Dynamic Fracture Behaviour Of Steel Fiber Reinforced Cementitious Composites

Because steel fiber reinforced cementitious composites are heterogeneous mixtures,there are usually some initial defects such as inclusions and micro-cracks in the matrix.Under the external stress,these initial defects expand and coalesce into macroscopic cracks,which may eventually lead to fracture and failure of the material.In order to improve the crack resistance of cementitious composites,steel fiber is used as a typical reinforcing material,but in the traditional steel fiber reinforced cementitious composites(SFRC),the steel fibers distribute randomly in the matrix which results that some steel fibers are not fully utilized.The steel fibers can be oriented along the internal stress direction in the matrix through some specific means,so the steel fibers can exert the reinforcing effect better.Some existing studies have shown that the aligned steel fiber reinforced cementitious composites(ASFRC)possess excellent static fracture properties,but there is less research about the dynamic fracture properties of ASFRC.Therefore,in order to study the effect of fiber orientation on the dynamic fracture properties of steel fiber reinforced cementitious composites,the following work is performed in this paper.(1)According to the static fracture test of three-point bending beams,the difference of static fracture property between SFRC and ASFRC was analysed quantificationally.The results indicated that when the fiber content was 0.8%,1.2% and 2.0%,the static fracture load capacity of ASFRC increased by 80%,105% and 114% respectively compared with the SFRC’s.(2)Based on the concrete damage mechanics and thermodynamics,a semi-analytical model for predicting the fatigue life of un-notched three-point bending beams of SFRC and ASFRC was established and the rationality of the model was verified by the existing fatigue test.According to theoretical calculations,the fatigue life of ASFRC increased by approximately 60%,160%,and 300%,respectively,compared to SFRC three-point bending beams’.(3)Fatigue fracture test of notched three-point bending beams of SFRC and ASFRC was carried out,and the crack extension under the fatigue loading was studied by Digital image correlation(DIC)method.According to the test results,under the same stress,the fatigue life of ASFRC increased by two orders of magnitude averagely compared with the one of SFRC.Once the precast crack of SFRC specimen had expanded,fatigue failure occurred rapidly,however an obvious crack propagation process had been on ASFRC before it was subjected to fatigue load,and the fatigue failure occurred only when the crack reached a critical unstable state.ASFRC not only had higher fatigue life,but also possess the better fatigue deformation capacity.(4)Through the impact fracture test of notched three-point bending beams,the effects of different impact heights and different fiber contents on the impact fracture properties of SFRC and ASFRC were researched.The results showed that the impact peak load and fracture energy of SFRC both increased with the increase of impact height,showing a significant rate effect.The fracture energy of ASFRC increased with the increase of impact height,but the peak load did not show a significant rate effect;with the increasing of fiber content,the impact peak load and fracture energy of SFRC and ASFRC both increased;compared with SFRC’s,the impact peak load of ASFRC with the same fiber content increased by about 30% ～ 40%,and the impact fracture energy increased by about 50% ～100%.