The challenge
Artificial turf is a surface of polymer fibres made to look like natural grass. Artificial turf for football pitches is designed to have similar mechanical behaviour to a natural grass pitch. The main advantage of an artificial turf football pitch is that it is more durable than natural turf and does not need sunlight and water. A third generation artificial turf consists of long plastic fibres and layers of sand infill and rubber or elastomer particles. The figure below shows a picture of such a third generation artificial turf system.
New artificial football turf systems are rigorously tested to ensure ball and surface interaction, and player and surface interaction are within regulation standards . At Reden, we can create finite element models to predict the properties of an artificial football turf field, in order to predict whether such a new system will comply with all mechanical requirements. The effects of parameters such as grass fibre geometry, grass fibre density, material properties, infill layer thickness and infill particle size can be investigated with our models before any part of the artificial turf system is produced.
A bouncing ball
One of the ball and surface interaction requirements is vertical ball rebound. This is tested by dropping a football from a certain height onto the turf, let it bounce and measure the rebound height. The movie below shows the result of a simulation of a ball bouncing at an artificial football turf system.
The grip of a football shoe
Another important property of an artificial turf field is grip. Grip can be considered as the force required to drag the studs of a football shoe through the top layer of the field. Good grip to the field is necessary to be able to play football at top level. The football player will slip in case of insufficient grip and may trip and fall in case of too much grip. Too much or too little grip can cause injuries.
Grip of a football shoe at artificial turf can be quantified by a rotational resistance test. The torque required to rotate a weighted disc with six studs mounted at the bottom through the top layer of an artificial turf field is measured during this test. This test can, of course be performed experimentally on an existing artificial turf field, but also on a model of the field, before the field is even produced. The movie below shows the results of a finite element simulation of the rotational resistance test. The arrow depicts the amount of torque (or rotational resistance) during rotation of disc in the simulation.
