Designing the right tire for large wheeled vehicles used to haul coal and other materials in underground mines presents an enormous design challenge. Pneumatic tires present risks because of the danger of an explosion in a confined space while solid tires are associated with relatively large vibrations experienced by the driver. Big Tyre, a company that specializes in producing solid tires for mining vehicles, is developing a unique alternative which uses arrays of leaf-springs, typically made of composite materials, to provide performance similar to pneumatic tires without the risk of blow-outs.
Big Tyre is a manufacturer of solid wheels that are primarily used in underground mining vehicles. “Many mining companies have switched from pneumatic tires to solid wheels because of the dangers presented by pneumatic tires underground,” Louden said. “Mines underground have bolts sticking out of the walls that can easily cause punctures. Tires on heavy vehicles are inflated as high as 170 psi, so when they are torn or punctured a considerable amount of force is released. Due to space constraints underground, workers are often in close proximity to the tires so the potential for injury when a tire is torn or ruptures is a major concern.”
The design concept provides the flexibility and challenge of defining various design parameters including the number of springs in an array, thickness of springs, curvature of springs, length of springs, material properties of springs, geometry and material properties of the segments that the springs attach to on the outer diameter of the wheel, as well as many others. The design criterion is to provide a very efficient vertical loading for the size of the wheel while providing similar if not equivalent suspension to a pneumatic tire, with excellent torque capacity and lateral stability.
Compumod first conducted a nonlinear static analysis on one spring to correlate the model material properties with experimental data. The material properties were tuned to replicate the measured reaction force in the experiment. Then a nonlinear analysis was performed on the entire wheel to assess its strength. The wheel was given an enforced displacement of 150 mm which was solved in 100 nonlinear increments. The reaction force was then measured on the ground and graphed against displacement. The first negative slope indicated failure of the wheel at 252 kiloNewtons or 25.7 metric tons, which is well over the target of 16 metric tons. After the first collapse of the wheel, the contact between the springs and between the springs and segments added stiffness to the wheel and the reaction force increased again for increasing displacements.
“After seeing the benefits of the software, we decided to purchase Patran and Marc,” Louden said. “Compumod organized training for us in their Sydney office and handed over the models they created in the consulting project. We very quickly began designing the second full-size version of our design, and have been able to improve the design at a much faster pace than in the past. It even allows us to simulate driving maneuvers of the vehicles, including obstacles on the road.