Mechanical Engineering Introduction
The first thing of importance, when doing mechanical design, engineering and manufacturing, is Mechanics. Mechanics deals with: determine how big the internal stresses, caused by external and internal forces, moments and torques are on and in the construction. What are the consequences for the designed product?
In general the ultimate consequences, in a mechanical sense, are:
- the product or part breaks or
- the product or part deforms too much to fulfil the desired functions.
In the first case the product is broken and is thus no longer useful. It is obvious this should be prevented. In the second case the product deforms too much to still be functional. Again this is not what you want.
1. The product breaks
But how to void breakage of products? Too often so-called ”trial and error” methodologies are used. Ultimately, these methodologies can be very expensive and/or are dangerous [Dorner1997] and should thus be avoided.
Better is the application of systematic methodologies like modelling based on science[Young2014, Grossmann1984]. In this case calculating on beforehand, while designing, whether the external and internal stresses on and in the product, caused by the loads, will exceed the failure stresses of the materials used. The failure stress is a material property thus we also need to know how materials behave under loading, see the section on Materials.
2. The product deforms too much
In the second case, the product deforms too much to still be functional. For instance a slider gets stuck in a slot of a part because of excessive deformations of the slider. Again, although the product does not break, it is obvious that you, as a designer, want to know this on beforehand before the product is in use. But how to avoid successive deformations of parts or products? Again by applying modelling methodologies based on science. In this case by calculating the internal stresses, caused by the loads, combined with the elasticity of the material and the shapes of the construction we can determine the to be expected deformation. The elasticity of a material is a material property thus again we need to know how materials behave, see the Elasticity section.
How to calculate the internal stresses given the external and internal loads and the shape of the parts? See the Mechanics page for how to calculate these internal stresses.
P.s. products consisting of moving parts made of different materials, thus with different thermal expansion coefficients, may get stuck due to excessive relative deformations. A method to avoid this is using Exact constraint design.