Studies On The Crack Turning Theories For Integrally Stiffened Structures And It's Application

The integrally stiffened aircraft structures, because of many advantages of its oneself, such as lower manufacturing cost and longer tired life span etc, is a new research direction of airplane structure in the last few years. However, this kind of low cost and integrally structure, because of lacking an expectation of the tolerance damage, repressing it's application, people already pay attention to the fracture mechanics characteristic and tolerance damage method. The abroad has already done a lot of researches in this aspect, and obtained some important research results. However, the domestic research just is starting in this aspect. The foundation theories and applications technique currently are all weak, and the related research and data are also very seldom.For all that, research experience of the abroad provides important foundation for us in researching the fracture mechanics characteristic and tolerance damage of the integrally fuselage of airplane .The research of the abroad express that in the integrally fuselage of airplane structure, the crack turn is thought to be a kind of latent and count for much mechanism of holding back the crack propagation. Therefore, predicting crack turn accurately and predicting the crack propagating trajectory accurately is a important researching content of fracture mechanics for integrally structure.Therefore, on the foundation of abroad research, this text describes the first and second order of crack turning theory, the influence of plasticity zone of crack tip and fracture resistance orthotropy of material to crack propagating trajectory. Making use of the Double Cantilever Beam(DCB),we have researched the phenomenon of crack turning and done some corresponding emulation by finite element method (FEM), and analyses the crack turning condition and influence of the characteristic length(r_c) and fracture resistance orthotropy. Furthermore, combining domestic existing condition, we gave the way of finite element emulation environment forcrack propagating trajectory and phenomenon of crack turning, and simulated crack turning of transverse crack in one of the integrally stiffened structures, and analyzed influence of T -Stress and different characteristic length to crack propagating trajectory.Because the existing technique is weaker, and the time is limited, the research of the text in the crack turning and predicting crack propagating trajectory is primary. Nevertheless, this text work has meaning of instruction to domestic research crack turning and holding back the crack propagation of the integrally fuselage of airplane...