Fatigue behavior and crack opening tests under tensile stress on HPSFRC: Experimental and numerical investigations

The capability of high-strength steel microfibers to control the degradation in high-strength concrete was experimentally examined and numerically simulated. To this end, notched prismatic highstrength concrete specimens with and without steel microfibers were subjected to static and cyclic tensile tests up to 100,000 cycles. The material fatigue was examined using microscopic analyzes. The increase in strain at the test specimens with high-strength steel microfibers was less than without fibers. And also, the strain stagnates after 10,000 Cycles at high-strength concrete with steel fibers. The microscopic examinations showed that more cracks developed in the microfiber reinforced high-strength concrete than in the unreinforced high-strength concrete. However, these were smaller and shorter, i.e., more finely distributed, and thus had a smaller total crack area than the high-strength concrete without fibers. To investigate the influence of fibers on the behavior of HPSFRC in the cracked state, displacement-controlled crack opening tests, as well as numerical simulations thereof, were carried out. In the finite element model, concrete cracking was simulated using zero-thickness interface elements, and fibers are modeled explicitly, using the Bernoulli beam elements, and bond elements tying microfibers and concrete. Experiments have shown, and the numerical simulations have confirmed, that the inclusion of steel microfibers didn't increase the strength, however, it significantly increased the post-peak carrying capacity, i.e., ductility of the material. Finally, the crack closure model introduced to analyze the unloading/reloading behavior has shown that in this experiment.