Ph.D. Dissertation Defense by Donald W. Rhymer
Thursday, October 27, 2005

(Dr. W. Steven Johnson, Chair)

"Stress Intensity Solutions of Thermally Induced Cracks in a Combustor Liner Hot Spot Using Finite Element Analysis "

Abstract

Thermally cycling a thin plate of nickel-based superalloy with an intense in-plane thermal gradient, or hot spot, produces thermally induced crack growth not represented by classic thermo-mechanical fatigue (TMF).  With the max hot spot temperature at 1093° C (2000° F) of a 1.5 mm thick, 82.55 mm diameter circular plate of B-1900+Hf, annular buckling and bending stresses result during each thermal cycle which drive the crack initiation and propagation.  A finite element analysis (FEA) model, using ANSYS 7.1, has been developed which models the buckling and as well as represents the stress intensity at simulated crack lengths upon cool down of each thermal cycle.  The model approximates the out-of-plane response at heat-up within 14% error and a difference in the final displacement of 0.185 mm after twelve thermal cycles. Using published da/dN vs. K eff   data, the number of cycles needed to grow the crack to the experimental arrest distance is modeled within 1 mm. The number of cycles to this point is within 5 out of 462 in comparison to the experimental test