Detection of the Fracture Path under Tensile Loads through in situ Tests in an ESEM Chamber

Frühmann, Klaus; Burgert, Ingo; Stanzl-Tschegg, Stefanie E.

doi:10.1515/hf.2003.048

Cited by 32 publications

(17 citation statements)

References 10 publications

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“…For details regarding the tensile apparatus, see Frühmann et al (2003). Testing the isolated compression wood tracheids requires a much more sensitive tensile device.…”

Section: Methodsmentioning

confidence: 99%

Structure?function relationships of four compression wood types: micromechanical properties at the tissue and fibre level

Burgert

Frühmann

Kečkéš

et al. 2004

Trees

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The mechanisms behind compressive stress generation in gymnosperms are not yet fully understood. Investigating the structure-function relationships at the tissue and cell level, however, can provide new insights. Severe compression wood of all species lacks a S3 layer, has a high microfibril angle in the S2 layer and a high lignin content. Additionally, special features like helical cavities or spiral thickenings appear, which are not well understood in terms of their mechanical relevance, but need to be examined with regard to evolutionary trends in compression wood development. Thin compression wood foils and isolated tracheids of four gymnosperm species [Ginkgo biloba L., Taxus baccata L., Juniperus virginiana L., Picea abies (L.) Karst.] were investigated. The tracheids were isolated mechanically by peeling them out of the solid wood using fine tweezers. In contrast to chemical macerations, the cell wall components remained in their original condition. Tensile properties of tissue foils and tracheids were measured in a microtensile apparatus under wet conditions. Our results clearly show an evolutionary trend to a much more flexible compression wood. An interpretation with respect to compressive stress generation is discussed.

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“…For details regarding the tensile apparatus, see Frühmann et al (2003). Testing the isolated compression wood tracheids requires a much more sensitive tensile device.…”

Section: Methodsmentioning

confidence: 99%

Structure?function relationships of four compression wood types: micromechanical properties at the tissue and fibre level

Burgert

Frühmann

Kečkéš

et al. 2004

Trees

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“…The structure-property relationships of wood was investigated by EM and ESEM ex situ and in situ (Tabarsa and Chui 2000 ;Sippola and Fr ü hmann 2002 ;Fr ü hmann et al 2003 ;M ü ller et al 2003 ;Vasic and Stanzl -Tschegg 2006 ). While optical microscopy was mainly used for ex situ observations, EM and especially ESEM are very suitable for various in situ experiments to evaluate crack propagation and reaction to load (Sippola and Fr ü hmann 2002 ;Fr ü hmann et al 2003 ;M ü ller et al 2003 ;Vasic and Stanzl -Tschegg 2006 ).…”

Section: Introductionmentioning

confidence: 99%

“…While optical microscopy was mainly used for ex situ observations, EM and especially ESEM are very suitable for various in situ experiments to evaluate crack propagation and reaction to load (Sippola and Fr ü hmann 2002 ;Fr ü hmann et al 2003 ;M ü ller et al 2003 ;Vasic and Stanzl -Tschegg 2006 ). Both methods have certain disadvantages for in situ tests under mechanical load: during sample preparation, defects can be induced (Jansen et al 2008 ).…”

Section: Introductionmentioning

confidence: 99%

Synchrotron-based tomographic microscopy (SbTM) of wood: development of a testing device and observation of plastic deformation of uniaxially compressed Norway spruce samples

et al. 2012

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To understand better the structure-property relationships of wood in situ, nondestructive synchrotron-based tomographic microscopy (SbTM) with subcellular resolution is useful. In this context, an in situ testing device was developed to determine the cellular response of wood to mechanical loading. Different rotationally symmetric specimens were tested to synchronize the failure areas to the given scanning areas. Norway spruce samples were uniaxially compressed in the longitudinal direction and scanned in situ at several increasing relative forces ending up in the plastic deformation regime. A suffi ciently high quality in situ tomography was demonstrated. The reconstructed data allowed the observation of the load-dependent development of failure regions: cracks and buckling on the microstructure were clearly visible. Future investigations with SbTM on different wood species, loading directions, and different moisture contents are promising in terms of the micromechanical behavior of wood.

