Shot Blasting To Increase Fatigue Resistance

Author:  Almen, J. O.
Source:  #430143, Trans. July, 1943, Vol. 51, No. 7, p.248-268
Doc ID:  1943003
Year of Publication:  1943
Abstract:  
While great strides have been made in most phases of engineering and metallurgy, it is doubtful that in dynamically loaded parts we are getting more net work from our metals today than was obtainable 25 years ago. The fact that modern airplane engines weigh only about one-half as much per horsepower as the engines of World War I is primarily due to improvements in fuels and increases in engine speed. The speed and performance of airplanes have increased because of the better power-weight ratio of engines and aerodynamic improvements in propellers and airplane structures. New fabrication techniques have made possible many design improvments, better bearing materials are available, lubricants have been improved; but the basic useful strength of our structural materials remains unaltered. Although no super-strength alloys have been discovered and no such discoveries seem to be imminent, there is much that can be done to increase materially the fatigue strength of many machine parts made from our ordinary structural materials. This fatigue strengthening does not require changes in design or in material, and in fact it does not require processes that are fundamentally new or untried. It is merely the extension of processes that, on the whole, have long and honorable histories, and the avoidance of processes and practices that are not known to reduce fatigue strength. The significance of these processes has only recently become clear through the introduction of new concepts of fatigue phenomena by which new avenues of reasoning are opened to us. These new concepts are: Fatigue failures result only from tension stresses, never from compressive stresses and any surface, no matter how smoothly finished, is a stress-raiser.