Moisture content penetration in wood elements under varying boundary conditions

Knowledge of effects of moisture exposure on timber structures is important for serviceability and load bearing capacity of timber elements and systems. Varying climate affects the moisture content profiles in timber as the relative humidity changes in the ambient air. This paper presents methods for calculation of diffusion based moisture transport and corresponding results on how timber responds to varying moisture with regard to moisture penetration and distribution. The calculations are based on measured outdoor relative humidity and temperature at different climatic locations in Sweden. No remarkably large deviations between the different climatic locations were found in general, which is positive in a design code perspective.     

Moisture content adjustments for dynamic modulus of elasticity of wood members

The influence of moisture content (MC) on the dynamic modulus of elasticity of structural lumber was investigated using transverse vibration testing methods. The flexural rigidity (EI) of a transversely vibrating beam was calculated as the modulus of elasticity (E) multiplied by the moment of inertia (I). The increase in E of lumber due to reduction in moisture content was computed by assuming that the flexural rigidity remains constant with changes in moisture content. Reductions in I due to shrinkage were compensated by the increases in E which led to a proposal for a species-dependent MC adjustment model for modulus of elasticity. The model was validated using 38 mm × 89 mm × 4,290 mm western Canadian Spruce–Pine–Fir dimension lumber evaluated in the “as-received” and “dry” conditions. Results obtained from the species-dependent model agreed closely with those from the E adjustment equation for dimension lumber given in ASTM D 1990. The results show that the ASTM moisture adjustment procedures can be used to adjust dynamic E values for changes in moisture content also.     

Moisture content profiles and uptake kinetics in wood cladding materials evaluated by a portable nuclear magnetic resonance spectrometer

Abstract

This study evaluated the capability of nuclear magnetic resonance (NMR) technology based on small portable magnets for in situ studies of the local moisture content in wood. Low-field and low-resolution [¹H]NMR with a unilateral permanent magnet was used to monitor and map the moisture content of wood cladding materials of various types in a spatially resolved manner. The results show that portable NMR equipment based on small open-access permanent magnets can be successfully used for non-invasive monitoring of the moisture content in various extended wood specimens. The moisture content was measured with a depth resolution of 0.2 mm and a maximum penetration depth of 3 mm. This makes the technique suitable for in situ local moisture content measurements beneath a coating layer in the cladding, for example, and it is also possible to relate the moisture level to specific properties of the wood material.     

Moisture content—water potential relationship of wood from saturated to dry conditions

Summary The water potential concept as applied to wood-water relations is presented. The gradient in water potential can be used as the driving force of moisture in wood in a model of drying in isothermal conditions provided the moisture content — water potential relationship is known. This relationship is established for aspen sapwood in desorption from saturated to dry conditions at 20, 35 and 50 °C for two specimen orientations. The tension plate, pressure plate and pressure membrane methods were used at high moisture contents and equilibration over saturated salt solutions was used at low moisture contents. The results obtained demonstrate that these methods can be used in combination in order to establish the relationship within the whole range of moisture contents. The equilibrium moisture contents obtained by the tension plate, the pressure plate and the pressure membrane methods for tangential desorption were slightly higher than those measured for radial desorption. The water potential increased with temperature at a given moisture content. This effect cannot be solely explained by the variation of surface tension of water with temperature.This research was supported by the Fonds pour la Formation de Chercheurs et l'Aide à la Recherche, Gouvernement du Québec, and by the Natural Sciences and Engineering Research Council of Canada     

Nondestructive testing method of wood moisture content based on a planar capacitance sensor model

For our research, a new hybrid experimental-computational method is presented. We applied a least squares fitting     

Detection of wood density by using a DOE sensor

HeNe laser light components scattered through small wood samples from Scots pine (Pinus sylvestris L.) were investigated using a diffractive optical element (DOE) sensor and the optical signals compared with optical density data extracted from x-ray negatives of the respective samples. Good agreement between the x-ray and optical signals was observed with respect to the gravimetric density of the Scots pine samples. Received 20 January 1999     

Exact analysis of shear strain in wood

Summary An analysis is given which enables the shear strain in a piece of timber to be specified in terms of the difference between tangential and radial strain, herein termed the angular strain. The angular strain is then evaluated in terms of the orientation of two lines at right angles prior to deformation. The equations involved are simple and facilitate the evaluation of strain parameters which would otherwise require numerical computation.Symbols a, b, c length parameters, Fig. 2 - C half chord length - k constant of proportionality - r radial coordinate (distance from pith) - x length coordinate (board) - , angle parameters, Fig. 1 - shear strain - width of segment - angular strain - #x025B; tangential strain - _r radial strain - ₁, ₂ components of shear strain, Fig. 1 - angle parameter, Fig. 2 - angle parameter, Fig. 3 - angle parameter, Fig. 2 The author wishes to thank Mr. J. W. Sutherland for his assistance with the presentation of this paper.     

