I am currently using Pro/MECHANICA to analyze a struture comprising of steel and aluminium. To analyze whether the structure will fail under certain load, i have to filled in the tensile yield stress of materials when editing the material. Is that we have to impose certain degree of safety factor to this tensile yield stress? I am in a dilema about what safety factor should i use for. Besides, there are 3 types of criteria to test for failure of structure(distortion energy or von mises, maximum shear stress or tresca and modified mohr), which is the best to used? Please advise, thanks.