Abradability defined

In our opinion, a general definition of hardness should be by hardness we define the resistance offered by a given material to external mechanical action endeavouring to scratch, abrade, indent or in any other way affect... 

For laboratory tests to determine tooth wear, typically a test specimen is subjected to an exaggerated wear regime, involving contact with the abradant (e.g. dentifrice slurry or restorative material sample) or erodent (e.g. acidic beverage) of interest, and wear is measured after a specific number of loading cycles or after a defined contact time. The tests are often designed to maximise wear within a short period of time, and therefore discriminate between products, rather than accurately mimic the oral environment. 

To examine dentifrice abrasivity, the most widely used methods are the radiotracer [13, 14] and profilometry methods [15, 16], In the radiotracer technique [14], samples of either enamel or dentine from extracted human teeth are exposed to a radiation source. The radioactive samples are then brushed with a slurry of the test dentifrice in a brushing simulator under defined conditions of loading, slurry concentration and number of cycles. The abrasion is measured by assessing the radioactivity of the resulting slurry following the test, which therefore gives a measure of the amount of material abraded from the enamel or dentine surface. A standard reference abrasive (usually calcium pyrophosphate or calcium carbonate) is also tested using the same conditions and the abrasivity... 

The cradle of glassmaking is difficult to define, both concerning the date and the place of birth of this new invention. Northern Mesopotamia at a time prior to 2500 BC is an estimation shared by many experts. At first, decorative objects and glass beads had been hand-formed or cast using simple tools and finished by abrading. Later on, glass was moulded or pressed to form vessels. 

Weight or volume loss can be related to unit distance travelled over the abradant, per 1000 cycles or whatever is convenient. If comparison is then made with a reference material, an abrasion resistance index can be defined by... 

Defined lesions were formed in rats by abrading the surface of the uterine horn and the adjacent sidewall. The injured tissues were kept in close proximity to each other by suturing the uterine horn to the side wall (Leach, 1990 Rice, 1993). Application of formulations containing poloxamer 407 to the injured tissues reduced adhesion formation by 30% to 55%. 

Hardness H defines the resistance to local deformation of a material when indented, drilled, sawed, or abraded. It involves a complex combination of properties (elastic modulus, yield strength, strain-hardening capacity). The prevailing deformation mechanism depends upon the material and the type of tester. Hardness is either measured by (1) static penetration of the specimen with a standard inden-ter at a known force, (2) dynamic reboimd of a standard indenter of known mass dropped from a standard height, or (3) scratching with a standard pointed tool under a load. The hardness tester, indenter shape, and force employed strongly influence the hardness numbers (1). 

Resistance to abrasion is defined as the ability of a material to withstand mechanical action that tends to progressively remove material from its surface. Abrasion resistance of polymeric materials is a complex subject. The resistance to abrasion is closely related to other factors such as hardness, resiliency and the type and amount of added fillers and additives. Resistance to abrasion depends on factors such as test conditions, type of abradant and development and dissipation of heat during the test cycle. This all makes abrasion a difficult mechanical property to define as well as to measure adequately. 

Another surface property of paper is the abrasion resistance. The mechanical abrasion resistance of surfaces is determined in the friction wheel process (DIN 53 109-93). In this process, the amount of abrasion which is obtained by abrading the conditioned or wet sample with an abrasion wheel of defined quality under defined conditions is measured. 

General Description. Abrasive wear is defined as wear due to hard particles or hard protuberances forced against and moving along a solid surface. This form of wear in metals is most frequently caused by non-metallic materials, but metallic particles can also cause abrasion. Generally, a material is seriously abraded or scratched only by a particle harder than itself. Figure 4 shows the damage caused on the surface of a soft copper substrate abraded by a hard ceramic particle. 

Low-stress abrasion (scratching) is defined as wear that occurs clue to relatively light rubbing contact of abrasive particles with the metal. The criteria established for low-stress abrasion is that the forces must be low enough to prevent crushing of the abradant. Wear scars usually show scratches, and the amount of subsurface deformation is minimal. Consequently, the surface does not work harden appreciably. Parts such as screens, chute liners, blades, and belts that are exposed to sand slurries or abrasive atmospheres could experience low-stress abrasion. Many machine components such as bushings, seals, and chains that operate in dust will wear by low-stress abrasion. Figure 6(a) shows a siuface that was subjected to low-stress abrasion. 

Despite the present early stage of comprehension, a direct relationship between the volume of abraded material AV and the coefficient of sliding friction f has been shown to exist for rubberlike materials. One of the more common Indicators of wear is the energy index of abrasion. Kg, which is defined as follows ... 

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