Predicting mechanical properties of clear wood from Acacia mangium provenances using ultrasound

Ultrasound was considered as a means for determining mechanical properties of clear wood in six different Acacia mangium provenances from a trial forest planted in Vietnam. A total of 30 trees (5 trees from each provenance) with no major defects were selected, and a 50-cm-long log was obtained at 1.3 m above the ground from each tree for the assessment of mechanical properties. The measured average ultrasound velocities for provenances tested in the longitudinal direction ranged from 4094 m/s to 4271 m/s. The predicted average dynamic modulus of elasticity (Ed) values varied from 7.42 GPa to 8.70 GPa among provenances. The Ed indicated significant positive correlation coefficients with modulus of elasticity (0.64 to 0.96), modulus of rupture (0.44 to 0.87), and compression strength (0.54 to 0.92) for provenances examined in this study. The results indicated that the use of ultrasound was feasible to determine the mechanical properties of A. mangium provenances planted in Vietnam.

Prediction of Mechanical Properties of Artificially Weathered Wood by Color Change and Machine Learning

Color parameters were used in this study to develop a machine learning model for predicting the mechanical properties of artificially weathered fir, alder, oak, and poplar wood. A CIELAB color measuring system was employed to study the color changes in wood samples. The color parameters were fed into a decision tree model for predicting the MOE and MOR values of the wood samples. The results indicated a reduction in the mechanical properties of the samples, where fir and alder were the most and least degraded wood under weathering conditions, respectively. The mechanical degradation was correlated with the color change, where the most resistant wood to color change exhibited less reduction in the mechanical properties. The predictive machine learning model estimated the MOE and MOR values with a maximum R2 of 0.87 and 0.88, respectively. Thus, variations in the color parameters of wood can be considered informative features linked to the mechanical properties of small-sized and clear wood. Further research could study the effectiveness of the model when analyzing large-sized timber.

An Investigation of the Duration of Load of Structural Timber and the Clear Wood

In this study, DOL of structural timber and the clear wood and DOL of modulus of elasticity of wood were investigated. The dimension lumber of Spruce-Pine-Fir of Grade No. 2 and Grade No. 3 and the small clear specimens of the same species of the dimension lumber were used to conduct the short-term and the long-term bending test. The short-term strength distributions of the dimension lumber and the small clear specimens were obtained. The long-term tests were conducted under constant environmental conditions for 18 months. The sample matching technique was used to estimate the short-term strength of the specimens that underwent long-term tests. It was found out that there is virtually no difference in DOL between different grades or quality of lumber and no difference between structural timber and clear wood, and DOL obtained from the test of this study is more in agreement with Wood’s curve. A threshold stress ratio of about 0.55, loaded above which the wood began to experience strength loss, was revealed from the test. Making use of the threshold ratio concept, the DOL of wood can be obtained not only from failed specimens under load in the process of the long-term loading, but also from the ramp loading test of the specimens that survived the long-term test. Sustained load also poses DOL on the modulus of elasticity of wood, though to less degree than DOL of strength of wood.

Prediction of shear strength parallel to grain in clear wood of oak (Quercus robur L.) on the basis of shear plane orientation, density and anatomical traits

Oak wood is popular for use in construction and as flooring. Evaluating the mechanical strength of oak timber is difficult and time consuming. Therefore, models for predicting mechanical properties, based on easy-to-obtain variables, may be useful. The purpose of the study was to build models for predicting shear strength parallel-to-grain in oak clear wood. With this goal, the shearing resistance was tested on 198 defect-free specimens (target dimensions 50 × 50 mm in tested section) obtained from a sample of 40 oak trees felled in north-western Spain. The mean shear strength of the sampled oak wood provenance was 15 N mm−2, which was almost equal to the highest mean value reported in previous studies. Analysis of the relationships between the variables tested enabled development of a model relating shear strength parallel to grain at 12% moisture content, with air-dry wood density and angle between tangential and shear plane as predictor variables ( R adj 2 ${R}_{\text{adj}}^{2}$ = 0.61, p < 0.01, bias = −0.80%, RMSE = 13.66%, for wood with wavy grain; R adj 2 ${R}_{\text{adj}}^{2}$ = 0.36, p < 0.01, bias = −1.46%, RMSE = 17.22%, for wood without wavy grain). The independence of shear strength relative to the presence/absence of sapwood or the annual growth ring width was also demonstrated.

