Showing papers on "Indentation published in 1981"
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.
4,642 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
01 Jan 1981
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 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 frac- ture 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. Frac- tographic 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 de- partures 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 hpie in procedure and economic in its use of material.
416 citations
TL;DR: In this paper, the mechanics of hardness indentation are considered and an expression for the relative depth recovery of the impression as a function of hardness/modulus, H/E, is derived.
Abstract: The mechanics of hardness indentation are considered. On the basis of a cycle in which the loading is elastic-plastic and the unloading (and subsequent reloading) elastic, an expression is derived for the relative depth recovery of the impression as a function of hardness/modulus,H/E. Experimental observations on indented surfaces of selected materials, mostly ceramics, using a tilting procedure in the scanning electron microscope to measure the residual depths, confirm the predicted trends. The analysis offers a simple means of characterizing the deformation properties of materials and should provide a basis for evaluating a range of contact-related properties, particularly surface damage phenomena in sharp-particle impact.
287 citations
31 Jul 1981
TL;DR: In this article, the structural properties of composite laminates with steel balls as the indentor are described and static indentation tests are described for glass/epoxy and graphite-epoxy composite lamination.
Abstract: Static indentation tests are described for glass/epoxy and graphite/epoxy composite laminates with steel balls as the indentor. Beam specimens clamped at various spans were used for the tests. Loading, unloading, and reloading data were obtained and fitted into power laws. Results show that: (1) contact behavior is not appreciably affected by the span; (2) loading and reloading curves seem to follow the 1.5 power law; and (3) unloading curves are described quite well by a 2.5 power law. In addition, values were determined for the critical indentation, alpha sub cr which can be used to predict permanent indentations in unloading. Since alpha sub cr only depends on composite material properties, only the loading and an unloading curve are needed to establish the complete loading-unloading-reloading behavior.
274 citations
TL;DR: In this paper, the authors present a theory for the indentation of a soft thin coating by a rigid body, where the coating is assumed to be bonded to a rigid substrate and to behave linearly elastically.
Abstract: This paper presents a theory for the indentation of a soft thin coating by a rigid body. The coating is assumed to be bonded to a rigid substrate and to behave linearly elastically. A simplifying approximation enables the stresses within the coating, averaged through its thickness, to be determined for particular indenter profiles. The results are shown to be sensitive to the thickness and compressibility of the coating material. Unlike much previous work, the results can be expressed analytically for certain indenter profiles and have been substantiated by experiment. The theory has many useful applications, in particular for situations where the layer acts as a protective coating and for the accurate, in situ and non-destructive measurement of the elastic modulus of the coating material.
136 citations
TL;DR: In this article, spherical indentation measurements were made on enamel surfaces of intact human teeth and Young's modulus was found to be typically 8.3×1010 Pa and the yield stress to be 3.3 ×108 Pa.
Abstract: Spherical indentation measurements were made on enamel surfaces of intact human teeth. From the load versus depth of indentation curve Young's modulus was found to be typically 8.3×1010 Pa and the yield stress to be 3.3×108 Pa. Young's modulus was observed to vary with moisture content and with the orientation of the enamel surface. Viscoelastic behaviour was evident, also depending on the moisture content of the enamel.
110 citations
TL;DR: In this article, a two-part study has been made of the fatigue characteristics of brittle solids using controlled indentation flaws, with explicit consideration being given to the role played by residual contact stresses in the fracture mechanics to failure.
Abstract: A two-part study has been made of the fatigue characteristics of brittle solids using controlled indentation flaws In this part a general theory is developed, with explicit consideration being given to the role played by residual contact stresses in the fracture mechanics to failure The distinctive feature of the formulation is a stress intensity factor for well-defined indentation cracks, suitably modified to incorporate the residual component Taken in conjunction with a standard power-law crack velocity function, this leads to a differential equation for the dynamic fatigue response of a given material/ environment system Reduced variables are then introduced to facilitate generation of “universal” fatigue curves, determined uniquely by the crack velocity exponent,n A scheme for using these curves to evaluate basic fracture parameters from strength data is outlined In this way the foundation is laid for lifetime predictions of prospective brittle components, as well as for reconstruction of the crack velocity function One of the major advantages of the analysis is the manner in which the residual stress parameters are accommodated in the normalized fracture mechanics equations: whereas it is understood thatall strength data are to be taken from test pieces in their as-indented state, so making it unnecessary to have to resort to inconvenient stress-removal procedures between the contact and failure stages of testing,a priori knowledge of the residual stress level is not required The method is proposed as an economical route to materials evaluation and offers physical insight into the behaviour of natural flaws
89 citations
TL;DR: In this paper, an expression for the slow growth of radial cracks after indentation using established notions of slow crack growth and residual stresses at the tip of the radial cracks was developed.
