PSI - Issue 10

V.N. Kytopoulos et al. / Procedia Structural Integrity 10 (2018) 264–271 V.N. Kytopoulos et al. / Structural Integrity Procedia 00 (2018) 000 – 000

270

7

1.8

1.2

I [sec -1 ]

0.6

0

0

5

10

15

ρ z [ μ m] Fig. 6. Microdamage distribution ahead of notch root for the 8090 MMC material (Strain rate [sec] -1 10 -2 ). Table 2. Basic, final results of microdamage evaluation measurements of the investigated materials MATERIAL Damage number q d =A d /A 0 Specific damage number δ = q d / ρ z

MMC 8090 (Strain rate 10 -5 /sec)

9 x 10 -4

0.27

MMC 8090 (Strain rate 10 -2 /sec)

3.1 x 10 -2

0.37

MMC 2124 (Strain rate 10 -2 /sec)

3.8 x 10 -2

0.58

MMC 2124 (Strain rate 10 -5 /sec)

5.5 x 10 -3

0.33

4. Conclusions

The experiments conducted showed that, within the experimental scatter range of the proposed semi-quantitative approach and under the same experimental conditions, the MMC material with higher ductility of the matrix exhibits a higher damage degree or liability compared to the MMC material with lower ductility. Based on the principle of elastic-plastic damage, this behavior can be explained by the general fact that larger differences in ductility between matrix and SiC- particles may result in a corresponding larger misfit and accommodation loss between inclusion and matrix. This, in turn, leads to an associated intensive microcracking and deboding damage activity, taking place within the matrix-particle interphase (interface) of the composite. Furthermore, it was also shown that increasing deformation rate leads to a marked change of the damage activity ahead of edge-crack, fact equivalent with a strain rate- induced embrittlment behavior of the material. This behavior seems to be more pronounced in MMC-material with higher matrix ductility. In general, it can be stated that the proposed technique can give a reliable semi-quantitative approach for microdamage evaluation and characterization of materials. Andrianopoulos, N., Kourkoulis, S.K., Saragas, S., 1997. COD measurements and optimum exploitation of metal matrix composites for aerospace applications. Engineering Fracture Mechanics 57, 565-576. Flewitt, P.E., Wild, R.K., 1994. Physical Methods for Materials Characterization, Institute of Physics Publishing , Bristol and Philadelphia. Goldstein, J.I., 1992. Scanning Electron Microscopy and X-Ray Microanalysis, A Text for Biologists, Material Scientists, and Geologists, sec. edition, Plenum Press-New York and London. Hellan, K., 1984. Introduction to Fracture Mechanics. McGraw-Hill, New York. Kourkoulis, S.K., Andrianopoulos, N.P., 2000. Plastically induced anisotropy on metal matrix composites. Mechanics of Composites Materials and Structures 7(1), 1-18. Kourkoulis, S.K., 2001. The influence of cracks on the mechanical behaviour of particulate MMCs: An experimental study. Archives of Mechanics 53(4-5), 439-456. References