Traditionally, such methods rely on the assumption that the factors affecting the behavior can be quantified precisely. An indicator of margin for the design is used in the process. The desired magnitude of the factor of safety for a design is determined based on experience and test. The fact that the value of factor of safety is desired to be greater than unity demonstrates that everything is not precisely predictable. Performance of a new design can be sensitive to small variations in input.
Sensitivity analysis is desirable to quantify the influence of variations.
One cannot argue that input parameters have variability, however small they might be. This paper describes a process that covers three design activities. First, without going into a complete detail of calculation, key element of stress estimation for a given set of dimensions and load is outlined. Secondly, from such calculation the effect of dimensional variation on resulting stress is quantified. Finally, a probabilistic method is applied to the stress estimation accounting for variation in the dimension.