Dimensional stability of Douglas fir and mixed beech?poplar plywood: experimental measurements and simulations

Constant, Thiéry; Badia, Miguel Angel; Mothe, Frédéric

doi:10.1007/s00226-003-0165-9

Cited by 5 publications

(4 citation statements)

References 10 publications

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“…A similar experience is described in the literature, where the FEM results underestimate the distortion of LVPs. Constant et al (2003) developed a FE model that predicted distortion in plywood and compared the results with empirical data observed under different climate conditions. Two types of simulation models were used; one describing the properties of each veneer according to the longitudinal and tangential swelling, as well as the wood density before the moulding, and the other using the mean density and average swelling coefficients for the LVP.…”

Section: Resultsmentioning

confidence: 99%

Distortion in laminated veneer products exposed to relative-humidity variations – Experimental studies and finite-element modelling

Blomqvist

Berg

Sandberg

2019

BioRes

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A shortcoming of the laminated bending process is that the product may become distorted after moulding. This study focused on the influence of fibre orientation deviation for individual veneers on the distortion of a moulded shell. The distortion of 90 cross-laminated shells of the same geometrical shape, consisting of seven peeled birch veneers, were studied under relative humidity variation. All the veneers were straight-grained in the longitudinal-tangential plane, but to simulate a deviation in fibre orientation, some of the individual veneers were oriented at an angle of 7° relative to the main orientation of the other veneers in the laminate. A finite element model (FEM) was applied to study the possibility of predicting the results of a practical experiment. The study confirms the well-known fact that deviation in fibre orientation influences shape stability. The results also show how the placement of the abnormal veneer influences the degree of distortion. From this basic knowledge, some improvements in the industrial production were suggested. However, the FE model significantly underestimated the results, according to the empirical experiment, and it did not show full coherence. The survey shows the complexity of modelling the behaviour of laminated veneer products under changing climate conditions and that there is a great need to improve the material and process data to achieve accurate simulations. Examples of such parameters that may lead to distortion are density, annual ring orientation in the cross section of the veneer, the orientation of the loose and tight sides of the veneer, and parameters related to the design of the moulding tool.

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Section: Resultsmentioning

confidence: 99%

Distortion in laminated veneer products exposed to relative-humidity variations – Experimental studies and finite-element modelling

Blomqvist

Berg

Sandberg

2019

BioRes

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“…Nevertheless, it seems as though something is missing in the models. Constant et al (2003) model underestimated the observed values. None of the models seems to take into account the stretching of veneers under uneven pressure and temperature.…”

Section: Calculation Modelsmentioning

confidence: 90%

“…Such differences are affected not only by dimensional changes but also by the modulus of elasticity (MOE) and veneer thickness. Constant, Badia and Mothe (2003) developed a FEM to predict the distortion of plywood panels from a description of the properties of the veneers in relation to MC changes, and they compared their predictions with experimental measurements. One simulation used individual measurements of each veneer according to longitudinal and tangential swelling, as well as wood density before the glueing process, and a second simulation used mean density and average swelling coefficients.…”

Section: Calculation Modelsmentioning

confidence: 99%

Shape stability of laminated veneer products – a review – defining and achieving shape stability

Blomqvist

2015

International Wood Products Journal

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Laminated veneer products (LVPs) consist of veneers bonded together with an adhesive into a predetermined shape. Deviation from the intended shape is a problem for both manufacturers and customers of the final products. The shape stability of LVP depends on a variety of material and process parameters, and this review identifies several important factors that influence shape stability, the purpose being to find ways of decreasing distortion and improving shape stability so that product quality can be improved.The review ends to the following statements:The fibre orientation of the veneer strongly influences the shape stability of LVP. The products can show considerable distortion (particularly twist) if the fibre orientation of the veneer is oriented in an unsuitable way in the assembly before moulding.The effect of fibre orientation on shape stability can be very small directly after moulding, but it can increase considerably when the moulded product is subjected to a change in moisture content (MC). In general, a change in moisture leads to distortion. Moisture changes alone, however, result in a controlled distortion.The orientation of the loose and tight sides of the veneers in LVP affects the shape stability. An asymmetrical construction, coupled with different levels of moisture in the different veneers in an assembly before moulding, will result in poor shape stability of the product.The choice of wood species affects shape stability. Beech shows more distortion and poorer shape stability than birch.Based on existing knowledge to produce shape-stable LVP, the veneers should be conditioned to uniform MC and sorted with regard to fibre orientation and loose or tight side of the veneer before bonding. End-user climates should govern the veneers' MC and added moisture from the adhesive during the process. Straight grain veneers and symmetry should always be sought.This review reveals several areas that need to be further clarified in order to achieve shapestable LVP, for example the influence of adhesive, the distribution of pressure, temperature, stresses and strains during moulding and the development of numerical methods to better predict the final shape.

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“…Efficient software makes virtual sawing or veneer cutting of a log described by 3D tomography a reality (Longuetaud et al 2007(Longuetaud et al , 2012Mothe et al 2002;Roussel et al 2014), opening the door to better sawing patterns in a sawmill for a known resource and a given market (Berglund et al 2014). By using a simple geometrical transformation to simulate the veneering process, the tree stem description given by growth and yield simulation software (Dufour-Kowalski et al 2012) allows the delivery of virtual maps of wood properties in veneers (grain angle and wood density) and prediction of the properties of secondary transformation products (Constant et al 2003;Mothe et al 2002).…”

Section: Wood Density Branching and Primary Conversionmentioning

confidence: 99%

Wood machining with a focus on French research in the last 50 years

Thibaut

Denaud

Collet

et al. 2016

Annals of Forest Science

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Abstract& Key message Wood machining is compulsory both for timber separation and the surfacing of wooden objects. The anisotropy, cellular nature and multi-scale level organisation of wood make its cutting complicated to study. During the last 50 years, most of the wood machining subjects were covered by French teams. & Context Woodcutting is a very old technology but scientific research is scarce on the subject. In the last 50 years, much work on basic mechanisms as well as on industrial processes has been done in France. In primary conversion such as sawing, veneer cutting or green wood chipping, huge progress comes from automation and the possibility of linking the process to log and product quality through new sensors. In secondary processing, much has been done on the links between the cutting process, surface qualification and the properties of these surfaces for further processing, such as gluing or coating. Tool wear depends on the cutting process, timber quality and species. Tradeoffs are required in tool technology and coating technologies may improve tool life. & Conclusion A large amount of knowledge and innovation has come from 50 years of worldwide research effort, with France being particularly active in this period. The transfer of skills from metals cutting industry was often a key, but much is needed to move closer to both metal cutting sector and woodcutting skills among craftsmen.

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Dimensional stability of Douglas fir and mixed beech?poplar plywood: experimental measurements and simulations

Cited by 5 publications

References 10 publications

Distortion in laminated veneer products exposed to relative-humidity variations – Experimental studies and finite-element modelling

Distortion in laminated veneer products exposed to relative-humidity variations – Experimental studies and finite-element modelling

Shape stability of laminated veneer products – a review – defining and achieving shape stability

Wood machining with a focus on French research in the last 50 years

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