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Authors
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Zhandarov, S. ; Pisanova, E. ; Mäder, E.
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Title
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Is there any contradiction between the stress and energy failure criteria in micromechanical tests? Pt. III. Experimental observation of crack propagation in the microbond test
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Date
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09.12.2005
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Number
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12796
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Abstract
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A direct observation of crack propagation in the microbond test was carried out for five different fiber/polymer matrix systems. This technique appeared to be a very effective tool for interface characterization. Experimental plots of the force required for further crack propagation as a function of debond length were analyzed using both energy-based and stress-based models of debonding. The fracture mechanics analysis was used to construct families of crack resistance or <I>R</I>-curves which showed the variation of energy release rate, <I>G</I>, with the debond length, and included the effect of interfacial friction in debonded regions. For the first time, analogs of the <I>R</I>-curves were created within the scope of the stress-based model to present the local shear stress near the crack tip, <IMG SRC="/iso-ents/isogrk32/tau-s.gif" ALT="tau">, as a function of crack length. In both models, the behavior of the interfacial parameter (<I>G</I> or <IMG SRC="/iso-ents/isogrk32/tau-s.gif" ALT="tau">) strongly depends on the assumed value of the interfacial frictional stress (<IMG SRC="/iso-ents/isogrk32/tau-s.gif" ALT="tau"><SUB>f</SUB>). However, for each matrix/fiber system there exists such a <IMG SRC="/iso-ents/isogrk32/tau-s.gif" ALT="tau"><SUB>f</SUB> value for which the investigated parameter is nearly constant over the whole region of stable crack propagation (70–90% of the embedded length). Moreover, these best-fit <IMG SRC="/iso-ents/isogrk32/tau-s.gif" ALT="tau"><SUB>f</SUB> values for each specimen appeared to be practically the same for both energy-based and stress-based approaches. Thus, both interfacial toughness, <I>G</I><SUB>ic</SUB>, and local interfacial shear strength, <IMG SRC="/iso-ents/isogrk32/tau-s.gif" ALT="tau"><SUB>d</SUB>, adequately characterize the strength of a fiber/matrix interface. Extrapolation of <I>R</I>-curves and their analogs to zero crack length allows measurement of <br />the interfacial parameters with good accuracy.
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Publisher
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Journal of Adhesion Science and Technology
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Wikidata
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Citation
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Journal of Adhesion Science and Technology 19 (2005) 679-704
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DOI
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https://doi.org/10.1163/1568561054890462
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Tags
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