European Journal of Wood and Wood Products最新文献

This work uses the M-theta method on a new proposed specimen called "I-specimen" for the numerical modeling of cracks on some tropical hardwoods in general and in particular on some Cameroonian woods. The finite element analysis of fracture in an orthotropic medium is developed. The fracture algorithm is introduced in a finite element software Cast3M and, with an incremental orthotropic formulation, the simulation of crack growth is computed. Using this method, stress intensity factors and energy release rate are calculated for Mode I and II failures. The energy release rate and stress intensity factors are numerically deduced using “I-specimen” to characterize three Cameroonian hardwoods under mode I and II loading for different crack growths. The specimen used has better characteristics than other samples generally used in the literature and its geometry is very simple to define. The proposal of a new geometry that can guarantee the reproduction of the different failure modes while exhibiting some stability of the crack parameters G and K during propagation was evaluated and compared to other specimens given by the fracture mechanics literature. For each fracture mode, the influence of the orthotropy rate parameters on the energy release rate was investigated.

The fire performance of buildings can be assessed through the thermal and charring characteristics of laminated bamboo lumber (LBL), due to its combustibility properties, which are akin to those of wood. This study employed Thermal Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and Hot Disk techniques to ascertain the thermal conductivity, heat flow, and mass loss rate of LBL at elevated temperatures. Thermal conductivity initially rises, then falls, as the temperature increases from 25 °C to 280 °C across both grain directions, peaking at 100 °C. The thermal conductivity ratio of LBL, from parallel to perpendicular to grain, ranges from 1.93 to 4.00. A distinct peak in heat flow of LBL, ranging from 1.00 to 2.23, is observed as the temperature increases from 23 °C to 200 °C. Beyond 200 °C, the mass loss rate of LBL accelerates, driven by the pyrolysis of phenolic resin and decomposition of bamboo cellulose. The normal and nominal charring rates for LBL specimens were established based on the detachment of charring layers at furnace temperatures, adhering to ISO 834 standards. These findings may serve as a foundation for advanced fire performance analysis of LBL structures.

Virgin cork is a little-known, sustainable and relatively scarce raw material. However, its global output is expected to increase substantially as recent cork oak plantations are stripped for the first time. The work described here aimed to examine the factors underlying the mechanical properties of granulated cork, most particularly the type of cork (virgin or reproduction), and to develop a technique to deliver fast and accurate assessments of the effects of said factors. A batch of virgin cork was boiled, dried, ground and graded following standard granule classification procedures according to size and density. The resulting granulates were then compared with equivalent commercial-grade reproduction cork granulates. Physical variables (tapped density and moisture content) were measured and elastic recovery and Young’s modulus were used as proxies for mechanical properties. Image analysis was used to study the size, shape and colour of the cork particles. ANOVA results show significant effects of particle size, density class, type of cork and first and second order interactions between most variables. Density class clearly reached the highest level of significance, whereas the type of cork was less critical. A very strong correlation was found between granulates’ elastic recovery and their tapped density (R² = 0.98; RMSE < 1%). Likewise, greyscale imaging revealed a good adjustment between tapped density and grey level (R² = 0.84; RMSE = 24 g·l⁻¹). The primary conclusion was that the differences between virgin and standard cork granulates are small and should have no effect on less demanding applications. Image analysis is likely to prove useful in further, more in-depth studies.

