Use of small fatigue crack growth analysis in predicting the S-N response of cast aluminum alloys

The development of a material model to estimate the S-N response of a cast aluminum alloy is described. An important requirement of such a model is se nsitivity to processing effects such as solidification time and subsequent material characteristics such as secondary dendrite arm spacing (SDAS), str ength, and porosity. It has been speculated that the fatigue properties of aluminum castings are dominated by the propagation of cracks which initiate from microshrinkage pores ranging in size from similar to 10 to 1000 mu m. A model was developed that calculates fatigue life based on small crack gr owth rates measured in cast 319 aluminum specimens with two different solid ification times. Results from this small crack model are compared with pred ictions from a traditional LEFM model using long-crack data and measured th resholds.