Abstract: An expression is developed for the slow growth of radial cracks after indentation using established notions of slow crack growth and residual stresses at the tip of radial cracks. This expression is substantiated by data gathered on indentation of microscope slides tested in air and water environments. The agreement is reasonable with the published values of the glass stress-corrosion susceptibility coefficients. It is suggested that the present approach represents a simple and straightforward method of measuring the stress-corrosion susceptibility of glasses.
58 citations
TL;DR: In this paper, a study was made of the strength characteristics of machined glass-ceramic surfaces using an indentation flaw technique, and the results were interpreted in terms of a residual compressive stress in the initial machined surface.
Abstract: A study has been made of the strength characteristics of machined glass-ceramic surfaces using an indentation flaw technique. The strength is found to decline or increase with progressive removal of the machining damage layer by a polishing procedure, depending on whether the indentation is made after or before the polishing. The results are interpreted in terms of a residual compressive stress in the initial machined surface. It is argued that failure to allow for the contribution of this stress in the fracture mechanics description of flaw growth could lead to significant errors in the evaluation of crack propagation parameters.
55 citations
TL;DR: In this paper, single crystals of NaCl, LiF and MgO were deformed at strain rates of 105 s−1 by impacting them with glass and tungsten carbide spherical particles of diameter in the range of 0·4-G l·0 mm.
Abstract: Single crystals of NaCl, LiF and MgO were deformed at strain rates of 105 s−1 by impacting them with glass and tungsten carbide spherical particles of diameter in the range of 0·4-G l·0 mm. By measuring the incident and rebound velocities and the size of the residual indentation, the dynamic hardnesses of these materials were determined and found to be several times the quasi-static values. At these strain rates the crystals behaved in a brittle manner. The fracture phenomena during the particle impact were investigated with a high-speed framing camera and from the photographic sequences velocities of cracks and impact times were also obtained. An attempt has been made to explain these results in terms of the dislocation densities, their velocities and the applied stress. Finally a brief comment is also made on the mechanism of material removal.
01 Jan 1981
TL;DR: An indentation method for determining the adhesion of interfaces between thin films and substrates has been developed in this paper, which provides a quantitative measure of the interface fracture resistance and has the advantage of simplicity and reproducibility.
Abstract: An indentation method for determining the adhesion of interfaces between thin films and substrates has been developed. The method provides a quantitative measure of the interface fracture resistance and has the advantage of simplicity and reproducibility The method has been demonstrated for a range of ZnO/Si systems and the adherence has been correlated with acoustic properties.
TL;DR: In this paper, it was shown that for a variety of ceramics, the threshold for microfracture during elastic-plastic indentation corresponds to radial, rather than subsurface median, crack formation.
Abstract: It is shown that for a variety of ceramics the threshold for microfracture during elastic-plastic indentation corresponds to radial, rather than subsurface median, crack formation. This is contrary to the fundamental assumption of current models for threshold crack nucleation by sharp indenters. The significance of this observation in terms of strength reduction is discussed.
Journal Article•
TL;DR: For a special class of elastic materials, the inverse deformation is always possible in the same material as mentioned in this paper, and this result is used to simplify the determination of second-order effects in problems for this special class.
Abstract: For a special class of elastic materials, the inverse deformation is always possible in the same material. This result is used to simplify the determination of second-order effects in problems for this special class. The second-order solution for indentation of a half-space by a smooth rigid sphere is determined. For indentation by a flat-ended circular punch it is found that the second-order solution for compressible materials is physically inadmissible, while the solution for incompressible materials involves a concentrated line load at the edge of the punch. A rigid spherical inclusion embedded in an elastic matrix with uniform stresses at infinity is considered, and the interface stresses are found to second order.
