Mechanical Properties of Norway Spruce: Intra-Ring Variation and Generic Behavior of Earlywood and Latewood until Failure

Abstract

The alternating earlywood and latewood growth ring structure has a strong influence on the mechanical performance of Norway spruce. In the current study, tensile tests in the longitudinal and tangential directions were performed on a series of specimens representing one growth ring at varying relative humidities. All tested mechanical parameters, namely modulus of elasticity and ultimate tensile stress, followed the density distribution in the growth ring, with the minimum values in earlywood and the maximum values in latewood. The samples were conditioned at three relative humidity levels 50%, 65%, and 95%. With increasing relative humidity, the values of the mechanical parameters were found to decrease. However, due to the high local variability, this decrease was not statistically significant. The test in the tangential direction on a set of earlywood and latewood specimens at 65% relative humidity revealed a similar limit of linear elasticity for both early-and latewood. Where the strength of both tissues was equal, the strain at failure was significantly greater for earlywood. Furthermore, the portion of the non-linear stress/strain behavior for earlywood was significantly greater. A Weibull analysis on the ultimate tensile strength revealed a tissue-independent Weibull modulus, which indicates similar defect distributions. For both, the failure occurred in the middle lamella.

Effect of loading rate on mechanical properties of micro-sized oak wood

“…Both Dinwoodie (2000) and Sugiyama (1967), using higher loading rates (2 days-2 years), determined that, as a result of creep, the mechanical properties of wood were influenced by the loading rate. Lanvermann et al (2014), however, reported that, because of the high local variability of the values, the mechanical properties were not significantly decreased. Moreover, Dinwoodie (2000) concluded that the effect of the loading rate depended on the size of the sample and that the rate was higher in structural timber than in small, clear specimens.…”

Mechanical Properties of Earlywood and Latewood Sections of Scots Pine Wood

“…Micro-scale sized samples have been used to determine the mechanical properties of earlywood and latewood sections, wood strands, and fibers Cramer et al 2005;Kretschmann et al 2006;Hindman and Lee 2007;Jeong 2008;Jeong et al 2009;Lanvermann et al 2014;Roszyk et al 2016). Cramer et al (2005) determined the elastic properties of EW and LW (longitudinal modulus of elasticity, shear modulus) in loblolly pine wood.…”

Effect of Loading Rate on Mechanical Properties of Micro-size Scots Pine Wood

“…Both Dinwoodie (2000) and Sugiyama (1967), using lower loading rates (2 days-2 years), determined that, as a result of creep, the mechanical properties of wood were influenced by the loading rate. Lanvermann et al (2014), however, reported that, because of the high local variability of the values, the mechanical properties were not significantly decreased. Moreover, Dinwoodie (2000) concluded that the effect of the loading rate depended on the size of the sample and that the rate was higher in structural timber than in small, clear specimens.…”