Study On Strain Rate Senstive Constitutive Relation Containing Damage Of Fiber Reinforced High Strength Concrete

This research is the subtask of "Study on constitutive relation of steel fiber reinforced high strength concrete (SFRHSC) under strong dynamic load" which is a major project of protective engineering and "experimental study on dynamic mechanics property of concrete" which belongs to national natural science fund project. The dynamic mechanics property of SFRHSC is investigated and strain rate sensitive constitutive relation containing damage is founded through experimental study and theoretical analysis.Firstly, the research purpose and significance of the paper are analyzed. Otherwise, the research history and present state of test technique, dynamic mechanics property and dynamic constitutive relation of concrete are summarized by the numbers at home and abroad based on a mass of literature.In this paper, one of the emphases is impact compression experimentation on SFRHSC of three kinds of strain rate, namely high strain rate, moderate strain rate and slow strain rate, besides, the SFRHSC contains three kinds of strength of concrete matrix (C60, C80, C100) and four kinds of percentage of steel fiber (0, 2%, 4%, 6%). The quasi-static and quasi-dynamic tests of SFRHSC mentioned above are carried out with test equipment. Then based on the reliable mechanical parameters of the materials, the correlation between dynamic strength increase factor, dynamic strain increase factor and strain rate of steel fiber reinforced concrete is educed. Moreover, the functions between all ranges of strength, dynamic strain increase factor and strain rate are gained, and respective strain rate critical values are concluded. Lastly, the correlation between dynamic temper factor of SFRHSC , percentage of steel fiber and strain rate is analyzed detailedly, and the strength and temper enhancement effect of steel fiber is discussed.In this paper, an elementary study on dynamic split strength of SFRHSC is carried. By usingΦ100 SHPB, dynamic split tests about four kinds of strain rate of SFRHSC which contains three kinds of strength of concrete matrix (C60, C80, C100) and four kinds of percentage of steel fiber (0, 2%, 4%, 6%) are carried out. And the quasi-static experimentation containing two kinds of strain rate is accomplished with test equipment. At the same time, the correlation between dynamic split strength and strain rate of SFRHSC is reasered, and the function between dynamic split strength enhanced factor and strain rate of SFRHSC is founded. Energy dissipation of SFRHSC specimen in the dynamicak splitting tests is analyed. The influences of strength of conerete matrix, percentage composition of steel fiber and silica-fume on dynamic split strength of SFRHSC are discussed.Another emphasis of this paper is the research on damage evolvement of SFRHSC and foundation of strain rate sensitive constitutive relation containing damage. Therefore, impact damage "freezing in" compression experiment of SFRHSC which contains three kinds of concrete matrix strength (C60, C80, C100) and four kinds of percentage of steel fiber(0, 2%, 4%, 6%) is carried out by the numbers. By restricting strain of specimen with steel ringer around the specimen and controlling strain rate of specimen through controlling impact speed, the strain and strain rate are controlled in some range. After that, the specimen is loaded by impact, then static compression experiment of the specimen mentioned above that contains impact damage is carried out with 25T MTS, meanwhile, the change of elastic module is measured, thereby, the damage extent under some strain and strain rate can be gained. Further, the correlation between damage extent , matrix strength, strain rate, strain and steel fiber content is analyzed. Considering the inertial effect of crack expansion under impact load, this paper brings forward that the correctional factor should be introduced in damage evolvement equation, which can delay the amendment. In the end, damage evolvement equation of SFRHSC is established.Finally, using the result of the experiment and corresponding analysis, ZWT nonlinear sticky-elastic constitutive model is improved, and the strain rate sensitive nonlinear constitutive model for SFRHSC containing damage is put forward. The forecast result of the model matches the test result.