The radial compression behavior of wood, governed by its multiscale structure and chemical composition, is profoundly affected by temperature. This comparative study of four wood species combines mechanical testing with microstructural analysis to elucidate the species-specific mechanisms underlying their compressive performance. Results demonstrate that energy absorption efficiency is optimized in structures with large lumens and moderate wall thickness, enabling progressive collapse. Hemicellulose enhances plastic deformation and recovery, whereas lignin facilitates permanent damage. A fundamental divergence in thermal response was identified: softwoods resist deformation by maintaining crystallinity until 300 degrees C, whereas hardwoods degrade earlier. Notably, we report a unique pore evolution pathway in Larch, which exhibits a substantial increase in porosity post-compression at 300 degrees C, deviating from the typical densification behavior. This work establishes structure-property-deformation relationships that are vital for the advanced application of wood under thermomechanical conditions.

Bamboo-wood composites hold promise for impact-resistant applications, yet their dynamic mechanical behavior remains insufficiently understood. This study investigated the axial compression response and failure mechanism transition of bamboo-wood-bamboo (BWB) composites across strain rates of 9.52 & times; 10-4 to 208 s-1 . BWB specimens, fabricated from bamboo scrimber and fast-growing Chinese fir, were subjected to quasi-static and low-velocity impact loading. Mechanical properties and failure morphology were systematically analyzed using digital image correlation (DIC), computed tomography (CT), and scanning electron microscopy (SEM), with pure wood as a control. Results demonstrate that BWB exhibits pronounced strain rate sensitivity: the compressive strength increases by 59.1% (from 71.5 MPa to 113.8 MPa) with the increase of strain rate, consistently surpassing that of pure wood. The failure mechanism transitions fundamentally with the increasing strain rate, from a progressive and cooperative mode to an instability-dominated mode. The former failure initiates by wood crushing and interfacial slip under quasi-static loading, while the latter failure characterizes by instantaneous bamboo scrimber buckling and severe interfacial delamination under impact. The volumetric energy absorption of BWB under impact is 160%-227% higher than that of pure wood. This study elucidates the strain-rate-driven transition in failure mode from "progressive cooperation" to "instantaneous instability," providing a theoretical basis for the application of BWB composites in new fields such as the impact-resistant of vehicle, building components and packaging.

Abstract Cross laminated timber (CLT) is recognized as alternative to traditional construction materials, which is composed of orthogonally bonded layers of solid sawn timber or structural composite materials (e.g., oriented strand board) using adhesive. The bonding performance of CLT is an important parameter to determine the structural safety at a high temperature environment. In this study, it was performed to clarify the deterioration mechanism of bonding interface of CLT and hybrid CLT (HCLT) after thermal treatment. CLT was prepared by the plantation Chinese fir using one component polyurethane, and HCLT was the use of oriented strand board (OSB) to replace the lateral layer of Chinese fir laminate. The block shear strength and the delamination of vacuum pressure impregnating were carried out on CLT and HCLT after thermal treatment. The changes of chemical components of Chinese fir, OSB and adhesives were analyzed, and the damage microstructure of bonding interface of CLT and HCLT were studied. The results showed that the qualified rate of delamination of vacuum pressure impregnating for HCLT still reached 90% at thermal temperature of 200 °C, which was higher than the qualified rate of CLT reached 40%. The block shear strength of HCLT was significantly higher than that of CLT. When in early-stage temperature from 20 to 80 °C, the main failure mode of CLT transitioned from sawtooth failures within the wood towards glue layer fractures and gradually extending to the direction of wood-ray. And the block shear strength decreased by 47.14%, the wood failure ratio decreased to 60%. The primary failure mode of HCLT transitioning from wood failures into OSB core layer failures. When treatment temperature rose to 80 °C–100 °C, PUR adhesive began to pyrolysis and formed –NCO group formation. Meanwhile, the small cracks occurred gradually at the bonding interface. During later stages where temperatures increased from 100 to 200 °C, the tracheid occurred deformation and intercellular layer was split of the bonding interface for CLT and HCLT.

