Showing papers on "Indentation published in 1977"
TL;DR: In this article, a model for the initiation of microfracture under sharp indenters is proposed, based on a simple approximation for the tensile stress distribution in the elastic/plastic indentation field, in conjunction with the principle of geometrical similarity.
Abstract: A model is proposed for the initiation of microfracture beneath sharp indenters. Using a simple approximation for the tensile stress distribution in the elastic/plastic indentation field, in conjunction with the principle of geometrical similarity, fracture mechanics procedures are applied to determine critical conditions for the growth of penny-like “median cracks” from sub-surface flaws. The analysis provides a functional relationship between the size of the critical flaw and the indentation load necessary to make this flaw extend. Initiation is well defined (unstable) only if the critical flaw lies within a certain size range; outside this range, large flaws can extend stably but small flaws can not extend at all. No flaws can extend below a characteristic minimum load, values of the indentation variables at this load accordingly providing useful threshold parameters. These quantities involve the intrinsic deformation/fracture parameters, hardness and toughness, in a fundamental way, thereby establishing a basis for materials selection in fracture-sensitive applications.
474 citations
TL;DR: In this article, a new indentation creep test is introduced in which the indenter is a circular cylinder with a flat end, and a steady state velocity is observed in this new test shortly after a transient period during which the indententer makes a shallow impression on the surface of the specimen; hence the name "impression creep".
Abstract: A new indentation creep test is introduced in which the indenter is a circular cylinder with a flat end Unlike conventional indentation tests, a steady-state velocity is observed in this new test shortly after a transient period during which the indenter makes a shallow impression on the surface of the specimen; hence the name “impression creep” This steady-state velocity is found to have the same stress and temperature dependences as the conventional undirectional creep tests using bulk specimens Three possible mechanisms are analysed in detail, bulk diffusion, surface diffusion, and dislocation creep They have different stress and indenter-size (radius) dependences Experimental results on succinonitrile crystals are reported
305 citations
TL;DR: In this paper, the relationship between indentation pressure produced by cones, pyramids and spheres and the mechanical properties of elastic-plastic materials is considered, based on previous work which uses the expansion of a cavity in an elasticplastic material, and an improved correlation with experimental results is obtained if it is assumed that the hemispherical core is a region in which the stresses are changing from purely hydrostatic to values which satisfy the Von Mises yield criterion.
Abstract: The relationship between indentation pressure produced by cones, pyramids and spheres, and the mechanical properties of elastic-plastic materials is considered, based on previous work which uses the expansion of a cavity in an elastic-plastic material. According to the earlier model, there are three zones: a hydrostatic 'core' of which the indenter is embedded; a hemispherical shell, where plastic flow is taking place; and beyond this the elastic hinterland. An improved correlation with experimental results is obtained if it is assumed that the hemispherical core is a region in which the stresses are changing from purely hydrostatic to values which satisfy the Von Mises yield criterion. A further improvement results if a correction is made for the lack of geometric similarity of the strain field in indentations by spheres.
269 citations
245 citations
TL;DR: In this paper, the damage caused by solid projectiles in the elastic and elastic/plastic target response regimes has been characterized and analyzed, based on quasi-static indentation fracture characterization schemes and quantification of the impact damage observations.
Abstract: The damage caused by solid projectiles in the elastic and elastic/plastic target response regimes has been characterized and analysed. Semi-empirical methods for establishing the relative importance of the target and properties on the impact damage have been derived, based on quasi-static indentation fracture characterization schemes and the quantification of the impact damage observations.
142 citations
TL;DR: In this article, the authors showed that the nominal pressure of indentation varies as a function of loading rates in a manner similar to that of the strength of S2 ice in uniaxial compression.
Abstract: This study gives the results and interpretation of tests made in a cold room on ice plates held vertically in a press and indented at various speeds with a rectangular indentor. These plates, 81 cm square, were held and frozen solid to a steel frame to represent semi-infinite ice sheets. The tests were carried out at — 10°C with indentation speeds varying from 6 × 10 -5 cm/s to 3 cm/s.It was found that the nominal pressure of indentation varies as a function of loading rates in a manner similar to that of the strength of S2 ice in uniaxial compression. The pressure increases rapidly with loading rates up to its maximum value at a strain-rate of 5 × 10-4 S-1. From there on, the pressure decreases. In the ductile range and up to the point of maximum pressure, a theoretical model was proposed where the theory of Hill (1950) of indentation of an ideal plastic body can be applied to predict an indentation pressure close to three times that of the uniaxial crushing strength.The tests did not show any so-called “ratio effect” caused by the ratio of the indentor width to the plane thickness. This effect could be explained by the influence of the geometry of the indentor on the strain-rate.
