Showing papers on "Indentation published in 1982"

A Simple Method for Determining Elastic-Modulus–to-Hardness Ratios using Knoop Indentation Measurements

Abstract: A simple indentation technique for measuring the hardness-to-modulus ratio of elastic/plastic materials was developed. The method, which is based on measurement of the elastic recovery of the in-surface dimensions of a Knoop indentation, allows ready evaluation of the hardness-to-modulus ratio to an accuracy better than 10%.

The response of solids to elastic/plastic indentation. I. Stresses and residual stresses

Abstract: A new approach for analyzing indentation plasticity and for determining indentation stress fields is presented. The analysis permits relations to be established between material properties (notably hardness, yield strength, and elastic modulus) and the dimensions of the indentation and plastic zone. The predictions are demonstrated to correlate with observations performed on a wide range of materials. The indentation stress fields are computed along trajectories pertinent to three dominant indentation crack systems: radial, median, and lateral cracks. The peak load and residual tensile stresses are shown to be consistent with observed trends in indentation fracture.

Dependence of Fracture Toughness of Alumina on Grain Size and Test Technique

Abstract: The fracture toughness (KIc) of sintered alumina was measured using notched beam (NB) and indentation/strength-in-bending (ISB) techniques. KIc (NB) decreases with increasing grain size. For fine-grained materials (<5 μm), NB results overestimate KIc, and exhibit a substantial notch-radius sensitivity. A stress-intensity-derived model is used to explain this notch sensitivity. The ISB results are very similar to those obtained using the double-cantilever-beam (DCB) method and show an increasing fracture toughness with increasing grain size. The differences between the NB and ISB (DCB) results for coarser-grained materials are thought to be related to R-curve behavior.

The effect of thin hard coatings on the Hertzian stress field

Abstract: In this paper the effect of thin rigid coatings on the stress field generated by a Spherical indentation on a flat halfspace is investigated using a finite-element program. It is shown that thin hard coatings can have a significant effect on the radial and circumferential stresses. Of particular interest is the reduction in the maximum (radial) tensile stresses, since this indicates that hard coatings can be used to protect brittle materials against elastic contact damage. The stress reduction increases with the Young's modulus and thickness of the coating. The reduction in the substrate stresses is, however, accompanied by an increase in the maximum tensile stresses in the coating itself.

Ceramic resonator and a ceramic filter using the same

Abstract: A ceramic resonator including an elongated piezoelectric ceramic platelet having an indentation formed in the center in the longitudinal direction, a polarization in the thickness direction where the polarization occurs at least in the indentation; first and second main surfaces; first and third metal thin film electrodes formed on said first main surface and second and fourth metal thin film electrodes formed on said second main surface, the third electrode being separated from the first electrode and the fourth electrode separated from the second electrode where the resonator has a constant vibration based on the dimensions of the region associated with the indentation the vibration being generated at the narrow part when an electrical signal is applied to the electrodes. Moreover, a ceramic filter consisting of plurality of the ceramic resonators connected in series can also be configured.

The effects of n2+ ion implantation on the hardness and wear behaviour of brittle materials

Abstract: Changes in the wear-related near-surface deformation behaviour of silicon and silicon carbide single crystals have been investigated following implantation of 80keV N2+ ions up to doses of 1017-1018 ions cm-2. Both microhardness and single point diamond cone scratch tests have been used to look for changes in indentation-induced plasticity and fracture behaviour as a function of dose. Both materials exhibited a ‘softening’ in the implanted layer together with suppression of the lateral crack mode of indentation fracture. By contrast, median/radial cracking appeared unaffected. In all cases, the effects were only found to become significant about a critical dose of ~4 × 1017N2+ cm-2. The observations are presented and their possible origins and implications discussed.

Equivalence of indentation and compressive creep tests on a WC/Co hardmetal

Abstract: For numerous applications in the aerospace, chemical and tool industries, when information is needed on high temperature mechanical properties, hot hardness measurements are used because of the simplicity and low cost of the tests [1, 2]. The common practice is to use the room temperature convention of measuring a material's resistance to deformation by dividing the applied load L by the indentation area A, and this provides a hardness value H equal to the indentation pressure P at a fixed, usually short, time of loading such that

Comparisons of Static and Impact Loading Damage in Zinc Sulfide

Abstract: Contact damage was induced in CVD zinc sulfide by static and impact loading using glass spheres. Calculations based on the relation between the residual depth of the indentation and the ratio of the hardness to Young's modulus were used to estimate the dynamic hardness and impact load. Comparisons of applied loads, threshold loads for crack formation, and crack lengths for static and impact indentations at equal indentation radii show that predictions of impact damage using data from static loading are inadequate.

