Indentation measurements

Rockwell. The invention of the Rockwed hardness tester in 1919 was an advance over previous indentation tests requiring accurate indentation measurement and tabular reduction to derive a hardness number. In the Rockwed test the hardness number is read direcdy from the instmment dial (1,3). 

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). 

Surface finish requirements for the Vickers test vary with the test load. Heavy load tests can be made on a 120 grit ground surface. At low loads increasingly finer surface preparation is required, approaching that for metaHographic specimens, to permit accurate diamond indentation measurements. 

VanLandingham, M.R., The effect of instrumental uncertainties on AFM indentation measurements. Microsc. Today, 97, 12-15 (1997). 

The mechanism by which the spring pressure is applied and the indentation measured varies, but Figure 8.6 shows, as an example, the principle of the IRHD meter. The type A meter uses an indentor in the form... 

Knoop F., Peters C. G., Emerson W. B., 1939, A sensitive pyramidal-diamond tool for indentation measurements, J. Research. NBS, 23, 39-61. 

Indentation measurement a measuring mechanism of the ocular micrometer allows measurements in the field of the indentation image. 

The craze length derived from microhardness indentation measurements has been compared with the length measured by interference optics. An enlarged section of Fig. 3.15 is shown in Fig. 3.16(a). Figure 3.16(/ ) shows the contour of the same craze measured by optical interferometry. It is seen that the craze length derived... 

One of the most simple approaches to analyze indentation measurements is based on Hertz theory. We discuss below an example reported by the Radmacher group on gelatin films (Fig. 4.20) [46]. 

The slope of a force curve on an infinitely stiff substrate is by definition one thus, the deflection equals the piezo z travel. In measurements of soft samples, the deflection is reduced by the indentation 8. Thus, employing the cantilever force constant k (which must be chosen appropriately in AFM indentation measurements),... 

For the practitioner, indentation measurements provide insight into essential dynamic processes of hardening of paints and coating, among others. In addition,... 

Then the AFM is switched to CM-operation, which may require a slight adjustment of the photodiode position. The indentation measurements are carried out at specified location (using the offset function of the scan menu) as detailed in hands-on example 43. 

In the f-d/indentation measurements discussed in the previous sections, one can also analyze the part of the curves corresponding to tip-sample contact as a function of sample temperature and loading rate ( frequency). At the glass transition temperature, the modulus will change by several orders of magnitude. Hence, the Tg in... 

Knoop hardness values of about 50 GPa for cBN and 25 GPa for amorphous BN (aBN) films were reported by Murakawa et al. [72]. From nanometer indentation measurements hardness H) and Young s modulus ( ) were derived for different sputter deposited cBN films (thickness some 100 nm) [54,55,73]. The hardness values ranged between 60 and 80 GPa which is close to the bulk hardness of cBN (up to 90 GPa [1]). On the other hand the Young s moduli, E, in the range 300-600 GPa, are lower than the cBN bulk values (800-900 GPa) [1]. Mirkarimi et al. [73] explain this discrepancy by substrate effects which decrease with increasing film thickness. 

In atomic force microscopy (AFM) indentation measurements, thin films of Ca " -PA gels displayed an apparent elastic modulus of 200 MPa, whereas HCl-PA gels had an elastic modulus of 100 MPa (Fig. 5d) [168]. The mesh size of Ca " -PA gels was calculated according to the MacKintosh model for sterically entangled semiflexible networks. The persistence length and the mesh size were estimated to be 102 and 20 nm, respectively [182]. 

Atomic force microscopy has been combined with nano-indentation measurements to map hardness variations on the surface of a CaCOg-filled sample of PDMS. ° In another application, PDMS-modified tips were used to obtain friction coefficients involving self-assembled monolayers. ... 

Normal Forcos. In the treatment of normal forces, a differentiation into the measurement of adhesive forces, related to, eg, surface chemistry, quantification of entropic and enthalpic forces, dealing with single polymer chain properties, and finally indentation measurements, yielding surface mechanical properties, has been made. 

Indentation Measurements. Indentation force measurements utilize the indentation part of a f-d curve (compare Figs. 4 and 5). In the case of a noncom-pliant sample surface, the SFM tip does not indent significantly the sample, and hence the deflection vs piezo position curve in the contact region has a slope of 1.0. For compliant samples, the slope is <1.0 (Fig. 9) and can be used to obtain the elastic modulus of the sample by fitting the measured indentation to a suitable model. Knowledge of the tip shape/geometiy and elastic constants of the tip is required to obtain the desired materials properties. 

Characterization and evaluation of performance by means of the torsional pendulum technique has been discussed by Hussain Wierenga et al. have used ultramicro indentation measurements for the determination of the viscoelastic properties of coated optical fibers... 

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