Numerical modeling of a post & dome snap-fit feature

Snap-fits are often designed using guides that rely an classic beam theory with the basic assumption that the beam undergoes small rotations and displ acements. This is a poor assumption, for they typically experience both lar ge rotations and displacements due to loading offset from the neutral axis and axial loading. This paper investigates the performance of the post & do me feature, establishes its nomenclature, and derives the equations needed to intelligently design different variations of it. The post & dome feature was selected for analysis because it is a high performance snap-fit that i s self-datuming and can withstand some shear loading in addition to retenti on. The design equations were generated in three steps. First, an experimen tal array was created using a design of experiments approach. Finite elemen t methods and multiple regression techniques were used in lieu of beam equa tions models for each of the trials in the experimental array. Finally, res ponse surface methods were used to develop response curves based on the per formance data generated by the finite element models. Sensitivity data was plotted for both the main effects and selected variable interactions. The t raditional benchmarks for defining high performance snap-fits are retention strength, insertion force, and insertion strain. This paper uses an expand ed definition of these benchmarks that also includes locking ratio (the rat io of retention force to insertion force).