| Autor: |
BUSSIBA, ARIE, PIAT, ROMANA, KUPIEC, MOSHE, CARMI, RAMI, ALON, IGAL, BÖHLKE, THOMAS |
| Zdroj: |
Journal of Acoustic Emission; Jan-Dec2009, Vol. 27, p77-88, 12p |
| Abstrakt: |
Carbon-carbon (C/C) composites with different densities (1.8, 1.35, 0.8 g/cm³), produced by chemical vapor infiltration (CVI) were tested mechanically under quasi-static loading in bending mode of uniform and notched beams. Acoustic emission (AE) technique was used to track the mechanical threshold parameters as well as to characterize the damage build-up profile to fracture. In both states of stress (uniform and tri-axial), threshold values detected by AE activity indicated the damage onset. The sensitivity of the AE method to the density changes was apparent by variations of the threshold values. Decreasing the density from 1.8 to 0.8 g/cm³ decreases the thresholds values (σth, KIth) from 25 to 2 MPa and from 0.8 to 0.1 MPa·m1/2, respectively. Three stages in damage evolution to fracture were observed: Stage I, with no AE activity, Stage II, gradual/linear growth in AE counts up to an abrupt jump and Stage III with exponential increase in AE counts. Similarity in profile and threshold value were found between the cumulative AE counts vs. strain data and the crack density vs. strain predicted by micro mechanical model, indicating the importance of using AE in monitoring the damage evolution in composites with regard to structural integrity aspect. Wave analysis using fast Fourier transform (FFT) and short-time fast Fourier transform (ST-FFT) points out four possible failure micro-mechanisms: multilayer cracking, breaking of fiber bundles, interfacial matrix de-bonding and micro-crack growth. Breaking of fiber bundles was found to be the major damage mechanism for the low density C/C composite. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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