ETH Zurich Institute for Building Materials (IfB), Wood Physics Group © ETH Zürich Solid wood panels – a new wood based material with high value added Peter Niemz

11/2006 Peter Niemz, IfB Wood Physics Group, 2 Outline 1.Introduction 2.Modelling of Properties 2.1 Mechanical Properties MOE MOR Experimental Tests 2.2Physical Properties Sorption Swelling Warping Internal stresses 3.Conclusions

11/2006 Peter Niemz, IfB Wood Physics Group, 3 1.Introduction What is a solid wood panel? 3 or 5 layer cross laminated board (system from plywood) Board: up to 0.5m (thickness)x3m x15m

11/2006 Peter Niemz, IfB Wood Physics Group, 4 What is a solid wood panel? Solid wood panels represent a new multilayer material based on boards, which are glued together crosswise, in most cases spruce wood is used Used more and more in timber constructions providing a high value added The utilisation of this kind of panel gains in importance in the Swiss, German and Austrian building industry It is possible to vary the properties of the panels through panel configuration

11/2006 Peter Niemz, IfB Wood Physics Group, 5 Utilisation of solid wood panels as building material

11/2006 Peter Niemz, IfB Wood Physics Group, 6 Industrial prefabrication (Schilliger AG, Switzerland)

11/2006 Peter Niemz, IfB Wood Physics Group, 7 Roof constructions with solid wood panels

11/2006 Peter Niemz, IfB Wood Physics Group, 8 House built with solid wood panels

11/2006 Peter Niemz, IfB Wood Physics Group, 9 2. Modelling of Properties 2.1Mechanical Properties Bending perpendicular to the surface

11/2006 Peter Niemz, IfB Wood Physics Group, 10 rolling shear (r-t) in middle layer

11/2006 Peter Niemz, IfB Wood Physics Group, 11 a) Modulus of elasticity, if L/h>35 Navier-Bernoulli pure bending E 1 (1):Elastic module 1 (surface layer) with load in direction 1 E 1 (2): Elastic module of layer 2 (middle layer) with load in direction 1 E b,ges : Elastic module of cross section L v :Relation of lamellas-thicknesses; L v = h (2)/h (1) h (1): Thickness of the surface layer h (2): Thickness of the middle layer (N/mm 2 ) MOE (Young’s modulus) For surface layer orientation parallel to the longitudinal axis: E1 (1) = E L = N/mm 2 ; v =  15% E1 (2) = E R/T = 450 N/mm 2 For surface layer orientation perpendicular to the longitudinal axis: E2 (1) = ER/T = 450 N/mm 2 E2 (2) = EL= N/mm 2 ; v =  20% (lower quality in the middle layer)

11/2006 Peter Niemz, IfB Wood Physics Group, 12 b) Modulus of elasticity, if L/h<35 (parallel) E b -E by pure bending E x b _ E diminished by shearing E = f (Bending + shearing)

11/2006 Peter Niemz, IfB Wood Physics Group, 13 calculated influence of the lamella ratio on the MOE (pure bending) cv=15%: surface layer parallel, cv=±20% surface layer perpendicular

11/2006 Peter Niemz, IfB Wood Physics Group, 14 Tests on an entire board, supported at all edges (together with the Empa/Dübendorf, Dep. of structural Engineering)

11/2006 Peter Niemz, IfB Wood Physics Group, 15 Overview of panel tests

11/2006 Peter Niemz, IfB Wood Physics Group, 16 Failure of an entire board, not failure by rolling shear

11/2006 Peter Niemz, IfB Wood Physics Group, 17 ProducernMin [N/mm 2 ] Mean [N/mm 2 ] Max [N/mm 2 ] Median [N/mm 2 ] s [N/mm 2 ] x 05 [N/mm 2 ] v [%] Beam tests A B tests at entire board A B Failure stresses determined from beam and panel tests maximal strain tested in tensile zone from the board: 2-3%, solid wood 1% publication „Holz als Roh und Werkstoff“ (2007), test of different models

11/2006 Peter Niemz, IfB Wood Physics Group, Physical Properties a) Equilibrium moisture content (calculated with Hailwood Horrobin)

