Testing tyres at the drawing board

Penn State researchers, in collaboration with the French company, ESI Group, have developed a computer simulation said to let engineers road test a tyre design virtually, while the tyre is still on the drawing board.

The international team developed the approach using Pam-Shock software, one of ESI’s simulation packages for predictive virtual testing of industrial prototypes or processes.

Dr El-Gindy, director of the Crash Safety and Vehicle Simulation Research Centres at Penn State’s Pennsylvania Transportation Institute, said that every tyre has a maximum speed limit at which a ‘standing wave’ occurs along the tyre circumference causing deformation, a temperature rise and eventual failure.

The speed at which the standing wave forms and failure occurs is often by found using a tyre-testing machine that rotates the tyre in contact with a drum to measure durability and endurance.

Using the new Penn State/ESI software, engineers can produce a computer simulation of any tyre type at any tyre inflation pressure rotating on a test drum and predict the formation of the standing wave.

They found that, as the inflation pressure is reduced below the manufacturer’s recommended value, the speed at which the standing wave forms is reduced and the energy consumed by the tyre is increased, resulting in a rapid increase in tyre temperature, energy consumption, rolling resistance and fatigue.

In addition, the Penn State researchers used the simulation to study the road vibrations transmitted from the tyre’s contact patch to the chassis, an objective index of ride comfort.

They also included a virtual road ‘bump’ in the simulation to look at the effect of obstacles on the tyre’s performance and the comfort index.

The Penn State/ESI team used non-linear finite element analysis, in which they ‘built’ the visualisation of the tyre by dividing it up into numerous regions and connected subregions or elements for which numerical values were known or could be estimated.

For example, their mathematical model of the tyre includes 7880 shell elements, 4200 solid elements, 1680 membrane elements, 120 beam elements, and two rigid body elements for the rim and the road obstacle.

‘Although the simulation will not replace actual road testing, it can help tyre manufacturers predict and understand critical phenomenon earlier in the tyre design process,’ said El-Gindy. ‘Designers will be able to input the specifications for their tyre designs in the program and predict and even preview the design’s road performance.’