A Critical evaluation of indentation techniques for measuring fracture toughness
09 Feb 2018-
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.
Abstract: 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.
Citations
More filters
TL;DR: In this paper, the authors used a Berkovich indenter to determine hardness and elastic modulus from indentation load-displacement data, and showed that the curve of the curve is not linear, even in the initial stages of the unloading process.
Abstract: The indentation load-displacement behavior of six materials tested with a Berkovich indenter has been carefully documented to establish an improved method for determining hardness and elastic modulus from indentation load-displacement data. The materials included fused silica, soda–lime glass, and single crystals of aluminum, tungsten, quartz, and sapphire. It is shown that the load–displacement curves during unloading in these materials are not linear, even in the initial stages, thereby suggesting that the flat punch approximation used so often in the analysis of unloading data is not entirely adequate. An analysis technique is presented that accounts for the curvature in the unloading data and provides a physically justifiable procedure for determining the depth which should be used in conjunction with the indenter shape function to establish the contact area at peak load. The hardnesses and elastic moduli of the six materials are computed using the analysis procedure and compared with values determined by independent means to assess the accuracy of the method. The results show that with good technique, moduli can be measured to within 5%.
22,557 citations
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.
Abstract: An examination is made of the sharp-indentation technique of strength-test precracking for toughness evaluation. The experimental approach follows that proposed by other workers but the theoretical analysis contains one vital new feature; the residual-stress term discussed in Part I of this study is now introduced explicitly into the strength formulation. This modification overcomes a major systematic discrepancy evident in the previous models and at the same time, by virtue of attendant changes in the nature of the crack stability prior to attaining a failure configuration, eliminates the need for frac-tographic measurements. Other advantages are also apparent, notably an insensitivity to postindentation radial crack extension. The main disadvantage is that only one result is obtained per specimen. Indentation/strength data from ceramics listed in Part I confirm the essential features of the theory and provide a suitable calibration factor. The method has special application to those materials which do not necessarily produce a well-defined radial crack pattern, in which case an “effective”Kc appropriate to fracture properties at the flaw level is obtained.
1,146 citations
TL;DR: The recent development in the field of superhard materials with Vickers hardness of ⩾40 GPa is reviewed in this article, where two basic approaches are outlined including the intrinsic superhard material, such as diamond, cubic boron nitride, C3N4, carbonitrides, etc. and extrinsic, nanostructured materials for which superhardness is achieved by an appropriate design of their microstructure.
Abstract: The recent development in the field of superhard materials with Vickers hardness of ⩾40 GPa is reviewed. Two basic approaches are outlined including the intrinsic superhard materials, such as diamond, cubic boron nitride, C3N4, carbonitrides, etc. and extrinsic, nanostructured materials for which superhardness is achieved by an appropriate design of their microstructure. The theoretically predicted high hardness of C3N4 has not been experimentally documented so far. Ceramics made of cubic boron nitride prepared at high pressure and temperature find many applications whereas thin films prepared by activated deposition from the gas phase are still in the stage of fundamental development. The greatest progress has been achieved in the field of nanostructured materials including superlattices and nanocomposites where superhardness of ⩾50 GPa was reported for several systems. More recently, nc-TiN/SiNx nanocomposites with hardness of 105 GPa were prepared, reaching the hardness of diamond. The principles of de...
1,122 citations
30 Sep 1998-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the use of sharp indenters and how they can be used to measure elastic modulus, hardness, and fracture toughness is discussed, which characterize the three primary modes of deformation in solids.
Abstract: Ultra-low load indentation, also known as nanoindentation, is a widely used tool for measuring the mechanical properties of thin films and small volumes of material. One of the great advantages of the technique is its ability to probe a surface and map its properties on a spatially resolved basis, sometimes with a resolution of better than 1 μm. In this paper, techniques for measuring mechanical properties by ultra-low load indentation techniques are reviewed and discussed. Emphasis is given to the use of sharp indenters and how they can be used to measure elastic modulus, hardness, and fracture toughness. These fundamental mechanical properties characterize the three primary modes of deformation in solids—elasticity, plasticity, and fracture.
970 citations
TL;DR: This work fabricated fully dense nanocomposites of single-wall carbon nanotubes with nanocrystalline alumina (Al2O3) matrix at sintering temperatures as low as 1,150 °C by spark-plasma sintered, demonstrating their potential use in reinforcing nanocrystaline ceramics.