Micromechanics approach to the indentation hardness of glass matrix particulate composites

Abstract: A theoretical analysis is made of the indentation hardness of glass matrix, particulate composites. It is hypothesized that glass is an elastic-plastic solid on a microscopic scale. Based upon the Marsh theory of indentation, expressions are formulated for indentation hardness of two-phase composites containing spherical particles. When hard particles are dispersed in a soft glass matrix, the overall hardness depends upon the matrix hardness, the volume-fraction of dispersed phase, the elastic properties of the two phases and also the matrix flow stress. On the other hand, when soft particles are dispersed in a hard glass matrix, the hardness and the elastic moduli vary in parallel with the volume-fraction of dispersed phase. Furthermore, the present analysis indicates that the hardness of a composite is independent of the particle size and interparticle spacing if the volume-fraction of the particles is kept constant. Experimental results of the Vickers hardness of phase-separated glasses as well as published hardness data for a glass-ceramic are used for the verification of the theory. The proposed theory explains well the hardness behaviour of such glass matrix composites in terms of the properties and amounts of the individual phases and the microstructural effects.

Indentation rosettes and dislocation locking by oxygen in silicon

Abstract: The characteristics of indentation behavior are investigated for float‐zone silicon crystals and Czochralski silicon crystals over a wide range of temperature. It is shown that the deformation process to produce an indentation is not influenced by the oxygen content. The wing length of the dislocation rosette around the indentation which is subjected to high‐temperature annealing is shorter in Czochralski crystals than in float‐zone crystals. The results are interpreted satisfactorily in terms of locking of dislocations by oxygen atoms in the former type of silicon crystal during their rearrangement.

Static Indentation Tests on Composite Plates for Impact Susceptibility Evaluation

Abstract: : Static indentation tests with spherical steel indenters were conducted on thin composite plates to assess the impact susceptibility of graphite epoxy composites. The data were used to validate an impact strength analysis based on large deflection plate theory. Tests and analysis were in good agreement on both plate stiffness and maximum strain energy at failure. A parametric analysis showed that for brittle matrix composites the matrix dominated the threshold of damage, while in tough matrix composites the fibers dominated the threshold of damage. Penetration was always dominated by large deflection membrane effects. (Author)

Fracture Toughness of Metaphosphate Glasses

Abstract: The fracture toughnesses and Young's elastic moduli of several metaphosphate glasses were measured by the indentation technique. The results show that the normal glasses lie along a KIc vs E line between (0.4, 40) and (0.7, 60) MPa-m112 and GPa, respectively. The abnormal ZnO and MgO metaphosphates appear to be tougher and are above the line of the normal glasses.

Comparison of Uniaxial and Biaxial Strengths for Test Pieces with Controlled Flaws

Abstract: Indentation cracks are used as controlled flaws in soda-lime glass specimens for failure tests in uniaxial and biaxial loading. The inert strength is independent of loading type within the scatter of data. This result is discussed in relation to the conclusions of other workers who have reported systematic differences in similar comparative tests on specimens containing natural flaws.

Dependence of Hertzian fracture angle on Poissons ratio and indentation techniques

Abstract: Sub-parallel concentric conic fractures can be produced consecutively in Perspex by “liquid indentation”. There is a linear relationshp between the conic angle, θ, of Hertzian fracture and the Poisson's ratio, Ν, of the material. This angle is about 10‡ higher than the calculated path of the principal stress trajectory for a given Ν. γ decreases with the increase of stress application rate. This dependence of θ is very marked in materials with high Poisson's ratios.

