Using the fracture mechanics and finite element analysis theory

the effect of section types of the ribs and multiple-site damage on the crack turning behavior and fracture characteristics of the integral stiffened panel is investigated. First the crack growth model of the integral stiffened panel was established

and the reliability of the established model was proved in comparison with the test results of the crack growth rates. Based on the above model

the influence of section types of the ribs on the crack fracture parameters and crack turning was discussed. Finally the multiple cracks problem was investigated. The study showed that the effect of the sectional types of the ribs on the fracture parameters was not significant and the crack turning was more likely to occur when the crack was growing far away from the ribs. In the case of multiple cracks

cracks will not turn

but grow straightly and connect to form a large crack. Moreover

the strong interference of adjacent crack tips can lead to the severe increase of stress intensity factor and acceleration of the crack growth. Furthermore

the crack propagation life will be seriously shortened. Therefore

effective repairing methods are needed to improve the residual strength and service life of the structure.