Indentation representative strain

The slope A or A is an adjustable parameter for fitting to measurements, which represents both the intrinsic properties and the extrinsic artifacts such as defects, the pileup of dislocations, shapes of indentation tips, strain rates, load scales, and directions in the test. The and b correspond, respectively, to the shear modulus and the Burger s vector modulus reduced by atomic size, d. The bulk modulus B is related to the shear modulus and the Poisson ratio vhy — B/[2(l -I- v)]. Using the dimensionless form of the normalized, yield strength aims to minimizing the contribution from artifacts due to processing conditions, crystal orientations, and the purity of the specimens if the measurement is conducted under the identical conditions throughout the course of the experiment. For convenience, we use both X = K and K as indicators of the dimensionless form of sizes. 

In ceramics, the extent of plasticity caused by dislocation, when tension tests are performed, is limited and very often accompanied by microcracking. Many of the tests are consequently performed by low-load indentation, such as microindentation, where the indenter may be focused on a grain. Nevertheless, other testing methods are also used. In the figure below, the stress-strain curves represent compressions at a constant strain rate at several temperatures starting with RT and up to 1423 K (Fig. 5.2). 

The //r-value of CZP increased with a decrease in hp as shown in Fig.3. Also, the grain size dependence of Hj was hardly observed in CZP. Moreover, the Ht-value of a cubic zirconia single crystal as a function of hp was superimposed just on that of CZP (see Fig.3). According to the theory of the strain gradient plasticity, " in which the building-up of geometrically necessary dislocations under an indentation was modeled, the indentation size dependence of hardness is represented as follows. 

When indenting a sample, a plastic zone is generated and surroimded by the undeformed solid. Hence, a plastic strain gradient remains in the specimens after unloading. The representative indentation strain Er is defined as (Tabor, 1951 Johnson, 1985)... 

Figure H.5 (a) FIB-TEM cross-sectional view percentage. The dark area drawn on the of an indented brittle semiconductor (AlAs/ graph represents the material punched into GaAs superlattice) (b) strain contours as the sample (residual indentation), obtained from (a). Strain values are given in...

Indentation with a conical tip allows determination of the representative flow stress Tr at the representative indentation strain Cr. Following Johnson s model, Harvey et al. (1993) and Kramer et al. (1999) suggested that the representative flow stress Tr of a material could be determined measuring the plastic zone... 

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