The discretization of a volume into elements is called a mesh; the meshes of the mesh are not regular and must be sized in relation to the complexity of the distribution of loads: only experience can lead to acquiring the necessary sensitivity to perform an optimal choice. There are routines that allow this operation to be performed automatically, however the quality of the elements used is not optimal and the intervention of an expert operator remains necessary to eliminate elements that are too distorted or to thicken the mesh where it is likely that voltage concentrations are likely to occur.
The choice of the type of elements must be made according to the type of stress that is considered to be pre-eminent (bending, cutting, behavior in the plane or out of plane); in particular, in the simulation of solid volumes tetrahedral solid elements (at four nodes or, better, at ten nodes) or esaedrici (at eight nodes) are usually used; while when the volume develops mainly in two directions (for example a cortical bone shell) it may be advisable to use flat elements (at three nodes or, better, with more than four nodes). If elements of different types are used at the same time, special care must be taken in taking care of the transition from one to the other.
There are also various applications that require the use of dedicated elements: for example, bone and implant in the immediate post-operative period are not perfectly integral and it is necessary to simulate contact: in other words, it is necessary to avoid interpenetration and allow slipping with or without friction. In all cases where this type of element is used, the analysis becomes forcibly non-linear.