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“…and yew (Taxus baccata L.) specimens were tested in displacement-controlled (with a linear-voltage induction sensor, LVDT) wedge-splitting experiments at 20 8C and 65% relative humidity (RH) after the specimens had obtained equilibrium moisture content. The specimen dimensions were: width W ¼ 32 mm, height h ¼ 20 mm, thickness t ¼ 5 mm, and they were tested in TR and RT orientation, after Frü hmann et al [10,12] studies of the LR and TR orientation of spruce and beech. The present experiments were performed with an experimental set-up that is a slight variation of the above-described wedge-splitting set-up for larger specimens: a loading wedge with two rollers moves against the sloped surfaces of the specimen, whereby the rollers reduce the effect of friction in contact.…”

Section: Influence Of Orientation On the Fracture Response Of Woodmentioning

confidence: 99%

“…c) Roughly straight crack path in TR orientation with mainly cell wall fracture in earlywood and intercellular fracture in latewood. d) Tortuous and cell wall fracture in the RT orientation [11,12]. and intercellular fracture in latewood) in the TR orientation (Fig.…”

Section: Influence Of Orientation On the Fracture Response Of Woodmentioning

confidence: 99%

Fracture Properties of Wood and Wood Composites

Stanzl-Tschegg

2009

Adv Eng Mater

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Wood is a highly anisotropic and complex material, which implies that fracturing is a complex process. It is similar with wood composites that are, on one hand, even more complex in their structure -consisting of wood and adhesives -but, on the other hand, are often more homogenous owing to the wooden constituents being mostly small.The mechanical and fracture properties of wood are mainly determined by its extraordinary structure. [1,2] Its density, for example, is low, since wood contains fibers, which are tubular (hollow) cells containing large or small lumina. The lengthy fibers of crystalline cellulose are embedded in an amorphous matrix of lignin and hemicelluloses and, as a whole, wood is a kind of polymeric composite. However, wood is not only a cellular material, but also a laminated composite on a mesoscopic (layers of early and late wood) as well as on a submicroscopic (cell-wall level) scale. There, the multilayer structure, composed of differently fiber reinforced lamina groups, gives stiffness and strength to the cell wall and, thus, to the entire cellular structure. A consequence of the cellular and laminate structure of wood, with fibers embedded in a homogeneous matrix, is the orientation dependence of different mechanical and fracture properties. They are completely different in longitudinal and transversal orientations, and wood may be considered and modeled as an orthotropic material.Another interesting feature of wood is its hierarchical structure, which means that on all scales, ranging from the macroscopic (centimeter to meter) down to the molecular (nanometer) regimes, special structural features are responsible for the special properties of wood. For example, in this context the stiffness, toughness, etc. may be understood and modeled on the basis of micro-and even nanometer scale properties. The fibril angle on the micrometer level and the elementary fibril angle as part of the cell wall (nanometer level) and the underlying molecular arrangements of the chemical constituents in chains are structural elements, which determine the mechanical and fracture properties and their orientation dependence strongly. Besides these ''intrinsic'' wood features, external influences, especially humidity and temperature, also essentially influence the mechanical and fracture properties of wood.In order to characterize the structural and mechanical properties, numerous experimental techniques and modeling approaches have been developed and applied with the aim of understanding the contribution of the smallest hierarchical units to the macroscopic mechanical properties of wood. The anisotropy, complexity and hierarchical structure of wood imply that more sophisticated methods than standard linear-elastic fracture mechanical (LEFM) procedures are needed for its quantitative characterization. Testing and modeling procedures have been developed that are appropriate for characterizing the various structure-function relationships and the influencing parameters. In many models, for example, a strain-softening pr...

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Detection of the Fracture Path under Tensile Loads through in situ Tests in an ESEM Chamber

Cited by 32 publications

References 10 publications

Structure?function relationships of four compression wood types: micromechanical properties at the tissue and fibre level

Structure?function relationships of four compression wood types: micromechanical properties at the tissue and fibre level

Synchrotron-based tomographic microscopy (SbTM) of wood: development of a testing device and observation of plastic deformation of uniaxially compressed Norway spruce samples

Fracture Properties of Wood and Wood Composites

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