The effect of shot particles on the fatigue of Kaowool fiber-reinforced 339 aluminum

The addition of Kaowool fibers substantially increases the fatigue strength of 339 aluminum at 300 degrees C. However, the fatigue life of these compo sites is limited by the presence of Kaowool "shot" particles, which act as crack initiation sites. An elastic analysis of the stress concentrations as sociated with this type of defect shows that a crucial parameter is the dis tance of the particle from the free surface. As the distance from the surfa ce decreases, the stress concentration factor increases substantially and a ttains maximum value when a small portion of the particle has been removed by machining. The relationship between the distance from the surface and th e stress concentration factor is in excellent agreement with the particle g eometries observed at fatigue crack initiation sites.