Cross-laminated timber (CLT) has become one of the most popular engineering wood in timber construction due to its better mechanical properties and bidirectional bearing capacity. In this study, the bending properties of Cunninghamia lanceolata CLT were studied with the method of full-scale bending test and theoretical calculation. The macroscopic bending properties, the strain field distribution under bending stress, and the influence of the knot on the bending properties were analyzed. The results showed the following: 1) The strength of CLT of Cunninghamia lanceolata plantation was up to 23.16 MPa, and the utilization rate of C-grade lamina was up to 83%. 2) The macro displacement load curve of Cunninghamia lanceolata CLT and the strain changes of different lamina are different in the major strength direction and minor strength directions. The lamina adjacent to the bottom lamina in the minor strength direction participates in the loadbearing work of the member earlier because of the orthogonal billet and the same lamina are not coated. 3) The CLT bending strength and coefficient of variation were significantly affected by wood knots. The CLT strength was increased by 11.70% and the coefficient of variation was decreased by 74.47% after wood knots control. 4) Rolling shear failure is still the main failure mode of CLT of Cunninghamia lanceolata. The first and largest strain changes occur in the transverse lamina between the load contact position and the bottom support position and close to the load contact position, and the earliest rolling shear failure occurs.

This study investigated the energy absorption mechanisms of Chinese fir (Cunninghamia lanceolata) under radial dynamic compression to support impact-protection applications. Radial compression testing, using both static and dynamic methods with digital image correlation (DIC) technology, was conducted across strain rates ranging from 9.52 x 10-degrees s-1 to 229 s-1 . The mechanical response, failure characteristics, and surface strain field distributions were systematically analyzed under varying strain rates. The results indicate that wood shows significant strain-rate sensitivity, with energy absorption parameters increasing as the strain rates increase. Furthermore, the stress-strain curves under dynamic compression show distinct oscillatory characteristics, with oscillation amplitudes proportional to the strain rates. The differences in energy absorption mechanisms under varying strain rate conditions are innovative revealed, which are primarily attributed to the wood failure transition from a combined shear-compression dominance under quasi-static conditions to a compression-dominated mode under medium strain rates. Finally, a finite element model is established and can accurately predict the energyabsorption behavior across the strain rates. These findings not only provide an important theoretical basis for the engineering application of Chinese fir in impact-protection systems, but also enhance our understanding of dynamic mechanics of wood.

Cross-laminated timber (CLT) has been recognized as an alternative to traditional construction materials. In this study, CLT was prepared using plantation-grown Chinese fir and a one-component polyurethane adhesive. The theoretical calculation of shear stress in CLT was conducted to establish a basis for testing its interlaminar shear strength. The mechanisms by which layup grade and gap width affect interlayer shear strength in CLT were explored. Scanning electron microscopy was used to examine the microstructural failure characteristics of interlayer shear in CLT were investigated. Acoustic emission (AE) technology evaluated damage evolution and failure modes during interlayer shear loading. The results showed that interlaminar shear stress in CLT was related to the number of CLT layers and the ratio of the elastic modulus of the parallel and vertical layers E1/E2. Interlayer shear stress in three- and five-layer CLT was 0.92 and 0.81 times that in glulam, respectively. Significant effects of the gaps on interlayer shear strength in CLT were observed. When the gap in the parallel layer was increased from 0 to 4 mm, the interlayer shear strength was reduced by 8.10%. Interlayer shear failure modes in CLT were primarily identified as rolling shear failure in the vertical layer and tensile fracture in the bottom layer. Rolling shear failure in the vertical layer mainly occurred at the earlywood-latewood interface and exhibited discontinuous failure in the wood ray direction. Variations in AE energy accurately reflect the evolution of CLT interlayer shear damage. During the deformation stage, AE energy signals were low, as wood fiber bundles buckled and tensile microcracks began to form. During the crack propagation stage, cumulative AE energy increased linearly, and shear crack signals with high RA and low AF values increased. During the failure stage, AE energy signals peaked locally; shear crack signals with high RA and low AF values comprised 25.99 % of the total. The fracture mode of CLT changed from tension-type failure to tension-shear composite failure.

