A method to determine fracture toughness using cube-corner indentation (original) (raw)
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Journal of the American Ceramic Society, 1981
The application of indentation techniques to the evaluation of fracture toughness is examined critically, in two parts. In this flrst part, attention is focused on an approach which involves direct measurement of Vickers-produced radial cracks as a function of indentation load. A theoretical basis for the method is first established, in terms of elasticlplastic indentation fracture mechanics. It is thereby asserted that the key to the radial crack response lies In the residual component of the contact fkld. This residual term has important implications concerning the crack evolution, including the possibility of postindentation slow growth under environment-sensitive conditions. Fractographic observations of cracks in selected "reference" mater-Ys are used to determine the magnitude of this effect and to investigate other potential complications associated with departures from ideal indentation fracture behavior. The data from these observations provide a convenient calibration of the indentation toughness equations for general application to other well-behaved ceramics. The technique is uniquely h p i e in procedure and economic in its use of material.
Journal of The American Ceramic Society, 1981
The application of indentation techniques to the evaluation of fracture toughness is examined critically, in two parts. In this first part, attention is focused on an approach which involves direct measurement of Vickers-produced radial cracks as a function of indentation load. A theoretical basis for the method is first established, in terms of elastic/plastic indentation fracture mechanics. It is thereby asserted that the key to the radial crack response lies in the residual component of the contact field. This residual term has important implications concerning the crack evolution, including the possibility of post indentation slow growth under environment-sensitive conditions. Fractographic observations of cracks in selected “reference” materials are used to determine the magnitude of this effect and to investigate other potential complications associated with departures from ideal indentation fracture behavior. The data from these observations provide a convenient calibration of the Indentation toughness equations for general application to other well-behaved ceramics. The technique is uniquely simple in procedure and economic in its use of material.
Multi-scale approach of the instrumented indentation technique on the fracture toughness estimation
2015
Instrumented Indentation Technique (IIT) is widely used to determine the mechanical properties of materials. The elastic modulus is usually determined by applying the methodology proposed by Oliver and Pharr [1] who supposed that its value is independent of the indentation depth. However, some authors [2, 3] have observed a decrease of the elastic modulus when the indenter displacement increases which allowed them to introduce a continuous damage theory used afterwards to estimate the fracture toughness of ductile materials. The assumption made by the authors is that a damage in the region very close to the bottom of the indent results in the formation of microvoids which leads to the variation of the elastic modulus as a function of the indenter displacement. Starting from this observation, Lee et al. [2] proposed an energy model based on the Griffith’s theory and the continuous damage mechanics (CDM) which states that the elastic modulus variation is related to the fraction void v...
Evaluation by indentation of fracture toughness of ceramic materials
Journal of Materials Science, 1990
A transition fracture mode from Palmqvist to median has been observed in a number of ceramic materials. A new expression to determine the fracture toughness (Krc) by indentation is presented. The K~c values calculated by this formula are independent of the crack profile (median or Palmqvist) and of the applied load. This formula has been obtained by modifying the universal curve of Evans and Charles to incorporate Palmqvist and median cracks over a wide range of loads in the case of brittle materials with different mechanical properties (elastic properties: E, v, Kic).
New developments for fracture toughness determination by Vickers indentation
Materials Science and Technology, 2004
Indentation is a traditional method used to determine the toughness of brittle materials. Different models are used for the calculation depending on the shape of the cracks that are initiated and developed as a result of the indentation. Recently it was observed that a transition between Palmqvist and median cracks is possible when increasing the indentation load. In the present study it is shown that this transition is not as sharp as is generally supposed, but is rather smooth. In these conditions standard calculation procedures cannot be applied. A new methodology is proposed here, which allows the calculation of a unique toughness value on the basis of the determination of the limits of the material cracking tendency.
Defence Science Journal
In this work fracture toughness is determined by the Toughness model; Critical Stress-Strain Model and Energy release rate model using unconventional test method referred to as Spherical Indentation test (SIT) to reduce the large and costly experimental set up as required in Conventional Fracture Toughness Test. The toughness model correlates the indentation energy to fracture with fracture toughness, Critical Stress-Strain Model assumes that the critical fracture toughness is equal to the critical plastic work done by the material when a crack tends to propagate and as per the Energy release rate model, indentation depth is given by loading-unloading cycles. The unloading slope which is elastic provides the reduced Young’s Modulus of the material from each unloading cycle which reflects the occurrence of damage in the material. For the determination of contact radius at different indentation points, finite element analysis is performed using the material data obtained from the tens...
Experimental Mechanics, 2016
We propose a generalized approach based on fracture mechanics and contact mechanics to estimate the fracture toughness in metallic materials from instrumented indentation testing. Models were developed for brittle and ductile fracture. Different criteria were applied to each model to determine the critical fracture point during indentation. For brittle fracture, the critical fracture point was defined in terms of the critical mean pressure; for ductile fracture, the critical fracture point was derived from fracture strain and critical plastic zone size. Each fracture criterion was used to determine the indentation fracture energy corresponding to the fracture energy required for crack extension. The fracture toughness was estimated for various metallic materials using each model and compared with standard fracture toughness tests.
Journal of Advanced Ceramics, 2013
In this article, a new method has been presented for the estimation of fracture toughness in brittle materials, which enjoys improved accuracy and reduced costs associated with fracture toughness testing procedure compared to similar previous methods, because a vast range of specimens with irregular cracks can be accommodated for testing. Micron-sized alumina powders containing 0.05 wt% magnesium oxide (MgO) nanoparticles were mixed and also together with 2.5 vol%, 5 vol%, 7.5 vol%, 10 vol%, and 15 vol% of silicon carbide (SiC) nanopowders separately. By making and testing various types of ceramics with different mechanical properties, and considering the irregular cracks around the indented area caused by Vickers diamond indenter, a semi-empirical fracture toughness equation has been obtained.
Crystal Research and Technology, 2009
Indentation size effect, indentation cracks and microhardness measurement of some brittle crystals are reviewed against the background of the existing concepts of indentation deformation of crystalline solids. Several approaches reported in the literature devoted to relationships between applied indentation test load P and indentation diagonal length d are applied to analyze the experimentally observed normal and reverse indentation size effect (ISE) in brittle compounds. Using typical examples of normal and reverse ISE it is shown that the indentation induced cracking model does not give load-independent hardness and the final expression describing the experimental data for various compounds is essentially another form of the Meyer law. Analysis of experiment data on crack lengths and indentation diagonals for different indentation loads suggests that the origin of ISE is associated with the processes of formation of indentation cracks following the general concepts of fracture mechanics. The load-independent hardness H 0 may be determined reliably from plots of P/d against d of the proportional resistance model or of H V against 1/d as predicted by strain gradient plasticity theories. It was found that the load-independent hardness of depends on crystal orientation and state of the indented surface. Finally, some comments on determination of fracture toughness and brittle index of crystals are made.