Abstract: The extraordinary mechanical, thermal and electrical properties of carbon nanotubes have prompted intense research into a wide range of applications in structural materials, electronics, chemical processing and energy management. Attempts have been made to develop advanced engineering materials with improved or novel properties through the incorporation of carbon nanotubes in selected matrices (polymers, metals and ceramics). But the use of carbon nanotubes to reinforce ceramic composites has not been very successful; for example, in alumina-based systems only a 24% increase in toughness has been obtained so far. Here we demonstrate their potential use in reinforcing nanocrystalline ceramics. We have fabricated fully dense nanocomposites of single-wall carbon nanotubes with nanocrystalline alumina (Al2O3) matrix at sintering temperatures as low as 1,150 degrees C by spark-plasma sintering. A fracture toughness of 9.7 MPa m 1/2, nearly three times that of pure nanocrystalline alumina, can be achieved.
958 citations
References
More filters
Book•
05 Oct 2000
TL;DR: Hardness measurements with conical and pyramidal indenters as mentioned in this paper have been used to measure the area of contact between solids and the hardness of ideal plastic metals. But they have not yet been applied to the case of spherical indenters.
Abstract: 1. Introduction 2. Hardness measurements by spherical indenters 3. Deformation and indentation of ideal plastic metals 4. Deformation of metals by spherical indenters. Ideal plastic metals 5. Deformation of metals by spherical indenters. Metals which work-harden 6. Deformation of metals by spherical indenters. 'Shallowing' and elastic 'recovery' 7. Hardness measurements with conical and pyramidal indenters 8. Dynamic or rebound hardness 9. Area of contact between solids Appendix I. Brinell hardness Appendix II. Meyer hardness Appendix III. Vickers hardness Appendix IV. Hardness conversion Appendix V. Hardness and ultimate tensile strength Appendix VI. Some typical hardness values
3,562 citations
1,926 citations
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.
Abstract: A theory for describing the evolution of the median/radial crack system in the far field of sharp-indenter contacts is developed. Analysis is based on a model in which the complex elastic/plastic field beneath the indenter is resolved into elastic and residual components. The elastic component, being reversible, assumes a secondary role in the fracture process: although it does enhance downward (median) extension during the loading half-cycle, it suppresses surface (radial) extension to the extent that significant growth continues during unloading. The residual component accordingly provides the primary driving force for the crack configuration in the final stages of evolution, where the crack tends to near-half-penny geometry. On the hypothesis that the origin of the irreversible field lies in the accommodation of an expanding plastic hardness impression by the surrounding elastic matrix, the ensuing fracture mechanics relations for equilibrium crack growth are found to involve the ratio hardness-to-modulus as well as toughness. Observations of crack evolution in soda-lime glass provide a suitable calibration of indentation coefficients in these relations. The calibrated equations are then demonstrated to be capable of predicting the widely variable median and radial growth characteristics observed in other ceramic materials. The theory is shown to have a vital bearing on important practical areas of ceramics evaluation, including toughness and strength.
1,862 citations
TL;DR: The basic principles and practical applications of indentation fracture are reviewed in this article, with a focus on the application of fracture fracture in the field of orthogonal fracture repair and alignment.
Abstract: The basic principles and practical applications of indentation fracture are reviewed.
1,172 citations
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.
Abstract: An examination is made of the sharp-indentation technique of strength-test precracking for toughness evaluation. The experimental approach follows that proposed by other workers but the theoretical analysis contains one vital new feature; the residual-stress term discussed in Part I of this study is now introduced explicitly into the strength formulation. This modification overcomes a major systematic discrepancy evident in the previous models and at the same time, by virtue of attendant changes in the nature of the crack stability prior to attaining a failure configuration, eliminates the need for frac-tographic measurements. Other advantages are also apparent, notably an insensitivity to postindentation radial crack extension. The main disadvantage is that only one result is obtained per specimen. Indentation/strength data from ceramics listed in Part I confirm the essential features of the theory and provide a suitable calibration factor. The method has special application to those materials which do not necessarily produce a well-defined radial crack pattern, in which case an “effective”Kc appropriate to fracture properties at the flaw level is obtained.
1,146 citations