Traditional passive front-end structure is limited by its fixed characteristics. The implication is that it performs well under given crash conditions only. Design compromise is a necessity to cope with both full Frontal and Offset crashes. A trade off between pulse requirements and intrusion injury requirements is also necessary in short front-end design. Energy management in passive structures is thus constrained by the fixed length and stiffness of the structure. Ideally it is required to make the structure longer and stiffer for high speed-high mass crashes, and softer for low speed-low mass crashes. Offset crashes ideally require stiffer structure on the impact side and softer structure on the other side. The way out of this impasse is to introduce the concept “Smart Structures” where the characteristics (length and stiffness) may be intelligently adjusted according to suit the particular crash circumstances.
This research is attempting to improve vehicle crashworthiness by introducing a novel system of “Smart Structures” to support the function of the existing passive structure. A ten-degrees of freedom, two-dimensional spring-mass-damper simulation model has been developed to study the dynamics of crash between two vehicles in head-on collisions. The model inputs mass and speed of both colliding vehicles as well as offset overlap ratio of the crash. Masses and stiffness of various parts of the front end are calculated according to the vehicle total mass. The model was shown to be capable of capturing deformation displacement of the front and backup rail separately. For offset crashes the model was shown to capture the rotation of the structure as well as the deformation of the LHS and RHS rails independently. The model assumes that the two colliding structures geometrically interact with each other. Two injury risk criteria have been considered in this study; average dynamic acceleration sustained by the passenger compartment throughout impact (shock injuries), and length of back up deformation (intrusion injuries).
The proposed “Smart Structures” consist of two independently controlled hydraulic cylinders integrated with the front-end rails. By applying active control strategy, this structure is characterised by variable crash zone length, variable Stiffness and independent or asymmetric characteristics of the left/right rails in offset crashes. This paper attempts to analyse the performance of “Smart Structures” applying active control to the crash process for the purpose collision mitigation and improvement of compatibility between vehicles of different masses.
It is shown that “Smart Structures” employing two hydraulic cylinders, that extend up to 0.35 meter, prior to collision, is capable of absorbing most impact energy at 30mph. The sustained average dynamic acceleration pulse is 15g. The main improvement is in reducing intrusion injuries at high impact speeds and offset crashes. At low impact speed lower acceleration pulse and lower delta V index are obtained. Deployment of “Smart Structures” in heavy vehicles was shown to have considerable improvement in the compatibility of frontal crashes with smaller vehicles. The intrusion injury index was nearly halved upon deploying the “Smart Structures” in a head-on collision with mass ratio of 10.