Mechanical properties of sawn timber from Norway spruce

Abstract

Dynamic and static tests were performed on 523 lumber specimens of Norway spruce (Picea abies) of three different cross sectional sizes: 38 x 89 mm 2, 38 x 140 mm 2, and 38 x 184 mm 2. Specific material characteristics for the lumber are presented. The tests also enabled comparison between results from two testing methodologies. The mean value for the modulus of elasticity established from the dynamic tests was found to be approximately 10% higher than the corresponding value established from static tests. The statistical correlation between statically and dynamically established moduli is very strong. The dynamic E modulus was found to be as good a strength predictor as the static E modulus. Cross sectional size and the existence of the pith in the sawn lumber were found to significantly influence the material properties. In general terms, it was found that deeper beams correspond to lower values for the E modulus and for the bending strength. The reason for this tendency is believed to be a combination of a volumetric effect (in the case of strength) and a phenomenon related to the log selection and sawing process in the mills. Lumber that comprises the pith has been found to have generally lower values of the E modulus and bending strength while the shear modulus is higher, compared to lumber without pith sawn further out in the log. Mechonische Eigenschcrften von FichtenschnittholzAn 525 Schnittholzproben (Picea abies) wurden dynamische und statische Priifungen vorgenommen. Die Proben hatten drei verschiedene Querschnitte: 38 x 89 mm 2, 38 x 140 mm 2 und 38 x 184 mm 2. Anhand der vorgelegten Ergebnisse wurden auch zwei Priifmethoden verglithen. Die Mittelwerte der dynamischen MOE-Prfifung lagen etwa 10% h6her als die statisch ermittelten Werte. Die Korrelation beider MOE-Werte ist sehr streng. Beide Werte k6nnen zur Vorhersage der Festigkeit verwendetThe dynamic tests and subsequent evaluation and comparison between dynamic and static test data were made within a project concerning the determination of viscoelastic properties of anisotropic materials by modal testing, which is financially supported by the Swedish Research Council for Engineering Sciences (TFR) in grant No. 261-94-344; this is gratefully acknowledged. werden. Der Querschnitt und die Anwesenheit von Markanteilen beeinflussen das Ergebnis wesentlich. Je tiefer die Balken waren d.h. je n~iher sie der Markr6hre lagen, desto geringer waren E-Modul und Biegefestigkeit. Die Grfinde dafiir werden tells einem Volumeneffekt zugeschrieben (ira Falle der Festigkeit), tells auf das Auswahlverfahren der St~imme im S~igebetrieb zurfickgeffihrt. Schnittholz mit Markanteil hatte allgemein, einen geringeren E-Modul und niedrigere Biegefestigkeit als Proben aus iiufleren Stammbereichen; die Scherfestigkeit lag dagegen h6her.

Comparison of Non-Destructive Methods Based on Natural Frequency for Determining the Modulus of Elasticity of Cupressus lusitanica and Populus x canadensis

“…The coefficient of determination (R 2 ) shows the degree of description given by the dependence or degree of reliability of MOE calculated according to the given equation. Dynamic MOE generally shows a lower correlation of dependence with bending strength than applies to the dependence of dynamic MOE and static MOE (Bodig and Jayne 1982;Larsson et al 1998;Guntekin et al 2013;Baar et al 2015). For samples with a lower defect content (especially knots), these dependencies increase and the prediction of mechanical properties by dynamic testing is more accurate (Ayarkwa et al 2000).…”

“…In the case of CL, on the contrary, a significant statistical deviation was registered between static MOE and both dynamic methods (15.5% for MTG and 12.7% for accelerometer). The difference between the results of the dynamic and static tests of solid wood may be caused by the viscoelastic properties of wood, which play a role in the static bending test; additionally, the duration of the load on the tested element, which causes creeping and distorts real MOE, is important (Bodig and Jayne 1982;Larsson et al 1998). If the creeping effect were eliminated, the deviations between the static and dynamic values would decrease (Teranishi et al 2008).…”

Prediction of timber bending strength on basis of bending stiffness and material homogeneity assessed from dynamic excitation

“…It should further be noted that the static MOE represents a local stiffness over the grade determining defect while the dynamic MOE represents a mean value over the full specimen. A study carried out by Larsson et al (1998) on more than 500 timber specimens of Norway spruce comprises results on dynamic axial stiffness, dynamic bending stiffness, static bending stiffness and bending strength. However, the results in terms of coefficients of determination do not indicate that the dynamic bending stiffness correlates stronger to the bending strength than the dynamic axial stiffness.…”

Material characterisation of fast-grown plantation spruce

“…Steffen et al (1997) reported that density and modulus of elasticity varied considerably over the cross-section of Norway spruce boards. Larsson et al (1998) found a coefficient of determination of 0 . 26 between bending strength and density.…”