TL;DR: In this paper, the response of a series of one and two-phase β-Si3N4 ceramic alloy surfaces to sharp diamond microindentation has been examined by optical and electron microscopy.
Abstract: The response of a series of one- and two-phaseβ-Si3N4 ceramic alloy surfaces to sharp diamond microindentation has been examined by optical and electron microscopy. The microhardness (H), which obeys the load-independent relationH=αP/a
2 (whereP anda are load and indent size, respectively) is nearly constant within the alloy series, indicating a retention of high covalency at large (Al and O) substitution levels. Indentation results from severe localized plasticity which is characterized by the operation of the dominant dislocation Burgers vectora[0 0 0 1] in the hexagonalβ lattice. The severe anisotropy in plasticity induces grain-boundary microcracking which is believed to nucleate median cracks which propagate away from the plastic zone on symmetry planes beneath the indenter. The relation between load, median crack size (c) and fracture toughness (K
c) is of the form,K
c=constant (P/c
3/2) predicted theoretically. Values ofK
c rank correctly with those from notched-beam measurements, but there is uncertainty about the value of the constant.
TL;DR: In this paper, a two-part study of the fatigue characteristics of brittle solids using controlled indentation flaws was made, with explicit consideration being given to the role played by residual contact stresses in the fracture mechanics to failure.
Abstract: A two-part study has been made of the fatigue characteristics of brittle solids using controlled indentation flaws. In this part a general theory is developed, with explicit consideration being given to the role played by residual contact stresses in the fracture mechanics to failure. The distinctive feature of the formulation is a stress intensity factor for well-defined indentation cracks, suitably modified to incorporate the residual component. Taken in conjunction with a standard power-law crack velocity function, this leads to a differential equation for the dynamic fatigue response of a given material/ environment system. Reduced variables are then introduced to facilitate generation of “universal” fatigue curves, determined uniquely by the crack velocity exponent,n. A scheme for using these curves to evaluate basic fracture parameters from strength data is outlined. In this way the foundation is laid for lifetime predictions of prospective brittle components, as well as for reconstruction of the crack velocity function. One of the major advantages of the analysis is the manner in which the residual stress parameters are accommodated in the normalized fracture mechanics equations: whereas it is understood thatall strength data are to be taken from test pieces in their as-indented state, so making it unnecessary to have to resort to inconvenient stress-removal procedures between the contact and failure stages of testing,a priori knowledge of the residual stress level is not required. The method is proposed as an economical route to materials evaluation and offers physical insight into the behaviour of natural flaws.
TL;DR: In this article, the fracture surface energy, γ, of ThO2 was measured between room temperature and 400°C using the Hertzian indentation technique with cold or preheated steel and alumina indentors.
Abstract: The fracture surface energy, γ, of ThO2 was measured between room temperature and 400°C using the Hertzian indentation technique with cold or preheated steel and alumina indentors. The value of γdecreased strongly with temperature with a suggested saturation at 350°C. This may indicate the change from an unrelaxed fracture surface to a relaxed surface at temperatures where oxygen becomes mobile. The result obtained at 400°C is γ=1.4 J m−2.
TL;DR: In this article, the reflection coefficient of a Rayleigh wave incident on a surface indentation crack has been measured as the sample is stressed to fracture, and acoustic measurements have been correlated with the stable crack extension that precedes final failure.
Abstract: An investigation of scattering from surface cracks has been conducted. In particular, the change in the reflection coefficient of a Rayleigh wave incident on a surface indentation crack has been measured as the sample is stressed to fracture. The acoustic measurements have been correlated with the stable crack extension that precedes final failure. The crack extension behavior of as-indented specimens was found to differ appreciably from that of annealed specimens. Cracks in the annealed samples exhibited partial crack tip closure, but little stable extension, whereas cracks in the as-indented samples displayed both crack closure and irreversible crack growth. This behavior has been rationalized by invoking concepts based upon the residual stresses created by indentation.
TL;DR: In this article, the nonlinear elastic problem involving the indentation of a slightly compressible rubber-like layer bonded to a rigid cylinder and indented by another rigid cylinder is analyzed by the finite element method.
