No abstract

Most current tools and methodologies to predict the life and reliability of fracture critical gas turbine engine components rely on stress intensity factor solutions that assume highly idealized component and crack geometries, and this can lead to highly conservative results in some cases. This paper describes a new integrated methodology to perform these assessments that combines one software tool for creating high fidelity crack growth simulations (FRANC3D) with another software tool for performing probabilistic fatigue crack growth life assessments of turbine engine components (DARWIN). DARWIN employs finite element models of component stresses, while FRANC3D performs automatic adaptive re-meshing of these models to simulate crack growth. Modifications have been performed to both codes to allow them to share and exchange data and to enhance their shared computational capabilities. Most notably, a new methodology was developed to predict the shape evolution and the fatigue lifetime for cracks that are geometrically complex and not easily parameterized by a small number of degrees of freedom. This paper describes the integrated software system and the typical combined work flow, and it shows the results from a number of analyses that demonstrate the significant features of the system.

The objective of this research was to determine the stress intensity multiplication factor (Y), as a function of the nondimensionalized crack depth (a/d), in the threads of a nut-loaded, aerospace, roll-threaded bolt under tensile fatigue conditions as a/d approaches zero. The proposed Y(a/d) solution can be used to improve fatigue crack growth life estimations. The research objectives were achieved through bolt material/stress state characterization, cyclic testing, and numeric modeling. The fracture analysis code FRANC3D was used because it could predict crack front shape and stress intensity factor (K). The numeric models predicted a changing crack front and stress intensity factors similar to the test data. The numeric studies accounted for the residual stresses measured by X-ray diffraction within the thread root of the test bolts. The FRANC3D model predicted Y(a/d) at shallow crack depths in the range of 0.01<a/d<0.11. By curve fitting the numeric and experimental data, a new Y(a/d) solution was determined: Y(a/d)=3079(a/d)6−6779(a/d)5+5757(a/d)4−2340(a/d)3+478.6(a/d)2−46.94(a/d)+2.506. The use of this Y(a/d) solution produces conservative crack growth life estimates relative to popular/benchmark methods. Based on test bolt fatigue data, greater accuracy may be possible with this Y(a/d) solution.

No abstract