Hardness, tests table

Hardness. Glass hardness tests usually measure the resistance to abrasion by grinding or grit-blasting, resistance to scratching, or penetration by an indenter. The method to be used depends on expected service conditions. Knoop hardness (Table 4) is commonly used, because other methods usually fracture the glass. 

Many types of hardness tests have been devised. The most common in use are the static indentation tests, eg, Brinell, Rockwell, and Vickers. Dynamic hardness tests involve the elastic response or rebound of a dropped indenter, eg, Scleroscope (Table 1). The approximate relationships among the various hardness tests are given in Table 2. 

Table 1. Hardness Tests Described by ASTM Standards...

This table shows the relationship between hardness testing scales, but should not be used for hardness converson. See ASTM E140 (2) for specific materials conversions. 

Table 3. Rockwell Hardness Testing Scale Designations...

Table 4. ASTM Standards Related to Hardness Testing ...

The Vickers hardness test is commonly made on a flat specimen on which the indenter is hydrauhcaHy loaded. When the desired number of indentations have been made, the specimen is removed and both diagonals of the indentations, measured using a caUbrated microscope, are then averaged. The Vickers hardness number may be calculated, or for standard loads taken from a precalculated table of indentation size vs VHN. The preferred procedures are described in ASTM E92 (2). 

MohsAn early (1822) hardness comparison test involved assigning a relative number to aH known materials (usuaHy minerals and pure metals) by virtue of their relative abHity to scratch one another. The results of this classification are not relatable to other properties of materials or to other measures of hardness. As a result of this limited useflilness, the Mohs hardness test is primarily used for mineral identification. Some examples of the Mohs hardness scale, which ranks materials from 1 to 10, are Hsted in Table 6. 

Despite variatioas ia hardness test procedures and the variations ia physical properties of the materials tested, hardness conversions from one test to another are possible (see ASTM E140 and Table 2). This approximate relationship is only consistent within a single-material system, eg, iron, steel, or aluminum. 

Many special appHcations of iadentation hardness testing techniques to unusual materials or conditions have been developed, some of which are hsted ia Table 4. 

Analysis of Table II shows discrepancies in the hardness and stress behavior of a-C(N) H films. Although all the works reported a clear stress reduction upon nitrogen incorporation, the hardness sometimes is quoted as almost constant, or on the other hand clearly decreasing. In addition to the possible effect of different deposition methods and conditions, it can be easily seen that the differences in hardness testing methods are the major source for discrepancies. Constant hardness behavior is only reported with the use microindentation methods, like Vickers and Knoop microhardness. On the other hand, the use of low-load nanoindentation methods always led to a nitrogen-induced decrease in hardness. This is basically the consequence of two factors. The first one is the higher penetration... 

Hardness testing limits after PWHT shall be per Table IP-10.5.7. Other hardness testing limits shall be based on the material specification and/or the engineering design. 

One simple hardness test is the Moh hardness test it is based on the fact that a harder material will scratch a softer material. Geologists and mineralogists frequently use this test. The Moh scale is an arbitrary scale of hardness based on the ability of ten selected minerals to scratch each other. The relative Moh hardness for several substances is given in Table 15.6. 

Table 15.8 compares selected hardness tests, showing scales, the indentor, and the major loads. 

The influence of fillers has been studied mostly at hl volume fractions (40-42). However, in addition, it is instructive to study low volume fractions in order to test conformity with theoretical predictions that certain mechanical properties should increase monotonlcally as the volume fraction of filler is Increased (43). For example, Einstein s treatment of fluids predicts a linear increase in viscosity with an increasing volume fraction of rigid spheres. For glassy materials related comparisons can be made by reference to properties which depend mainly on plastic deformation, such as yield stress or, more conveniently, indentation hardness. Measurements of Vickers hardness number were made after photopolymerization of the BIS-GMA recipe, detailed above, containing varying amounts of a sllanted silicate filler with particles of tens of microns. Contrary to expectation, a minimum value was obtained (44.45). for a volume fraction of 0.03-0.05 (Fig. 4). Subsequently, similar results (46) were obtained with all 5 other fillers tested (Table 1). 

The shore durometer is a simple instrument used to measure the resistance of a material to the penetration of a blunt needle. In the Barcol approach, a sharp indentor is used to measure the ability of a sample to resist penetration by the indentor (Figure 14.18). The values given in Table 14.3 are for one specific set of conditions and needle area for the Barcol and Brinell hardness tests. 

A small amt of the expl was spread on a large stone table and then struck a glancing blow with a mallet made either of rawhide or beech wood. The expl was thus subjected to the combined effect of shock and friction. If the sample exploded, the test was repeated by hitting the expl a glancing blow with a broomstick held at an angle of 60° against the table, taking care that the movement of the stick is in the direction of its axis. If an expin were obtd, the test was repeated on a hard wooden table and finally on a soft wooden one. If an expl, other than those used for caps, detonators, etc exploded, even partly on soft wood, it was considered to be too sensitive for use (Compare with Torpedo Friction Test, described as quantitative test i, Fi g F22)... 

Oven testing was performed using 0.4 g of a selected polymer sample that were dissolved in screening formulation (20.00 g) and then applied to white coil-coat aluminum and baked in an oven at 160°C for 30 minutes and a tack free dry film with a thickness of approximately 25 cm obtained. After curing for 45 minutes, the pendulum hardness testing was conducted and results summarized in Table 3. 

TABLE 3. Pendulum Hardness Testing Results for Cured Polymers Prepared Using Selected Dialkylthiocarbamic Acid Esters as Initiators... 

The tables given at the end of the book, as well as the hardness testing results by various methods included in the text itself, are meant to serve as a rough guide in the choice of an appropriate test method, whilst simultaneously providing the reader with reference details. 

The influence of atmospheric air on the properties of mineral materials manufactured in thermal processes is generally known. An example of the nature of this phenomenon as regards hardness, is a series of Vickers hardness tests of a material made of sintered corundum modified with 0.6% MgO sintered at 1950-2050 K in various environments. The sintering process is accelerated in the presence of hydrogen and is slowest in air thus allowing a material with optimum parameters to be obtained at a significantly lower temperature. The results, specified in Table 6.2.4, show the gases used as... 

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