though the final preload value were higher for "Standard Heli-Coil with Loctite."