Material Brittleness and the Energetics of Acoustic Emission
This paper will review energy aspects of the acoustic emission (AE) phenomenon and its relationship to material properties especially brittleness. The spectral energy density of the AE wave at low frequencies is related to the moment tensor, but this is only a fraction of the total energy converted in the deformation or damage process. The “conversion efficiency” from static elastic energy to dynamic AE energy is governed by the source speed, and this in turn is related to the brittleness of the material. Meanwhile, the spectral bandwidth of the AE near the source is governed by the duration of the source event. The resulting relationships between brittleness and acoustic emissivity will be discussed. Examples will be drawn from metals, fiber reinforced composites and geological materials. A further factor that has a strong influence on a material’s damage tolerance is its heterogeneity. This also has a strong influence on its acoustic emissivity, specifically on the amplitude distribution. In a recent development in the practical application of AE to industrial plant monitoring, these factors and others are integrated in a model of the Probability of Detection (POD) for fatigue cracks growing in a mixed mode comprising both ductile and brittle deformation mechanisms.
KeywordsAcoustic Emission Nondestructive Test Moment Tensor Strain Energy Release Rate Double Cantilever Beam
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