Description: A Probabilistic Fatigue Damage Assessment Network (PFDAN) toolkit for Abaqus will be developed for probabilistic life management of a laminated composite structure with both microcracking induced stiffness degradation and cyclic loading induced delamination crack growth without remeshing. It is based on a high fidelity Fatigue Damage Assessment Network (FDAN) which includes 1) a coupled continuum damage and discrete crack model for ply damage characterization; 2) a moment schema finite element coupled with XFEM for efficient crack growth simulation in a thin ply; 3) a mixed mode fatigue delamination module to account for the mode mixity and failure mode interaction; and 4) an adaptive fracture process zone model for mesh independent delamination growth. A reduced-order model of FDAN will be generated using a combined response surface and a Gaussian process surrogate model builder to perform the subsequent probabilistic analysis efficiently. For the module verification and validation, experimental studies at the sub-component level will be performed along with the use of a damage monitoring and characterization system. The developed toolkit will be used to perform damage prognosis and risk informed life management using SHM data. GEM has secured commitments for technical support and commercialization assistance from Clarkson University, Sikorsky Aircraft, and Boeing.

Benefits: The results from this research will have significant benefits to enhance the aviation safety program in NASA. It will result in: 1) a commercially viable, accurate, computationally efficient, and user-friendly probabilistic residual life assessment tool for characterizing fatigue crack growth and performing damage analysis at the presence of uncertainties in design and loading parameters; 2) an integrated analysis framework for fatigue damage prognosis and health management of aging structures; 3) a virtual testing tool to reduce current certification and qualification costs which are heavily driven by experimental testing under various stress conditions; and 4) innovative probabilistic methods and reliability assessment procedures to facilitate the structural health management. The developed tool integrates advanced crack insertion and growth characterization, innovative fatigue damage modeling, and efficient probabilistic methods into a seamless framework for probabilistic crack growth analysis and structural damage prognosis.

Structural aging under fatigue loading is one of the most common failure mechanisms in civilian structures such as buildings, bridges, power lines, pressure vessels, and ship structures. The developed probabilistic fatigue life prediction tool can be used effectively and efficiently to assist a designer and rule-maker to answer the following questions: 1) does a proposed design have an acceptable risk of fatigue failure; 2) how tolerant is a proposed design of a crack without the risk of catastrophic failure; 3) if a crack is found in service, how long is it safe to leave the crack before repair; 4) the vessel's mission and operational profile have changed, what are the implications for fatigue and fracture risks; 5) how often should the vessel be inspected for fatigue cracks; 6) what crack size does a structural health monitoring system need to be able to detect to reduce the risk of fracture; and 7) how can measured loads from a structural health monitoring system be used to update the fatigue risks? The tool can be used to assist commercial and military industries to reduce the cost of test-driven design and process iterations with the use of the virtual testing tool. Finally, teaming with LM and Sikorsky, highly visible aircraft manufacturers, will considerably shorten our development cycle from producing a prototype research orientated tool to commercially accessible design software.