Evaluation of moisture content distribution in wood by soft X-ray imaging

A technique for nondestructive evaluation of moisture content distribution in Japanese cedar (sugi) during drying using a newly developed soft X-ray digital microscope was investigated. Radial, tangential, and cross-sectional samples measuring 100 × 100 × 10 mm were cut from green sugi wood. Each sample was dried in several steps in an oven and upon completion of each step, the mass was recorded and a soft X-ray image was taken. The relationship between moisture content and the average grayscale value of the soft X-ray image at each step was linear. In addition, the linear regressions overlapped each other regardless of the sample sections. These results showed that soft X-ray images could accurately estimate the moisture content. Applying this relationship to a small section of each sample, the moisture content distribution was estimated from the image differential between the soft X-ray pictures obtained from the sample in question and the same sample in the oven-dried condition. Moisture content profi les for 10-mm-wide parts at the centers of the samples were also obtained. The shapes of the profiles supported the evaluation method used in this study. Part of this work was presented at the 57th Annual Meeting of the Japan Wood Research Society, Hiroshima, August 2007     

Image analysis to measure strain in wood and paper

Summary A fast and accurate strain measurement method was developed to quantify microscopic deformation in wood and paper using video images. Two or more video images, one of which was undeformed and the others of which were deformed, were digitized and compared using the image correlation technique. This digital computer pattern recognition technique permitted the displacement of any point in the image to be measured. Then, strain between any two points in this observation field could be calculated and, hence, normal, shearing strains and Poisson's ratio could be measured directly. Independent strain measurements showed that the method using video images provided accurate strain measurements and could be applied to complex materials like wood and wood products. The strain measurements using the image analysis produced not only normal strains but strain profiles of the normal strains. From the strain profiles, it was possible to detect local areas of strain concentration which might be beyond the elastic range. As it measures displacements and strains from a set of video images using the image correlation technique, the method is non-contact and the observation field can be adjusted easily by changing magnifying power of the optical devices. Thus, the method can be applied to mechanical testing of wood and wood products from the cellular level to full size lumber and will no longer be limited by the fragile nature of the material being tested, industry standards, or equipment restrictions.Authors are grateful to U.S.D.A. for supporting this investigation which is a part of the USDA funded project Initiation and Propagation of Failure in Wood. Authors are also grateful to N. C. Brown Centre for Ultrastructure Studies, CESF, SUNY, Syracuse and Empire State Paper Research Institute, Syracuse for providing research facilities     

A portable NMR sensor for moisture monitoring of wooden works of art, particularly of paintings on wood

It is proposed the use of a mobile device based on a NMR single-sided sensor for in situ non-invasive determination of the moisture content (MC) of wood items, especially items of Cultural Heritage interest. The MC is obtained through the moisture volume fraction, which is an appropriate quantity for the sensor and corresponds to the fraction of its measurements sensitive volume occupied by water. The device has been used here to track changes in MC of wood specimens caused by changes over time of the environmental relative humidity. The kinetics of water adsorption has been related to results obtained with the gravimetric method. Measurements on an old painting, the Pietà (1516–1517), oil on a poplar wood panel by Sebastiano del Piombo (1485 Venice, 1547 Rome), Civic Museum, Viterbo, Italy, have shown, conclusively, the good sensitivity of the sensor and its capability to behave as a non-invasive and in situ utilizable device. Results of in situ painting measurements show that the NMR sensor can track moisture fluctuations that are outside the sensitivity range and precision of electro-hygrometric approach.     

Moisture content target optimization in lumber drying

Abstract

A Lumber Quality Model developed to predict lumber grade after drying was applied and validated in industry. The model was calibrated with a 198-piece lumber package that was dried at a local sawmill in British Columbia, Canada, and 30 sawmill grade reports were recorded from 2008 to 2010. The calibrated model was then used to predict the target moisture content that would result in the maximum lumber value. It was predicted that lumber value should increase by approximately 17 CAD (Canadian dollars) m^?3 if the target moisture content were reduced from the historic 17% to an optimum of approximate 13%. The sawmill implemented the recommendations and the predictions were validated with another seven industrial drying runs.     

