Moisture-dependent, viscoelastic creep of European beech wood in longitudinal direction

Hering, Stefan; Niemz, Peter

doi:10.1007/s00107-012-0600-4

Cited by 40 publications

(34 citation statements)

References 18 publications

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“…In relation to the wood, Mukudai (1983) mentions that the functional form represented by the Voigt and Maxwell models is very efficient since they can be conveniently applied to assess the viscoelastic behavior of that material through mathematical models. In this sense Hering;Niemz (2012) have used the Kelvin-Voigt model, together with experimental activity to descript the creep in bended pieces. A Burger chain of four elements was used by Gao;Shao (2016) to study the behavior of Xuan paper, making possible to description convenientily the elastic, viscoelastic and plastic deformations presented by the material.…”

Section: Mathematical Simulation Supportmentioning

confidence: 99%

Creep in the Fundamental Frequency and Stability of a Slender Wooden Column of Composite Section

2016

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-Creep is a phenomenon that can occur in wooden structures since wood is a viscoelastic material. Creep may change the purely elastic parameters determined in wood characterization initial tests, as its behavior depends on the rheology of the material, even under a constant stress level. Mathematically, creep can be characterized by models in which the immediate elastic deformation is increased by a viscous deformation, resulting in a temporal function. For this reason, the calculation of the natural frequency of vibration and the stability verification of a slender column should include the reducing effects of stiffness both of axial force and creep. The first one can be considered through the geometrical portion and the second one by the introduction, in the conventional portion, of a variable elasticity modulus over time, obtained in relation to the adopted rheological model. A numerical simulation was performed to evaluate the aspects above, considering a bar compressed by a force at the free end equivalent to 10% of the Euler critical force, plus its own weight, adopting a rheological model with three parameters for the variation of the elasticity modulus. The results show differences of 60% and 50% for the frequency and elasticity modulus, besides defining the exact instant of column collapse in the case of its non-observance.Keywords: Three-parameter model; Vibration; Stability.A FLUÊNCIA NA FREQUÊNCIA FUNDAMENTAL E NA ESTABILIDADE DE UMA COLUNA ESBELTA DE MADEIRA DE SEÇÃO COMPOSTA RESUMO -A fluência é um fenômeno que pode ocorrer em estruturas de madeira por ser esse um material viscoelástico. A fluência pode alterar os parâmetros puramente elásticos determinados nos ensaios iniciais de caracterização da madeira, pois o seu comportamento depende da reologia do material, mesmo com um nível de tensão constante. Matematicamente, a fluência pode ser caracterizada por modelos onde a deformação elástica imediata é acrescida de uma deformação viscosa, resultando em uma função temporal. Por essa razão, o cálculo da frequência natural de vibração e a verificação da estabilidade de uma coluna esbelta devem incluir os efeitos redutores da rigidez tanto da força axial quanto da fluência. O primeiro pode ser considerado por meio da parcela geométrica e o segundo pela introdução, na parcela convencional, de um módulo de elasticidade variável com o tempo, obtido em relação ao modelo reológico adotado. Para avaliar os aspectos mencionados, foi realizada uma simulação numérica, considerando uma peça comprimida por uma força na extremidade livre equivalente a 10% da força crítica de Euler, mais o seu peso próprio, adotando-se um modelo reológico de três parâmetros para a variação do módulo de elasticidade. Os resultados indicaram diferenças de 60% e 50% para a frequência e para o módulo de elasticidade, além de definir o instante exato de colapso da coluna em caso de sua inobservância.Palavras-chave: Modelo de três parâmetros; Vibração; Estabilidade.

