Identification of viscoplastic parameters of phenomenological constitutive equations for polymers by deterministic and evolutionary approach

Abstract

This study is concerned with the viscoplastic behaviour of polymers. A modified viscoplastic Bodner–Partom model was extended to include successively the post-yield (strain softening and strain hardening) and the pre-yield behaviour. In order to identify material parameters of the constitutive law, an analytical scheme and a numerical method based on evolutionary algorithms were developed. The capacity of the proposed viscoplastic approach is investigated for a representative glassy polymer (polycarbonate). The results and the efficiency of both approaches are discussed.

Modelling of Innovative Controllable Structures Made of Granular Materials

“…A similar algorithm has been successfully applied in [18] for evaluation of Bodner-Partom model parameters for metals. The same universal methodology has been implemented to identification of the model parameters for polymers [13], textile fabric "Panama" and solid propellants [20]. Results presented in the next section reveal that it is also valid for investigated special granular structures.…”

“…Since these nonlinear equations contain a lot of parameters, all ambiguity in identification result must be removed by a robust identification scheme. Considered in this paper analytical methodology of parameters identification is presented in details in [13]. A simplified schematic algorithm is presented in this section.…”

“…2, and then initially pretreated according to remarks in [13]. The next stage is eliminating the influence of experimental error.…”

“…obtained from expressions (15) and (16) for γ = 0, where σ b and σ s are intersection points of lines tangential to γ with the force axis [13]. A similar algorithm has been successfully applied in [18] for evaluation of Bodner-Partom model parameters for metals.…”

“…The problem can also be described phenomenologically with regard to the basic principle of thermodynamics of continuous media and by defining adequate internal variables. According to these phenomenological considerations, models developed for metals can be used also for the description of the nonlinear behaviour after yielding of polymers [10,11,12,13]. However to date, the investigation of the viscoplastic response of polymers is still an important challenge.…”