Determination hardness

For all design temperatures, the maximum hardness shall be Rockwell C35 immediately under the thread roots. The hardness shall be taken on a flat area at least 3 mm ( A in) across, prepared by removing threads. No more material than necessary shall be removed to prepare the area. Hardness determination shall be made at the same frequency as tensile tests. 

A problem exists with this procedure, however, in that at basic pH values, many metal ions precipitate as the hydroxide, e.g., Mg(OH)2, and thus would be lost to the analysis. This occurs with the magnesium in the water hardness procedure alluded to earlier. Luckily, a happy medium exists. At pH =10, the reaction of the metal ion with the predominant HY - and Y4- species (Figure 5.21) is shifted sufficiently to the right for the quantitative requirement to be fulfilled, while at the same time the solution is not basic enough for the magnesium ions to precipitate appreciably. Thus, all solutions in the reaction flask in the water hardness determination are buffered at pH = 10, meaning that a conjugate acid-base pair... 

Heat aging Exposure of polymeric materials under specified conditions (temperature, time, presence or absence of air or oxygen, etc.), then testing them in stress-strain and hardness, determining the change of properties in comparison to the original (unaged materials). 

Indentation hardness determinations were performed in dynamic mode ( 1500 mm/sec impact speed) using a pendulum impact device and in quasistatic mode ( 0.008 mm/sec impact speed) with a custom-built indentation tester. The spherical indenters were of 2.54 cm diameter and 65.6 g mass, and the pendulum length was 92.3 cm with a release angle of 30°. Quasistatic indentation forces were selected to produce indentations of a similar size to the dynamic indentation test (1.5 to 2.0 mm radius). The compact indentations were measured using a white light interferometer (Zygo Corporation, Middlefield, Connecticut, U.S.A.) and the dent depth, dent diameter, apparent radius of curvature, and pendulum initial and rebound heights were used to calculate the indentation hardness of the compacts. 

Solutions Used in Hardness Determination. Standard Solution. It is prepared from a mixture of 0.1 N solutions of calcium and magnesiiun salts in the ratio 3 1. 

The simplest check on cure is by a hardness determination which is to be done after the vulcanizate is sufficiently cooled to room temperature and the test is done better after 24 hours of cure. 

Hardness determination methods find wide uses in basic research on the mechanical properties of minerals and their deformation. In the face of the rapid development of industrial uses of natural minerals, as well as manmade, in monocrystal or grain form or as polymineral materials, there is a definite need for more comprehensive crystallomechanical investigations. Apart from the above aspects, hardness determination should furnish valuable information on the genesis of minerals. These authors consider that it would well serve the purpose to examine the mechanical properties of all minerals so as to obtain their allround crystallomechanical characterization and to investigate into their anisotropy and relationship to the structure and composition of minerals. By determining the typomorphism of the mechanical parameters of minerals and its involvement in the conditions of their formation, and also by investigating the specificity of occurrence of deformations in minerals under natural conditions and of the deformative mechanism, it should be possible to develop a general theory of mechanical properties of crystals. 

Wallerius in 1747 used a finger nail, knife, file or diamond powder for hardness determination. Werner in 1774 rubbed a mineral against a finger nail, knife or piece of steel to determine the quantities of powder thus derived. Hatty (1801) used calcite and quartz as well as glass for this purpose. The first arbitrarily chosen scale of hardness, containing exclusively minerals, was devised in Sweden by Kvist in 1768. It covered diamond—20, topaz—15, zeolite—13, quartz—11, fluorite—7, calcite—6, gypsum—5 and chalk—2. 

A further development of static methods of hardness testing was a method devised by Brinell (1900), which consisted of driving a steel ball into the mineral to be tested for hardness under a pressure of 29.4 kN for about 30 seconds. Brinell hardness is defined as the ratio of load to surface of round indentation. The method has found wide use in engineering—for metals it is excellent, but in mineralogy it has proved unsatisfactory because of the high brittleness of most minerals and their non-deformability under the action of the steel ball. The ever wider application of Brinell s method and of a similar method developed by Janko in hardness determination of wood (Krzysik, 1974) should be noted. They are most useful in testing hard wood-base materials, such as compressed wood. 

A device called a sclerometer constructed by Seebeck in 1833 has contributed to a significant advancement of the scratch method of hardness determination. Over the years, the instrument has been steadily perfected. 

The name assigned in metallurgy to the scratch method of hardness determination. 