Based on the theory of stress wave propagation in solid media, this paper conceptualizes standing trees as a three-layer composite material comprising the pith, heartwood, and sapwood. Assuming that standing trees exhibit orthotropic anisotropy, the propagation process of stress waves within the trees is simulated and analyzed using the finite element simulation software. The paper investigates the effects of diameter at breast height (DBH) of 40-year-old standing larch trees and the proportional composition of pith, heartwood, and sapwood on the propagation of stress waves. The results reveal that, despite variations in DBH and the relative proportions of the three components, the overall propagation patterns of stress waves remain largely consistent across models. Initially, stress waves propagate in the form of an inclined curved surface. As the propagation distance increases, the inclination of the wavefront gradually decreases, eventually approaching a plane perpendicular to the longitudinal axis of the standing tree. When the DBH increases from 30 cm to 50 cm, the stress wave velocity rises significantly from 3,450 m/s to 3,620 m/s. Additionally, as the proportion of sapwood increases, the velocity increases from 3,529 m/s to 3,916 m/s. A strong correlation is observed between wave velocity and the compositional ratio of the three components, with a correlation coefficient (R²) of 0.98.

High-performance wood scrimber (HPWS) is a novel wood composite that uses oriented wood fiber mats from veneers as raw material instead of the small-diameter timbers used in traditional wood scrimber. HPWS exhibits excellent mechanical properties and dimensional stability, making it a promising material for load-bearing components in construction. Similar to other biomass materials, the effect of size on the strength of HPWS is critical. As the volume of a member increases, the likelihood of fatal defects within it rises, resulting in a decrease in strength. However, there is a lack of knowledge regarding the size effect on HPWS. To address this issue, HPWS specimens with a broad range of sizes were tested to determine the effect of size on their compressive strength. Then, a random simulation method was applied to further investigate the source of the strength-dependency on size and to extrapolate the size effect to a wider range of sizes. Results indicated that both the size of the cross-sectional area and length significantly influenced the compressive strength of HPWS. The size effect strength-dependency was attributed to variations in the load redistribution capability between specimens with higher and lower strengths. The size effect of HPWS was found to be weaker compared to other structural wood or bamboo-based products. Calculation methods were proposed to quantify the size effect on HPWS. These findings lay a solid foundation for advancing the use of HPWS in construction.

The lignocellulosic feedstock of woody bamboo shows promising potential as an alternative to conventional wood, attributed to its excellent properties. The content and distribution of lignin serve as the foundation of these properties. While the regulation of lignin biosynthesis in bamboo has been extensively studied at the transcriptional level, its posttranslational control has remained poorly understood. This study provides a ubiquitinome dataset for moso bamboo (Phyllostachys edulis), identifying 13015 ubiquitinated sites in 4849 unique proteins. We further identified Kelch repeat F-boxprotein 9 (PeKFB9) that plays a negative role in lignin biosynthesis. Heterologous expression of PeKFB9 resulted in reduced accumulation of lignin and decreased phenylalanine ammonia-lyase (PAL) activities. Both in vitro and in vivo assays identified interaction between PeKFB9 and PePAL10. Further examination revealed that SCFPeKFB9 mediated the ubiquitination and degradation of PePAL10 via the 26S proteasome pathway. Moreover, PebZIP28667 could bind to the PePAL10 promoter to significantly inhibit its transcription, and ubiquitination of PebZIP28667 weakened this inhibition. Collectively, our findings reveal a PeKFB9-PePAL10/PebZIP28667-PePAL10 module that acts as a negative regulator of lignin biosynthesis. This study advances our understanding of posttranslational regulation in plant lignification, which will facilitate the improvement of the properties of bamboo wood and the breeding of varieties.

The aim of this study was to explore the feasibility of manufacturing high-strength laminates from smalldiameter plantation wood. A Chinese fir (Cunninghamia lanceolata) plantation comprising trees with a diameter at breast height of less than 30 cm was selected as the material in this study. The flatwise bending mechanical properties of the Chinese fir laminates with both non-finger-jointed (NFJ) and finger-jointed (FJ) were investigated. The results indicated that finger jointing did not affect the bending elastic modulus (MOE) of the laminates, but it could reduce the bending strength index and the coefficient of variation of the bending strength (MOR). Notably, an optimal correlation existed between the MOE and MOR for both NFJ and FJ laminates, indicating that the MOE could serve as the dominant control variable for the machine grading of laminates. The failure mode significantly influenced the bending mechanical properties of both the NFJ and FJ laminates, whose dominant failure modes were fiber failure near the knot and whole fractures of the finger jointing teeth roots, respectively. For both the NFJ and FJ laminates, the overall macroscopic morphology of the high-strength specimen was relatively flat, but the microscopic morphology was uneven owing to fiber pull out, while the low-strength specimen was the opposite. Compared to the traditional visual grading method, the proposed machine grading method could more scientifically and effectively identify the quality, reduce the coefficient of variation of the bending mechanical properties, and significantly improve the strength index of laminates. This study provides basic support for manufacturing high-strength laminates from small-diameter plantation wood.

