Study On Impact Splitting Tensile Properties Of Concrete With Hollow Sphere Defect

As a kind of building material used in engineering,concrete has excellent physical and mechanical properties,and is widely used in building construction,ports,nuclear power plants and other aspects.However,in the concrete pouring process,in its internal inevitably there is a macroscopic initial defect hole,lacuna and large cracks are typical,and the study showed that the macroscopic initial defects of concrete will cause a great impact on the mechanical properties of concrete.For the concrete structure with macro defects,not only bear the static load,also can produce such as earthquake,storm,explosion impact load,although the effects of these impact loads on buildings in a relatively short time,but more dangerous,concrete structure may be localized under tension,but tensile strength ratio of concrete compress strength compared to a lot of weak,causing serious consequences.Therefore,it has important theoretical and practical significance to study the high loading rate engineering containing tensile mechanical properties of typical initial internal defects of concrete.This paper mainly studies the following aspects:(1)A new method for the preparation of concrete specimens with initial spherical defects is proposed by means of the continuous improvement and the test of the preparation method.The results show that the step pouring method can not only affect the strength of the concrete matrix,but also can make the initial spherical defect more accurately.The popularization and application of the method provides an important technical support for the further research on the test of concrete specimens with initial spherical defects.(2)Using pressure testing machine for initial spherical defects of concrete specimen containing internal force loading rate 0.5k N/s or 5k N/s of the quasi static split strength test and research,the synchronous high-speed cameras photographed crack propagation process and its supporting system device,and the test results are synchronous analysis,studies the quasi static test failure process and failure mechanism of concrete specimen,the different force loading rate,the diameter of the spherical defects,the influence law of spherical defects of concrete splitting tensile strength.Research shows that: regardless of the force loading rate,defect diameter,defect position,spherical defects do not affect thewhole failure process and the final failure pattern,but the existence of defects were significantly accelerated the crack extension speed,affect the strength of concrete;Concrete splitting tensile strength of the specimens is decreased with the increase of defect diameter,and changes obviously;Working condition of all the specimen are obvious force loading rate effect.(3)Use of southwest university of science and technology,independent research and development of initial spherical SHPB device of internal defects of concrete specimens was carried out force loading rate of about 6x105 k N/s ?9x105k N/s dynamic split strength test and research,using high-speed cameras photographed crack propagation process and its supporting system device,and the test results were analyzed,and studied the dynamic test failure process and failure mechanism of concrete specimen,the different force loading rate and the diameter of the defect of splitting tensile strength of concrete are studied.Research shows that: regardless of the force loading rate,defect diameter,defect position,spherical defects do not affect the whole failure process and the final failure pattern,the spherical defects affect the concrete strength and toughness,mainly in the "loading force-time" reflect in curves and energy dissipation;spherical diameter of the influence of dynamic splitting tensile strength of concrete defects have no obvious regularity,working condition of all the specimen are obvious force loading rate effect.(4)According to the test results of all conditions of this paper,and considering the effects of spherical defect diameter of two kinds of factors,the rate of loading,fitted the splitting failure criterion with spherical defect impact,and compared the test results and the relative deviation of the values of the quasi failure criterion.