Abstract: The nonlinear elastic problem involving the indentation of a slightly compressible rubber-like layer bonded to a rigid cylinder and indented by another rigid cylinder is analysed by the finite element method. Both the geometric and material nonlinearities are accounted for. The finite element formulation of the problem is based upon a variational principle recently proposed by Cescotto and Fonder, and is valid for both slightly compressible and incompressible materials. The results computed and presented graphically include the shape of the indented surface, the pressure distribution over the contact surface, and the stress distribution at the bond surface. For the same contact width, the results for the compressible material are found to differ significantly from those for the case when the rubber-like layer is assumed to be incompressible.
TL;DR: In this paper, the authors used transmission electron microscopy and the scanning electron microscope to study indented MgO single crystals and to relate luminescence emission and defect structure.
Abstract: Transmission electron microscopy and the cathodoluminescence mode in the scanning electron microscope have been used to study indented MgO single crystals and to relate luminescence emission and defect structure. Color images of cathodoluminescence indentation rosette have been also obtained. Marked differences in the emission and the defect structure in different areas of indentation have been found and in particular a high density of defects have been observed in the center of indentation including some defects which seem to be characteristic of this region.
TL;DR: In this paper, the authors compared the scratch hardness (Hs) and the indentation hardness of cubic single crystals, and showed how these measurements may be used to identify the operative slip systems in a given crystal.
Abstract: Some comparisons are made between the scratch hardness (Hs), as determined by the width of a groove formed under conditions of plastic deformation, and indentation hardness (H) of crystalline materials. It is shown that the Hs/H ratio is dependent on the ‘effective’ strain developed beneath the indenter. or slider, the homologous temperature and the crystallographic characteristics of the solid. The nature of anisotropy in cubic single crystals, now established for both indentation and scratch processes, is briefly compared and contrasted. It is shown how these measurements may be used to identify the operative slip systems in a given crystal.
TL;DR: In this paper, the authors considered a rigid half-wedge which simultaneously translates tangentially and normally at constant speeds with respect to the surface of an elastic half-plane, and showed that the coupling effect may be small for low indentation speeds and relatively flat half-wedges.
TL;DR: In this paper, the cleavage surfaces were examined by multiple-beam interferometry, and solvent etching was used to delineate the dislocations, and their distribution and branching were investigated.
Abstract: Potassium acid phthalate (COOKC6H4COOH) single crystals were grown from aqueous solutions. The cleavage surfaces were examined by multiple-beam interferometry. Solvent etching was used to delineate the dislocations, and their distribution and branching were investigated. The (001), (010) and (100) faces were subjected to pyramidal indentation to study the slip process.
Patent•
18 Nov 1981
TL;DR: A linear shaped charge has a v-shaped indentation cladded with e.g. lead, and the explosive body is formed of discrete explosive elements, such as detonator cords, at least one of which is positioned along the apex of the indentation so that detonation can be initiated as mentioned in this paper.
Abstract: A linear shaped charge has a v-shaped indentation cladded with e.g. lead. The explosive body is formed of discrete explosive elements, such as detonator cords, at least one of which is positioned along the apex of the indentation so that detonation can be initiated in that region.
TL;DR: In this article, the authors investigated the possibility of using indentation tests to extract time-dependent flow property information from small cylindrical specimens and found that the indentation load relaxation test should be easier to scale down to smaller specimens.
TL;DR: In this paper, a semi-empirical analysis of the indentation process is made as a result of which the hardness indentation data obtained with ball, cone and square-based pyramid indenters are related to the uniaxial stress-strain curve of the indented material.
Abstract: A semiempirical analysis of the indentation process is made as a result of which the hardness indentation data obtained with ball, cone and square-based pyramid indenters are related to the uniaxial stress-strain curve of the indented material. It is shown that deductions from the analysis are valid only for annealed materials. The factors liable to result in erroneous hardness readings are considered and the influence of residual stresses in the surface and the subsurface layers of the material under examination are shown to explain (i) the dependence of cone and pyramid hardness on the applied load and (ii) the anomalous influence of cone angle on the measured hardness when large angle indenters are pressed into materials which have been strain-hardened prior to the hardness measurement.
TL;DR: It is concluded that the matrix around the indentation is highly strained and can be released by dissolving the crystallites, and it is shown that the indentations do vanish when the tissue is demineralized.