SEM study of tyre wear

WEARING OF TIRES MEL 416 FINAL REPORT

PREPARED BY

MUDIT VERMA (P2009ME1096)

AJEET (P2009ME1090)

JAVED KHAN (P2009ME1098)

ABHISHEK GHOSH (P2009ME1074)

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TABLE OF CONTENTS

ABSTRACT ............................................................................................................................................ iii

MEL 416 FINAL REPORT ..................................................................................................................... 1

1. INTRODUCTION .............................................................................................................................. 1

2. CAUSES OF WEAR ............................................................................................................................ 3

3. EFFECTS OF WEARING OF TIRES ................................................................................................. 5

4. PROJECT WORK ............................................................................................................................... 5

4. RESULTS ............................................................................................................................................ 7

5. CONCLUSIONS………………………………………………………………………………………………10

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ABSTRACT

The issue of irregular tire wear has always been a concern even in the days when most vehicles ran bias ply tires. With todays longer wearing radial tires, irregular wear has surfaced as the primary concern of most vehicles maintenance managers. In fact, it is the ability of today’s advanced radial tires to deliver long original tread life, which requires even more attention to good maintenance practices and vehicle alignment.

Tire wear is a complex phenomenon. It depends non-linearly on numerous parameters, like tire compound and design, vehicle type and usage, road conditions and road surface characteristics, environmental conditions (e.g., temperature) and many others. Yet, tire wear has many economic and ecological implications. The possibility to predict tire wear is therefore of major importance to tire manufacturers, fleet owners and governments. Understanding of wear procedure could help to improve the quality of tires and other rubber parts working in heavy terrain conditions.

In this project we need to sample a used tire (in our case, a bicycle tire) and try to find out which type of wear is dominating on the tire.

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WEARING OF TIRES

MEL 416 FINAL REPORT

1. INTRODUCTION

Tires are probably not something you think about every day. But they’re an essential technology that touches countless aspects of our daily lives. Think about it. If you take a school bus, city bus, your mom’s car or even a bike to school, you wouldn’t get far without tires. The big trucks that bring food to your neighborhood grocery use them. And so do the forklifts that help pack those supply trucks. Delivery vans, mail carriers, ambulances, and police cars – they all use tires.

The tread of a tire or track refers to the patterns on its rubber circumference that makes contact with the road. As tires are used, the tread is worn off, limiting its effectiveness in providing traction. Tire tread is the lined or blocked pattern on the surface of a tire that provides traction for the tire. Often referred to as a caterpillar track, tread is found on the tire of any automobile. The tread pattern differs with different tires and different automobiles, but the use is the same. Found on the surfaces of the wheel that come in contact with the ground, tire tread is often patterned in lines or blocks, and can be up to many inches or centimeters deep. The tread allows rain, snow, mud, or any other element to pass through the tire without the automobile losing traction. Tread patterns can appear in symmetric, asymmetric, and directional tread patterns. Symmetric treads, the pattern most common on wheels (and found in Pirelli's Scorpion ATR tires), have continuous ribs or tread blocks where inboard and outboard sides match. Asymmetric tread patterns, effective in both dry and slick driving, vary the groove pattern along the surface of the tire such that as it turns, the tire can deflect water and grip snow while increasing contact area on dry roads; a balance of two

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worlds; this pattern is especially common for all-season tires. Directional tires have lateral grooves that form a V-shape across a tire's center as in Pirelli Winter Carving tires. The V-shape formation, much like a snowplow skiing method, reduces the hydroplaning potential. Typically, tires with deeper grooves are better able to handle wetter conditions. The treads are cut deep to allow substances to pass through them without interfering with the motion of the wheels, and then pass back out. They are essential in preventing hydroplaning and from keeping some automobiles from getting stuck in snow or mud. Some tires, known as slicks, are made with little or no tread, and are used strictly for racing on dry surfaces. The picture below shows very clearly the treads patterns on the surface of a new tire.