Press tool for cutting and creasing viscoelastic thermoplastic sheet - for box blanks, having cutting blades and shallower hot indenting blades on one tool

Abstract: A tool for creasing and cutting sheet material to make flat blanks for folded boxes has a press plate fitted with a combination of a profile cutter and one or more heated indentation blades. The levels of the cutter and the indentation blades are set so that when the cutter breaks through the sheet to a hard backplate, the indentation blade is impressed to 75-80% of the thickness of the sheet. Used esp. for preparing box blanks from materials having a high elastic resistance to folding, e.g. flexible PVC or polypropylene, to reduce the fold zone thickness sufficiently to ensure the required crease alignment. Also maintains reproducible alignment and spacing of the fold axes relative to the cut borders.

Indentation study of cadmium oxalate trihydrate single crystals

Abstract: Vickers microhardness indentation studies have been made on the as-grown (¯2¯21), (110) and (001) planes, and on the only cleavage plane (1¯10) of gel-grown cadmium oxalate trihydrate single crystals. The material chipping off and slip lines observed around indentation figures have been discussed. The anisotropy in microhardness of the crystals is indicated.

Vickers indentation anisometry on thin cylindrical materials

Abstract: The required anisometric correction to be made when using Vickers indentations on filaments with radial dimensions of the order of those of the microindenter, is evaluated. For an isotropic plastic material the anisometry of indentation. Δl=l∥{-l1 increases with decreasing cross-section of the filament. If the calculated correction, Δ/c, is in agreement with experiment the interest lies in the fact that the material preserves the indentation shape after removal of the indenter. Values of Δ/≠Δ/c reveal the presence of a mechanical anisotropy on metallic filaments due to processing. Furthermore, in the case of thin highly oriented polymeric fibres the inherent microindentation anisotropy is masked by the anisometry effect. Consequently, the proposed correction is very important and particularly valuable when anisotropic cylindrical material surfaces are being studied.

Method of manufacturing a hollow package with a sponge and hollow package manufactured by the method

Abstract: The hollow package has a flanged edge, an indentation, a closure film and a sponge which is accommodated in the indentation and is impregnated with an application medium. The indentation contains a continuation of smaller cross-section. Only the continuation is filled with the application medium and a swelling sponge is placed in the indentation. The impregnating operation is begun only after closure of the package by separating the package. When the package is opened, the swelling sponge swells out of the flanged edge and can be moved conveniently over the application surface by means of the continuation serving as a gripping strip.

Surface Acoustic Wave Measurements of Surface Cracks in Ceramics

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.

Mechanical indentation testers designed to allow the continuous microscopic observation of the controlled indentation of transparent materials

Abstract: The design of two mechanical indentation instruments are described which can operate on the stage of an inverted type microscope so that continuous in situ observations of the fully controlled indentation process can be made The two instruments are for different load ranges, and have been successfully used in research on the mechanical properties of glass, alkali halide crystals and polymeric materials

Inductive sensor for the detection of low velocities

Abstract: An inductive sensor or penetrographic sensing device has been applied directly to a hardness tester for the detection of the indenter axial velocity under various conditions for the loading-unloading cycle. The device has not been used previously in this type of application. The sensor under consideration is capable of detecting very low velocities, giving information on the mechanism of the indentation on solid materials. Technical data and the performance of the device are also discussed.

Effects of environment on microhardness of magnesium oxide

Abstract: Micro-Vickers hardness measurements of magnesium oxide single crystals were conducted in various environments. These environments included air, nitrogen gas, water, mineral oil with or without various additives, and aqueous solutions with various pH values. Indentations were made on the (100) plane with the diagonals of the indentation in the (100) direction. The results indicate that a sulfur containing additve in mineral oil increased hardness, a chlorine containing additive in mineral oil decreased hardness, and aqueous solutions of hydrogen chloride decreased hardness. Other environments were found to have little effect on hardness. Mechanically polished surfaces showed larger indentation creep than did as-cleaved surfaces.

The technique of scleral indentation.

Abstract: The technique of scleral indentation, or depression, shall be presented in both mechanical and clinical manners. Explanation and diagrams of several optical principles involved in indentation precede a discussion of clinical performance. Indications, cautions, and suggestions for improving skill are cited.

Interaction between internal loading and surface indentation for a transversely isotropic elastic half-space

Abstract: An analytical solution is given for the axisymmetric indentation problem of a half-space loaded by internal forces. Closed form results are presented for an interior point force and a flat-ended indenter. The interaction between internal and external loadings is discussed using numerical results and graphs.