Physics of Failure is a term used when discussing equipment reliability. It refers to the microstructure science that explains how and why parts fail. By understanding the Physics of Failure, you appreciate the true cause of breakdowns in all physical assets – from plants to vehicles, and all machinery and equipment – is microstructure failure.

There are two main types of part failure. The first is caused by the part’s microstructure being overloaded, and the material-of-construction is pulled apart. This occurs when the stress placed upon a component that is greater than the material-of-construction strength range. It is known as deformation and includes instances where a component may fail due to fracture or wear.

The second is when the material-of-construction degrades, known as degradation. Examples of this include corrosion, chemical attack, or material fatigue. The result of these is that the material separates at a microstructure level and the remaining structure can no longer bare the load. Image 1, below, illustrates how these failures occur and provides visual examples.

By applying an understanding of the Physics of Failure, we can understand why failures occur and seek to eliminate or mitigate their occurrence before unplanned breakdowns happen. This is done by developing work processes which actively prevent defects or causes of component failure entering the system, and monitoring those that cannot be prevented. The Plant Wellness Way EAM methodology guides you to identify and implement the most effective processes for each component.

Why Parts Fail

Gear tooth’s are a common component that experiences unplanned and seemingly unpredicted failure events. There are two reasons as to why a gear tooth may fail, which are explored below through the lens of physics of failure.

One reason is because its material experiences a massive overload (Image 1, Graph 1). This can occur when a wear particle, only a few microns in size, becomes trapped between the teeth of the driven gear and the driving gear. Now, all the forces are directed through the few-microns sized particle and onto each tooth’s material-of-construction. Instead of the force being distributed over the whole area of each tooth, the load is now focused on a very small surface area. This results in the stress on the area becoming so massive, the material’s microstructure begins to fail, and the tooth shears off.

Another reason that a gear tooth may break is when the component is damaged due to degradation and can no longer carry the load. This causes the load carrying capacity of the material to decrease (Image 1, Graph 2). As the microstructure available to carry the load reduces, the component reaches a point where even a normal load is too much for the remaining material and the part fails.