Source: http://static.ddmcdn.com/gif/self-regenerating-tire-tread-1.jpg

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2. CAUSES OF WEAR

n Tread wears away due to the friction between the road and the tire. Over time the tread can wear down to a point that makes the vehicle unsafe to drive. Scuffing is the most basic and dominant wear mechanism. It includes adhesive, abrasive as well as fatigue mechanisms due to cyclic nature of the loads.

n Some types of wear, especially tire treads wear, are very similar to machining. The tire tread is a part of tire that which is in direct contact of a vehicle with the road and thus, it is responsible for driving force transfer. The wear of the tire tread of passenger cars and trucks travelling on common roads is characterized by its abrasion. The tread of a car tire is disposed towards abrasive effect of the road.

n However, mechanism of tyres wear working in very hard terrain conditions is absolutely different. Sharp stone edges and terrain irregularities gradually cut (tear off) parts of rubber tread surface, which can be understood as a way of working – e.g. milling, although under very specific conditions. The mechanism of tyre tread wear working in hard terrain conditions is technically called Chip-Chunk effect and it can be considered as “workability” of rubber surface.

n Aggressive Driving: Tires don't last long on race cars, so they may need to be changed several times during a race. The same is true for tires on a vehicle that is driven aggressively. Hard cornering, spinning the tires when accelerating, and standing on the brakes can all wear tread off the tires very quickly. Changing your driving habits can extend tire life and save you the cost of having to replace your tires prematurely.

n Toe or Camber Misalignment: The tires have to roll straight and true, be perpendicular to the road surface (camber) and be parallel to each other (toe) to minimize tread wear. If the wheels are out of alignment, tread wear will increase. Toe misalignment has the greatest effect on tread wear, while camber misalignment causes wear on the inside or outside edge of the tread.

n Cheap Tires With a Rubber Compound That Is Too Soft: The ingredients that go into the rubber compound to make the tread have a huge bearing on how well a tire can resist wear. The higher the amount of carbon black, silica and other wear-resistant ingredients in the compound, the tougher the tread and the longer it will

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last. But the trade off may be increased ride harshness and loss of dry traction. Tire manufacturers choose formulate compounds to optimize traction, tread wear and cost. Cheaper tires as well as racing tires typically use softer rubber compounds. Softer rubber is good for dry traction, but not for wear resistance.

n Underinflated Tires: If the tires are not maintained at the recommended pressure and are underinflated, the tread flexes more than usual as the tire rotates. Over many miles, this will increase tread wear.

Source: http://www.tire-information-world.com/tire-wear-problems.html

All tires have a tread wear rating, which helps users determine how long a tire will last. A standard testing tire has a rating of 100. This means that if a tire has a tread rating of 300, the manufacturer expects the tire to have a lifespan 300 percent of the test tire.

Usually the lifespan is slightly exaggerated by the manufacturer. Tire ratings should only be compared between each manufacturer's lines of tires, as each manufacturer uses a different rating system.

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3. EFFECTS OF WEARING OF TIRES

n Worn tread can cause wheel alignment to be off, just as misconfigured wheel alignment can cause tread to wear faster. Misalignment can cause your tires to wear down more quickly by putting too much pressure on one side of the tire.

n Tire treads also aid a vehicle in stopping by providing traction and friction on the road. When tire treads wear out, the capacity to stop or slow down your vehicle is reduced. Skidding and sliding can occur without warning with warn-down treads. And hence worn tread can also slow the braking time.

n Driving on an uneven road with tire treads worn down can cause jolting in the car.

n Excessive wear, if not checked may lead to catastrophic failure of the tyre resulting in loss of vehicle control.

n A vehicle with worn-out tire treads can actually flip over when making a sharp turn.

n If the tread becomes too low the tires may also burst.

4. PROJECT WORK

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4. RESULTS

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5. CONCLUSIONS

From the above experiment it can be concluded that the wear part of the tire shows most prominently surface fatigue because of which cracks developed in the tire.

The cracks developed from this fatigue have become prominent site for corrosive wear.

Abrasive wear can also be seen in the sample.

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Bibliography

[1] http://www.ehow.com/how-does_4672524_worn-tire-tread-affect-tire.html

[2] http://www.goodyeartrucktires.com/pdf/resources/service-manual/Retread_S7_V.pdf

[3] http://www.journalamme.org/papers_vol37_2/37245.pdf

[4] http://www.ehow.com/how-does_4762454_tread-wear-affect-ride-quality.html

[5] http://www.wisegeek.com/what-is-a-tire-tread.htm#

[6] http://autos.aol.com/article/techsplanation-tire-tread-technology/

[7] http://www.aa1car.com/library/tire_wear.htm

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