Engineering Complex Three-dimensional Structure Of Crack Fracture Properties

Aircraft structure is most sheet structure, but most structural components of supporting load and linked components are the fairly thick block structures. Especially, due to warplane air speed increase , wing loading increase and thickness increase of aircraft skin-panel structure, analysis to thick skin-panel structure and block structure becomes key problem of aircraft structure fatigue analysis , durability assessment , damage tolerance assessment and reliability analysis. Therefore, the research on fracture characteristics of three-dimensional cracks structure, especially on stress intensity factor (SIF) of three-dimensional crack is very important.On the basis of the existing slice synthesis method, the slice synthesis Method is developed to calculate SIF of three-dimensional crack with complex boundary, this method is named the extended slice synthesis method, and the continuity of displacements are deduced. The extended slice synthesis method is used to analyze and discuss SIF for surface crack in normal structures. Comparing the computed results with Newman results, curvilinear trend is rational and computed precision meets the engineering needs; At the same time, to analyze and discuss numbers identify points at which slice displacements are matched how to affect SIF. It is used to calculate SIF for a surface crack in thick plate with flange complex boundary. Some results and conclusions, which are of practical value, are given in this paper.On the basis of computing the SIF of three dimensional crack with the slice synthesis method, the formula of SIF of three-dimensional crack front at the small yield scope is deduced, considering the plastic zone's effect, and discusses the plastic zone size to the effect of the SIF, especially considering the plastic zone's negative effect to the growing of the crack. The results are analyzed and discussed in this paper, and a principle that can be referred in engineering. The calculation results show that after the plastic zone's negative effect to the growing of the crack is considered, the SIF will be less 7%~30% than the case in which the effect is ignored.Applied compounding method creates the single and double crack weight function of elliptic holes. Computing corner crack and surface crack SIF's formula,applied the slice synthesis method, is gained. SIF of Corner crack and surface crack is computed. At the same time, research on elliptic holes radius of curvature how to affect SIF. SIF decreases along with radius of curvature increases.