Various physical phenomena are involved in the fracture process of steel fiber reinforced concrete (SFRC). Although pullout of the fiber has been the most intensively investigated parameter in studying the micromechanics of these materials, other mechanisms could be dominant, depending on the nature of the loading and the fiber orientations. Pullout tests were conducted on isolated fibers embedded in a mortar matrix with different orientations to the direction of loading.

The specimens were loaded in the chamber of a scanning electron microscope (SEM), and on an optical table with instrumentation for Laser holographic interferometry (HI). The relative contribution of the various mechanisms, such as: fiber debonding and pullout, mortar crushing, friction at comers, and plastic energy dissipation on the fibers were evaluated. When the specimens were tested in the SEM, it was observed that compressive failure with crushing of the mortar is an important physical phenomenon, in addition to plastic bending of the fiber. HI studies also indicated the crushing of mortar prior to interface debonding.

The relative amounts of energy dissipated by the various mechanisms were evaluated using experimental observations and analytical approximations. The importance of the different mechanisms at progressive stages of fiber pullout was estimated.