Abrasive wear test methods

In addition to chemical analysis a number of physical and mechanical properties are employed to determine cemented carbide quaUty. Standard test methods employed by the iadustry for abrasive wear resistance, apparent grain size, apparent porosity, coercive force, compressive strength, density, fracture toughness, hardness, linear thermal expansion, magnetic permeabiUty, microstmcture, Poisson s ratio, transverse mpture strength, and Young s modulus are set forth by ASTM/ANSI and the ISO. 

The wear resistance of rubber compounds is of great practical importance for tires, but the mechanisms involved in tire wear are multiple and may vary depending on the vehicle, the driving conditions, and other extraneous variables. Many attempts have been made to develop laboratory test methods to simulate tire wear under various conditions. Whilst none can fully replicate road wear, various laboratory abrasion tests can be used to provide an indicator of wear resistance of tires under certain conditions. 

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... 

This opens up the possibility of linking the Mohs scale and related hardness test methods additionally to another group called abrasiveness tests. These include Bohme s, Scott s, Mackensen s and other methods which are dynamic hardness test methods unlike the previously mentioned static methods. In many cases they are more useful than static tests, since they resemble better the conditions under which wear of a material takes place during commercial use. 

Rattling method. In many countries, the United States in particular, the previously mentioned rattler test is used for measurement of abrasive wear of mouldings. In the United States, it is widely used for testing paving stone. By this method, data on abrasion resistance and also edge-preservation resistance (Fig. 4.4.19) are obtained. The rattling is carried in mills... 

For testing dental restorative materials, many regimes exist that use similar principles to those described for assessing toothpaste abrasivity. These tests may be conducted under conditions of two-body or three-body wear [25], i.e. focussing either on attrition or abrasion. Two-body tests for restorative materials either use human enamel [26] or a hard material, such as alumina [27] or steatite [28], as the abrader. For three-body tests, an abrasive medium, such as toothpaste slurry [29, 30], or an abrasive food, such as rice or millet seeds [31,32], is typically used. These test methods are usually not truly representative of the oral environment rather, they are designed to assess the wear resistance of restorative materials under extreme conditions. 

There is currently only one standard test method in ISO devoted to the measurement of abrasion resistance for plastics materials, this being the "Taber test standardized in ISO 9352 [101]. In this test a specimen is clamped onto a turntable that rotates at either 60 rev per min (where the electrical mains frequency is 50 Hz) or 72 rev per min (where the electrical mains frequency is 60 Hz) and weighted abrasive wheels press against the surface of the te.st piece. The center of rotation of the test piece is offset from the line of contact of the wheels, and so as the former is rotated this caiuses the wheels to rotate and to wear an annular track into the specimen surface. Figure 19 gives an illustration of the test piece... 

Hardness, scratch and abrasion resistance, and wear (friction) properties are characteristics which can be important for the selection of the most suitable material for a specific job. For the purpose of comparison, the designer must make sure that the data shown in the various charts have been produced using the same test methods. 

The determination of wearing is carried out according to CEN EN 12274-5 (2003). The test method determines the minimum binder content of the mix under wet track abrasion conditions. It also covers the compatibility between aggregate fillers and cationic bitumen emulsion. The test is similar to wet track abrasion loss described in ASTM D 3910 (2011), a brief description of which is given in Section 6.8.3.1. 

Wear cycles In abrasion resistance tests using the Taber Abraser, the number of cycles of abrasion required to wear a film of specified thickness through to the test plate under a specified set of test conditions (Federal Standard 141a, Method 6192). 

Significant research and developmental efforts have been placed to characterize and improve abrasion and wear resistance of polymers (2-5). However, advances in fundamental knowledge on abrasion and wear are limited mainly because of the complexity of the available test methods, such as the Taber abrasion test. No direct correlation between the applied loading conditions and the observed abrasion damage can be made. As a result, no definitive relationship between material parameters and abrasion resistance can be established. 

An objective comparison of the abrasion resistance of superhydrophobic surfaces has been hampered by the lack of a single, standardized test method. Likewise, no single measure has been used for characterizing the effect of wear. Moreover, all these different approaches induce very diverse surface topography modifications but at the same time all of them are referred as mechanical durability tests. This is very confusing for someone who wants to evaluate how durable is one surface compared to the other. Generally, abrasion resistance is most directly and commonly measured using linear shear abrasion. In this form, shear stress arises from the force vector component parallel to the cross section of the material. The most common approach, based on the number of published papers, for the evaluation of the mechanical durability of liquid repellent surfaces is... 

Currently, however, quantitative assessment of the mechanical durability of non-wetting surfaces is difficult due to the diversity of wear testing and characterization methods discussed above. Ideally, the evaluation techniques should be more standardized and possibly reduced in number, as this would be beneficial for focused efforts to develop resilient coatings. From all the techniques that we described above, there seem to be some of them that are more commonly accepted. Linear abrasion, for instance, seems to be a very well accepted and is a common method to evaluate the mechanical durability. Sand, water/jet and gas impact are also good techniques to evaluate the stability of the surfaces for outdoor applications. Nevertheless, the range of possible applications for super hydrophobic surfaces may call for specialized mechanical tests like laundry tests, finger touch, etc. 

Abrasion resistance is another complex area. One of the reasons for confusion is that the various test methods do not agree well with each other. There is a perception that hard surfaces lead to the best abrasion resistance, however, that does not jibe with the facts. In actuality, it is elastomeric surfaces that have excellent abrasion resistance. Look, for example, at rubber car tires and PVC flooring, which is always coaled with a polyurethane elastomer layer to provide wear resistance. Elastomers deform and spring back undamaged, so scratch and wear resistance is good [17]. 

The wear resistance of refractories is determined according to ASTM C-704-01 [56]. This test method measures the relative abrasion resistance of various refractory samples under standard conditions at room temperature. The abrasion resistance of a refractory material provides an indication of its suitability for service in abrasion or erosive environments. 

Test methods such as ASTM D 1044 (resistance of transparent plastic materials to abrasion) are also developed for estimating the resistance of transparent plastic materials to one kind of abrasion by measurement of its optical affects. The test is carried out in similar manner to that described above, except that 100 cycles with a 500-g load is normally used. A photoelectric photometer is used to measure the light scattered by abraded track. The percentage of the transmitted light that is diffused by the abraded specimens is reported as a test result. Test method ISO 9352 describes resistance to wear by abrasive wheels. 

Abrasive wear, 2-body 0 56 Test Method for Abrasiveness of Ink-Impregnated Fabric Printer Ribbon Surface profiling or other method... 

Abrasive wear, 3-body 0 65 Test Method for Measuring Abrasion Using the Dry Sand/Rubber Wheel Apparatus Mass loss... 

Erosive wear, slurry 0 75 Test Method for Determination of Slurry Abrasivity (Miller Number) and Slurry Abrasion Resistance Response of Materials (SAR Nomber) Mass loss... 

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