DERIVATION OF ENVIRONMENT DESCRIPTIONS AND TEST SEVERITIES FROM MEASURED ROAD TRANSPORT DATA - PART 2

This paper presents the final part of the discussions on the vibration and shock environments perceived by equipment when transported by wheeled vehicles. Dynamic response data from wheeled vehicles can be characterised as a random vibration, but it is often of a non- stationary and non-gaussian form. The method described superposes a number of independent gaussian processes that are defined by a root- mean-square (rms) value and a participation value that takes into account the total time a particular process is active. An example is given of three gaussian processes developed to measure amplitude data. Test durations are sometimes arbitrarily chosen such that a total of 50 hours is shared between three orthogonal axes. This procedure is not entirely satisfactory and Miners Rule is used to produce data that can be used to derive test times when higher levels of vibration can be used for an appropriate short time as part of a multi-level test. Care must be taken to account for likely differences in peak to rms ratios when comparing measured data with that from specification documents or test houses. It is unlikely that comparisons can be made on the basis of Power Spectral Density plots alone. Test house simulations could be more precise if the amplitude distributions and peak to rms ratios of the applied vibration could be customised. For the abstract to Part 1 see IRRD 855529. This paper is reprinted from the Proceedings of the 38th Annual Technical Meeting of the Institute of Environmental Sciences, Nashville, Tennessee, May 1992.