No abstract

Many high-energy turbine engine components are fracture critical. However, the complex three-dimensional (3d) geometries and stress fields associated with these components can make accurate fracture analysis impractical. This paper describes a new computational approach to efficient fracture design for complex turbine engine components. The approach employs a powerful 3D graphical user interface (GUI) for manipulation of geometry models and calculated component stresses to formulate simpler 2D fracture models. New weight function stress intensity factor solutions are derived to address stress gradients that vary in all directions on the fracture plane.

A probabilistically-based damage tolerance analysis computer program for engine rotors has been developed under Federal Aviation Administration (FAA) funding to augment the traditional safe-life approach. The computer program, in its current form, is designed to quantify the risk of rotor failure due to fatigue cracks initiated at hard alpha anomalies in titanium. The software, DARWIN™ (Design Assessment of Reliability With Inspection), integrates a graphical user interface, finite element stress analysis results, fracture-mechanics-based life assessment for low-cycle fatigue, material anomaly data, probability of anomaly detection, and inspection schedules to determine the probability-of-fracture of a rotor disk as a function of operating cycles with and without inspections. The program also indicates the relative likelihood of failure of the disk regions. Work is underway to enhance the software to handle anomalies in cast/wrought and powder nickel disks, and manufacturing and maintenance-induced surface anomalies in all disk materials.

This paper describes some of the new surface damage capabilities in DARWIN™, a probabilistic fracture mechanics software code developed to evaluate the risk of fracture associated with aircraft jet engine titanium rotors/disks. An initial framework is presented in which a graphical user interface (GUI) is used to explicitly define the stresses and temperatures at the crack location for several crack geometries. A summary of the approach used to develop new stress intensity factor solutions for these geometries is also presented, including selected validation results.

Titanium gas turbine disks are subject to a rare but not insignificant probability of fracture due to metallurgical defects, particularly hard ␣. A probabilistic methodology has been developed and implemented in concordance with the Federal Aviation Administration (FAA) Advisory Circular 33.14-1 to compute the probability of fracture of gas turbine titanium disks subject to low-frequency metallurgical (hard ␣) defects. This methodology is further developed here to ensure that a robust, converged, accurate calculation of the probability is computed that is independent of discretization issues. A zonebased material discretization methodology is implemented, then refined locally through further discretization using risk contribution factors as a metric. The technical approach is akin to "h" refinement in finite element analysis; that is, a local metric is used to indicate regions requiring further refinement, and subsequent refinement yields a more accurate solution. Supporting technology improvements are also discussed, including localized finite element refinement and onion skinning for zone subdivision resolution, and a restart database and parallel processing for computational efficiency. A numerical example is presented for demonstration.