RESUMO
Finite element (FE) modeling has been coupled with resonant ultrasound spectroscopy (RUS) for nondestructive evaluation (NDE) of high temperature damage induced by mechanical loading. Forward FE models predict mode-specific changes in resonance frequencies (ΔfR), inform RUS measurements of mode-type, and identify diagnostic resonance modes sensitive to individual or multiple concurrent damage mechanisms. The magnitude of modeled ΔfR correlate very well with the magnitude of measured ΔfR from RUS, affording quantitative assessments of damage. This approach was employed to study creep damage in a polycrystalline Ni-based superalloy (Mar-M247) at 950°C. After iterative applications of creep strains up to 8.8%, RUS measurements recorded ΔfR that correspond to the accumulation of plastic deformation and cracks in the gauge section of a cylindrical dog-bone specimen. Of the first 50 resonance modes that occur, ranging from 3 to 220kHz, modes classified as longitudinal bending were most sensitive to creep damage while transverse bending modes were found to be largely unaffected. Measure to model comparisons of ΔfR show that the deformation experienced by the specimen during creep, specifically uniform elongation of the gauge section, is responsible for a majority of the measured ΔfR until at least 6.1% creep strain. After 8.8% strain considerable surface cracking along the gauge section of the dog-bone was observed, for which FE models indicate low-frequency longitudinal bending modes are significantly affected. Key differences between historical implementations of RUS for NDE and the FE model-based framework developed herein are discussed, with attention to general implementation of a FE model-based framework for NDE of damage.
RESUMO
OBJECTIVES: To describe relapse rates in steroid-responsive meningitis-arteritis and to describe clinical and laboratory parameters in dogs with and without relapses. METHODS: Seventy-four dogs with steroid-responsive meningitis-arteritis were retrospectively identified and assigned to one of three groups: (1) without relapse; (2) at least one relapse and (3) unknown relapse status. The following parameters are reported for the first two groups: sex, age, breed, body weight, nucleated cell count, total protein concentration and percentage of neutrophils on initial cerebrospinal fluid analysis, immunoglobulin A in serum and initial cerebrospinal fluid analysis, nucleated cell count on cerebrospinal fluid analysis at 3-month re-evaluation, C-reactive protein in serum and initial cerebrospinal fluid analysis and at 3-month re-evaluation. RESULTS: Relapses occurred in 32 · 4% of dogs (one relapse: 62 · 5%; two relapses: 25 · 0%; three relapses: 8 · 3%; four relapses: 4 · 2%), 55 · 4% were relapse-free and in 12 · 2% the relapse status was unknown. C-reactive protein in serum and cerebrospinal fluid on 3-month re-evaluation was normal in 80% and 75% of dogs with relapses, respectively. In dogs without relapse, C-reactive protein in serum and cerebrospinal fluid on 3-month re-evaluation was normal in 100% and 90% of dogs, respectively. CLINICAL SIGNIFICANCE: Relapses are frequent but no reliable predictive indicator has emerged in this study. Nevertheless, elevated C-reactive protein in serum warrants continuing therapy; normal C-reactive protein in serum does not exclude future relapse.