The physical meaning of hardness determined by Bierbaum s method is exactly equal to load P divided by the projected contact surface of pyramid with material under test in the scratch process. It should be mentioned here that the result obtained under Bierbaum s method is roughly directly proportional to the hardness number obtained by the pyramid indenter method, and the relation has the form... 

Khrushchev (1957) considers that the need to measure the force T has not been sufficiently well substantiated, nor has a sufficiently precise and easy in service hardness tester been developed yet for determinations of this type. However, he appreciates the usefulness of scratch hardness tests, especially at low loads, as a non-destructive technique. He recommends these methods as very useful for hardness determination of metallic layers or of materials exposed to abrasive wear under operating conditions (plastics, organic coatings, such as varnishes and paints, etc.). Scratch methods are especially important in tests of anisotropic materials where a change in scratch width is the measure of anisotropy. In static indentation methods, the indentations obtained in anisotropic materials are misformed, varying... 

Of the methods discussed above, the Brinell method is particularly useful in hardness determination of metals and soft materials of heterogeneous structure, but its drawback is that it leaves distinct postmeasurement deformation and the measurement of indent diameter and depth is difficult. 

Mineral Grain size, No. (mm) Hardness, on Mohs scale //M Hardness determined by Knoop method HK Cleav- ability Degree of brittleness... 

Included in the most popular test methods in this group is hardness determination with the Shore sclerometer. Dynamic hardness (HSb) is taken as the criterion in estimating the comminution resistance of brittle bodies, and it has found wide use in the study of the mechanical properties of rocks. The method consists of lowering a beater terminating in a diamond ball onto the surface under test (Fig. 4.4.20) and measuring the... 

Hardness determined by j Hardness determined by inden-scratch and abrasion methods I tation methods... 

Vickers hardness determination with correction for degree of brittleness and converted to hardness classes, compared with quartz grain dynamic abrasion hardness, for example, of microcrystalline steatitic ceramics... 

Manufacturer (country) Glaze hardness Hardness determined with Mackensen blower (sand), 28 cm3 chamber on glazed surface ... 

Knoop hardness determined at indenter loading 981 mN for selected hard materials... 

Kuritsina A. G., 1967, Metodika opredeleniya mikrotverdosti plastmass na pribore PMT-3 (Hardness Determination Methods for Plastics with PMT-3 Tester), Zavod. Lab., 33 (8), 1009-1010. 

Szymanski A., 1972, Okreslenie twardosci mineralow i skal naturalnych i syntetyeznych (Hardness determination in minerals and natural and synthetic rocks), Post, nauk geol., 4. 

There is a trend in commercial testing of product quality to introduce non-destructive methods, in other words, tests that leave no defects in the tested materials that would affect their working properties. The use of these methods not only spares products but also permits more frequent testing, and gives better product quality control. This should be considered in the choice of hardness determination method. 

Also used for hardness determination are impact abrasion and rattle methods. In impact abrasion methods (impact abrasion hardness), three abrasive techniques are used a freely falling abrasive grain flow—the Scott tower method (Fig. 4.4.3a and b), pressure abrasion—the Macken-sen-Zeiss blower method (Fig. 4.4.7), and ultrasonic drilling—the Sonic Mill method (Fig. 4.4.18). 

Moreover, the accuracy in calculating the hardness of a mineral from crystallochemical data, both in relation to Mohs numbers and Khrushchev hardness classes, follows from Table 4.2.2. The hardness classes proposed by Khrushchev are sometimes described as absolute hardness (Bolewski, 1963 Hurlbut and Klein, 1977), which in our view does not appear justifiable, since with the hardness determination results, the conditions in which the measurement has been made are not specified, and in interpreting the results, corrections consequent upon deformations of the indent caused by hardness anisotropy or by brittleness are not considered. 

In hardness determination by the scratch method, the results can be produced in three ways ... 

Some investigators believe that the best course to follow in scratch hardness determination is to find the tangential force acting on the surface of material under test required to obtain a scratch of width b. In this case, hardness is expressed as the ratio of that force to the scratch cross-section or a magnitude proportional to it, or else as a quotient of the work necessary to produce the scratch and its volume. Proponents of this method (Yushkin, 1971) consider that scratch hardness tests in the present form play only a marginal role. Unlike Shreyner (1949), who contended that the results obtained under these methods are less accurate than those for mineral-bymineral scratch after Mohs, they accept that these tests have certain usefulness, but only of a complementary nature. The differences of opinion arise from the different approach to the question of accuracy of the method of determination itself, since as can readily be proved, a strict relationship exists between hardness defined as the ratio of load P to square of... 

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