The Variability of Strains in Bolts and the Effect on Preload in Jointed Structure
Brake, Matthew R.W.
Master of Science
Torque wrenches are the most common method used for tightening bolts; however, this method can cause a large amount of uncertainty in the resulting bolt preload. With the inability to determine the preload in bolted structures precisely, overdesign is necessary for bolts to meet safety requirements and prevent jointed structures from looseness failure. A series of comparative experiments are completed to quantify the influence of bolt strain variation based on strain gauges, force transducers, and accelerators. Moreover, this research uses the Peak Finding and Fitting (PFF) PFF algorithm to analyze nonlinear dynamics of the experimental system, which demonstrates the ramifications of the experimental results. Measured strains in bolts showed significant variabilities, which indicates larger the expected uncertainty in preload. Impact test results also indicate the advantages of pre-strain method for tightening bolts compared to torque wrenches.
Variability; Bolt strain; Bolt preload; Jointed structure