Hybrid cross-laminated timber (CLT), being a derivative of generic CLT, offers the advantages of combining different materials to achieve improved performance. This study focused on investigating the withdrawal capacity of self-tapping screws (STS) in a hybrid CLT, i.e., cross-laminated timber-bamboo (CLTB), which is composed of high-density bamboo scrimber and low-density fast-growing Chinese fir lumber. The effects of screw diameters, penetration length and penetration sides on withdrawal performance were evaluated and the experimental results were further compared with the predicted values obtained from existing theoretical formulas. The experimental findings revealed a significant increase of 297% in withdrawal capacity when the outer layer of CLT is replaced with high-density bamboo scrimber. Compared to Chinese fir CLT, the penetration length of STS has a smaller influence on the withdrawal capacity of CLTB, with a minimum increase of 20.9% for CLTB, and a maximum increase of 119% for Chinese fir CLT. In addition, STS diameter significantly affects the CLTB withdrawal capacity by 66.4%, whereas the effect is 9.9% for Chinese fir CLT. When inserted into the narrow side, STS should only penetrate the transverse layer. The withdrawal capacity of bamboo scrimber transverse layer in type A was 260% higher than those of Chinese fir transverse layer in types B and C. Finally, significant differences were found between the predicted and experimental values for all three types of CLT. One of four existing theoretical formulas demonstrates improved accuracy in predicting the withdrawal capacity of CLTB.

Nowadays, using flame-retardant chemicals is gaining importance in chipboard production. Melamine resins to produce chipboard are preferred to provide flame retardancy properties with a cost of approximately 2.5 times the urea–formaldehyde (UF) resin. In this study, the UF resin to produce the chipboard was preferred due to its economical availability. To improve the flame retardancy properties of the chipboard, phosphate-based and inorganic flame retardants were used in the chipboards. In chipboard production, oak, pine, poplar, sawdust, urea–formaldehyde resin as adhesive, flame retardant chemicals like triphenyl phosphate (TPP), ammonium polyphosphate (APP), and calcium gluconate (CaG) were used. Flame retardant chemicals were added to chipboards in single and double compositions and prepared by pressing method. Mechanical (tensile, bending, and surface strength), physical (humidity, density, formaldehyde emission), and fire (limiting oxygen index (LOI), cone calorimeter, and UL-94 vertical) tests were performed on wooden boards. It has been observed that the use of different types of flame retardant and their combinations in chipboard does not significantly change the mechanical properties. It was seen that the free formaldehyde emission rate decreased by using flame retardant added compared to the control sample. The chipboard samples with added flame-retardant chemicals have entered the V-0 rating in the UL-94. LOI values of the chipboard samples containing 50% CaG-50% APP and 50% TPP—50% CaG were observed as 29.7% and 29.8%, respectively. Besides, the highest heat release rate (HRR) reduction was obtained in the chipboard sample containing 50% CaG—50% APP.

Wooden pallets can straightforwardly sustain fractures during storage and transportation. This shortens their service life. To minimize the economic losses caused by damage to wooden pallets, this study aimed to 1) investigate the falling damage behavior of wooden pallets by piezoelectric technology and acoustic emission (AE) and 2) evaluate a nondestructive method for damage-degree detection. The piezoelectric signal of the wooden pallets during the falling process was collected and analyzed for the variation law. The corresponding AE parameters were obtained when the different damage status occurred. It was observed that the peak voltage piezoelectric signal of the pallets decreased with an increase in the number of falls, and rebounded after damage occurred. The rebounding amplitude depended on the damage degree. The AE parameters of ringing count, energy, and amplitude reduced significantly as the pallet damage degree aggravated. The high-frequency proportion of the AE signal was observed to decrease as the damage strengthened. From undamaged to completely broken, the damage behavior of the wooden pallet generally underwent four stages: nondestructive, nail loosening, nail withdrawal, and the deck board off stage. The boundary of each damage stage could be clearly identified and read from the profile of the piezoelectric signal. Moreover, each stage could be effectively monitored and characterized by the AE parameters. Therefore, the combination of piezoelectric sensors and AE technology is capable of determining the structural health status of wooden pallets in use and predicting the remaining life.

This paper presents an experimental study on the flexural behavior of hybrid Pine-Birch Glued-Laminated Timber (GLT) beams. The study focuses on the performance of GLT beams with different lengths (2.1 and 2.8 m) and different compositions of birch (30 and 50%) and pine lamellas. The experiments were conducted using a four-point bending test and data were analyzed using Linear Voltage Displacement Transducers and Digital Image Correlation techniques. The results highlight that pure pine GLT beams exhibited brittle failure, while pure birch beams displayed a more ductile behavior. The hybrid GLT beams demonstrated a transitional behavior between the two. The presence of birch lamellas in the hybrid beams highlights the potential of these beams in structural applications, and significantly improves the global bending modulus of elasticity, bending strength, and flexural ductility compared to pure pine beams.

