Many industrial units apply wanted or unwanted impact loads to particles. Such units include comminution units as ball-mill, pin-mill or jet-mill, as well as conveying systems such as pneumatic conveying pipelines and chutes. Regardless of whether the impact load is wanted or unwanted, it causes damage to the particles. The number of collisions also has a major effect on the damage caused to the particles. Since systems commonly used in industry are similar in many ways (differing only by the range of impact velocities and number of impacts) their effect on the damage caused to the particles could be commonly evaluated based on the impact velocity and the number of collisions. In this paper, the fatigue behavior of the same material tested in four impact comminution and attrition units is compared for the first time. Fatigue curves common to the four impact units are presented. The ability to plot a single fatigue curve for various impact systems enables to predict the expected size reduction in any new impact system based on past experience with other impact systems, as will be demonstrated in the paper. (C) 2004 Elsevier B.V. All rights reserved.