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Escola Superior de Tecnologia e Gestão (ESTG) >
Artigos em Acta de Conferência Internacional (ESTG) >
Utilize este identificador para referenciar este registo:
http://hdl.handle.net/10314/3417
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| Título: | FLUÊNCIA DE POLÍMEROS – FENOMENOLOGIA E MODELAÇÃO DINÂMICA MOLECULAR |
| Autores: | José, André |
| Palavras Chave: | Fluência
Poli(metacrilato de metilo) |
| Data: | 2004 |
| Editora: | Universidade de Aveiro |
| Resumo: | In the present work, dynamic molecular models with physically interpretable parameters were developed to predict the non-linear creep compliance as a function of temperature and applied stress, for amorphous and semi-crystalline polymers, and they were compared with the experimental creep behaviour of both types of polymers.
To objectively evaluate the models, creep strain measurements were carried out at three temperatures – 30, 40 and 50 oC – and five tensile stress levels – 10, 16, 20, 25 and 32 MPa for two amorphous polymers (PMMA and PC) and, for two semi-crystalline polymers, 1, 2, 4, 6 and 8 MPa (PE-UHMW) and 2, 4, 6, 8 and 10 MPa (PP).
The analytical models developed, based on concepts of non-simulative molecular dynamics, account for a truncated log-normal retardation time distribution, such that a minimum (1) and an average (*) retardation time are quantitatively predicted, as functions of temperature and applied stress, for each of the materials studied.
The model-predicted shift of the retardation time spectra towards shorter times, when temperature or stress increases, is in agreement with other published results and our own experimental data. In addition, a clear change in the shape (width decrease) of the spectra has been identified and quantified, after increases in the same two operating variables.
The fit of the model predictions to the experimentally measured behaviour is of good quality, enabling quantitative estimates of the various physical parameters involved. Thus, for the most refined model developed so far – Model IIB – at each temperature, and for all five tensile stress levels experimentally tested, the number of parameters is seven: b0, related to the width of the retardation time spectrum, constants 1,0 and of the minimum and average retardation times, a minimum, β1, and a average, β*, activation volume, and both asymptotic creep compliances – the instantaneous and the long-term (infinite time) ones.
In contrast with most previously published works, which are semi-empirical, interpolative and (limitedly) extrapolative, the models developed here enable the prediction of the non-linear creep compliance of a given amorphous or semi-crystalline polymer, providing the values of the physical parameters have been experimentally determined, for a not too extensive set of temperature and applied stress values. |
| URI: | http://hdl.handle.net/10314/3417 |
| Aparece nas Colecções: | Artigos em Acta de Conferência Internacional (ESTG)
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Ficheiros deste Registo:
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Descrição |
Tamanho | Formato |
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| Resumo_tese_Doutoramento_UA_2004.pdf | | 170Kb | Adobe PDF | Ver/Abrir | |
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