Essay, Pages 7 (1512 words)
The value of Formula One tires is the consistency of a F1 engine. F1 tyres falsely imitate a normal road tyre. Although the standard tires have a useful life of up to 80,000 km (50,000 miles), on average, the tires used in Formula One are built to last less than 120 km of race distance. To understand the tyre’s failure, in a critical condition, we need to consider the material of the tyre and the tyre’s behaviour. The tire’s inside is a bunch of old gum that keeps it all in place.
The rubber is on the tyre’s surface. They have an underlying structure of nylon and polyester designed to withstand much greater forces than road cars in a complex weave pattern. The rubber that contacts the surface, called the tread, is the most common wear area on the F1 tyre.
Mechanical properties (stress-strain)
Rubber has a low module of elasticity, capable of deformation of up to 1000 percent. Following such deformation, it retracts quickly and forcefully to its original dimensions.
It’s robust, but there is internal damping. Rubber refers to vulcanized or compounded. The vulcanized rubber property is shown in Figure. It is an elastomer if rubber is in natural conditions. Table shows the characteristics of the rubber of the F1 tyre.
Table: The properties of rubber for F1 tyre (Butler, 2016)
|Tensile max, Psi||4500|
|Elongation Max, (%)||650|
The failure mode
For typical F1 tyre, or any standard rubber tyre, failure does not occur under a single loading resulting in a catastrophic crack production, but due to relatively high repeated pressure.
The Formula One tyre’s failure mode is due to exhaustion. The fatigue failure process for the Formula One tyre can be distinguished by two phases. The first is a nucleation phase that was originally thought free of cracks during the cracks appearing in the region. The second is an increasing step that raises the initial crack until the split occurs (Baumard, 2016).
Fracture type – Brittle
F1 tire consists of rubber created by combining materials and chemicals with mechanical processes and heat and pressure cycles of varieties. There’s no ductile thing about rubber. It’s the opposite of fragility. Before it divides, it can be up to 500 million. Nonetheless, depending on how it is handled, rubber has a shelf life of between 3 and 5 years. Rubber is becoming fragile as its ages. Like the tires of the F1. Once fitted to a vehicle, whether used or not, in about 4 to 5 laps it becomes brittle and needs to be replaced even if it appears to be in good condition. If exposed to pressure or flexion as shown in Figure, the tread of old rubber tires chip.
The failure of tyre occurs at the part of the rubber that touches the track, called the tread.
The failure mechanism
Tyre wear and tear
Tyres heat up across corners as slipping and lateral forces will always work on the tyre. A lateral force is a force that, as shown in Figure, works across the direction the car is going. It is referred to as bringing the tyres up to working temperature through a heat cycle. As the rubber in the tread heats up and cools down, as shown in Figure, the chemistry that makes up the rubber specifically the polymers that have long chains of interlaced molecules will begin to degrade. It will be deformed by putting heat energy through the rubber. Most of the structure of rubber will spring back to its original shape, but under this heat energy, some of the chemical bonds crack and permanently deform. The heat will change the rubber nature itself over time. The rubber’s internal structure will change from soft and sticky to less grippy or less usable tyre permanently. This process is known as the lifetime of the tyre. When the tyres overheat, the inside of the rubber becomes much hotter than the outside surface, a hot pocket of air rubber is created and expanded under the tread that ultimately bursts and breaks away a large chunk of the tyre. This is referred to as blistering.
There are strong lateral forces pulling on the rubber as its grips into the track as the car turns very quickly through a corner. Under wrong circumstances, under this abrasion, the rubber may deform in waves. These waves will eventually deform so badly that the peaks will begin to tear off. The tiny bits of torn rubber will be hot and sticky and will usually adhere to the tyre’s surface tread. Overtime will have grainy texture on the rough areas of the sole, so this is known as grain. As a result, the tyre’s main tread is no longer making proper contact with the surface track. At the key point of contact, the rubber with the grains is much slipperier. This results in less grippy grained tyres than a fresh tyre. Some of the rubber pieces are also thrown out of the tyre and dropped on the track. Such layers of recycled rubber are referred to as marbles. As with graining, it is less grippy to run over these marbles than to run the tyre directly on the track. The problem comes when there are plenty of marbles, which will reduce the track’s raceable part. As they drive through the track, especially through corners, they will begin to lay down a small amount of rubber wearing from the tyres. This rubber layer begins to build up as more and more cars repeatedly follow the same line.
Ideally, under braking, the wheel should always rotate. It means that the car can still be steered so easily, and that the car can slow down faster than if the non-rotating tyre is locked. As shown in Figure, the total frictional force on the brakes is much greater than the average frictional force between the tyre and the ground. As the brakes are applied, the brake disk should be able to keep moving through the brake pads. If the brake pads grip too hard, the wheel will lock in place and the only braking force will occur between the tyre rubber and the track as it slides down the ground. Therefore, it heats up one layer of the tyre and wears it away in a flat slice. This is referred to as flat spot. A heavy flat spot will make the car judge vibrate as it wrecked the tyre’s beautiful smooth roundness. This can damage the suspension as discovered in 2005 by Kimi Raikkonen. Rotating a tyre from it flat section is harder than rotating along its roundness. The tyre will slip onto its flatspot the next moment of braking and stubbornly refuse to rotate, flattening it even more.
The cause of failure
For tyre wear and tear
Usually, the cause is overly aggressive driving with a tire that is too weak and rough for conditions, or the driver has overworked the tires before it reaches the working temperature. The rubber in tires is undergone very high cyclic pressure. The work these rubbers do leads to the generation of heat. The combination of high cyclic pressure and high temperature can produce mechanical and chemical rubber changes.
For flat spot
Braking that make the car’s tyres locks up.
The suggested prevention method
Fresh tyres are not ready to deliver flat out speed straight away. We need to put them through a heat cycle by doing a warmup lap to treats the rubber making it just right for racing. Putting the tyres through warm-up heat cycles is known as scrubbing. When the rubber is heated, it become more viscous. This essentially means it is a little bit more melty or malleable. When the tyre rolls over the rough surface of the track, the soft melty rubber squeezes into the surface the texture and grips nicely.
Prepare more layer of rubber on every corners of the track. This is because driving over this rubber is grippier than driving directly onto the track and less wearing the tyres. The coefficient of friction between the tyre and the rubber layer is much higher, and the surface is smoother so, less wearing.
To reduce the pressure on the tyre, the driver needs to drive very smoothly. This is because the when tyre is braking vigorously, the downward force exert on the tyre is very high thus will wear the tyre faster.
Managing the condition of tyres is a tricky thing for a driver to do as they need to keep the rubber consistently within the correct temperature range or working range to ensure that the rubber is heated correctly not only at the surface or at the core. A nice consistent temperature must be right through the depth of the tyre, not too hot or not too cold.
- Baumard, T. L. M. (2016). Investigation on Fatigue Failure in Tyres. (June), 1-220.
- Butler, T. I. (2016). Mechanical Properties of Rubber. 381-410.