Fracture And Crack Propagation Research Of Stiffened Panels

Ship and marine structures are complex spatial welded structures and cracks can be easily formed on welded seams,connection joints and other weak places.High strength Steel structures are more sensitive to internal crack defects and tend to fail in typical brittle fracture rather than large elastic-plastic deformation when they are exposed to cold and suffer from external shock loadings or static loading considerably larger than the critical value.Under the development of high strength and light self-weight,the static and dynamic fracture laws of ship and marine structures should be studied to prevent brittle fracture under low stress.The fracture problem mainly depends on the numerical analysis method.Given that the previous methods are cumbersome to use and have poor generality,a new numerical analysis method associated with relevant fracture mechanical models was firstly introduced to attempt to analysis the static and dynamic fracture problems.The main researches are as follows:The current research status of static and dynamic fracture problems for plates and stiffened panels were reviewed by presenting numerous domestic and foreign papers;the various kinds of classic fracture analysis methods were summarized and compared;fracture theory and the principle of extended finite element method were explained in detail.The extended finite element method with J-Integral technique was used to calibrate the values of the stress intensity factor for finite plate with single edge crack,center crack or semielliptical surface crack under certain loadings.Simulation results proved the efficiency of the method compared with reference values and the empirical formulas.The affected parameters on stress intensity factor were discussed.The residual strength of a cen ter-cracked stiffened plate subjected to remote uniform traction was confirmed under different initial crack length.The influence of stiffener stiffness and reinforcement spacing on stress intensity factor and residual strength were also discussed.The change of stress intensity factor along the plate thickness was analysis and the practice of taking the same value through the thickness is unreasonable.A stiffened panel with an edge-notched crack on its stiffener was selected to research dynamic fracture characteristic.The extended finite element method and local stress and damage model were combined to analysis the dynamic crack growth under lateral impact.The mode I and mixed-mode I-II dynamic crack propagation situations were constructed and the automatic crack extension was successfully realized.Furthermore,crack propagation characteristics are achieved on the condition of different fracture energy,several initial crack lengths and multiple locations of crack initiation on the longitudinal stiffener.The research of the thesis shows that the approaches used in this paper can provide certain guidance for fracture prevention design and the implementation of repairing crack;It can also provide an effective and economical way to study impact fracture of the complex structure and predict dynamic crack growth that traditional methods can't make.