Time dependence of the orthotropic compression Young’s moduli and Poisson’s ratios of Chinese fir wood

Abstract

The time dependency of the orthotropic compliance for Chinese fir wood [Cunninghamia lanceolata (Lamb.) Hook] has been investigated by performing compressive creep experiments in all orthotropic directions. Time evolution of the creep strain in the axial and lateral directions was recorded by means of the digital image correlation (DIC) technique, to determine the diagonal and nondiagonal elements of the viscoelastic compliance matrix. The results reveal the significant influence of time on the mechanical behavior. The orthotropic nature of the viscoelastic compliance is highlighted by the different time dependency of the Young's moduli and the Poisson's ratios obtained for the individual directions. Differences among the time-dependent stress-strain relationship determined at the 25, 50, and 75% stress levels indicate that the viscoelastic behavior of wood is also load-dependent. A Poisson's ratio values, which are increasing with time in ν LR , ν LT , ν RT , ν TR , and decreasing in ν RL and ν TL , demonstrate that the creep strain is influenced by loading directions. The substantially different time dependency of the nondiagonal elements of the compliance matrix further reveals the orthotropic compliance asymmetry and emphasizes the complexity of the viscoelastic character of wood.

Evaluating the viscoelastic shear properties of clear wood via off-axis compression testing and digital-image correlation

“…This is similar to other creep investigations of wood materials, e.g. Ozyhar et al (2013), Hayashi et al (1993) and Jiang et al (2016). For design purposes, much longer test times are obviously needed to reduce errors stemming from extrapolation.…”

“…There have been numerous research studies on the static and time-dependent behaviour of wood in the normal directions, i.e. the L, T and R directions [Vorobyev (2017), Ozyhar et al (2013), Jiang et al (2016), Afshar et al (2020)]. An experimental method to find the normal-creep properties of wood using small cubic samples under compression has been used, see Afshar et al (2020).…”

Influence of Additional Bracing Arms as Reinforcement Members in Wooden Timber Cross-Arms on Their Long-Term Creep Responses and Properties

“…On the other hand, the left main member had higher A parameter value compared to the right main member in both cross-arms. This indicated that the left main member had grain orientation in either radial, tangential, or longitudinal direction which differed in terms of their creep resistance performance [42,43]. In terms of stress-independent material exponent, the findings showed that the average value for the existing right cross-arm (0.8016) was higher than the existing left crossarm (0.5188) as shown in Table 3.…”

Creep Properties and Analysis of Cross Arms’ Materials and Structures in Latticed Transmission Towers: Current Progress and Future Perspectives

“…However, a coupon-scale test analysis can only describe the long-term properties of specimens in a controlled environment. In this case, the results of a coupon-scale creep test cannot explain the creep behaviour in terms of structural applications such as cross arms in transmission towers [ 65 , 113 ]. Despite these limitations, a creep study can be conducted in a controlled laboratory environment, which can demonstrate the creep properties under ideal conditions by neglecting other combined environmental factors such as humidity, temperature, sunlight rays, and fungi degradation.…”