Orthotropic Viscoelastic Properties of Chinese Fir Wood Saturated with Water in Frozen and Non-frozen States

Abstract

In order to better understand the differences in orthotropic viscoelastic properties of Chinese fir (Cunninghamia lanceolata) in frozen and non-frozen states, the storage modulus (E′) and loss modulus (E″) of the longitudinal, radial, and tangential specimens were investigated under water-saturated conditions with temperatures ranging from −120°C (or 30°C) to 280°C. Results revealed that the order of magnitude in E′ for each orientation was consistent for temperatures below 0°C, while the anisotropy in E′ was reduced due to the enhancement effect of ice. Frequency-dependent γ-relaxation was observed at approximately −96°C for all orthotropic directions. A sharp discontinuity in E′ occurred at approximately 0°C for each specimen, together with the corresponding sharp peak in the E″ spectrum. Furthermore, the frozen free water had an effect on the orthotropic viscoelastic behavior in the water-saturated specimens within the range of −120°C to 280°C. Specimens with a frozen history leveled off at the initial temperature ramping phase for each orientation, while a frozen history reduced the decline in stiffness of the wood specimens. Similar to the variations in E′, the dramatic loss of water increased the complexity of the E″ values. The loss of free water also had a pronounced effect on the viscoelastic properties during the temperature ramping process. Thus, in the wood industry, it necessary to consider the variations in the orthotropic viscoelastic performance of specimens under water-saturated conditions during the water loss process.

Effect of Samples Length on the Characteristics of Moisture Transfer and Shrinkage of Eucalyptus urophylla Wood during Conventional Drying

“…These findings indicate that the drying rate of free water has less effect on collapse for samples with a length below 200 mm. When the MC is lower than the FSP, the collapse of the 30 and 100 mm samples had a small change, but the collapse of the 200 mm samples increased to a peak after the MC reached the FSP and subsequently deceased with MC reducing due to the recovery of cell walls [41]. The differences of final shrinkage of three sets of samples were not great in this study.…”

“…The transversal shrinkage curves of the samples during the drying are shown i ure 7. Generally, normal shrinkage occurs at an MC below the FSP [41]. However, al ples shrink both in the tangential and radial direction above the FSP.…”

Calibration of Acoustic Emission Parameters in Relation to the Equilibrium Moisture Content Variations in a Pinus sylvestris Beam

“…Finally, the energy attenuation rate along the samples at the end of the drying process (after 160 days) can be calculated as the sum of the difference between the initial and final state of EMC, from the pith to the outmost layers of the sample. Analytically, this can be expressed using Equation (6), where β is the coefficient of the energy attenuation rate.…”

“…Specifically, Scots pine shows a density that ranges between 505 kg/m 3 and 540 kg/m 3 when the moisture content is varied between 12% and 12.4% [5]. Indeed, recently, Li et al demonstrated that moisture content has a direct effect on the mechanical properties of wood by modifying orthotropic viscoelastic performance during a water loss process [6], and other recent studies assessed that this change in the mechanical behaviour of wood leads to differences in energy release for acoustic emission monitoring during fracture when moisture content changes [7,8]. Indeed, fluctuations in ambient relative humidity (RH) are considered the main factor that contributes to the deterioration of wooden objects and acoustic emissions are able to detect the stress induced by such climate variability [9].…”