87 citations
TL;DR: In this article, a self-consistent analysis of the fractographic nature of Palmqvist cracks and the potential for the growth of these cracks in the near-surface region adjacent to an indentation is presented.
82 citations
TL;DR: In this paper, the authors described the range of fracture processes which may occur beneath Vickers indentations in sintered tungsten carbide-cobalt composites and the mode of fracture may be altered by changing the conditions of loading.
63 citations
48 citations
TL;DR: The dependence of the rate of material removal from glass and fused silica specimens on the carrier fluid used in free abrasive grinding was observed and other abrasion parameters, i.e., surface roughness, bed thickness and drag force, were measured.
43 citations
TL;DR: In this paper, the authors discuss the stress field in the neighbourhood of an indentation made by a steel ball in poly(methyl methacrylate), the special characteristics of which have been described by Puttick (1973), and suggest that the deformation in the interior of the solid approximates to that round a spherical cavity expanded by internal pressure in a plastic-elastic medium.
Abstract: The authors discuss the stress field in the neighbourhood of an indentation made by a steel ball in poly(methyl methacrylate), the special characteristics of which have been described by Puttick (1973). These results suggest that the deformation in the interior of the solid approximates to that round a spherical cavity expanded by internal pressure in a plastic-elastic medium, as proposed for other materials both by Marsh (1964) and by Johnson (1970). The approximations required to apply ideal plastic-elastic theory to polymers are discussed, and Hill's solution (1950) of the equilibrium equation for the expanded cavity is modified to take into account the sensitivity of the yield stress of PMMA to strain rate and hydrostatic pressure; the result gives the indentation pressure in terms of the radius of the plastic zone. The latter dimension is experimentally determined by measuring the indentation pressure, so that the scale of the stress field in the interior is known. The state of plane stress in the surface is interpreted in terms of the plastic-elastic expansion of a hole in a plate. The tensile component of the stress field thus derived appears to explain well the orientation, shape and size of the stable cracks initiated at such indentations.
TL;DR: In this article, a method is presented which makes possible the determination of the critical resolved shear stress, τc, for dislocation movement in a crystal, based on the analysis of dislocation rosettes which are generated either by microindentation, or by precipitates of a second phase.
Abstract: A method is presented which makes possible the determination of the critical resolved shear stress, τc, for dislocation movement in a crystal. The method is based on the analysis of dislocation rosettes which are generated either by microindentation, or by precipitates of a second phase. The method does not require a knowledge of the indentation (or precipitate) stress field; it requires only information on the positions of a set of leading dislocation loops. At once one can also obtain the effective indentation stress field and, for the first time, the precipitate stress field. For illustration, the method is applied to the determination of τc in silicon, using both indentation and precipitate dislocation rosettes. The value of τc thus obtained varies from a low of 3×107 dyn/cm2 in oxygen‐free samples to a high of 5.5×108 dyn/cm2 in a sample containing ∼2×1018 atoms/cm3 of oxygen with clustering. The SiO2 precipitate stress field in the present case was found to vary as x−1, suggesting that the precipita...
TL;DR: In this article, continuous indentation tests using a 6.35 mm diameter steel ball were carried out on polycrystalline aluminium (99.995%) at forces up to 942 N (96 kg) and a total displacement of 65μm.
Abstract: Continuous indentation tests using a 6.35 mm diameter steel ball were carried out on polycrystalline aluminium (99.995%) at forces up to 942 N (96 kg) and a total displacement of 65μm. On loading the results were observed to follow the classical Hertz equation until the elastic limit was reached at 4.6±0.2 N (0.47 kg), 1.02±0.05μm. The unloading results after plastic indentation were found to fit the Hertz solution for an indenter in a spherical hole. Using the Hertz theory it was possible from the unloading results to determine the mean stress and strain under the ball, together with the indentation diameter, plastic strain, Meyer stress and ratio of elastic to total strain, enabling a stress-strain curve for hardness to be drawn. The elastic limit of aluminium occurred at a stress of 4.7±0.2×108Pa (46kg mm−2) and a strain of 1.27±.05%. At a total strain of 11.25% the stress was 11.7±0.2×108Pa (115 kg mm−2).
