Why do parts, working components or machine elements fail? This is the basic question one asks to himself or others on a failure. The answer to this can be given only if the various modes of failure are known to us. We will start with the foremost mode of failure “Static Failure Mode". In particular these failure modes apply only to metals to be very clear.
When I say Static failure mode, I mean to say that the failure has occurred due to a static load. Well, then what is a Static Load?
“Static loads can be defined as the one which is very slowly applied and remain constant without any change for a long duration of time." A good example for the static load would be the television on your television stand; the television is a static load for the table.
Loads alone don’t cause a static failure. It involves two other important factors – the material of the part and the constructional features of the part. The material of the part contributes more towards the static failure. The failure modes are basically classified based on the type of material namely
· Ductile and
How do we determine whether the material we use is ductile or brittle? Here is a simple way to determine or know that
v Any material that can elongate to more than 5% of its length before failure can be termed as a ductile material. Normally all ductile materials tend to have an elongation of 10% of its length before failure.
v Well, a brittle material is just the opposite of this, any material that fails before elongating to 5% of its length is termed as brittle.
The static failure theories have been hence formulated based on the material type. These theories are formulated to enable us to design a part or the component based on the loading it is subjected to. To be more precise, the theory gives an empirical formula enabling us to check our designs. Moreover other considerations that are taken care of in the theories are
1. The type of stress that leads to the failure, whether it is compressive, tensile or shear.
2. The capability of the material in handling tensile, compressive and shear stresses or to be more precise the material properties.
We will look into the failure modes of ductile materials in the forthcoming articles.