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      Understanding the edge crack phenomenon in ceramic laminates

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          Abstract

          Layered ceramic materials (also referred to as “ceramic laminates”) are becoming one of the most promising areas of materials technology aiming to improve the brittle behavior of bulk ceramics. The utilization of tailored compressive residual stresses acting as physical barriers to crack propagation has already succeeded in many ceramic systems. Relatively thick compressive layers located below the surface have proven very effective to enhance the fracture resistance and provide a minimum strength for the material. However, internal compressive stresses result in out-of plane stresses at the free surfaces, what can cause cracking of the compressive layer, forming the so-called edge cracks. Experimental observations have shown that edge cracking may be associated with the magnitude of the compressive stresses and with the thickness of the compressive layer. However, an understanding of the parameters related to the onset and extension of such edge cracks in the compressive layers is still lacking. In this work, a 2D parametric finite element model has been developed to predict the onset and propagation of an edge crack in ceramic laminates using a coupled stress-energy criterion. This approach states that a crack is originated when both stress and energy criteria are fulfilled simultaneously. Several designs with different residual stresses and a given thickness in the compressive layers have been computed. The results predict the existence of a lower bound, below no edge crack will be observed, and an upper bound, beyond which the onset of an edge crack would lead to the complete fracture of the layer

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              Laminar Ceramics That Exhibit a Threshold Strength.

              Thin compressive layers within a laminar ceramic arrest large cracks (surface and internal) and produce a threshold strength. This phenomenon increases the damage tolerance of ceramics and will allow engineers to design reliable ceramic components for structural applications. The stress intensity factor derived for a crack sandwiched between two compressive layers suggests that the threshold strength is proportional to the residual compressive stress and the thickness of the compressive layer and is inversely proportional to the distance between the compressive layers. Laminates composed of thick alumina layers (605 +/- 11 micrometers) and thin mullite/alumina compressive layers (37 +/- 1.4 micrometers) fabricated for this study had a threshold strength of 482 +/- 20 megapascals, in fair agreement with the theory.
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                Author and article information

                Journal
                Frattura ed Integrità Strutturale
                Gruppo Italiano Frattura
                01 October 2015
                : 9
                : 34
                : 362-370
                Affiliations
                [1 ] Brno University of Technology,Czech Republic
                [2 ] Sorbonne Universités,France
                [3 ] Université de Bordeaux,France
                [4 ] Montanuniversität Leoben ,Austria
                0ee27c855d684db5bfc4f72900cdd5a9

                This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

                Categories
                Technology
                T
                Electrical engineering. Electronics. Nuclear engineering
                TK1-9971
                Materials of engineering and construction. Mechanics of materials
                TA401-492

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