TL;DR: In this paper, Johnson's analysis of the residual surface stress distribution produced in a flat surface by a spherical indenter is presented, which suggests that high residual stresses develop just outside the contact area as a result of the superposition of elastic unloading stresses onto the stresses at maximum load when the specimen has deformed plastically.
Abstract: Experimental evidence to support Johnson's [6] analysis of the residual surface stress distribution produced in a flat surface by a spherical indenter is presented. The theory suggests that high residual stresses develop just outside the contact area as a result of the superposition of elastic unloading stresses onto the stresses at maximum load when the specimen has deformed plastically. The experiments involved the use of a semi-brittle steel, sufficiently hardened so that, while tensile stresses in the surface produced cracks, the substrate deformed plastically under the triaxial stress system beneath the indenter. Radial cracks produced by the indenter frequently extended after load removal, implying the presence of the high tensile circumferential residual stresses predicted by the theory. This work and recent studies of indentation loading of glasses show that there are important situations where residual stresses can contribute to their failure and wear.
TL;DR: In this article, a numerical method of solution for the contact problem between a rigid die and an elastic half-space is proposed, which involves an iterative process which is continued until the correct solution is obtained according to certain criteria.
TL;DR: In this article, the effect of interference between the deformation zones produced by two punches, when they are applied sufficiently close together, is investigated experimentally using etching techniques and force-indentation measurements, and theoretically using upper-bound techniques.
Patent•
10 Jan 1977
TL;DR: In this paper, the displacement of the entire surface of the object to be measured having indentation or pattern on the surface is measured with high precision, and the displacement is determined by a linear regression model.
Abstract: PURPOSE:To measure with high precision the displacement of plane of the entire surface of the object to be measured having indentation or pattern on the surface.
TL;DR: In this paper, the effect of formation anisotropy on the hole deviation force acting on a single bit tooth was analyzed for a plastically deforming rock for a yield condition which allows a nonlinear dependence of strength on confining pressure.
Abstract: The effect of formation anisotropy on the hole deviation force acting on a single bit tooth is analyzed for a plastically deforming rock. A yield condition which allows a nonlinear dependence of strength on confining pressure is used in a numerical analysis of the plane strain indentation of a porous rock by a single bit tooth. The hole deviation force was approximately 50 percent of the vertical indentation force for the example calculation.
Patent•
03 Aug 1977
TL;DR: In this article, an indentation is formed on the insulating substrate which has electric wiring thereon; a light emitting element is arranged inside the indentation so that the end of the former is exposed from the opening surface of the latter.
Abstract: PURPOSE:An indentation is formed on the insulating substrate which has electric wiring thereon; a light emitting element is arranged inside the indentation so that the end of the former is exposed from the opening surface of the latter; and also a light receiving device is provided in such a way as to face the light emitting element - thereby obtaining a photo-coupling array that has an excellent lighttransmitting effect
Patent•
28 Feb 1977
TL;DR: In this article, a microscope tube is directly installed to a frame separate from a loading lever, whereby it is protected from shock at application and removal of a load and accurate indentation projection can be made.
Abstract: PURPOSE:A microscope tube is directly installed to a frame separate from a loading lever, whereby it is protected from shock at application and removal of a load and accurate indentation projection can be made.
Patent•
24 Dec 1977
TL;DR: In this article, the authors proposed to abolish marking with inks by giving an indentation to element surface thereby identifying any defect, and they used the indentation as a way to identify any defect.
Abstract: PURPOSE:To abolish marking with inks by giving an indentation to element surface thereby identifying any defect.
TL;DR: In this paper, the authors evaluated the durability of PVC by using traction and indentation methods, in order to define the brittle transition in time-temperature space, and then they studied the change in brittle transition after artificial weathering of the PVC.
Abstract: The purpose of this study was the evaluation by mechanical testing of the durability of PVC. To that end, the mechanical behavior of PVC was subjected to systematic testing by traction and indentation methods, in order to define the brittle transition in time-temperature space. In a second portion we began a study of the change in the brittle transition by indentation methods after artificial weathering of the PVC.