Development of a lead spring u-bolt load transducer : part of an onboard weighing system for off-highway log trucks

This thesis was motivated by the current concern of brake failure in off-highway log trucks descending steep grades. In order to utilise a guideline being developed for the prediction of safe maximum grades for descent under a range of truck payloads, it is necessary to measure axle weights during loading. A background review found that there are no commercially available on-board weighing systems that can be retrofitted to the drive axles of an off-highway tractor. Therefore, an investigation into the development of an on-board weighing system for the off-highway log trucks was initiated. This research was divided into two stages: preliminary strain measurement with a loaded off-highway tractor, and finite element modelling of a U-bolt from the tractor’s leaf spring suspension. A preliminary measurement test was carried out to identify potential suspension components that could act as load transducers for measuring axle weight. The preliminary results showed that incremental strain at two locations on the U-bolt varied linearly with payload, for an incremental load of 22.5 kN. Finite element modelling of the U-bolt was carried out to predict the maximum incremental strain occurring on the U-bolt surface. The model was calibrated with the measured data and a sensitivity analysis was done on key modelling parameters to determine the most suitable level of leaf spring block length, preload and U-bolt-to-Ieaf spring friction coefficient. Incremental strain on the top of the curved portion of the U-bolt was found to be relatively consistent and close to the maximum level of incremental strain and is recommended as a preferred position for strain gauging.Forestry, Faculty ofGraduat