Wyniki wyszukiwania - Biblioteka Nauki

1

Modelling of linear elasticity and viscoelasticity of thermosets and unidirectional glass fibre-reinforced thermoset-matrix composites. Part 2, Homogenization and numerical analysis

100%

Klasztorny M. , Nycz D. B.

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tom R. 22, nr 1

25--39

EN

The study continues the advanced analytical modelling of the linear elasticity and viscoelasticity of thermosets and unidirectional glass fibre-reinforced thermoset-matrix (UFRT) composites. The thermosets are isotropic materials with viscoelastic shear strains and elastic bulk strains, and the fibres are isotropic and elastic. The modified homogenization theory for UFRT composites, based on the selected tasks of the linear theory of elasticity, is developed. The modifications include a volumetrically equivalent cylindrical representative volume cell, solutions determined for an isotropic fibre based on the solutions for a monotropic (transversely isotropic) fibre, and certain modifications in the third task of the theory of elasticity. The viscoelastic constants of the thermoset are derived analytically and validated by fitting of the simulation and experimental shear strains on a logarithmic time scale in the unidirectional tension creep test. The viscoelastic constants of the UFRT composite are derived analytically and validated by fitting of the storage compliances corresponding to the new viscoelastic model and one obtained from the viscoelastic-elastic correspondence principle. The tension creep experiment is performed on the selected structural unsaturated polyester resin. Identification and validation are carried out for that thermoset and the corresponding UFRT composite with long E-glass fibres. All the modelling hypotheses are confirmed.

2

Novel rheological modelling of thermosets and unidirectional monotropic fibre-reinforced thermoset matrix composites

100%

Klasztorny M. , Nycz D. B.

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tom R. 23, nr 1

3--21

EN

A refined, fully analytical rheological modelling of thermosetting polymers and unidirectional monotropic fibre-reinforced thermoset matrix (UFRT) composites is presented. New polymers and composites under normal conditions, fully relaxed from curing and post-curing stresses, are modelled. The theory includes quasi-static short-term/medium-term/long-term reversible rheological processes. Thermosets are isotropic materials exhibiting linearly viscoelastic shear strains and linearly elastic bulk strains. Fibres are monotropic (transversely isotropic) and linearly elastic materials. A generic function well reproducing the viscoelastic characteristics of thermosets and UFRT composites is a Mittag-Leffler fractional exponential function in an integral form. Coupled/uncoupled standard/inverse constitutive equations of linear rheology are formulated for thermosets and UFRT composites. The equations are mutually analytically transformable. New rheological models (coded H-R/H) for thermosets and UFRT composites are described by the smallest possible number of material constants. The thermoset is described by two independent elastic constants and three independent viscoelastic constants. The homogenized UFRT composite is described by five independent elastic constants and four independent viscoelastic constants, whereby two visco-elastic constants are common to the matrix and the composite. An improved homogenization theory of UFRT composites, based on analytical solutions of the selected tasks of the theory of linear elasticity, is formulated for monotropic fibres and positively validated experimentally. The viscoelastic constants of the thermoset are calculated analytically in an iterative loop using a long-term unidirectional tension creep experimental test. The viscoelastic constants of the UFRT composite are calculated analytically employing H-R/H shear/quasi-shear storage compliances and VECP (the viscoelastic-elastic correspondence principle) shear/quasi-shear storage compliances. The H-R/H rheological model was validated numerically for selected UFRT composites. The validation tests were performed on the enhanced reliability UFRT composites reported by Soden, Hinton, and Kaddour (Composites Science and Technology, 1998, 2002).

3

Rheological effects in in-plane shear test and in-plane shear creep test on glass-vinyl-ester lamina

80%

Klasztorny M. , Nycz D. B. , Bogusz P.

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2020

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tom R. 20, nr 1

35--42

EN

The research concerns an E-glass/vinyl-ester composite reinforced with a balanced orthogonal stitched fabric. According to the EN ISO 14129 standard, the in-plane shear modulus and in-plane shear strength for this composite type are identified from a ±45º off-axis tension test at the crosshead displacement rate of 2 mm/min. The study presents the results of experimental quasi-static ±45º off-axis tension tests in a small shear strain range, aimed at demonstrating that the high nonlinearity of the shear stress-shear strain curve is caused by viscoelastic flow of the resin at low levels of shear stress and by viscoelastic flow and plastic micro cracks of the resin at high levels of shear stress. The tests were conducted applying four quasi-static displacement rates. It was shown that the shear stress-strain curve course and the shear strength value strongly depend on the crosshead displacement rate. To confirm the nonlinearity explanation, a classic short-term (1 hour) in-plane shear creep test was carried out on ±45º off-axis specimens subjected to in-plane shear stress equal to 67% of the average in-plane shear strength calculated according to the EN ISO 14129 standard. The ply sequence blocking viscoelastic flow and plastic micro cracks of the resin was recommended.

PL

Przedmiotem badań jest kompozyt polimerowy winyloestrowo-szklany (szkło E) wzmocniony tkaniną zszywaną ortogonalną zrównoważoną. Zgodnie z normą PN-EN ISO 14129, moduł ścinania i wytrzymałość na ścinanie w płaszczyźnie laminy tego typu kompozytu wyznacza się z próby ścinania przez rozciąganie po kątem ±45º do kierunku wątku/osnowy, przy szybkości przemieszczenia trawersy maszyny wytrzymałościowej 2 mm/min. Przedstawiono wyniki eksperymentalnej quasi-statycznej próby ścinania przez rozciąganie po kątem ±45º do kierunku wątku/osnowy ukierunkowane na wykazanie, że silna nieliniowość wykresu naprężenie styczne-odkształcenie postaciowe jest wywołana płynięciem żywicy przy małych poziomach naprężenia stycznego oraz płynięciem i mikropęknięciami żywicy przy dużych poziomach naprężenia stycznego. Próby quasi-statyczne przeprowadzono dla czterech szybkości przemieszczeń trawersy. Wykazano, że kształt wykresu naprężenie styczne-odkształcenie postaciowe oraz wartość wytrzymałości na ścinanie w płaszczyźnie laminy silnie zależą od szybkości przemieszczenia trawersy. W celu potwierdzenia wyjaśnienia nieliniowości przeprowadzono próbę pełzania krótkotrwałego (1 godzina) przy ścinaniu w płaszczyźnie laminy na próbkach rozciąganych pozaosiowo ±45º, poddanych działaniu naprężenia stycznego w płaszczyźnie laminy równego 67% średniej wytrzymałości na ścinanie w płaszczyźnie laminy według normy PN-EN ISO 14129. Rekomendowano sekwencję warstw blokującą płynięcie lepkosprężyste i mikropęknięcia żywicy.