Structural Interaction between Vehicles. An Investigation of Crash Compatibility between Cars and Heavy Goods Vehicles

Doctoral thesis, 2014

While frontal collisions between Heavy Goods Vehicles (HGVs) and passenger cars are rare compared to car-to-car frontal crashes, they are much more severe. Between 43% and 73% of all frontal car-to-truck accidents result in fatalities. The severity is due to crash incompatibility between the vehicles that has been generally agreed to arise from differences in mass, stiffness and geometry and it refers not only to car-to-truck collisions but also to most vehicle-to-vehicle collisions. To address incompatibilities between passenger cars and HGVs, Front Underrun Protective Devices (FUPDs) are obligatory equipment for HGVs produced after August 2003. To date, there is insufficient research describing the efficiency of statutory and energy absorbing (e.a.) FUPDs in real traffic collisions. The aim of the research presented in this thesis is to understand and suggest improvements for the compatibility between trucks and passenger cars through parametric studies of different design and collision configurations where the compatibility between trucks and cars is seen as an indivisible part of overall crash compatibility between vehicles. The focus was the requirements for energy absorbing FUPDs to overcome the unpredictable behaviour of passenger cars in frontal collisions by studying the links between geometry and stiffness as influenced by crash configuration and structural interaction. The bending stiffness of e.a. FUPD cross-beams, their height, and triggering force for energy absorbing elements were found to be important characteristics of e.a. FUPD that influence the outcome in collisions between HGVs and passenger cars. The stable response of vehicle structures was identified as an important issue to understand. A new analysis approach, called the RED method, was developed and presented. Using energy absorption and impact forces calculated in FE simulations, the RED method gives more insight into structural deformation processes than other methods and thereby improves the evaluation of vehicle structures. Information derived from the procedure was used to develop two new assessment criteria - Structural Efficiency and Crash Stability – that can be used to objectively quantify the crash response of vehicles. Because the method is based on FE crash simulations it can be used in the development as well as production phase of a vehicle crash structure or even other structures where deformation modes are important. It was shown that these criteria can be used in compatibility rating where a new perspective on compatibility is introduced and applied.