Vicker’s hardness

Brinell and Vicker s hardness numbers are comparable upto value of about 300. For higher hardness materials than this the Brinell values are slightly lower than HD numerals for the same material. 

Hardness (annealed condition) Vicker s hardness number 41... 

The particle shape was determined by visual inspection of the particles. To determine the particle diameter xp, the volume of individual particles was measured in a He-pycnometer and the diameter of the sphere possessing the same volume was calculated. The solid density /0p was measured in the He-pycnometer as well. The Vicker s hardness //y was determined in a microhardness tester while Young s modulus E and yield stress ay were given by the manufacturer. Finally, the J-integral value Jqci which... 

One of the most important tasks in the determination of the material function is to identify those material properties relevant to attrition formation. A comparison of the above results to classic mechanical material properties, e g. Young s modulus E or Vicker s hardness Hy as given in Table 1 suggests that these are not suitable to describe attrition formation. 

Table 4.1. Average Vicker s hardness and percent improvement of 2 wt% NT-NC/epoxy composites with different NT-NC concentration. Reprinted with permission from ref (62).

Sample Average Vicker s hardness no. Percent improvement (%)... 

The pore volume increased as the HTT temperature was raised. This is reasonable considering the mechanism of HTT. However, the strength of the interparticle binding is smaller at the beginning but rises above 100°C as seen in the Vicker s hardness per particle contact point in Fig. 4 in which the curve shows a mild HTT below 100°C. 

Figure 4. The Vicker s hardness per interparticle contact point versus the HTT temperature.

Vicker s hardness number (VHN). Hardness on Rockwell and Brinell scales are also reported for metals and alloys. In both KHN and VHN measurements, the approach is to make an indentation on the surface of the sample using a diamond micro-indenter. In the Vicker s method the indenter has the shape of a square pyramid, while in the Knoop s method it has the shape of an elongated pyramid. The indentation is generally of the order of few microns and a load of 5 to 1000 gm are used (in order to determine fracture toughness, it becomes necessary to use higher values of load (due to the necessity of initiating cracks)), VHN is given by. 

The modulus of rupture and the Vicker s hardness were measured at room temperature using a LR 30K machine (Lloyd Instruments, UK) and M-type microhardness-tester (Shimadzu, Japan), respectively. 

Table 3. Vicker s hardness of glass-ceramic layers ( 100 gm) deposited onto the surface of various solid-electrolyte ceramics under conditions, identical to sealing conditions...

The alternative approach used in published studies has been to determine the micro-hardness at varying depths [18,19], an approach that assumes the existence of a correlation between micro-hardness and degree of conversion (DC) of monomer to polymer. Studies using this approach have shown that depth of cure does not correlate well with measurements made using a proper hardness measurement technique, in this case Vicker s hardness [20], In particular, for the so-called bulk fiU materials the ISO 4049 method, which involves scarping away unset material from the base of a cylinder of composite that has been exposed to light from the top, was found to overestimate the depth of cure compared to that determined from Vickers hardness number. 

Physical and chemical properties of Biodentine are shown in Table 9.8. The material can be seen to set rapidly, and to have a reasonable compressive strength and Vicker s Hardness Number at 24h [85,86]. It shows a snbstantial wash out (solubility) in Hank s balanced salt solution (HBSS), which is presumably at least matched in deionized water. However, the pH of deionized water following storage of set Biodentine is only around 9 at 24h, rather than the 11-12.5 of traditional calcium hydroxide chelate cements or supersaturated solution. This may suggest that Biodentine is less bioactive than such materials, and hence less effective at promoting the growth of reparative dentine. 

FIGURE 14. Vicker s hardness, as a function of sintering time at 1920°( (Reprinted with permission of The American Ceramic Society, www.ceramics.org. Copyright [2001]. All rights reserved.)... 

Rockwell s hardness test works in a similar way to Brinell s hardness test, i.e., it uses the depth of penetration. Contrary to Brinell s method, however, it measures the penetration of a sphere while still under a load, and then measures the remaining elastic deformation. For this reason, the Rockwell method always gives lower degrees of hardness than the Brinell method. In addition, the degrees of hardness according to the Rockwell method are not measured in physical units, but in scale numbers of 0-120. Steel balls are used with soft materials, and diamond points with hard ones. The Vicker s hardness test uses a diamond pyramid. A modified Rockwell method is used for plastics. It should be noted that, with the Rockwell hardness thus determined, the plastic deformation contribution increases only gradually, because of creep. With metals, on the other hand, the deformation is always plastic, and therefore, also independent of time. Plastics, therefore, exhibit a relatively high Rockwell hardness compared to metals. 

The mechanism of material removal in abrasive machining of brittle ceramics has been well documented by Evans and Marshall who developed the lateral-crack chipping model. They demonstrated that material removal rate, AT caused by a passage of each grinding particle is related to the peak normal penetration forces, Fn, Vicker s hardness and fracture resistance as follows, ... 

Figure 5. NPm versus Vicker s hardness obtained at a load of 98 N. Error bars are 1 standard deviation.

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