Mechanical properties of Papua New Guinea balsa wood

Abstract

The mechanical properties of plantation-grown balsa wood from Papua New Guinea (PNG) were determined according to American Society for Testing and Materials D143-09. Static bending, hardness, compression parallel and perpendicular to grain, and shear parallel to grain tests were performed on kiln-dried specimens segregated into the three international density classes (80 ≤ 120, 120 ≤ 180 and 180 ≤ 220 kg/m³). The literature states balsa with a density between 120 and 180 kg/m³ has the most commercial value in contemporary markets. The results presented in this study indicate that balsa with a density around 150 kg/m³ can have superior strength properties to balsa with a higher and lower density (this was most evident in the compression perpendicular and shear tests). Specimen moisture content and air dry density were calculated to identify elements which may affect the strength properties of balsa. Generally, the greater the density of a specimen, the greater the strength. However, unusual patterns were noted in this study where density had little impact on the increase in strength (particularly in the hardness and shear tests). Average strength results for the medium density class of PNG-grown balsa were: modulus of elasticity 2037 MPa, modulus of rupture 16.6 MPa, hardness tangential surface 307 N, hardness radial surface 291 N, hardness axial surface 426 N, compression parallel 9.2 MPa, compression perpendicular 1.1 MPa and shear 1.9 MPa.