Studying effects of joint characteristics on the performance of a cantilever beam shaped piezoelectric energy harvester through joint identification

In energy harvesting systems, specifications of the generated electrical energy depend on the structure’s dynamics. This dependence can be used to identify the system’s joint characteristics. To this end, an innovative frequency-response-function (FRF) based identification method is presented. The investigated system is a cantilever beam shaped structure with an embedded bimorph piezoelectric bender, connected to a base via bolted joint as a depiction for wing of a UAV connected to fuselage. The implemented FRF is ratio of the piezoelectric output voltage to the base input displacement. The joint identification procedure consists of analytical modeling of the system with joint, experimental testing of the system and a real-coded Genetic Algorithm (GA) method. The joint is modeled as a combination of longitudinal and torsional springs, whose stiffnesses are obtained using the GA method. The obtained results indicate that the analytical model has good correlation with the experimental data. Then, effects of the joint characteristics on the energy harvester’s performance are investigated by comparison of the system with two different joint assumptions, namely, rigid and realistic joint. Finally, the effects of various joint characteristics on the energy harvester’s performance are presented and approaches to achieve the maximum performance of the system are suggested.

A Review of the T-Stub Components for the Analysis of Bolted Moment Joints

The analytical method for the calculation of the properties of a bolted joint established by the structural Eurocodes proposes the T-stub as a component for the characterization of the tension and compression zones in moment joints. In this article, a review of the state of the art on the T-stub component is developed, where the works developed since it was initially defined, and from the perspectives of formulation, experimentation and numerical simulation are summarized and discussed. Additionally, possible future lines of work are proposed.

Bolted Joint Preload Distribution from Torque Tightening

The purpose of this paper is to develop an understanding of how bolt preloads are distributed within a joint as each bolt is tightened in turn by the use of a calibrated torque wrench. It discusses how the order that the joints nuts/bolts are tightened can affect the final bolt preload. It also investigates the effect on incrementally increasing the bolt preload through a series of applications of the controlled torque tightening sequence. Classical analysis methods are used to develop a method of analysis that can be applied to most preloaded bolted joints. It is assumed that the static friction coefficient is approximately 15% less than the dynamic friction. It is found that the bolt preload distribution across the joint can range from slightly above the target preload to significantly less than the target preload. The bolts with a preload greater than the target preload are found to be those tightened towards the end of the tightening sequence, usually located close to the outer edges of the joint’s bolt array. The bolts with a preload less than the target preload are those tightened early in the tightening sequence, located centrally within the joints bolt array. The methods presented can be used to optimise bolted joint design and assembly procedures. Optimising the design of preloaded bolted joints leads to more efficient use of the joints.