Resistance strain gauges have been used for the measurement of strain for more than 50 years; however, research to quantify the inherent uncertainty in a strain-measuring system has been scarce hitherto. Nevertheless, resistive strain gauges are the most widely used tool to measure strain owing to their simplicity, apparent accuracy, low cost, and ease of use. In spite of this, at times they are used improperly, and the sources of error are neglected. Every type of measurement has an uncertainty associated with it. As it is impossible to eliminate error completely, the goal must be to quantify it and to reduce it to a value that is acceptable for the purposes of the measurement being taken. The novelty of the present research is to put forward a new methodology for determining the uncertainty in a strain gauge measuring system. To achieve this, the principal sources of error that influence the measuring system are formulated in order to develop an error model. Subsequently, the law of propagation of uncertainty is applied, together with a type A and B evaluation approach to determine the combined uncertainty of the entire measuring system, taking into consideration the correlation between variables, when applicable. The new methodology is then applied to a series of strain measurements taken on an aluminium flat bar subject to a bending load, and the results are discussed.
Abstract. In Europe, traffic road safety has clearly improved due to many factors. One of them is the improvement of the roadworthiness. However, accidents of vans and light goods vehicles have not followed the decreasing tendency of other vehicles.Several studies suggest that vehicle defects are relevant to the cause of accidents. It would be ideal if vehicle owners continuously kept their vehicles in compliance with the roadworthiness standards. Another important aspect to operate with roadworthy vans is the maintenance programs. It is probable, that many van owners do not adequately maintain their vehicles or the maintenance programs are not sufficient with the Periodic Motor Vehicle Inspections (PMVI) intervals or with the items inspected. This paper analyses the maintenance schedules and PMVI of vans in order to assess the influence of these parameters in their higher accident rate.The conclusions provided can enable public administrations to modify enforcement laws, regarding time control of driving and Periodic Motor Vehicle Inspection.
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