by the fact that the indentation modulus on impression becomes higher than that on flat surface as shown in Fig. 37.3. On the other hand, the values evaluated by FEM are comparable to that by stress relaxation test. Therefore, considering the shape of impression, creep compliance of polymer can be evaluated by 5-step indentation test. Also, this result means that 5-step indentation can separate viscoelastic deformation and plastic deformation by shifting theF-hcurve of the second indentation cycle. However, in order to evaluate more precise creep compliance, the effect of shape of the impression is required as mentioned above. Furthermore, the value evaluated by FEM could not account time-dependent characteristics. Therefore, it is necessary theoretical or empirical time-dependent equation with regard to the actual shape of the impression through various analyses by FEM. 37.4 Conclusions In the present study, 5-step indentation test is applied to evaluate creep compliance of ABS resin. In order to evaluation the precise value of the creep compliance, the problem of the second cycle of 5-step indentation test is analyzed by FEM, in which an axisymmetric indenter impresses on an impression with certain depth. The results show that the values of the creep compliance evaluated by the equation for a indentation problem on flat surface are smaller than that evaluated by stress relaxation test. On the other hand, the values evaluated by FEM are comparable to that by stress relaxation test. Therefore, considering the shape of impression, creep compliance of polymer can be evaluated by 5-step indentation test. Acknowledgments We thank T. Hoshino and K. Kato, graduate students in Shibaura Institute of Technology, for support of this study. References 1. Fischer-Cripps, A.C.: Nanoindentation, 2nd edn. Springer, New York (2004) 2. Sneddon, I.N.: The relation between load and penetration in the axisymmetric Boussinesq problem for a punch of arbitrary profile. Int. J. Eng. Sci. 3, 47–57 (1965) 3. Christensen, R.M.: Theory of viscoelasticity, 2nd edn. Dover, New York (2003) 4. Lu, H., Wang, B., Ma, J., Huang, G., Viswanathan, H.: Measurement of creep compliance of solid polymers by nanoindentation. Mech. TimeDepend. Mater. 7(3), 189–207 (2003) 5. Huang, G., Wang, B., Lu, H.: Measurements of viscoelastic functions of polymers in the frequency-domain using nanoindentation. Mech. TimeDepend. Mater. 8(4), 345–364 (2004) 6. Sakaue, K., Okazaki, S., Ogawa, T.: Indentation technique for evaluation of master curve of creep compliance. Exp. Tech. 35(5), 16–22 (2011) 7. Sakaue, K., Isawa, T., Ogawa, T., Yoshimoto, T.: Evaluation of viscoelastic characteristics of short-fiber reinforced composite by indentation method. Exp. Mech. 52(8), 1003–1008 (2012) 8. Stan, F., Fetecau, C.: Characterization of viscoelastic properties of molybdenum disulphide filled polyamide by indentation. Mech. TimeDepend. Mater. 17, 205–221 (2013) Fig. 37.5 Creep compliance evaluated by 5-step indentation test 37 Evaluation of Viscoelastic Characteristics of Polymer by Using Indentation Method 307
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