PSI - Issue 37

Almudena Majano-Majano et al. / Procedia Structural Integrity 37 (2022) 492–499 Almudena Majano-Majano et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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MPa derived from edgewise bending tests under four-point loading (UNE-EN 408:2011) and a mean density ρ =793 kg/m 3 determined for a reference moisture content of 12%. Other material parameters required for this study are the modulus of elasticity in the radial direction, E R =1820 MPa, and the shear modulus of elasticity in the LR plane, G LR =1926 MPa. These values were taken from Crespo et al. (2017), who used eucalyptus boards from the same origin and similar density. Eleven Double Cantilever Beam (DCB) specimens were prepared to evaluate the fracture properties in mode I loading. Each specimen consisted of a rectangular beam of eucalyptus composed by two parts glued at mid-height. They were oriented along the RL crack propagation system (the first letter denotes the direction normal to the crack plane and the second letter refers to the crack propagation direction). The global specimen dimensions were L 1 =250 mm, L =240 mm, 2 h =20 mm, B =20 mm and t =0.1 mm as shown in Fig. 1. A mid-height pre-cracked surface of initial length a 0 =100 mm was performed by means of a thin Teflon ® film in the bonding operation.

Fig. 1. DCB specimen geometry.

One-component polyurethane (1C-PUR) adhesive type I, PURBOND ® HB S109 was used for this purpose. This adhesive contains isocyanate pre-polymer and has a Brookfield viscosity of approx. 20000 mPa.s and a density of around 1100 kg/m 3 . It also has important advantages such as fast curing at room temperature, invisible glue joints, being formaldehyde and solvent-free and not requiring mixing. Pressure was gradually applied to the DCB specimens (Fig. 2 left) by a universal Instrom ® testing machine until the target end pressure was reached, which was then held for 25 minutes complying with the adhesive manufacturer ’s details. The final bond strength was attained after approximately 12 hours.

Fig. 2. Bonding process of a group of four DCB specimens (left).; DCB test set-up coupled with DIC (right).

2.2. Experimental set-up DCB fracture tests were performed (Fig. 2 right). A mode I fracture was assumed to occur along the extension L a 0 (Fig. 1) by applying a load perpendicular to the pre-cracked surface through a symmetrical pair of pins inserted into