R‐Curve Determination for the Initial Stage of Crack Extension in Si3N4

Fett, T.; Fünfschilling, Stefan; Hoffmann, Michael J.; Oberacker, R.; Jelitto, Hans; Schneider, Gerold A.

doi:10.1111/j.1551-2916.2008.02750.x

Cited by 33 publications

(41 citation statements)

References 23 publications

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“…It is well-known from ceramic materials that toughness measurements with SingleEdge-Notch-Beam (SENB) or CompactTension (CT) specimens are usually not able to measure the crack tip toughness, K I0 , in particular when steep crack resistance curves prevail (Fett et al, 2008;Fünfschilling et al, 2009;Özcoban et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Sub-10-micrometer toughening and crack tip toughness of dental enamel

Ang

Schulz

Fernandes

et al. 2011

Journal of the Mechanical Behavior of Biomedical Materials

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In previous studies, enamel showed indications to occlude small cracks in-vivo and exhibited R-curve behaviors for bigger cracks ex-vivo. This study quantifies the crack tip toughness (K I0, K III0 ), the crack closure stress and the cohesive zone size at the crack tip of enamel and investigates the toughening mechanisms near the crack tip down to the length scale of a single enamel crystallite. The crack-opening-displacement (COD) profile of cracks induced by Vickers indents on mature bovine enamel was studied using atomic force microscopy (AFM). The mode I crack tip toughness K I0 of cracks along enamel rod boundaries and across enamel rods exhibit similar range of values: K I0,Ir =0.5-1.6MPa.m 0.5 (based on Irwin's 'nearfield' solution) and K I0,cz =0.8-1.5MPa.m 0.5 (based on the cohesive zone solution of the Dugdale-Muskhelishvili (DM) crack model). The mode III crack tip toughness K III0,Ir was computed as 0.02-0.15MPa.m 0.5 . The crack-closure stress at the crack tip was computed as 163-770MPa with a cohesive zone length and width 1.6-10.1µm and 24-44nm utilizing the cohesive zone solution. Toughening elements were observed under AFM and SEM: crack bridging due to protein ligament and hydroxyapatite fibres (micro-and nanometer scale) as well as microcracks were identified.

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Section: Introductionmentioning

confidence: 99%

Sub-10-micrometer toughening and crack tip toughness of dental enamel

Ang

Schulz

Fernandes

et al. 2011

Journal of the Mechanical Behavior of Biomedical Materials

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“…Herewith, this technique provides the opportunity to perform several loading cycles on one specimen. It should also be mentioned that performing controlled fracture tests on particular brittle materials (like Si 3 N 4 [6,7] and zirconia-toughened alumina [8]) were only possible by means of this computer-aided technique and the high stiffness of the device. Especially, materials with constant fracture toughness like glass require an even stiffer device and a faster response time to unload to perform stable crack growth.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…2. Knowing the increase of compliance, the crack propagation l i was calculated by solving numerically Eq 2 with respect to the upper integration limit [6]. Thus, the crack propagation was calculated for every t i .…”

Section: Fig 2: the Relevant Force-displacement Curve Range Of The Fimentioning

confidence: 99%

“…This enables automatic stable crack growth measurements without much operation of the user. It was already successfully applied to silicon nitride [6,7] to measure extremely steep R-curves and to zirconia-toughened alumina [8] to determine the fracture toughness with automated control of stable crack growth. The advantage of this computer-controlled system is that manifold routine measurements without the necessity of highly qualified research assistants are possible.…”

Section: Introductionmentioning

confidence: 99%

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Computer-Controlled Stable Crack Growth as a Reliable and Fast Method to Determine Subcritical Crack Growth

Özcoban¹,

Fett²,

Schneider³

2012

Journal of Testing and Evaluation

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Subcritical crack growth of synthetic fused silica glass is investigated using the Single-Edge-VNotched-Beam (SEVNB) method. The measurement was performed in a very stiff four-point bending device, which is equipped with a computer-aided control system. This technique enables several loading cycles of controlled crack growth with one measurement and sample. The control system is based on an online compliance measurement that enables an automatic measurement routine without much operation of the user and without the necessity of the optical observation of the crack. The crack velocity as a function of the applied stress intensity factor was determined by analysing the measured specimen compliance. The presented method allows determining a large number of v-K I curves under identical conditions by measuring only one sample.

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“…A measurement with controlled crack growth helps to determine the influence of the notch radius and thus to get the true fracture toughness. Especially for materials with very strong rising R-curves like Si 3 N 4 , the notch effect has to be taken into account in order to determine the correct R-curve [10][11][12].…”

Section: Notch Effectmentioning

confidence: 99%

Influence of finite notch root radius and optically determined crack length on the measured fracture toughness of brittle materials

Özcoban

Jelitto

Schneider

2010

Journal of the European Ceramic Society

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When measuring the fracture toughness of ceramics, for instance with the Single Edge VNotched Beam (SEVNB) method, a known problem is given by the finite notch root radius. If this radius is larger than a certain small value of a few micrometers, the measured stress intensity factor is higher than the true intrinsic value. Another problem is that due to technical and physical reasons the optically measured crack length at stable crack growth is smaller than the true crack length, which might lead to an underestimation of the fracture toughness.In the given paper an experimental approach is presented to register these effects quantitatively with stable crack advance and to finally obtain the correct fracture toughness. This is achieved by applying a new computer aided automatic control system for stable crack advance and by analyzing the results in force -displacement and crack length -force diagrams. The used material is zirconia-toughened alumina.

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R‐Curve Determination for the Initial Stage of Crack Extension in Si₃N₄

Cited by 33 publications

References 23 publications

Sub-10-micrometer toughening and crack tip toughness of dental enamel

Sub-10-micrometer toughening and crack tip toughness of dental enamel

Computer-Controlled Stable Crack Growth as a Reliable and Fast Method to Determine Subcritical Crack Growth

Influence of finite notch root radius and optically determined crack length on the measured fracture toughness of brittle materials

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