A three-dimensional numerical analysis of moisture flow in wood and of the wood’s hygro-mechanical and visco-elastic behaviour

A three-dimensional numerical model was employed in simulating nonlinear transient moisture flow in wood and the wood’s hygro-mechanical and visco-elastic behaviour under such conditions. The model was developed using the finite element software Abaqus FEA®, while taking account of the fibre orientation of the wood. The purpose of the study was to assess the ability of the model to simulate the response of wood beams to bending and to the climate of northern Europe. Four-point bending tests of small and clear wood specimens exposed to a constant temperature and to systematic changes in relative humidity were conducted to calibrate the numerical model. A validation of the model was then performed on the basis of a four-point bending test of solid timber beams subjected to natural climatic conditions but sheltered from the direct effects of rain, wind and sunlight. The three-dimensional character of the model enabled a full analysis of the effects of changes in moisture content and in fibre orientation on stress developments in the wood. The results obtained showed a clear distinction between the effects of moisture on the stress developments caused by mechanical loads and the stress developments caused solely by changes in climate. The changes in moisture that occurred were found to have the strongest effect on the stress state that developed in areas in which the tangential direction of the material was aligned with the exchange surface of the beams. Such areas were found to be exposed to high-tension stress during drying and to stress reversal brought about by the uneven drying and shrinkage differences that developed between the outer surface and the inner sections of the beams.

Compression Properties of Small Clear Southern Yellow Pine Specimens Tested across Five Decades

Southern yellow pine (SYP) is one of the most used softwood species in the world. Most of this raw material come from fast-grown plantation trees. It is of interest to determine if SYP clear wood properties may have changed over the long term, in particular whether such properties may have declined. Herein, specific gravity (SG), ultimate compression strength parallel to grain (UCS‖), and UCS perpendicular to grain (UCS⊥) from three samples were compared: Sample 1 tested in 2014; Sample 2 from molding and millwork producers tested in 2017–2019; and Sample 3 from a study conducted in the mid-1960s. With respect to specific gravity (SG), the wood in Sample 1 was significantly lower than that from Samples 2 and 3. With respect to UCS‖, all three samples were statistically different. Adjusting to 12 percent moisture content had no influence on the mean separation of UCS‖. With respect to UCS⊥, no statistically significant differences were detected among the test data from any of the three samples. However, for the UCS data generated from the SG and moisture content–related model, Sample 2 was higher than Sample 3, and Sample 3 was higher than Sample 1, and these differences were statistically significant. Overall, these findings do not suggest that broad or consistent changes or declines of these wood strength properties have occurred during the past five decades.

Evaluation of texture feature based on basic local binary pattern for wood defect classification

Wood defects detection has been studied a lot recently to detect the defects on the wood surface and assist the manufacturers in having a clear wood to be used to produce a high-quality product. Therefore, the defects on the wood affect and reduce the quality of wood. This research proposes an effective feature extraction technique called the local binary pattern (LBP) with a common classifier called Support Vector Machine (SVM). Our goal is to classify the natural defects on the wood surface. First, preprocessing was applied to convert the RGB images into grayscale images. Then, the research applied the LBP feature extraction technique with eight neighbors (P=8) and several radius (R) values. After that, we apply the SVM classifier for the classification and measure the proposed technique's performance. The experimental result shows that the average accuracy achieved is 65% on the balanced dataset with P=8 and R=1. It indicates that the proposed technique works moderately well to classify wood defects. This study will consequently contribute to the overall wood defect detection framework, which generally benefits the automated inspection of the wood defects.

