Dimensional instability of cement bonded particleboard: Modelling CBPB as a composite of two materials |
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Authors: | Email author" target="_blank">M?Z?FanEmail author J?M?Dinwoodie P?W?Bonfield M?C?Breese |
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Institution: | (1) Centre for Timber Technology and Construction, Building Research Establishment Ltd., Watford, Hert., WD2 7JR, UK |
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Abstract: | Previous papers have quantitatively indicated that the total movement of cement bonded particleboard (CBPB) is equal to the sum of the movement of its components. This paper examined the efficacy of the law of mixtures when applied to the movement of a wood-cement composite under internal swelling or shrinkage stresses. Abundant data generated in companion papers were first manipulated to develop the universal formulae for predicting the movement of components. In conjunction with previous numerical results from image analysis of the structure of CBPB, and the orientated elasticity and stress algorithms, the models for theoretically predicting mass and dimensional changes of CBPB were derived. Validation studies were conducted and these demonstrated an excellent agreement of the theoretical predictions with experimental data for both mass and dimensional changes of CBPB due to internal swelling or shrinkage stresses during adsorption and desorption. The success also implied that CBPB can be treated as a composite and its properties can be well derived by the law of mixtures even though CBPB is an unusual type of composite having a very high volume fraction of wood chips, but a very high mass fraction of cement paste.Notation ERT
Mean transverse modulus of elasticity of wood
- EL
Longitudinal modulus of elasticity of wood
- Ep
Modulus of elasticity of cement paste
- Ewa
Modulus of elasticity of embedded wood chips at angle
- E
Modulus of elasticity of wood chips at direction
- E
Modulus of elasticity of wood chips at direction
- GLRT
Mean transverse shear modulus of wood
- L(T)cp
Length/width (thickness) change of CBPB at angle
- L(T)p
Length (thickness) change of cement paste
- mpf
Mass fraction of cement paste in unit mass of CBPB
- mwf
Mass fraction of wood chips in unit mass of CBPB
- Mcpj
Mass change of CBPB at the various conditions tested
- Mpj
Mass change of cement paste at corresponding conditions
- Mwj
Mass change of wood chips at corresponding conditions
- M(L; T)w/P
Mass, length or thickness changes of wood chips or cement paste at various conditions
- t
Duration of exposure
- LRT
Mean transverse Poissons ratio of wood
- Vpf
Volume fraction of cement paste in unit mass of CBPB
- Vwf
Volume fraction of wood chip in unit mass of CBPB
- cp
Density of CBPB
- k
Density of wood chip or cement paste
- cp
Overall stresses of CBPB at angle
- L
Stress in the longitudinal direction of wood
- RT
Mean stress in the transverse direction of wood
- p
Stress of cement paste
- w
Stress of the wood chips at angle
-
Stress of the wood chips at direction
-
Stress of the chip at direction
- cp
Strain in CBPB
- p
Strain of cement paste
- WL
Strain in the length of wood chips
- WT
Strain in the thickness of wood chips
- w
Strain in wood chips
-
Angle between the longitudinal direction of wood chips and surfaces or edges of CBPB
-
Angle between wood chips and edges (length direction) of CBPB
-
Angle between wood chip and vertical coordinate
- A, B, C
Coefficients related to the feature of materials and exposure conditions
The senior author wishes to thank Professor W.B. Banks of University of Wales, Bangor for his constructive discussions and assistance and the British Council for partly financial support. |
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Keywords: | |
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