This paper details the manufacturing and dynamic performance evaluation of bamboo spur gears utilizing bamboo powder. The research involved a comparison between the accuracy and dynamic performance of a bamboo gear and a POM gear. Initially, a disk-shaped preformed bamboo product was created and transformed into a gear using a gear hobbing machine. Subsequently, the gear's accuracy was assessed, and the dynamic gear testing machine was employed to measure gear temperature, generation noise, and wear volume. The bamboo gear produced in this study exhibited accuracy nearly equivalent to that of the injection-molded POM gear. The wear volume of the bamboo gear was reduced by elevating the molding temperature. Furthermore, the bamboo gear fabricated at 200 °C, under torque conditions of 0.5 Nm and 1.0 Nm, with a range of revolutions from 500 to 1500 rpm, demonstrated comparable performance in terms of temperature, noise, and wear to that of a POM gear. However, gears comprised entirely of bamboo powder proved incapable of withstanding a load torque of 1.5 Nm. This limitation stemmed from the fact that the flexural strength of POM was 90 MPa, whereas that of the bamboo powder molding product was 60 MPa. Therefore, when fabricating a bamboo gear using bamboo powder reinforced with bamboo fiber bundles, it withstood up to 10⁷ rotations even under a load torque of 1.5 Nm.

This study focuses on the utilization of bolaina sawdust waste from the Peruvian Amazon for the production of cellulose nanofibers (CNFs). Bolaina is known for its rapid growth and extensive wood usage, which generate significant amounts of sawdust waste. The objective of this research was to physicochemically study this biomass source and the conversion of this waste into valuable nanocellulosic materials. The results showed that CNF yields from holocellulose (CNF-BH) and alpha-cellulose (CNF-Bα) gave high nanofibrillation yields of 80.6% and 74.7%, respectively. The CNFs were disintegrated into nanoscale fibers using microfluidizer treatment, resulting in CNF-BH displaying a thicker, gel-like aspect, while CNF-Bα showed a more liquid aspect. The FTIR spectra showed peaks associated with -CH₂ groups, C = O stretching vibrations of carboxyl and acetyl groups in hemicelluloses, and cellulose I and II vibrations. TGA analysis demonstrated that both CNFs had two stages of degradation, with a maximum peak degradation temperature of 240 °C in the first stage and 310 to 350 °C in the second stage. The XRD patterns of CNF-BH and CNF-Bα showed differences in the crystallinity index, with values of 68.1% and 75.4%, respectively. The differences in crystallinity between the two CNFs can be explained by the alkaline purification method to which the alpha-cellulose sample was subjected. Overall, the CNFs exhibited a high crystallinity index and thermal stability, making them promising candidates for various applications in materials science and aiding in the development of sustainable materials.

Fine adjustment of manufacturing parameters as a function of the experience of the technical manpower plays a vital role in any production line. The objective of this study was to propose an adaptive controller framework to improve the overall accuracy of the parameters regulating particleboard manufacturing. This framework has four main steps: (1) In the data gathering process, the production parameters and the sample test results were collected from the randomly picked and tested specimens in each round, (2) Relevance analysis was used to select high-power relevant variables influencing the overall quality of the final product. Those relevant variables will be inputs to construct the classification model, (3) A decision tree was employed to construct the classification model and reveal split points of the process parameters to determine the distinction between passed and failed panels, and (4) The production parameters in the next round will be adjusted according to the defined split points so the quality of the particleboard can be enhanced. Continuous improvement of the production parameters, within the perspective of the proposed framework, enables us to go back to step (1) again as desired, especially in the long production run. Based on the findings of this work, the experimental results revealed that the model could classify the failed particleboard with a specific rate of 92.50%. The model also demonstrated that resin characteristics, namely pH value and viscosity, impacted the overall performance of the particleboard.