I came across this SolidWorks white paper and found it excellently written. It gives a clear and practical introduction to nonlinear finite element analysis. It explains when a linear analysis is usually sufficient and when nonlinear effects, such as large deformation, material yielding, contact, or buckling, need to be considered. The examples are simple and easy to relate to, which makes the article useful for both students and practising engineers. Although the paper is not new, the main ideas are still relevant and provide a good starting point for understanding why nonlinear analysis is sometimes necessary for more realistic and reliable design decisions. The paper has been attached below.