The use of Ashby Materials Selection Maps ( See the TLP - Optimisation of Materials Properties in Living Systems )
Stress states and Mohr's circle (these are covered in the TLP - Theory of Metal Forming - Stress States and Yielding Criteria )
Tensors and matrices.
Some basic knowledge of plastic deformation and brittle and ductile fracture is also useful.
These are not pre-requisites and it should be possible to make use of this TLP even without knowledge of these concepts.