3 research outputs found
Vibration-Based Bolt Tension Estimation for Multi-bolt Joints
No full textCritical bolted connections exist in many engineering structures, from pressurized pipelines to wind turbines. Often there are legal demands for maintaining necessary bolt tension in such joints to prevent failure. The available tools for tightening makes it challenging to obtain the correct tension in a bolt, as well as subsequently checking if a bolt is in fact tightened to the correct level. Recent work proposes to use vibrations for estimating tension in a bolt. Estimation is possible by measuring and analysing transverse natural frequencies and damping ratios induced by e.g. a transversal or longitudinal hammer impact on the bolt itself. The work so far has focused on a single bolt. Most bolted joints consist of many bolts, e.g. a flange connection often has a ring of almost identical bolts. Identical bolts, with almost the same tension, will also have very similar boundary conditions and thus almost the same natural frequencies. If there is only very light damping between two adjoining bolts, a frequency response measured on one bolt after an impact might include the vibrational response of both bolts (the coupling might even be so strong that the two bolts cannot be viewed as entities on their own) leading to the question: How to separate which frequencies belong to which bolt
Coupling effects with vibration-based estimation of individual bolt tension in multi-bolt structures
No full textRecent work with various single-bolt experimental setups has shown promising results for applying a vibration-based bolt tension estimation procedure. To estimate tension, the novel procedure models a bolt’s transverse vibrations with a single Euler–Bernoulli beam. The present work investigates the applicability of that novel approach when a structure contains more than one bolt. The principal question is if the vibrational response obtained from excitation of a specific bolt, mounted in a structure with other similar bolts, can still roughly be modelled as an independent single-bolt system, or if the other bolts affect the vibrational response in an undesirable way. To determine if the novel single-bolt approach is applicable, it is necessary to gain insight into possible coupling phenomena. For this, a two-bolt problem is investigated, modelled both as a coupled two-beam Euler–Bernoulli model and numerically with FEM software, and with experimental testing of two real bolts mounted in the same structure. It is found that strongly coupled bending vibrations, with in-and out-of-phase modes, only occur when tension and boundary stiffness in the two bolts are very close to identical. When the bolts have different boundary parameters, the coupling is weak, and the two bolts can roughly be treated as two independent single-bolt systems. In both situations, it is actually possible to estimate bolt tension and boundary stiffness based on measured transverse natural frequencies using a single-bolt beam model