China has been increasingly promoting the use of prefabricated timber structure buildings in recent years. However, unlike other countries, China lacks a diverse range of local tree species and engineered wood products suitable for load-bearing components in timber structures. This shortage poses a risk to the sustainable development of timber structures in China. This issue is addressed in this study, which focuses on the development and manufacture of glued laminated timber (GLT) using Chinese fir from plantation forests. The dynamic elastic modulus of 549 laminae was evaluated using the FAKOPP stress wave approach. A total of 28 laminae were randomly selected from Classes I, II, and III to assess the influence of stress grading on bending performance. This study included an analysis of failure modes, bending capacity, and the prediction model for bending stiffness of GLT with different layups and cross-sectional heights. The findings showed that the dynamic elastic modulus of the laminae followed a normal distribution. The bending strength and modulus of elasticity of finger-jointed laminae across different grades were 29.59 MPa to 37.05 MPa and 8.13 GPa to 10.94 GPa, respectively. The mechanical properties of both same-grade and mixed-grade composition GLT manufactured from Chinese fir met the TC(T)28 (MOR >= 28 MPa, MOE >= 8000 MPa) and TC(YD)24 (MOR >= 24 MPa, MOE >= 8000 MPa) garde requirements in GB/T26889, respectively. Failure modes in the GLT specimens typically began at the knots or finger joints of the bottom layer laminae. The cross-sectional height had no significant effect on the modulus of elasticity of GLT but exerted a significant effect on bending strength. The prediction model for bending stiffness, developed using the transformed section method, agreed with the experimental results. The outcome of this research provides a scientific and data-driven foundation for the application of Chinese fir in the field of structural materials.

Cross-laminated timber (CLT) has become a popular engineered wood product, mainly prepared from imported wood in China. More extensive research is needed to improve the local production of cross-laminated timber with fast-growing coniferous wood species. Chinese fir (Cunninghamia lanceolata) and one component polyurethane (1C-PUR) adhesive were selected to prepare CLT under different process parameters. International standard methods, scanning electron microscopy (SEM), optical microscopy (LM), confocal laser scanning microscopy (CLSM), and nanoindentation (NI) were applied. The bonding performance and failure mechanism of Chinese fir CLT were investigated and clarified. The results showed that the optimal gluing parameters for preparing CLT from Chinese fir wood were 160 g/m2 of glue, 0.9 MPa of pressure, and 180 minutes of pressing time. Failure of CLT made from Chinese fir lumber was mainly due to the shear failure of the vertical layer board. Cracks often appeared in the earlywood cells near the boundary between earlywood and latewood. The impact of adhesive penetration on the mechanical properties of the wood cell wall showed that adhesive penetration increased the elastic modulus of the cell wall at earlywood and latewood cells.

Timber structure buildings are set to bring new development opportunities and market prospects. Glued laminated timber (GLT) is the predominant material for beam-column frame construction, supported by credible data and environmental product declarations (EDPs) established in foreign countries. However, no standardized reference values were set for carbon emissions (CEs) from GLT in China. This study tracked the CEs of GLT manufacturing stages based on real-time monitoring data from Chinese GLT manufacturing factories. A power monitoring system was used to monitor the electricity consumption for each process in GLT production. The CEs of 1 m(3) GLT cradle-to-gate were calculated using the process analysis method. The cradle-to-gate CEs of 1 m(3) GLT were 198 kgCO(2)e, with the CEs of the A3+ stage totaling 54.94 kgCO(2)e, comparable to that of North America. The CEs of 1 m(3) GLT cradle-to-gate (A1-A3+ stage) followed the order embodied CEs > direct CEs > indirect CEs. With wood carbon sequestration performance considered, the cradle-to-gate CE of 1 m(3) GLT was -784.97 kgCO(2)e, highlighting the potential for wood building materials to achieve a negative carbon impact. Domestic timber manufacturing in China effectively reduces generated CEs relative to imported timber at the transportation stage. This study provides scientific background data supporting embodied carbon accounting in glued laminated timber frame buildings for practical projects. Such efforts can further contribute to realizing carbon peaking and carbon neutrality goals in China.

