Research On The Fracture Characteristics Of Steel Fiber Reinforced Concret

Due to the complexity of the composition of concrete materials,there are natural defects inside the material.When subjected to stress,these defects become the weakest points and are prone to damage due to stress concentration,ultimately leading to the general failure of the concrete structure.As a result,the actual strength of concrete materials is often lower than their theoretical strength.Steel fiber reinforced concrete(SFRC)is a type of concrete that has been strengthened by the addition of steel fibers.However,SFRC also has defects due to the uneven distribution of the concrete matrix and fibers.Fracture theory is a mechanical approach that research the relationship between structural defects and overall quality,and can complement and develop the traditional strength theory.Therefore,investigating the mechanical strength and fracture characteristics of SFRC is crucial for assessing the safety,stability,and durability of engineering structures.This article employs digital image correlation(DIC)technology to study the propagation of defects and mode I and mode II fracture parameters of SFRC.The main works of this study are as follow:1.To investigate the development of defects and failure mechanisms of SFRC,cube specimens were subjected to compression tests.Analysis of the strain field on the specimen surface yielded the failure pattern and curve(i.e.,the statistics of all strains in the field).The curve indicates that as stress levels increase,the range of strain distribution also increases,but the number of strains with larger absolute values decreases.The majority of strains remain at low levels.The area with defects is the primary region controlling specimen failure.2.The three-point bending tests was performed on the center-notched beam of SFRC to investigate the mode I fracture of SFRC.In the study,different parameters such as fracture toughness,displacement at the notch end and tip,crack propagation law,and the variation of crack length with fiber volume fraction were analyzed.Additionally,the study compared the fracture characteristics of SFRC and ordinary concrete in terms of strain release at the notch tip,fracture toughness,crack length,and crack opening displacement.The findings indicate that steel fibers impede crack propagation,decrease crack opening displacement and crack length,and enhance the fracture toughness of the beam.3.Compression tests were conducted on the double-edge notched prism(DENP)specimen and the double-notched cube(DNC)specimen so as to investigate mode II fracture of SFRC.The failure phenomena and crack propagation laws of both specimens were analyzed,and their fracture toughness and fracture energy were determined.The opening displacement and slip displacement of shear crack of DNC specimens under different fiber volume content were analyzed.It was observed that the shear crack mainly expanded due to the mode II crack-driven propagation force.The results indicated that fracture toughness of the DNC specimens was higher than that of the DENP specimens.4.To study mode II fracture of ultra-high performance concrete(UHPC),compression tests were conducted on the DNC specimens of UHPC.In the tests,the failure phenomena and crack propagation laws of the specimens was analyzed,and fracture toughness and fracture energy were determined.The effect of the ratio of notch depth to specimen width(a/W)on fracture toughness,crack opening displacement and slip displacement,angle and length of diagonal cracks was also analyzed in the study.Results showed that as a/W increased,fracture toughness and fracture energy initially increased and then decreased,while the length and starting angle of diagonal cracks decreased.Additionally,crack opening displacement(COD)at the notch tip of diagonal cracks decreased,while slip displacement(CSD)remained unchanged.Finally,the article summarized the research contents and main conclusions,and provided suggestions for future research work.