340 Prakt. Met. Sonderband 46 (2014)
The plastic zone of a stage-I-crack is a slip line in front of the crack tip and the length of DER
this slip line can be detected by Nomarski-DIC in optical microscopy and AFM contact ERK
mode measurements. The dislocations in the plastic zone also cause a lattice rotation that
can be detected using the electron channeling contrast. Here the images were taken by a SCH
forward-scatter detector at a HKL/Oxford EBSD detector system to optimize channeling
contrast without performing imaging for different tilt angles. G. Dief
The so measured plastic zone sizes are compared to those predicted by the one-
dimensional crack model of Bilby, Cottrell and Swinden. The well-known BCS-condition Institut
a c = Deutsc
— = cos | —
C 47f 1)
allows the prediction of the plastic zone size based on the crack length if the friction stress KURZ
tr is known. Tt was measured in a former study with a stage-I-crack with a slip direction that
causes a high slip step (Burgers vector parallel to surface normal) so that the values in fig In der
9 are under the BCS-model line. techni
_ damit
+ bic Verbes
29 + BCS-model Felon
® Normanski-DIC
200 O AFM - contact mode Malina
O ECCI (FSE) einzule
A ovclic PZ
| 1. EIN
110 [IN
crack length [pm] Die be
Fig. 9: comparison of different plastic zone size measurement techniques hinsich
Werkst
von er
5. SUMMARY Herstel
wesent
The versatility of DIC for the measurement of elastic dominated and plastic amounts of a Optimı
stage-I-crack strain field was shown. The strain field of a stage-I-crack was measured for Kosten
the first time. The results are in good agreement with the analytical predictions. The plastic Im vorl
zone size measurement by DIC was compared to other techniques. DIC was shown to be anhan
a valuable new strain measurement technique for high resolution elastic and plastic strain. einfach
brachte
REFERENCES
[1] W. Zaohyang, D. Fulong, J. Xialon, “High resolution high sensitivity moire method”, 2. ER
Acta Mechanica Sinica, 1999 UNTE
[2] Jerry D. Lord, D. Penn, P. Whitehead, “The application of digital image correlation for Zu ein
measuring the residual stress by incremental hole drilling”, Applied Mechanics and Merkm
Materials, 2008 Stahl °
[3] J.D. Carroll, W. Abuzaid, J. Lambros, H. Sehitoglu, “High resolution digital image Stahlb
correlation measurements of strain accumulation in fatigue crack growth”, Internation Gestar
J. of Fatigue, 2013 Dauert
[4] M. Marx, W. Schaef, H. Vehoff, “Interaction of short cracks with the local
microstructure”, Procedia Engineering 2, 2010
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