Journal ArticleDOI
Sigmoidal Indentation–Strength Characteristics of Polycrystalline Alumina
TLDR
In this paper, the fracture properties of a series of polycrystailine aluminas were examined using indentation strength and double cantilever beam techniques, and a model was developed for the general response, combining increasing toughening by ligamentary bridging at small crack lengths and increasing residual-stress relief by lateral cracking at large indentation loads.Abstract:
The fracture properties of a series of three polycrystailine aluminas are examined using indentationstrength and double cantilever beam techniques The indentation-strength response is shown to be sigmoidal with concave-down behavior at small indentation loads and concave-up behavior at large indentation loads A model is developed for the general response, combining increasing toughening by ligamentary bridging at small crack lengths and increasing residual-stress relief by lateral cracking at large indentation loads The model is fit to the strength data and used to deconvolute the underlying toughness variation and predict the intrinsic strength of the materials Direct measurements of toughness using the “long-crack” double cantilever beam geometry are shown to overestimate the toughness variations effective during “short-crack” strength testsread more
Citations
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Journal ArticleDOI
What Can We Learn from R‐Curve Measurements?
TL;DR: In this paper, a review of the literature on crack growth resistance curves (R curves) has been conducted for many ceramic materials and the authors concluded that the behavior of specimens with natural flaws cannot be predicted directly from the results of tests with macro-cracks and no established framework exists to correlate the two.
Journal ArticleDOI
Probing material properties with sharp indenters: a retrospective
Brian R. Lawn,Robert F. Cook +1 more
TL;DR: A retrospective on the use of sharp, fixed-profile indenters as materials probes is presented in this paper, where the utility of indentations as controlled flaws in the context of strength of materials is outlined.
Journal ArticleDOI
The Utility of R‐Curves for Understanding Fracture Toughness‐Strength Relations in Bridging Ceramics
Jamie J. Kruzic,Raphaelle Satet,Michael J. Hoffmann,Rowland M. Cannon,Robert O. Ritchie,Robert O. Ritchie +5 more
TL;DR: In this article, the early part of the fracture-resistance curve (R-curve) of rare earth (RE)-Mg-doped Si 3 N 4 ceramics (RE = La, Lu, Y, Yb) with varying grain-boundary adhesion has been examined with emphasis on materials containing La and Lu (which represent the extremes of RE ionic radius).
Journal ArticleDOI
Flat R‐Curve from Stable Propagation of Indentation Cracks in Coarse‐Grained Alumina
Detlef Bleise,Rolf W. Steinbrech +1 more
TL;DR: In this paper, the fracture toughness of coarse-grained A12O3 was studied in the short-crack regime utilizing the stable propagation of indentation cracks in bending.
Journal ArticleDOI
Method for Measuring Short-Crack R-Curves without Calibration Parameters: Case Studies on Alumina and Alumina/Aluminum Composites
Martin Stech,Jürgen Rödel +1 more
TL;DR: In this paper, a method to measure short-crack R-curves is introduced which does not require an independent determination of calibration factors and utilizes an equilibrium crack shape condition to compute the shape factor of a surface crack R-Curves of an alumina with two different grain sizes and of an aluminum/alumina composite.
References
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Journal ArticleDOI
A Critical Evaluation of Indentation Techniques for Measuring Fracture Toughness: I, Direct Crack Measurements
TL;DR: In this paper, the application of indentation techniques to the evaluation of fracture toughness is examined critically, in two parts: the first part is focused on an approach which involves direct measurement of Vickers-produced radial cracks as a function of the indentation load.
A Critical evaluation of indentation techniques for measuring fracture toughness
TL;DR: In this paper, the application of indentation techniques to the evaluation of fracture toughness is examined critically, in two parts: the first part is focused on an approach which involves direct measurement of Vickers-produced radial cracks as a function of the indentation load.
Journal ArticleDOI
Elastic/Plastic Indentation Damage in Ceramics: The Median/Radial Crack System
TL;DR: In this article, a theory for describing the evolution of the median/radial crack system in the far field of sharp-indenter contacts is developed, based on a model in which the complex elastic/plastic field beneath the indenter is resolved into elastic and residual components.
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A Critical Evaluation of Indentation Techniques for Measuring Fracture Toughness: II, Strength Method
TL;DR: In this paper, the sharp-indentation technique of strength-test precracking for toughness evaluation is examined and the residual-stress term discussed in Part I of this study is now introduced explicitly into the strength formulation.
Journal ArticleDOI
Direct Observation and Analysis of Indentation Cracking in Glasses and Ceramics
Robert F. Cook,George M. Pharr +1 more
TL;DR: In this paper, the authors investigated the material dependence of the initiation sequence of indentation cracks (cone, radial, median, half-penny, and lateral) using an inverted tester allowing simultaneous viewing of the fracture process and measurement of the indeter load and displacement during contact.