Here are some notes about stress analysis in the field of Finite Element Analysis:
Stress is simply a measurement of the internal forces in a body, as a result of the externally applied loads.
Force is a vector - it has both magnitude and direction. As a result, stress actually has direction as well. So what happens when you have complex (multi-directional) loading? Your stress inside your part will have components in each of these different directions.
Assume a part centered at the origin. If you pull on it only in the direction of the X-axis, it will only have stress values normal to that direction. However, if you also pull on it in the Y-direction, it has stress normal to X from the original force in the X-direction, but also stress normal to Y from the Y-direction force. In addition, an angled force load with respect to geometry will causes the material try to slide past, and shear the part. This contributes to what are called shear stresses.
As a result of this, looking at a 3-D part we can actually have up to 3 different stress normal directions, as well as up to 3 different shear directions (X on Y, Y on Z, and X on Z). This means we can in theory have 6 different stress values. That‘s a lot to try to calculate or interpret!
Original URL : http://blog.design-point.com/blog/2013/january/solidworks-simulation-what-is-von-mises-stress-part-1-of-2.aspx