Indenters smoothness

Test pieces for Brinell testing must have two parallel sides and be reasonably smooth for proper support on the anvil of the test machine. Minimum sample thickness must be 10 times indentation depth. Successive indentations must not be closer than three indentation diameters to one another or to the edge of the test piece. 

Ultrasonic Microhardness. A new microhardness test using ultrasonic vibrations has been developed and offers some advantages over conventional microhardness tests that rely on physical measurement of the remaining indentation size (6). The ultrasonic method uses the DPH diamond indenter under a constant load of 7.8 N (800 gf) or less. The hardness number is derived from a comparison of the natural frequency of the diamond indenter when free or loaded. Knowledge of the modulus of elasticity of the material under test and a smooth surface finish is required. The technique is fast and direct-reading, making it useful for production testing of similarly shaped parts. 

There is space here for a brief account of only one technique, that is, hardness measurement. The idea of pressing a hard object, of steel or diamond, into a smooth surface under a known load and measuring the size of the indent, as a simple and... 

Equation (24) is originally derived for a conical indenter. Pharr et al. showed that Eq (24) holds equally well to any indenter, which can be described as a body of revolution of a smooth function [67]. Equation (24) also works well for many important indenter geometries, which cannot be described as bodies of revolution. 

Both the indenter and the specimen surfaces should be smooth and homogeneous in order to minimize friction. If the indenter is not smooth, under pressure that is sufficient to cause plastic flow. The specimen will become embossed by the indenter, tending to lock the surfaces. This will induce a large effective friction coefficient. 

The surface characteristics of excipients have also been studied and related to the dispersion and dissolution of poorly soluble drugs [58]. It was found that excipients with rough surfaces (such as Emcompress, with a porous surface) trap the drug particles in the indentations, which can then be blocked by fine excipient particles and decrease dissolution. Smooth surfaces (such as spherical sugar beads), however, produced high dissolution efficiency of the poorly soluble drugs. 

Quantitative hardness tests slowly apply a fixed load to an indentor that is forced into the smooth surface of the specimen. After the load is removed, either the diameter across the impression or the depth of the impression is measured. The size of the penetration is proportional to the material s hardness. Rockwell, Brinnell, Vickers, and Knoop are well-known indentation hardness testing instruments. 

BM, basement membrane ER, rough endoplasmic reticulum (with ribosomes attached smooth ER is depicted nearer the nucleus and on the right side of the cell.) DI, deep indentation of plasma membrane... 

Brinell method. The measurement is made by driving a calibrated hardened steel ball of diameter D into a flat and smooth sample under variable pressure P, perpendicular to the surface, and then measuring the diameter of the indentation d left on the surface (CMEA ST. 468-77 ISO R 79-68). Brinell hardness HB is the ratio of pressure P to area S of a spherical cup-shaped indentation... 

Usually, the contact is not smooth. It can be demostrated that the result of allowing for friction on the indenter-sample contact surface is equivalent to replacing f by y> = +arc tan p (p —coefficient of friction), which corresponds to a blunting of the indenter point. If friction is neglected, this may result in too high a value of K% in equation (6.2.9). Simultaneously the intersecting cracks may merge into others. 

Feed material is fed into the groove ahead of the roller and is pressed into a continuous hoop-shaped strip which may contain indentations caused by projections on the roller surface. The compacted strip is continuously removed from the groove by a stripping tool or finger and breaks into briquets when indented or random pieces when a smooth roller is used. 

The carvings are made up of individual little bits of chalk, but when we are a long way from it they are so small that we cannot see them - all we see is the smooth horse-shaped figure. In the same way the edge of this paper looks perfectly smooth, but if you look at it with a powerful magnifying glass or microscope, you will see that it is actually quite ragged. It s just that the indentations are so small they cannot be seen with the naked eye. 

Microhardness tests upon the same worn hip cups have provided direct supporting evidence for the changed nature of PE adjacent to the wear surface (Flores et al, 2000). An increased microhardness of the used cups, at their wear surfaces, in comparison to the control was apparent. Attention turned, accordingly, to the lateral surfaces of the cups (Fig. 7.16) which did possess the smooth planar condition required for optimum microhardness measurements. Figure 7.16 shows microhardness measured as a function of the radial distance, h, from the indent to the edge of the concave surface. The microhardness of the control sample H 57 MPa) does not vary with h. however, H for the hip cups, after implantation and removal from... 

Cox et al. [101] used several kinds of enhanced tubes to improve the performance of horizontal-tube multiple-effect plants for saline water conversion. Overall heat transfer coefficients (forced convection condensation inside and spray-film evaporation outside) were reported for tubes internally enhanced with circumferential V grooves (35 percent maximum increase in U) and protuberances produced by spiral indenting from the outside (4 percent increase). No increases were obtained with a knurled surface. Prince [102] obtained a 200 percent increase in U with internal circumferential ribs however, the outside (spray-film evaporation) was also enhanced. Luu and Bergles [15] reported data for enhanced condensation of R-113 in tubes with helical repeated-rib internal roughness. Average coefficients were increased 80 percent above smooth-tube values. Coefficients with deep spirally fluted tubes (envelope diameter basis) were increased by 50 percent. 

The rollers themselves or pockets and indentations that are machined into the working surfaces of the rolls form compacts or briquettes. Between smooth, fluted, corrugated, or waffled rollers, material is compacted into dense sheets (Fig. 8.118, see also Chapter 6, Fig. 6.5, lower left). Normally, these sheets are crushed and screened to yield a granular product. This process is called compaction/granulation. If the two rollers carry rows of identical pockets or moulds and the rolls are timed such that the pockets, representing roughly one half of the final product shape, match exactly (Fig. 8.119), so called briquettes are produced (see also Chapter 6, Fig. 6.5, lower right). 

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