11/2006 Peter Niemz, IfB Wood Physics Group, 19 sample  m 2 /g U FS UPUP UMUM MHP-3-27pa MHP-3-27pe MHP-3-30pa MHP-3-30pe Surface layer: Pa: parallel; Pe: perpendicular Calculated parameters for sorption (Hailwood Horrobin)  =specific surface, u p = polymolecular water, u m = monomolecular water

11/2006 Peter Niemz, IfB Wood Physics Group, 20 b) Swelling (board thickness 60mm) thickness 0,3-0,5%/% length 0,045 %/%, (20/20/20) 0,016 %/%, (10/40/10) 0,021%/%, (12/12/12/12/12) Influence from board structure (relation surface/middle layer)

11/2006 Peter Niemz, IfB Wood Physics Group, 21 c) Diffusion resistence Adhesive types tested : PVA, UF, PUR (2 types), Resorcin 3 and 5 layer solid wood panels with different lamella ratios

11/2006 Peter Niemz, IfB Wood Physics Group, 22 Influence of the number of gluelines (for 1K PUR)

11/2006 Peter Niemz, IfB Wood Physics Group, 23 The water vapour diffusion resistance is strongly related to the number of glue layers per panel thickness No influence on the water vapour diffusion resistance by the utilisation of different types of adhesives was found The diffusion resistance decreased while the EMC increased Results diffusion resistance

11/2006 Peter Niemz, IfB Wood Physics Group, 24 d) Internal stresses Moisture distribution in wood panels 2 o C/90% RH

11/2006 Peter Niemz, IfB Wood Physics Group, 25 Result: Internal cracks or warping from boards different EMC during production and use different EMC at both sides from the board

11/2006 Peter Niemz, IfB Wood Physics Group, 26 Hindered shrinking of a 3-layer solid wood panel

11/2006 Peter Niemz, IfB Wood Physics Group, 27 Modelling of warping and internal stresses in glued wood a) example: 3-layer parquet element, oak-spruce-spruce veneer; thickness: 14mm (3/8/3mm), diploma thesis b) 2006 we started a PHD about internal stresses in solid wood panels

11/2006 Peter Niemz, IfB Wood Physics Group, 28 Moisture transfer Transfer model, Diffusion 1DModel in ABAQUS Iteration-method simplification - D eff constant - without glueline - without surface material Calculation of the influence from glue lines is possible, but material parameters are necessary

11/2006 Peter Niemz, IfB Wood Physics Group, 29 Model A: Warping from parquet ABAQUS FE Model Model - 3D brick Elements - 20 Points, quadr. interpolation - mash size 2mm Beam theory

11/2006 Peter Niemz, IfB Wood Physics Group, 30 Influence of the grain angle in the surface layer

11/2006 Peter Niemz, IfB Wood Physics Group, 31 Influence of the layer thicknesses

11/2006 Peter Niemz, IfB Wood Physics Group, 32 Model B: Stresses in the glue line and gap opening

11/2006 Peter Niemz, IfB Wood Physics Group, 33 Stress analysis (for parquet; investigations on solid wood panels are ongoing) Longtime study cut A-A Periodic loading increases the creeping, effect delamination can occur after several summer – winter cycles.

11/2006 Peter Niemz, IfB Wood Physics Group, 34 ongoing works

11/2006 Peter Niemz, IfB Wood Physics Group, 35 On-line testing free swelling hindered swelling Testing of internal stresses

11/2006 Peter Niemz, IfB Wood Physics Group, 36 Results (spruce)  Swelling pressure time [d] pressure p Q [kN/mm²] Fichte (tangential) Fichte (radial) Fichte (longitudinal) MDF (Plattenebene) Dreischichtplatte

11/2006 Peter Niemz, IfB Wood Physics Group, 37 Results (spruce)  Free swelling time [d] swelling α [%/%] Fichte (tangential) Fichte (radial) Fichte (longitudinal) MDF (Plattenebene) DSP (stehende Jahrringe) DSP (liegende Jahrringe)

11/2006 Peter Niemz, IfB Wood Physics Group, 38 3.Conclusions  Solid wood panels have a very high value added (producer mostly saw mills)  Properties can be calculated  Scientifically interesting field of work

11/2006 Peter Niemz, IfB Wood Physics Group, 39 IfB, Wood Physics Any Questions?