Assessment of material damage in a nickel-base superalloy using nonlinear Rayleigh surface waves

Abstract

Articles you may be interested inExperimental characterization of fatigue damage in a nickel-base superalloy using nonlinear ultrasonic waves A reliable laser-based ultrasonic technique is developed to measure the second order harmonic amplitude of a Rayleigh surface wave propagating in metallic specimens. Rayleigh waves are experimentally generated with a wedge transducer and detected with a heterodyne laser interferometer. The capability of this system to measure the nonlinear contribution present in Rayleigh surface waves is demonstrated, and these results are interpreted in terms of a parameter developed for Rayleigh surface waves which corresponds to the nonlinear parameter of a longitudinal wave, ␤. The proposed measurement technique is used to assess damage in nickel-base high temperature alloy specimens, and the evolution of material nonlinearity under various loading conditions is quantitatively measured in terms of the increasing amplitude of the second order harmonic. These results show that there is a significant increase in the second order harmonic amplitude at monotonic tensile loads above the material's yield stress, and that during low cycle fatigue tests, the increase in the second order harmonic amplitude is considerable, although less significant than that in the monotonic loading case. The results from this study show the major role that accumulated plasticity plays in the increase in material nonlinearity, and demonstrate the effectiveness of the proposed experimental procedure to track damage in high temperature alloys.

Feasibility and Reliability of Grain Noise Suppression in Monitoring of Highly Scattering Materials

“…Also the tests were done in a lab environment with no changes to the sample surface due to oxidation or corrosion that would significantly affect the ultrasonic signals. It has also been assumed that no changes to grain structure affecting the ultrasonic signal occur with exposure to service environments as indicated in [11]; if this assumption is not valid in a particular application then baseline subtraction could not be used.…”

“…The split spectrum processing [4][5][6] and wavelet transform de-noising methods [7][8][9] are widely researched techniques but show limited improvement [10]. If we assume that the ultrasonic properties of the grains are unaffected by ageing [11], grain noise is coherent and an opportunity then exists to use a structural health monitoring (SHM) approach in which a baseline reading is subtracted from the current reading, thus removing the grain noise and producing a residual signal which reveals the presence of defects. This idea has been researched extensively in guided wave health monitoring [12][13][14] ; this paper assesses the feasibility of applying the idea to the bulk wave ultrasonic testing of materials that generate substantial grain noise.…”

New Trends in Materials Nondestructive Characterization Using Surface Acoustic Wave Methodologies

“…If one considers a Rayleigh wave propagating in the positive x direction, assuming the z axis into the material, the displacement potentials describing the longitudinal and shear ultrasonic waves, where, k R , k l , k s are the wave-numbers for Rayleigh, longitudinal, and shear ultrasonic waves, respectively [56].…”

“…Taking into account that the surface acoustic waves are a superposition of longitudinal and shear waves propagating along a stress-free surface that have the same velocity, the displacement components can be decomposed into their longitudinal and shear components [56][57][58][59][60]: Taking into account the fact that the acoustic nonlinear behavior of the shear waves in an isotropic medium ceases to exist due to the symmetry of the third order elastic constants, it can be inferred that the longitudinal wave component is only one contributing to the higher www.intechopen.com …”

Third Harmonic Generation of Shear Horizontal Guided Waves Propagation in Plate-like Structures

“…However, although nonlinear ultrasonic measurement has been a subject of considerable interest, most of the researches were about the nonlinear bulk and surface waves [9][10][11]. There is rarely investigation of nonlinear SH guided waves in plate-like structure.…”