Indentation creep

The analysis of indentation creep data as an important aspect of material characterization. 

Fig. 4.200 Schematic load-time, depth-time and load-depth curves for indentation creep (a, c) and indentation relaxation (b, d) tests.

Indentation creep parameter Cit Ctt — Relative change of indentation depth at constant test load. 

Bae Beake, B. Modelling indentation creep of polymers a phenomenological approach. J. Phys. D 39 (2006) 4478 85. 

Figure 4.11. Anisotropic rates of indentation creep in magnesia. After Brookes. ...

Figure 6.8. Hardness of cubic BN at 500°C showing an indentation creep effect and comparing it to some single crystal data for alumina and silicon. ...

The work hardening demonstrated by the slider experiments clearly shows the effect of dislocation mobility on this rock-salt-structure material, and it is not unexpected to find much evidence for a load hardness effect with a range of n values at room temperature depending on plane and direction this is shown in Table 4.3. Dislocation mobility under the influence of the stress fields found in indentation hardening also manifests itself as an indentation creep effect as shown in Figure 4.11. 

In some systems, increasing the dwell time —that is, the time over which the full load is applied to the surface—results in an increase in the size of the indentation and hence an apparent reduction in the hardness of the material. This effect is called indentation creep. 

Anomalous indentation creep. This has been observed at room temperature in ceramic materials when light loads are used. It is called... 

The results for aggregated BN cubic crystals shown in Figure 6.8 demonstrate a surprisingly high rate of indentation creep (see Section 4.4) at such a low homologous temperature—i.e., 0.2T . 

J P. Guin, T. Rouxel, V. Keryvin, J C. Sangleboeuf, I. Serre, J. Lucas, Indentation creep of Ge Se chalcogenide glasses below Tg elastic recovery and non Newtonian flow, J. Non cryst. Sol., 298, 260 269 (2002). 

W.T. Han and M. Tomozawa, Indentation creep of Na20 3S1O2 glasses with various water... 

Kolarik J and Pegoretti A (2004) Indentation creep of heterogeneous blends poly(ethyl-ene-terephthalate)/impact modifier, Polym Testing 23 113-121. 

Figure H.10 Viscoelastic solids (Maxwell, Voigt and spring in series, Burger) used to modei the indentation creep of viscoelastic solids.

The models are applied to a HEMA-TEOS sol-gel film under indentation creep (Figure H.11). The Maxwell element shows the expected linear dependence of the square of the penetration. This does not fit the experimental data well. In feet, it is necessary to consider a more complex scheme of the solid in order to obtain a representative behaviour. A satisfactory fit is obtained using either a combination in series of Voigt and spring elements or a Burger solid. 

Figure H.11 Indentation creep curve of HEMA-TEOS thin film (Chemin, 2007).

Rostoker W, Galante JO. Indentation creep of polymers for human joint applications. J Biomed Mater Res 1979 September 13(5) 825-8. 

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