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Section: Mathematical Simulation Supportmentioning

confidence: 99%

Creep in the Fundamental Frequency and Stability of a Slender Wooden Column of Composite Section

2016

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“…Creep experiments are usually conducted in a controlled temperature and humidity chamber (Moutee 2006;Hering and Niemz 2012). To investigate the creep behavior of wood, a constant temperature and relative humidity must be maintained to keep MC constant during the test (Jin et al 2016).…”

Section: Intuitive Analysis Of Datamentioning

confidence: 99%

Effect of Drying Temperature and Relative Humidity on Contraction Stress in Wood

Liu

Wang

2016

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As wood shrinks during the drying process, various stresses may develop and cause surface and internal checking. The aim of this study was to systematically investigate the effect of the drying temperature, relative humidity, and specimen thickness on the contraction stress in elm wood (Ulmus pumila L.) specimens during drying. The contraction stress was used as an indirect indicator of drying stresses. A measurement system was developed in-house and used to simultaneously and continuously obtain the required measurements during drying, which were then used to determine the moisture content, amount of shrinkage, and contraction stress of the wood specimens. In the process of drying, the contraction stress was initially negative with a decrease in the moisture content and an increase in the shrinkage. Then the contraction stress increased gradually and eventually stabilized upon reaching the maximum. The results also showed that as the temperature increased, the moisture content decreased, the shrinkage decreased, the maximum contraction stress decreased, and the contraction stress reached a maximum in a shorter amount of time.

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“…Moisture in wood (MC < 30%) could affect the internal hydrogen bonds between wood polymers, thereby influencing the wood's plasticity and deformation. There has been considerable research in creep behavior of wood at both varying MCs (Armstrong andKingston 1960, 1962;Armstrong and Christensen 1961;Armstrong 1972;Ranta-Maunus 1975;Wu 1995;Zhan and Avramidis 2011)), and constant MCs (Youngs 1957;Clouser 1959;Kingston and Budgen 1972;Armstrong 1972;Breese and Bolton 1993;Tissaoui 1996;Jong and Clancy 2002;Kojima and Yamamoto 2005;Moutee 2006;Engelund and Salmén 2012;Hering and Niemz 2012). When creep behavior of wood is investigated at low temperatures, the controlled MC value of the wood during the test is not very difficult to realize.…”

Section: Introductionmentioning

confidence: 99%

“…When creep behavior of wood is investigated at low temperatures, the controlled MC value of the wood during the test is not very difficult to realize. Creep experiments at low temperature were carried out using a water-saturated cloth (Youngs 1957) and chemical materials such as aqueous NaCl and P2O5 powder (Kojima and Yamamoto 2005), or by simply putting wood specimens in a conditioning room (Clouser 1959;Armstrong 1972), which consisted of a controlled humidity generator with nitrogen as the carrier gas (Engelund and Salmén 2012) and a controlled temperature and humidity chamber (Moutee 2006;Hering and Niemz 2012). With increasing temperature, however, maintaining a constant MC at elevated temperatures is very difficult because changes in MC take place simultaneously with changes in the temperature of the wood.…”

Section: Introductionmentioning

confidence: 99%

Creep Behavior of Wood Plasticized by Moisture and Temperature

Jin¹,

Jiang²,

Wu³

2015

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Moisture in wood acting as a plasticizer will strongly affect the wood's viscoelastic properties. However, achieving the desired moisture content (MC) at elevated temperatures during creep tests is difficult. The aim of this study is to accurately and systematically investigate the creep behavior of birch wood at high temperatures. Experiments were conducted using a dynamic mechanical analyzer with a relative humidity accessory coupled with polyvinylidene chloride (PVDC) film for wrapping samples. Creep behavior was examined at six MCs (0%, 6%, 12%, 18%, 24%, >30%) and 11 temperatures (5 to 105 °C). The MC of wood was strictly and accurately controlled during creep tests. Instantaneous compliance (IC) and creep compliance (CC) increased with the increase of both temperature and MC, with significant changes at higher temperatures and MCs. The effects on IC and CC were more pronounced when the subject was influenced by MC, with readings approximately three times and one time greater than those influenced by temperature, respectively. Dramatic increases in CC were found at certain temperatures and MC values. There was a complex interaction between temperature and MC on IC and CC.

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Moisture-dependent, viscoelastic creep of European beech wood in longitudinal direction

Cited by 40 publications

References 18 publications

Creep in the Fundamental Frequency and Stability of a Slender Wooden Column of Composite Section

Creep in the Fundamental Frequency and Stability of a Slender Wooden Column of Composite Section

Effect of Drying Temperature and Relative Humidity on Contraction Stress in Wood

Creep Behavior of Wood Plasticized by Moisture and Temperature

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