Plywood rib stiffened sandwich type panels could be used to substitute conventional plywood boards in structures where weight reduction is necessary. Filling core between plywood ribs with lightweight polymer will give additional benefit of soundproofing and it will increase the thermal insulation properties moreover it will enable improved production process of sandwich panels. Rigid polyurethane (PU) foams provide those mentioned manufacturing and physical benefits. In current research all plywood rib stiffened sandwich type panels were produced by direct PU foam injection into core between ribs. Such foam application allowed to produce sandwich panels without preliminary use of adhesive for structural integrity. Two different PU foam formulations were examined and tested as core filler. Commercial PU foam system from BASF (Elastopor H 1700/10) was initial choice-used as reference material. A second one – PU foam formulations based on polyols from renewable resources were used as sustainable alternative. PU foams from renewable resources were developed from tall oil, which is cellulose production by-product. Polyols were synthesized from tall oil by carboxylic acid esterification with polyfunctional amide based alcohol – diethanolamine. PU foam formulation with slow technological parameters (cream time – 20-30 s) were developed to be used for injection into core of plywood sandwich panels. PU foam morphology in core of PU foam and in adhesion layer was evaluated by SEM microscopy. The adhesion strength and the mechanical (tensile and compression strength) properties of PU foams were used as input data in numerical modelling. Sandwich panel stiffness and effective thermal conductivity were acquired by means of numerical analysis in ANSYS software. Consequent numerical optimization was performed to evaluate trade-off between sandwich panel masss, stiffness and thermal conductivity. Comparing rib stiffened sandwich structures with tradition plywood boards it is possible to found an equivalent stiffness sandwich panels with weight reduction up to 35 % and effective thermal conductivity of 0.029 W/m·K (reference to 0.12 W/m·K for solid plywood board).
Keywords: plywood composite, rigid polyurethane foam, lightweight structure, finite element modelling, mechanical testing, ANSYS, Pareto optimality front
Authors
Labans E.
Institute of Materials and Structures, Riga Technical University, Riga, Latvia
Delft University of Technology, Faculty Aerospace Engineering, Delft, The Netherlands
Kirpluks M.
Latvian State Institute of Wood Chemistry, Riga, Latvia
Kalnins K.
Institute of Materials and Structures, Riga Technical University, Riga, Latvia
Japins G.
Institute of Materials and Structures, Riga Technical University, Riga, Latvia
Cabulis U.
Latvian State Institute of Wood Chemistry, Riga, Latvia
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