Developing Test Schedules for Simulating Multiaxial Vibratory Motions of Delivery Vehicles

Abstract

Until recently, a vehicle’s vertical vibrations were considered the main cause of damage during transport. Consequently, laboratory testing has been undertaken by simulating heave (vertical) vibrations alone. However, with increasing demand for a reduction in packaging waste, there is an impetus to use lightweight systems, such as stretch film, for containing unitized loads. Such containment systems are susceptible to the lateral forces generated by the vibratory motions that arise from the pitch and roll vibratory motion of vehicles due to road surface unevenness. If laboratory simulation is to be realistic, multi-axial motion must be taken into account and an understanding of the relationships between the random heave, pitch, and roll vibrations is essential. This paper uses vibration data collected from a number transport vehicles traveling along typical urban and suburban routes to establish the nature and level of the multi-axial vibrations that exist. These are presented with average Power Density Spectra (PDS) as well as time histories and statistical distributions of salient moving statistics such as the root-mean-square (rms). The paper analyses the data for correlation of the rms levels with respect to nonstationarity. This is important when simulating nonstationary (randomly fluctuating rms) vibrations across the three degrees of freedom (DoF) namely, heave, pitch and roll. These statistical correlation functions are used to manage the relative rms levels of each of the three DoFs when undertaking vibration simulations using multi-axis vibration test systems. The results show that the relationships between moving rms of heave, pitch and roll vibrations are not highly correlated but can be characterized statistically as joint distributions to enable realistic simulation of multi-axial random vibrations of road transport vehicles under controlled laboratory conditions.