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© 2013 American Physical Society (APS). This is the accepted version of the following article: Barai, Pallab & Nukala, Phani K. V. V. & Alava, Mikko J. & Zapperi, Stefano. 2013. Role of the sample thickness in planar crack propagation. Physical Review E. Volume 88, Issue 4. 042411/1-7. ISSN 1539-3755 (printed). DOI: 10.1103/physreve.88.042411, which has been published in final form at http://journals.aps.org/pre/abstract/10.1103/PhysRevE.88.042411.