Friction – Stress vs Strain

“The elements of change,

Just as the engineer masters the elements, the mechanic evaluates the car, the doctor reads the temperature levels, the lawyer understands the communication chemistry at play and the Poet reads below the lines to tell another story.” Natasha

Chemistry and physics a matter of reflection

Internal friction is the force resisting motion between the elements making up a solid material while it undergoes deformation.

 As deformation occurs, internal forces oppose the applied force. If the applied stress is not too large these opposing forces may completely resist the applied force, allowing the object to assume a new equilibrium state and to return to its original shape when the force is removed.

Deformation is often described as strain.

A larger applied force may lead to a permanent deformation of the object or even to its structural failure.

The concept of a rigid body can be applied if the deformation is negligible.

This type of deformation is not undone simply by removing the applied force. An object in the plastic deformation range, however, will first have undergone elastic deformation, which is undone simply be removing the applied force, so the object will return part way to its original shape.

There are two ways to determine when a part is in danger of metal fatigue; either predict when failure will occur due to the material/force/shape/iteration combination, and replace the vulnerable materials before this occurs, or perform inspections to detect the microscopic cracks and perform replacement once they occur. 

A common way to reduce friction is by using a lubricant, such as oil, water, or grease, which is placed between the two surfaces, often dramatically lessening the coefficient of friction. 

The work done by friction can translate into deformation, wear, and heat that can affect the contact surface properties (even the coefficient of friction between the surfaces). 

Friction is an important factor in many engineering disciplines.

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