Impregnation of radiata pine wood by vacuum treatment II: effect of pre-steaming on wood structure and resin content

Radiata pine sapwood and heartwood were dried using high-temperature, conventional-temperature, and air drying schedules with and without pre-steaming. They were then impregnated by vacuum treatment with double-distilled water, toluidine blue, and fluorescein dye. For sapwood, there were only minor differences in uptake between drying methods and when pre-steaming was used. Using microscopy, the primary flow pathways in sapwood were found to be the resin canal network and ray parenchyma cells, which provided conduction without large resistance. In heartwood, uptake was strongly influenced by pre-steaming the green lumber. After pre-steaming heart-wood, there was an increase in uptake from all surfaces but especially from the radial surfaces. Lower extractive contents, disruption of epithelial and ray parenchyma cells, and alteration of the condition of bordered pits were also associated with pre-steaming. It was therefore possible to classify flow paths in radiata pine heartwood five ways, according to uptake values and wood anatomical features.This research was presented in part at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998.     

Improved methodology of measuring moisture content of wood by a vibrational technique

Abstract

A method of measuring moisture content of wood is introduced. This method uses a vibrational technique. A shaker driven by swept sine signals was used for the accurate generation of vibration. A cylindrical wood sample was used to verify the method of measuring the moisture content. Resonance frequencies of the wood sample decreased as its moisture content increased. An experiment was performed by measuring the vibration of a tree to explore the feasibility of applying the method to the measurement of the moisture content of trees. The circumferential mode, which is independent of the height of a tree, was identified using a white oak tree.     

Moisture content and temperature effect on ultrasound timber grading

Summary Because wood is a natural material, the variability of its properties is very large. In order to use wood efficiently in building, it has to be stress graded. The ultrasonic stress grading was developped as an improved alternative to visual grading. This non destructive evaluative technique allows reliable higher strength values while working with new products. Corrected models were studied to reference the ultrasonic propagation speed at constant moisture content and temperature. Using a referential ultrasonic wave velocity, stress grading can be carried out on trees or logs before cutting, or on fresh beams. The correlation between conditioned beams and test specimens is very high, especially for the strongest material.The author wishes to thank the Swiss Federal Institute of Technology Lausanne for acceptance of his doctoral thesis work, June 1990     

Improved methodology of measuring moisture content of wood by a vibrational technique

A method of measuring moisture content of wood is introduced. This method uses a vibrational technique. A shaker driven by swept sine signals was used for the accurate generation of vibration. A cylindrical wood sample was used to verify the method of measuring the moisture content. Resonance frequencies of the wood sample decreased as its moisture content increased. An experiment was performed by measuring the vibration of a tree to explore the feasibility of applying the method to the measurement of the moisture content of trees. The circumferential mode, which is independent of the height of a tree, was identified using a white oak tree.     

Moisture storage and transport properties of preservative treated and untreated southern pine wood

Moisture storage and transport properties of southern pine (Pinus spp.) wood were measured for implementation into hygrothermal models. Specimens were untreated or pressure-treated with alkaline copper quaternary (ACQ) preservative. Moisture storage was characterized with sorption isotherms in the hygroscopic region (high capillary pressures) and documented with mercury intrusion porosimetry in the overhygroscopic region (low capillary pressures). The data were then combined into a single moisture retention curve as a function of capillary pressure. Moisture transport was evaluated from steady-state water vapor transmission and dynamic capillary water absorption experiments. These data were used to calculate the moisture permeability over the entire range of capillary pressures using the diffusivity approach of Carmeliet et al. Moisture storage and transport properties were similar for the untreated and ACQ-treated southern pine, except for the permeability of the treated wood which was lower in the radial direction. The data presented here can be used to improve the accuracy of hygrothermal and combined hygrothermal–corrosion modeling simulations.     

Evaluation of surface smoothness by laser displacement sensor 1: effect of wood species

The best methods for determining surface roughness in an industrial environment are of the noncontact variety, with reproduction of the profile. The objective of this work was to compare the roughness profile obtained by a contact stylus with a commercial laser displacement sensor (LDS). Measurements were done using 15 wood species with different densities and colors, based on which special triangle profiles were prepared. The accuracy of the laser sensor was examined by statistical analysis of roughness parameters measured from the profiles. Experimental results show that LDS profiles were imitated correctly. However, LDS accuracy depends on the scanned wood properties (density and color), installation position of the sensor, and profile shape. It was found that evaluation of dark and high-density wooden surfaces was imperfect.Part of this work was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000; and at the 51st Annual Meeting of the Japan Wood Research Society, Tokyo, April 2001