Hardness micro tests

Morgans et al61 carried out comprehensive trials to compare the IRHD and Shore micro tests concluding that the IRHD was better for very small test pieces but the Shore better for bent test pieces. They also note the fact that the Shore test is not totally non-destructive. This work was continued to include the normal IRHD and Shore A scales and to consider curved surfaces62. The results are a good illustration of the differences in measured hardness that can be found between different instruments with variation of test piece geometry. 

Tate D. R., 1945, A comparison of micro-hardness indentation tests, Trans. Am. Soc. Metals, 35, 374-389. 

The normal tests use indentors with dimensions of the order of mm, but there are also micro tests that are scaled down by approximately an order of magnitude and allow thinner test pieces to be used and, on rigid materials, produce less damage. With rubbers hardness test are essentially nondestructive. A review of micro tests has been given by-Lopez [5]. 

Procedure I. A few grains of the powdered substance are placed in a micro test tube of hard glass or, alternatively, a drop of the test solution is evaporated to dryness in the tube. Several mg of ignited lime are mixed in and the tube is heated, gently at first, and finally to redness for a few minutes. After cooling, a 10-15-fold excess of sodium formate is added and the open end of the test tube is covered with a disk of filter paper moistened with 10 % silver nitrate solution. The tube is heated until its contents turn slightly brown. A positive response is shown by the formation of a dark or brown circle on the paper. 

The hardness of carbides can only be deterrnined by micro methods because of britdeness, the usual macro tests caimot be used. Neither can the extremely high melting points of the carbides be readily deterrnined by the usual methods. In the so-called Priani hole method, a small hoUow rod is placed between two electrodes and heated by direct current until a Hquid drop appears in the cavity. The temperature is determined pyrometricaHy. When high temperature tungsten tube furnaces are used, the melting point can readily be estimated by the Seger-type cone method. The sample may also be fused in a KroU arc furnace and the solidification temperature determined. 

Perhaps the most significant complication in the interpretation of nanoscale adhesion and mechanical properties measurements is the fact that the contact sizes are below the optical limit ( 1 t,im). Macroscopic adhesion studies and mechanical property measurements often rely on optical observations of the contact, and many of the contact mechanics models are formulated around direct measurement of the contact area or radius as a function of experimentally controlled parameters, such as load or displacement. In studies of colloids, scanning electron microscopy (SEM) has been used to view particle/surface contact sizes from the side to measure contact radius [3]. However, such a configuration is not easily employed in AFM and nanoindentation studies, and undesirable surface interactions from charging or contamination may arise. For adhesion studies (e.g. Johnson-Kendall-Roberts (JKR) [4] and probe-tack tests [5,6]), the probe/sample contact area is monitored as a function of load or displacement. This allows evaluation of load/area or even stress/strain response [7] as well as comparison to and development of contact mechanics theories. Area measurements are also important in traditional indentation experiments, where hardness is determined by measuring the residual contact area of the deformation optically [8J. For micro- and nanoscale studies, the dimensions of both the contact and residual deformation (if any) are below the optical limit. 

Vickers and Knoop Micro Hardness Tests, British Standard 5411 Part 6 1981... 

After the micro wear tests, the dependence of worn depth of PTFE and PTFE/Si3N4 film on load is shown in Fig. 13. The worn depth of both PTFE and PTFE/Si3N4 film is in the nanometer scale. It can be seen that the worn depth increases linearly with load. However, the worn depth of PTFE/Si3N4 multilayers is about one-tenth of PTFE film at the same load. All these results demonstrate that the wear resistance of PTFE/Si3N4 multilayers is greatly improved after micro-assembling of soft and hard layers. 

As a kind of specialty solutions for the real hard cases where fouling is intense and unavoidable, IMM first proposed ideas to develop special micro mixers for fouling-intense reactions and conducted feasibility tests, among them very fast organic reactions with spontaneous precipitation such as the amidation of acetyl chloride in THF [134]. The Forschimgszentrum Karlsruhe developed special anti-foul-ing coatings in cooperation with partners [135]. 

A growing number of research groups are active in the field. The activity of reforming catalysts has been improved and a number of test reactors for fuel partial oxidation, reforming, water-gas shift, and selective oxidation reactions were described however, hardly any commercial micro-channel reformers have been reported. Obviously, the developments are still inhibited by a multitude of technical problems, before coming to commercialization. Concerning reformer developments with small-scale, but not micro-channel-based reformers, the first companies have been formed in the meantime (see, e.g., ) and reformers of large capacity for non-stationary household applications are on the market. 

