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Obreimoff revisited: controlled heterogeneous fracture through the splitting of mica

Johnson, M. T. and Brodnik, N. R. and Ekeh, T. and Bhattacharya, K. and Faber, K. T. (2019) Obreimoff revisited: controlled heterogeneous fracture through the splitting of mica. Mechanics of Materials, 136 . Art. No. 103088. ISSN 0167-6636.

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Obreimoff reported his first instrumented measurements of the cleavage of muscovite mica in 1930 and that work helped to propel a greater understanding of fracture. This study builds upon that effort by investigating the role of compliance heterogeneities in brittle materials through mica splitting in a manner similar to Obreimoff. The natural layered structure of mica makes it ideal as a model system for studying fracture as crack propagation can be constrained along a single controlled cleavage plane. Cleavage through the insertion of a rounded wedge provides a straightforward mechanical setup that produces stable crack propagation, so long as the effects of friction and wedge geometry are properly considered. First, homogeneous mica sheets of uniform thickness are cleaved in ambient atmosphere to establish a baseline splitting force and critical strain energy release rate, similar Obreimoff’s original work. After establishing this baseline, mica sheets with prescribed thickness heterogeneities are investigated. It is found that the splitting force required to propagate a crack along a specimen with a sharp increase in layer thickness is significantly larger than the analogous homogeneous splitting forces, even though the crack is not deflected. This indicates that a sharp increase in stiffness can produce an increase in toughness in layered structures without the need for any actual toughness contrast between constituent components or any crack deflection. This toughening effect produced by compliance contrast may have implications in the context of layered ceramic composite design, where systems are often composed of a stiff outer shell and a more compliant and damage-tolerant functional layer.

Item Type:Article
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URLURL TypeDescription
Johnson, M. T.0000-0002-3710-1070
Bhattacharya, K.0000-0003-2908-5469
Faber, K. T.0000-0001-6585-2536
Additional Information:© 2019 Elsevier. Received 9 November 2018, Revised 8 March 2019, Accepted 13 June 2019, Available online 14 June 2019.
Funding AgencyGrant Number
Subject Keywords:Mica; Fracture; Layered Structure; Ceramic; Composite
Record Number:CaltechAUTHORS:20190614-153313032
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Official Citation:M.T. Johnson, N.R. Brodnik, T. Ekeh, K. Bhattacharya, K.T. Faber, Obreimoff revisited: Controlled heterogeneous fracture through the splitting of mica, Mechanics of Materials, Volume 136, 2019, 103088, ISSN 0167-6636, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:96452
Deposited By: George Porter
Deposited On:17 Jun 2019 14:31
Last Modified:03 Oct 2019 21:22

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