Concrete Fatigue Fracture And Size Effect Study

In order to study mechanism of fatigue fracture of concrete specimen,according to "Study on I-II Mixed-Mode Dynamic Fracture Property and Mechanism of Concrete" supported by Youth Foundation of National Natural Science Foundation ,the following research work was carried out in this paper:1 The influences of the specimen height h and relative crack length a/h on double-K fracture parameter of concrete were investigated by using two sorts of abnormally standard three-point bend beams whose his 200mm initial a/h are 0.2 N 0.3 0.4 0.5 for one sort and h are 200mm 300mm N initial a/h is 0.2 for another. Results show that double -K fracture parameter which is calculated by Fictitious Crack Model is a constant.2 The whole procedure of crack propagation of abnormally standard three-point bend beams was researched by photoelastic coating. Through analysis of isorchromatic -fringe patterns taken in the experiment ,the fracture process of concrete includes the crack' s initiation ,the stable propagation and the final failure.3 Based on the static experiment mentioned above,the research of stable crack growth process of concrete under fatigue loads was carried out. Crack growth length A a under different number of cycles was attained by compliance method and strain gauge method. On the basis of this,the law of fatigue crack growth rates were gotten.lt is found that the law of fatigue crack growth is suitable for Paris law:5 To know more about the law of fatigue crack growth of concrete under fatigue loads ,using the photoelastic coating,the fatigue fracture test of wedge splitting specimen whose h are 200mm 300mm and initial a/h is 0.2 is carried out. Results show that the fatigue crack growth rate on the process of concrete fatigue fracture hassize effect.