All conventional reactors, tested before using the micro reactor (simply since micro reactors were hardly available at that time), only fulfilled the demands of one measure, at the expense of the other measures. For instance, a single-tube reactor can be operated nearly isothermally, but the performance of the oxidative dehydrogenation suffers from a too long residence time. A short shell-and-tube reactor provides much shorter residence times at improved heat transfer, which however is still not as good as in the micro reactor. 

B. W. Mott, Micro-indentation Hardness Testing, p. 247, Butterworths Scientific Publications, London, UK (1956). 

Tensile testing or a hardness test is a basic requirement of most metal specifications. Some product specifications also require impact-testing, bend and other ductility tests, proof testing, flange or flare tests. The size of the sample may limit which tests can be performed. Macro, superficial, and micro-hardness tests are routinely done in failure analysis even if the original product specification did not require them. 

Mohs hardness is a measure of the relative hardness and resistance to scratching between minerals. Other hardness scales rely on the ability to create an indentation into the tested mineral (such as the Rockwell, Vickers, and Brinell hardness - these are used mainly to determine hardness in metals and metal alloys). The scratch hardness is related to the breaking of the chemical bonds in the material, creation of micro fractures on the surface, or displacing atoms in the metals of the mineral. Generally, minerals with covalent bonds are the hardest while minerals with ionic, metallic, or van der Waals bonding are much softer. 

Mott B. W., 1960, Micro-Indentation Hardness Testing, Butterwords, London. 

Bergsman E. B., 1946, Micro-hardness testing. Description of a technique developed in Sweden, MetaI Ind., London, 69, 6, 109-112. 

Taylor E. W., 1948, Micro-Hardness testing of metals, J. Inst. Metals, 74, 10, 493-500. 

Fig. 8. Result of hardness tests on a series of TiX alloys (where X is a combination of Fe, Co, and Ni). Diamond pyramid indenter in a standard Tukon micro hardness tester was used.

A range of functionalized and unfunctionalized self-assembling fibrous structures have been tested for their biocompatibility and ability to provide cells with a favorable micro- and nanoenvironments for soft tissue engineering. In this section, studies that focus on amyloid fibrils, on peptide amphi-philes, on ionic complementary peptides, and on dipeptide structures are reviewed. Hard tissue engineering, composites, and coating are also explored followed by macroscopic structures and networks that can be created from fibrous protein structures. 

Hardness measurements were made at 23 °C on 500 Angstroms gold-decorated epoxy square plates (2.50 cm by 2.50 cm, 2.00 mm thick) using a Leitz miniload micro-hardness tester, supplied by Ernst Leitz Company, Midland, Ontario, Canada. A load of 200 g was applied to the specimen. Experiments were done in accordance to ASTM D-785 and ASTM D-1706 test procedures. 

Figure 12.4 depicts the correlation between instrumental texture measured by the force required in a penetration test of cooked beans and the micro structure of hard and soft cotyledons. Individuals also discriminate between hard and soft beans as they are compressed between molars. In soft beans, individual cells, whose middle lamella have been dissolved during cooking, slide one past another during compression. Hard beans with rmdissolved cell walls cells feel tougher because they are fractured across the cotyledons. Think of how effortless it would be to tear down a brick wall that had no mortar binding the bricks. 

Texture determination textural properties of starch gels were determined using a TA-XT2 texture analyzer (Stable Micro Systems, Scarsdale, NY, USA). A textural profile analysis (TPA) test was performed using a 0.50 S sphere (0.5 in. diameter) probe on gels equilibrated to room temperature to measure hardness and adhesiveness. Only the samples with starch concentration of 10% (% s/w) could be analyzed because they had a texture that fell within the detectability limit of the instrument. At least ten replicates were rim for each gel. 

The plastic strains are measured by means of point marking method. The markings with 1 mm interval in a direction of tensile axis were made by a micro-vickers hardness tester before tensile tests. Tensile tests were conducted at room temperature at a cross-head rate of 0.5 mm/min with an Instron-type testing machine. After the tensile deformation, the relative displacements between markings were measured under a precision machinery microscope, and the corresponding local strains in the direction of tensile axis were calculated. Then deformed specimens were cut into pieces of 1 mm width by a low speed cutter perpendicular to the tensile axis. The saturation magnetization of each piece was measured by magnetic balance at room temperature. 

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