Modeling and Measurement of Residual Stresses and Machining Distortions in Aircraft Engine Disks

摘要

A study was undertaken to quantify the effects of residual stresses on machining distortion. Distortion can be caused by material bulk stresses resulting from heat-treating operations and/or by local near-surface machining induced stresses. There is a strong need to understand the effects of heat treating and machining on distortion and to predict, minimize, and control these distortions. A 3-D finite element model (FEM) was developed and validated to predict machining distortions of aircraft engine and airframe structural forgings. An automated procedure was developed to simulate the distortion due to material removal in multiple operations in the presence of bulk residual stresses. Residual stress measurements using neutron diffraction, hole-drilling and contour methods were performed for model validation. The residual stresses measured by the different methods were qualitatively in agreement with one another. The model was first validated on 3-D shaped Alloy 718 parts similar to production engine forgings and then on a production Alloy 718 disk. Good agreement was obtained between the measured distortions and the model predictions. The predicted residual stresses agreed with the measurements qualitatively in the regions where the different measurement methods showed low variability.