A Mathematical Solution for Calculating the Springback of Laminated Beech Stacks Molded within the Elastic Range

• Main Authors: Moritz Sanne, Gudrun Ahn-Ercan, Alexander Pfriem
• Format: Article
• Language: English
• Published: MDPI AG 2020-07-01
• Series: Forests
• Subjects: elasticity value of lamination stacks; form relaxation; shape distortion; springback; wood moldings
• Online Access: https://www.mdpi.com/1999-4907/11/7/725

The springback effect in molded wood laminations within the elastic range has, to date, not yet been mathematically described. Once cured, residual internal stresses within the laminations cause the final form to deviate from that of the die. Test pieces of beech laminations of 1 mm, 2 mm and 4 mm thicknesses and stack sizes of between 2 and 16 laminations were used. The elasticity value of each stack was obtained using non-glued laminations in a three-point bending test within the elastic region. The laminations were glued with polyurethane resin and mounted in a radius form die. The stress induced by the die onto the stack is within the elastic region of the material without any prior chemical or physical plasticisation of the wood. After curing was complete and the laminations removed from the die, the actual radius was calculated using a circular equation within the CAD program, using three measurement points taken from the stack. The radius of the die within the limits of this study has a negligible effect when predicting the springback of the stack. The exponential correlation between springback and the number of laminations, was used to calculate the springback effect on molded laminated stacks.