Modelling the Effects of Surface Residual Stresses on Fatigue Behavior of PM Disk Alloys

A finite element based model will be developed and validated to capture the evolution of residual stresses and cold work at machined features of compressor and turbine powder metallurgy superalloy disks. The focus will be to quantify, model and validate residual stress and cold work evolution at stress concentration features during simulated service in aerospace gas turbine engine disk materials. This will be accomplished by first utilizing existing NASA Test data. If the existing test data are insufficient, a minimum number of specimens will be tested if the resources permit. These specimens will have varied surface finish conditions to be determined in consultation with NASA personnel and will be tested using a thermal mechanical load history that will simulate the operating conditions of new generation of gas turbine engines and include the effect of superimposed dwell cycles. The deliverables will include effects of service history on residual stress and cold work depth profile evolutions within notches, and analytical modeling descriptions of the evolution of these parameters as a function of simulated service history. Also included will be models and algorithms extrapolating the predicted residual stresses and cold work to service conditions outside of those tested during the program.

The results of this proposal and potential products will be of interest to the commercial gas turbine industry in general. This includes large aircraft engine companies such as General Electric and Pratt & Whitney. This is especially true for smaller companies in the private sector that cannot afford a research effort of this magnitude. Honeywell has expressed specific interest in this work and has provided a letter to this effect, which is provided with this proposal. The methodologies (and supporting analysis/design tools) as well as improved PM disk designs are both considered products of this effort. The primary market for the compressor and turbine disk designs includes gas turbine engines for use in military and civilian aircraft applications. Gas turbine engines are also used for ground power applications. These projects identify advanced materials as key technologies for future power generation systems based on gas turbine engines.

The long-term goal of this research effort is to improve the life and durability of turbomachinery disk components made from advanced powder metal alloys. These improvements are critical to the success NASA programs such as Environmentally Responsible Aircraft (ERA) program. This program has the goal demonstrating technologies that can reduce aircraft emissions and fuel consumption. This requires that components operate at increased temperatures and/or with reduced cooling air. Advanced metal alloy and composite materials can operate under these conditions, but durability and life must be assured. One of ERAs approaches to accomplishing these goals is to focus on "advanced multi-discipline based concepts and technologies," which is exactly the approach of this proposal. Structural, thermal, materials, reliability and systems engineering expertise must be brought together to achieve the objectives in Phase I

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