Study On Brazilian Splitting Process And Tensile Characteristics Of Concrete And Reinforced Concrete

Concrete and reinforced concrete are widely used in the field of military and civilian construction,the dynamic tensile stress test methods,and the research of its characteristics have been concerned,because the tensile strength of this kind of materials is far less than the compression strength,and in most cases the damage of this material and structural is caused by the tensile fracture,such as bending failure,compression fracture,and the spalling,which occurs when stress waves reflect at the interface.The Brazilian test,a specimen and widely used indirect tensile testing method,has the advantages of easy loading,and could loaded by Hopkinson pressure bar to measure dynamic tensile strength.Since the Brazilian disc splitting experiment method was proposed,researchers have been testing and improving this method,which has always been a hot research issue.Based on Digital Image Correlation method（DIC）,this thesis analyzed and studied the splitting process of static and dynamic Brazilian splitting tests,and discussed the influence of different loading boundaries and different loading rates on the stress state,failure process,and splitting tensile strength of the specimen.Furthermore,the strain rate effect of splitting strength of concrete and reinforced concrete was studied.The main research work and results are as follows:（1）By the elastic theory resolution,and the digital image correlation（DIC）method,the evolution of strain field,crack initiation and propagation during the process of splitting were studied.The results show:（a）The evolution of strain concentration caused by nonlinear tensile properties of the concrete is sensitive to loading conditions.Under flat plate load,strain concentration earlier initiates from the loading point and evolves to the specimen center.In this case,even the experimental condition of the crack initiates from the specimen center is satisfied,compared to the loading condition of cushion load,the strength is still lower,and the difference could reach 17.9%.（b）As long as the contact angle is designed properly under cushion load,the stress field of the specimen can develop more stable than that of direct flat plate load.It is better to meet the requirements of the Brazilian splitting test that ensuring strain concentration as well as initial fracture start from the specimen center.（c）Only satisfying the condition of crack initiates from the center is insufficient,we should design appropriately to make the Brazilian test efficient.This work is of great reference significance for the application of the Brazilian test.（2）The analysis of Hopkinson concrete dynamic splitting test shows that:（a）The Brazil dynamic splitting test has ultimate loading strain rate,if the loading rate is too high,the stress equilibrium hypothesis of Hopkinson test cannot be satisfied,and the experimental results are invalid.For a concrete specimen with a diameter of 74mm,the ultimate strain rate is about 6s^-1.（b）Dynamic Brazilian splitting failure does not occur at the peak of the loading force,but before the peak of the loading force.Therefore,the traditional calculation of dynamic splitting tensile strength using the peak of the loading force will overestimate the tensile strength of the material,and make the result larger by 20%-30%.（3）When the Brazil splitting material using reinforced concrete,the concrete matrix first cracks,the crack extends to the whole specimen along the loading radial.As the steel bar can continue to bear the tensile stress,the tensile load increases,and the specimen will not disconnect.When the reinforced concrete matrix dynamic initial fracture,the apparent and peak strength of reinforced concrete improved slightly compared with the results of concrete specimen.（4）The dynamic tensile strength of concrete and reinforced concrete has strain rate effect,and the strain rate effect of dynamic tensile strength of concrete was more obvious than that of reinforced concrete.When the reinforcement was added into concrete,compared to dynamic loading,the splitting tensile strength of the sample were obviously improved under quasi-static loading.