With its high strength and excellent dimensional stability, high-performance wood scrimber (HPWS) holds significant promise for applications in load-bearing structures within buildings. However, understanding its behavior concerning size effects, particularly in terms of strength variation with stressed volume dimensions, is essential for establishing design parameters. Despite this importance, research on this aspect remains scarce. To address this gap, this study conducted tension tests on 304 specimens divided into 10 groups, covering a wide range of sizes, with the largest specimen’s volume 162 times that of the smallest. Utilizing the weakest link theory, the study investigated the size effect on tensile strength parallel to grain. Size effect factors were estimated using the shape parameter and slope methods, with discussions on differences related to volume, length, and cross-sectional area factors. It was found that the size effect related to the length and cross-sectional area were 0.0804 and 0.0671, respectively. This difference was due to the load-sharing ability within the cross-section, as the HPWS in tension resembles a net-like structure more than a chain-like structure. The specimens with the smallest cross-section didn’t exhibit the greatest strength. This was because the effects of sawing are particularly severe for very small specimens. This issue requires careful consideration when developing calculation methods. Finally, a calculation method for the tensile strength reduction coefficient, considering size effects, was proposed and demonstrated to align well with experimental findings. This comprehensive analysis serves to advance the structural utilization of HPWS as an innovative building material.

Cross laminated timber (CLT) is recognized as alternative to traditional building materials, which is mainly used as wall or floor of buildings. The heat transfer coefficient of wall is an important indicator of building energy saving, but there are relatively few studies on it of CLT wall. This paper mainly studied on the thermal performance of CLT walls by experiments, theoretical formulae and simulation. Based on hot box-heat flux method, the heat transfer coefficient values of CLT walls were measured and the influence of wall structure and thermal insulation materials were analyzed. Then, the heat transfer coefficient of different CLT walls was predicted by theoretical calculation and theoretical methods were compared based on calculation results. Finally, the temperature distribution, heat flux distribution and heat transfer coefficient of CLT wall were simulated and the applicable climate regions of CLT wall were proposed. The results showed that the double-layer structure or hollow structure had little effect on the heat transfer coefficient of CLT wall. The heat transfer coefficient of CLT wall significantly reduced by 37%-50% after adding internal or external thermal insulation materials. The lowest heat transfer coefficient of CLT walls in this study was 0.278 W/(m2*K). The arithmetic mean relative error of composite method is lower than the parallel-path method and the isothermal planes method, which was 6.38%. And the arithmetic mean relative error of heat transfer coefficient between simulation and experiment results was 7.46%. Thermal bridge structures in buildings, such as corners and partitions, will bring about 35%-38% increasement in heat transfer coefficient. These findings should be able to provide scientific basis for the use of CLT buildings in different cold regions.

This study explores the application of oriented strand board (OSB) to hybrid cross-laminated timber (HCLT). OSB and larch were used to fabricate hybrid forms of HCLT for analysis. Firstly, the impact of surface treatment on OSB was investigated in terms of its influence on the bonding line between materials, encompassing both pre-treatment and post-treatment surface properties of OSB. The findings indicate that sanding has the ability to alter the surface properties of OSB, leading to an increase in surface roughness and surface free energy, and reduce the pre-cured layer. Notably, there is no significant disparity observed in both the shear failure mode and shear strength of the bonding line of CLT, and the failure is in the core layer of OSB. Secondly, two layups of HCLT were prepared by combining OSB with larch. The interlaminar shear strength was assessed in both the major and minor strength directions using a three-point bending test. The results showed that, due to the low density and mechanical properties of the core layer of OSB, its application in HCLT as perpendicular layer is not a favorable choice, because it cannot prevent the rolling shear failure in perpendicular layer, and it also diminishes the interlaminar shear strength of HCLT in the minor strength direction. However, the interlaminar shear strength increases in the minor strength direction when OSB was used as the parallel layer, and larch was used as the perpendicular layer, even stronger than that in major strength direction.

This study aims to investigate the relationship between the anatomical features and the mechanical behavior of poplar wood and reveal the deformation mechanism of hardwood under transverse compression. We conducted a transverse compression test of the poplar wood, a typical diffuse porous wood, under uniaxial, laterally restrained, and circumferentially restrained conditions. Subsequently, a finite element model was developed based on SEM images of poplar wood. Finally, the deformation mechanism of the wood was analyzed based on the test and modeling results. This study is helpful for understanding the mechanism of poplar wood under transverse compression and the development of constitutive models based on its mechanism.