The behaviour of rollover protective structures subjected to static and dynamic loading conditions

摘要

The Rollover of heavy vehicles operating in the construction, mining and agricultural sectors is a common occurrence that may result in death or severe injury for the vehicle occupants. Safety frames called ROPS (Rollover Protective Structures) that enclose the vehicle cabin, have been used by heavy vehicle manufacturers to provide protection to vehicle occupants during rollover accidents. The design of a ROPS requires that a dual criteria be fulfilled that ensures that the ROPS has sufficient stiffness to offer protection, whilst possessing an appropriate level of flexibility to absorb some or most of the impact energy during a roll. Over the last four decades significant research has been performed on these types of safety devices which has resulted in the generation of performance standards that may be used to assess the adequacy of a ROPS design for a particular vehicle type. At present these performance standards require that destructive full scale testing methods be used to assess the adequacy of a ROPS. This method of ROPS certification can be extremely expensive given the size and weight of many vehicles that operate in these sectors. The use of analytical methods to assess the performance of a ROPS is currently prohibited by these standards. Reasons for this are attributed to a lack of available fundamental research information on the nonlinear inelastic response of safety frame structures such as this. The main aim of this project was to therefore generate fundamental research information on the nonlinear response behaviour of ROPS subjected to both static and dynamic loading conditions that could be used to contribute towards the development of an efficient analytical design procedure that may lessen the need for destructive full scale testing. In addition to this, the project also aspired to develop methods for promoting increased levels of operator safety during vehicle rollover through enhancing the level of energy absorbed by the ROPS. The methods used to fulfil these aims involved the implementation of an extensive analytical modelling program using Finite Element Analysis (FEA) in association with a detailed experimental testing program. From these studies comprehensive research information was developed on both the dynamic impact response and energy absorption capabilities of these types of structures. The established finite element models were then used to extend the investigation further and to carry out parametric studies. Important parameters such as ROPS post stiffness, rollslope inclination and impact duration were identified and their effects quantified. The final stage of the project examined the enhancement of the energy absorption capabilities of a ROPS through the incorporation of a supplementary energy absorbing device within the frame work of the ROPS. The device that was chosen for numerical evaluation was a thin walled tapered tube known as frusta that was designed to crush under a sidewards rollover and hence lessen the energy absorption demand placed upon the ROPS. The inclusion of this device was found to be beneficial in absorbing energy and enhancing the level of safety afforded to the vehicle occupants.