A software framework for simulating curvilinear crack growth in pressurized thin shells

A methodology for simulating crack growth in pressurized, stiffened, thin shell structures is described. Crack trajectories are allowed to be arbitrary and are computed as part of the simulation. The methodology is implemented within a software framework that consists of a fracture simulation code and a separate analysis code. The fracture simulation code embodies a representational model that supports a high-level problem description that is independent of the discretization. The representational model--consisting of a constrained hierarchy of topology-based, boundary representation, geometric models with which simulation attributes may be associated--is well-suited for tracking the geometry changes resulting from crack growth. Cracks are represented discretely in the mesh and crack growth results in localized mesh deletion. The deleted regions can be remeshed automatically using a newly developed arbitrary region, all-quadrilateral element surface meshing algorithm.; Structural response of pressurized, stiffened, thin shells is computed using a geometrically nonlinear shell finite element analysis procedure installed in the STAGS (STructural Analysis of General Shells) code. Crack growth is characterised by four stress intensity factors that model the membrane behavior using two dimensional, plane stress elasticity and the bending behavior using Kirchhoff plate theory. The four stress intensity factors for mixed-mode problems are computed from the results of a finite element shell analysis using an extension of the modified crack closure integral method. Crack trajectory is determined by applying the maximum tangential stress criterion to a point on the shell midsurface.; The effectiveness of the methodology is demonstrated by simulating crack growth in a typical narrow-body pressurized aircraft fuselage idealized as a stiffened, thin shell structure. A hierarchy of structural models, ranging from a relatively coarse global shell model to a highly refined local shell model, provides the kinematic boundary conditions for the 2 x 2 bay stiffened panel model represented within the fracture simulation code. Crack trajectory and stress intensity factor variation as a function of total crack length are computed and a fatigue life prediction is made. The predicted crack trajectory and life compare well with measurements of these same quantities from a full-scale pressurized panel test.