Issue 49

Y. Saadallah et alii, Frattura ed Integrità Strutturale, 49 (2019) 666-675; DOI: 10.3221/IGF-ESIS.49.60 674 C ONCLUSION n this work, we have mainly studied the sensitivity to the strain-rate of the viscoelastic and viscoplastic parameters of a rheological model applied to thermoplastics. The proposed behavior model takes into account several elementary responses including instant elasticity, viscoelasticity, viscoplasticity and hardening. The identification of the parameters was carried out on the basis of the experimental results obtained following a simple tensile test at different strain rates. The parameters were identified by means of inverse analysis by genetic algorithms. The comparison of the test-model results reveals a very good coherence. Except the modulus of elasticity and the exponent of work hardening, the results obtained reveal a strong dependence of the other viscoelastic and viscoplastic parameters to the strain rate. A nonlinear regression technique has made it possible to establish dependence functions which show relations in power law. R EFERENCES [1] Maurel-Pantel, A., Baquet, E., Bikard, J., Bouvard, J. L., and Billon, N. (2015). A thermo-mechanical large deformation constitutive model for polymers based on material network description: Application to a semi-crystalline polyamide 66, International Journal of Plasticity, 67, pp. 102-126. [2] Colak, O. U. (2005). Modeling deformation behavior of polymers with viscoplasticity theory based on overstress, International Journal of Plasticity, 21, pp. 145-160. [3] Müller, S., Kästner, M., Brummund, J., and Ulbricht, V. (2011). A nonlinear fractional viscoelastic material model for polymers, Computational Materials Science, 50, pp. 2938-2949. [4] Zhang, C., and Moore, I. D. (1997). Nonlinear mechanical response of high density polyethylene. Part II: Uniaxial constitutive modeling, Polymer Engineering & Science, 37, pp. 414-420. [5] Miled, B., Doghri, I., and Delannay, L. (2011). Coupled viscoelastic–viscoplastic modeling of homogeneous and isotropic polymers: Numerical algorithm and analytical solutions, Computer Methods in Applied Mechanics and Engineering, 200, pp. 3381-3394. [6] Abdul-Hameed, H., Messager, T., Zaïri, F., and Naït-Abdelaziz, M. (2014). Large-strain viscoelastic–viscoplastic constitutive modeling of semi-crystalline polymers and model identification by deterministic/evolutionary approach, Computational Materials Science, 90, pp. 241-252. [7] Zaïri, F., Naït-Abdelaziz, M., Woznica, K., and Gloaguen, J.-M. (2007). Elasto-viscoplastic constitutive equations for the description of glassy polymers behavior at constant strain rate, Journal of Engineering Materials and Technology, 129, pp. 29-35. [8] Tscharnuter, D., Jerabek, M., Major, Z., and Pinter, G. (2012). Uniaxial nonlinear viscoelastic viscoplastic modeling of polypropylene, Mech Time-Depend Mater, 16, pp. 275-286. [9] Ferry, J. D. (1980) Viscoelastic properties of polymers, John Wiley & Sons. [10] Davoodi, B., Muliana, A., Tscharnuter, D., and Pinter, G. (2015). Analyses of viscoelastic solid polymers undergoing degradation, Mech Time-Depend Mater, 19, pp. 397-417. [11] Golberg, D. E. (1989). Genetic algorithms in search, optimization, and machine learning, Addion wesley. [12] Holland, J. H. (1975). Adaptation in natural and artificial systems: an introductory analysis with applications to biology, control, and artificial intelligence, U Michigan Press. [13] McCall, J. (2005). Genetic algorithms for modelling and optimisation, Journal of Computational and Applied Mathematics, pp. 184, 205-222. [14] Kohandel, M., Sivaloganathan, S., and Tenti, G. (2008). Estimation of the quasi-linear viscoelastic parameters using a genetic algorithm, Mathematical and Computer Modelling, 47, pp. 266-270. [15] Feng, X.-T., Chen, B.-R., Yang, C., Zhou, H., and Ding, X. (2006). Identification of visco-elastic models for rocks using genetic programming coupled with the modified particle swarm optimization algorithm, International Journal of Rock Mechanics and Mining Sciences, 43, pp. 789-801. [16] Wang, G. Y., and Wang, M. (2011). Multi-Parameter Identification of Geomembrane Viscoelastic-Plastic Creep Constitutive Model by Genetic Algorithm, In Applied Mechanics and Materials, pp 182-188, Trans Tech Publ. [17] Dusunceli, N., Colak, O. U., and Filiz, C. (2010). Determination of material parameters of a viscoplastic model by genetic algorithm, Materials & Design, 31, pp. 1250-1255. [18] Zhang, W., Cho, C., and Xiao, Y. (2014). An effective inverse procedure for identifying viscoplastic material properties of polymer Nafion, Computational Materials Science, 95, pp. 159-165. I