Updated on 26 January 2021
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Tribology is the science and technology that investigates the interaction of surfaces in relative motion in the form of friction, wear, lubrication and other design aspects of materials science. These concepts of tribology have several practical implications in our everyday lives. For example, the friction between our feet and the ground allows us to walk and drive each day.
Friction
Friction is defined as the resistance to relative motion between two bodies of contact. The force of friction is independent of the area of surfaces in contact and is directly proportional to the applied load. The force of friction is attributed to the electromagnetic attraction that exists between the charged particles within the two surfaces of contact.
The Amonton’s law describes the relationship between the frictional force (F) and the applied load (L) as F = mL, in which the coefficient of friction ‘m’ depends on the materials that are in contact with each other. The coefficient of friction can vary, depending on whether the objects in contact with one another are stationary or in motion.
The frictional force is considered a non-conservative force and non-fundamental force since the work is done against friction is path-dependent. Friction is therefore considered a system property, rather than material property.
Types of Friction
There are various types of friction, which include static, rolling, kinetic, sliding and fluid friction. Static friction is the friction present between two objects that have no relative motion, such as a block of wood left on the table. Rolling friction describes the frictional force that exists when one object rolls on the other surface, such as that which occurs when the wheels of a car move against the street. Kinetic friction is the friction that occurs when the two objects in contact move relative to each other and rub together, such as that which would occur when a child goes down a slide. Sliding friction occurs when one object slides on the surface of the other, like a block of wood sliding across the table when pushed. The final type of friction, fluid friction, occurs when a solid object moves through a liquid or gas, such as that which occurs when an aircraft is in flight.
Wear
Wear is defined as the phenomenon of the gradual removal, damaging or displacement of material at solid surfaces that occurs as a result of relative motion occurring between two contact surfaces. Wear that occurs in machinery components has the potential to cause degradation of the functional surface and ultimately loss of functionality. Various factors, such as the type of loading, the nature of the motion between the contact surfaces and temperature, determine the rate of wear.
Types of Wear
Abrasive wear occurs as a result of abrasion that happens when a hard and rough surface of one object slides across the surface of another object that is significantly softer. Adhesive wear occurs when the displacement or attachment of unwanted substances or debris from one material adheres to the surface of another object. Fretting wear is a type of wear that occurs as a result of repeated cyclical rubbing between the surfaces of two different objects. When solid or liquid particles of one object impinge against the surface of another object, the resulting wear is known as erosive wear. Surface fatigue is known as weakening of surface material that occurs as a result of cyclic loading, as well as corrosion and/or oxidative wear that occurs as a result of chemical reactions that occur between the worn material and a corroding medium.
Conclusion
Friction is the force that occurs between two contact surfaces in relative motion, whereas wear is the phenomenon of mechanical and/or chemical damage that affects the quality of the materials in contact with each other. The contact surfaces in relative motion can be lubricated to minimize friction and reduce mechanical wear.
Sources and Further Reading
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