Moisture-induced stresses and distortions in spruce cross-laminates and composite laminates

Abstract

The crosswise gluing of cross-laminated panels made of solid wood can cause problems when exposed to moisture variations. In the present study, the substitution of the spruce middle layer by a wood composite is tested for its influence on moisture-induced stresses and deformations in laboratory tests and numerical simulations. Furthermore, slits in the spruce middle layer were investigated. The hygroscopic warping due to a moisture gradient, stresses caused by moistening and cracks due to drying were studied. The results show larger warping in composite laminates compared to the spruce cross-laminate, which is governed by the modulus of elasticity of the middle layer. The in-plane swelling was found to be larger in composite laminates, while stresses were lower. The drying test discovered that cracks develop in the middle layer of spruce-medium density fiberboard laminates due to shear stresses and tensile stresses in the thickness direction. It was concluded that slits can be applied in the middle layer, as they have no significant influence on moisture-induced stresses but increase the thermal insulation. If the substitution of the spruce layer is required, the application of oriented strand board in the middle layer is recommended.

Internal stress measurement during drying of rubberwood lumber: effects of wet-bulb temperature in various drying strategies

“…Moistureinduced stresses were recently reviewed by Angst and Malo (2010) and Gereke et al (2010) . If the IS is ignored, or if it is not properly accounted for, an attempt to improve drying performance simply by accelerating the drying rate, e.g., by raising the drying temperature or lowering the relative humidity, might easily lead to the formation of various drying defects such as surface and end checking, splitting, collapse, and honeycombing.…”

Improved weathering performance and wettability of wood protected by CeO2 coating deposited onto the surface

“…In principle, wood is hydrophilic and water or water vapor is absorbed quickly by capillary action on its surface followed by a penetration in deeper layers (Eichhorn et al 2001;Stark and Rowlands 2003;Soykeabkaew et al 2004;Hakkou et al 2005). Water gradients cause different swelling and shrinking effects resulting in warping, cupping, face checking, and new cracks, which accelerate the weather ing process (Gereke et al 2010;Clair 2012;Gamstedt et al 2013).…”

Finite element modelling of moisture related and visco-elastic deformations in inhomogeneous timber beams

“…This dynamic moisture process can result in solid timber and laminated timber products becoming markedly distorted (twisted, bowed, cupped or crooked) when they are exposed to climatic variation; see e.g. Johansson and Kliger (2002), Ekevad (2005), Ormarsson and Cown (2005), Astrup (2009) and Gereke et al (2010). It is also well documented that wood is an inhomogeneous material concerning such parameters as the modulus of elasticity (MOE) [Dahlblom et al (1999a)] and shrinkage coefficients in the fibre direction [Yamashita et al (2009), and Dahlblom et al (1999b)].…”