In this paper, a flexible fiber model, based on the Discrete Element Method (DEM) and the bonded-particle model by Potyondy and Cundall (International Journal of Rock Mechanics & Mining Sciences 41 (2004) 1329-1364), is comprehensively examined by considering the cases of the bending, stretching, and twisting of a fiber under static loads and dynamic vibrations. The numerical simulation results are in good agreement with the analytical predictions from elastic thin beam theories. In addition, a time step criterion is discussed and proposed in order to ensure numerical stability and obtain correct dynamic behaviors of fibers. It is found that the time step should be less than the time it takes for an axial extensional/compressional wave to travel a single bond length. (C) 2013 Elsevier B.V. All rights reserved.