Flexural characteristics of Eucalyptus nitens timber with high moisture content

The demand for timber resources in the building industry has been increasing. Plantation Eucalyptus nitens is of interest because of its sustainable supply and potential for structural applications. However, few design standards cover strength values of plantation eucalypt timber, especially flexural failure below and above the fibre saturation point, which is an important mechanism of failure in bending members used in the building industry. Static bending tests were undertaken using a universal testing machine to examine nonlinear bending behaviour of 130 fibre managed E. nitens small clear wood samples at low and high moisture contents (MC). The mean bending modulus of rupture (MOR) was 80.7 MPa for low MC and 59.0 MPa for high MC. The high MC samples exhibited larger displacements at low ultimate loads, while the low MC samples showed abrupt failures at relatively small displacements with high ultimate loads. The design characteristic values for low and high MC E. nitens were 68.5 MPa and 39.8 MPa, respectively. This research demonstrates that fibre managed E. nitens timber is a promising timber for structural applications, especially when exposed to water, as the MOR reduction of E. nitens timber above FSP is relatively lower than those of P. radiata, which is a traditional construction material.

Automatic detection of annual rings and pith location along Norway spruce timber boards using conditional adversarial networks

In the woodworking industry, detection of annual rings and location of pith in relation to timber board cross sections, and how these properties vary in the longitudinal direction of boards, is relevant for many purposes such as assessment of shape stability and prediction of mechanical properties of timber. The current work aims at developing a fast, accurate and operationally simple deep learning-based algorithm for automatic detection of surface growth rings and pith location along knot-free clear wood sections of Norway spruce boards. First, individual surface growth rings that are visible along the four longitudinal sides of the scanned boards are detected using trained conditional generative adversarial networks (cGANs). Then, pith locations are determined, on the basis of the detected growth rings, by using a trained multilayer perceptron (MLP) artificial neural network. The proposed algorithm was solely based on raw images of board surfaces obtained from optical scanning and applied to a total of 104 Norway spruce boards with nominal dimensions of $$45\times 145\times 4500\,\hbox {mm}^{3}$$ 45 × 145 × 4500 mm 3 . The results show that optical scanners and the proposed automatic method allow for accurate and fast detection of individual surface growth rings and pith location along boards. For boards with the pith located within the cross section, median errors of 1.4 mm and 2.9 mm, in the x- and y-direction, respectively, were obtained. For a sample of boards with the pith located outside the board cross section in most positions along the board, the median discrepancy between automatically estimated and manually determined pith locations was 3.9 mm and 5.4 mm in the x- and y-direction, respectively.

Dog-bone Samples may not Provide Direct Access to the Longitudinal Tensile Strength of Clear-wood

Background: Testing standards prescribe dog-bone samples for the determination of clear-wood longitudinal tensile strength. However, the literature reports a high number of invalid tests due to the unexpected failure of the sample outside the gauge length. Motivation: The paper aims at understanding the reason for the premature failure of dog-bone samples and suggesting possible strategies for improving testing protocols. Methods: The paper starts with a comparative review of standards for different orthotropic materials. Thereafter, it analyzes the stress distribution in a clear-wood dog-bone sample using a recently proposed stress-recovery procedure and Finite Elements. Finally, the sample failure is considered applying Tsai-Wu and SIA criteria. Results: Comparative review highlights the controversy on the choice of the sample geometry. Both analytical and numerical results confirm the presence of shear and transversal stresses in necking regions, overlapping with axial stress greater (up to 2%) than the one in the gauge region. As a consequence, clear-wood dog-bone samples fail not due to a pure axial stress state in the gauge region (as expected), but due to complex stress state in necking region, where failure index is 4 ~ 5% greater than the one in gauge region. Conclusion: Assuming that dog-bone samples fail in the gauge region due to pure axial stress is simplistic, as demonstrated by analytical and numerical evidence. As a consequence, interpretations of experimental results based on this belief are misleading and testing protocols should be refined. Indeed, the presence of spurious stresses interfering with expected pure axial stress seems unavoidable. Therefore, clear-wood testing standards should allow to use prismatic samples or, alternatively, to consider as valid also tests on samples breaking outside the gauge region. Both the proposed solutions apparently reduce the accuracy of the experiments, while in contrast, they provide the best achievable results, speeding up the testing procedure and reducing the testing costs.