Project: PEDestrian protection using Shock Absorbing LIquid technology (PEDSALI)

Reference: C3/P35

Last update: 13/04/2006 12:43:55


At the end of the project it is anticipated that, using Finite Element techniques, it will be possible to predict the performance characteristics of a SALi based shock-absorbing component. Physical testing be will used to confirm the predicted results and validate the model. The chosen materials will be assessed using FMEA techniques to ensure that any adverse effects, such as toxicity and corrosive properties, are recognised and evaluated.


This highly innovative project is researching a new composite, impact energy absorbing material that can in effect, automatically alter its stiffness, to cope with different types of impact. At present it is being evaluated with respect to the reduction of serious and fatal pedestrian casualties as the result of road accidents, in line with DTLR targets.

The patented material being investigated is a Shock Absorbing Liquid (SALi) which consists of lots of small resilient elastomeric capsules immersed in a matrix liquid and stored in a strong flexible package. Upon impact, all of the capsules are compressed by the matrix liquid and the front face of the package deforms to the shape of the applied load. The compressive stiffness of SALi filled packages increases as the area of applied load is increased. Consequently, a suitable sized package would be soft for a small child's head impact, but stiff for an adult head impact. If SALi filled packages are integrated into car bumper systems, then the bumpers will be soft for lower leg impacts, but stiff for low speed bumper-to-bumper impacts. This will help to make vehicles safer for pedestrian accidents, while keeping vehicle repair costs low.

The unusual cushioning properties of SALi can be illustrated by comparing its impact absorbing performance with that of a block of elastomeric closed cell foam.

The project is investigating the three parameters that influence the physical characteristics of a SALi filled impact absorber: the matrix liquid, the size and nature of the elastomeric capsules and packaging design.

The matrix liquid acts as a lubricant to facilitate the movement of the capsules and to transmit the hydraulic pressure changes when a load is applied. Additionally the liquid provides viscous damping when the steady state condition is disturbed due to its shear viscosity and bulk viscosity properties.

The capsules can vary from expanded polystyrene beads to bubble packing. The size distribution of the capsules need to be optimised in order minimise the total weight of the impact absorber, without compromising on impact absorbing performance.

The packaging provides a flexible leak-proof envelope to contain the liquid and capsules but, importantly, it must not stretch significantly during load application. Also, the package must not burst open and eject its contents during a violent impact. The size and shape of the package will affect impact energy absorbing performance.


University of Manchester
Oxford Road, Manchester, M13 9PL

Cheshire Innovation
17 Vale Road, Timperley, Altrincham, Cheshire, WA15 7TQ
0161 980 5191

Contract details

Cost to the Department: £44,200.00

Actual start date: 01 March 2001

Actual completion date: 22 July 2004