Mechanical engineer (research)Member of ASTM, U. S. Army Research and Development Command, Large Caliber Weapon Systems Laboratory, Benet Weapons Laboratory, Watervliet, NY
In this paper it is reemphasized that the effect of residual stress in fatigue is analogous to but not the same as the mean stress effect from applied loads. By including a residual stress term in the stress intensity factor range of the fatigue crack propagation rate equation, one is permitted to include the residual stress in calculations of fatigue life estimates. Using crack shape factors calculated for given aspect ratios of surface flaws and integrating the fatigue crack growth rate da/dN, one obtains an equation for the applied stress-cycles to failure S-N curve that includes the residual stress effect on fatigue performance. In this process of calculation that fact that compressive residual stress has a much stronger influence on fatigue life than tensile residual stress is revealed, mainly because the former decreases the stress intensity factor range and increases the critical crack size while the latter only decreases the critical crack size. A numerical solution of an example illustrates an application of these concepts.
Paper ID: JTE11588J