The Influence of Thickness on the Tensile Strength of Finnish Birch Veneers under Varying Load Angles

Abstract

The development of high-performance, veneer-based wood composites is a topic of increasing importance due to the high design flexibility and the comparable mechanical performance to solid wood. Part of this improved mechanical performance can be contributed to the size effect present in wood. Based on previous findings in the literature, this size effect can be either strengthening or weakening. The presented study investigates the influence of thickness and load angle on the tensile strength and tensile stiffness of peeled veneers compared to thin sawn timber. Veneers with thicknesses of 0.5 ± 0.05 mm, 1.0 ± 0.05 mm and 1.5 ± 0.05 mm as well as sawn wood with thicknesses of 1.5 ± 0.1 mm, 3.0 ± 0.1 mm and 5.0 ± 0.1 mm were tested in tension under different load angles (0°, 45° and 90°). The results only partly confirm a size effect for strength parallel to the grain. The strength perpendicular to the grain increased significantly between 0.5 mm and 1.5 mm, with a significant decrease between 1.5 mm and 5.0 mm. The presence of lathe checks diminished the strength perpendicular to the grain of the veneers by about 70% compared to solid wood, partly overshadowing a possible strengthening effect. It was concluded that a transition from a strengthening to a weakening behaviour lies in the range of multiple millimetres, but further investigations are needed to quantify this zone more precisely. The presented results provide a useful basis for the development of veneer-based wood composites with a performance driven layer-thickness.

Toward the modelling of laminated veneer lumber stiffness and the influence of the number of plies

“…A strong dispersion was observed on the longitudinal Young's modulus [0°]1 specimens. It should be noted, however, that the dispersion observed was of the same order of magnitude as that observed by other authors on tensile tests on 1-ply 1 mm veneers (Pramreiter et al 2021). In addition, the average stiffness value obtained in these tests was of the order of magnitude of the values found in the literature.…”

“…The standards for tensile tests on wood-based panels, and therefore on plywood and LVL, recommend the design of 'bone-shaped' specimens to reduce the transverse cross-section of the specimen and avoid breakage of the specimen in the jaw area (ASTM D1037-99 and NF EN 789). Given the small thickness of wood veneers and their fragility, their machining to obtain a bone shape causes the specimens to break (Pramreiter et al 2021). The choice to characterize specimens with rectangular geometry and to add beads is, therefore, often made to avoid breaking of the jaws during the tensile test (Shupe et al 1998;Wu et al 2005;Jeong et al 2010;Pramreiter et al 2021;Lechner et al 2021).…”

“…Given the small thickness of wood veneers and their fragility, their machining to obtain a bone shape causes the specimens to break (Pramreiter et al 2021). The choice to characterize specimens with rectangular geometry and to add beads is, therefore, often made to avoid breaking of the jaws during the tensile test (Shupe et al 1998;Wu et al 2005;Jeong et al 2010;Pramreiter et al 2021;Lechner et al 2021).…”

Evaluation of Oak-Specific Consumption, Efficiency, and Losses from an Aesthetic Veneer Factory

“…Pramreiter et al [22] presented the importance of the development of veneer-based wood composites due to the high flexibility of design and mechanical strength compared to solid wood. The study showed the influence of veneer thickness on tensile strength compared to solid wood.…”

The Influence of Slicing Thickness on the Perpendicular to Grain Tensile Properties of Oak (Quercus robur L. and Quercus petraea L.) Lamellae

“…Due to the occurrence of slicing checks being mainly in the wood radial direction and surface checking occurring when the material is under surface tension loading, it is assumed that tensile strength perpendicular to the grain is a critical parameter that could describe veneer or sliced lamellae mechanical performance. Regarding this aspect, a relevant study represents the investigation of the mechanical properties of plainand lengthwise-sliced beech lamellae [6] and birch rotary-cut veneers [23]. Hence, these studies evaluated low slicing thicknesses, i.e., 0.5-1.5 mm.…”