Wood Bending Research Articles

Study of ternary deep eutectic solvents to enhance the bending properties of ash wood.

Deep eutectic solvents (DESs) are considered one of the most promising biomass pretreatment reagents, and their research applications in woody fibrous biomass are increasing yearly. Inspired by the research related to wood bending, we explored the effects of different DES systems on the bending development of wood, and the results showed that the addition of anhydrous ferric trichloride to the DES system of lactic acid/choline chloride could enhance the treatment effect that increased the bendability and torsion resistance of ash wood. The anhydrous FeCl3 could act as an active site and provide acidic protons to improve the treatment efficiency of DES. In addition, the addition of an appropriate amount of water can reduce the viscosity of the DES system, and the highest lignin removal rate was obtained at 10 wt% of water in the DES, which resulted in the best mechanical properties and tensile resilience of ash wood, with the tensile strength and stability of 97 MPa and 13.6%, respectively, as determined by experiments with different water contents in different mass fractions. Therefore, using a DES can effectively improve the bending properties of wood.

Impact of thermal modification on swelling and mechanical behavior of Couratari spp.

Thermal modification mechanisms and their effects on physical and mechanical properties of native Amazon hardwoods are not yet completely understood. It is expected that such treatments can improve the properties of low-value Amazonian woods and sapwood residues. This study aimed to investigate the impact of heat treatment on the swelling and mechanical properties (strength and stiffness to Static Bending and Janka hardness) of tauari wood (Couratari spp.), a low-value Amazonian hardwood. For this, tauari wood samples were thermally modified in an electric oven under hot air irradiation at final temperatures of 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, and 210 °C for 2.5 h. The main results showed that thermal modification increased the hydrophobicity of tauari wood without any noticeable effects on the mechanical behavior of the wood up to 200 °C. It was stated that up to 200 °C thermal modification is beneficial in terms of gains in hydrophobicity. In contrast, above 200 °C, despite an increase in hydrophobicity, consistent decreases in strength (MOR) and hardness were observed.

The Influence of Processing Conditions on the Quality of Bent Solid Wood from European Oak

Bending of solid wood from European oak is one of the most demanding technological processes due to its specific structural and physical properties and variability. We investigated the influence of wood moisture content (MC) and stiffness, determined by NDT, as well as previous drying methods on the bending ability of the wood. The best quality was obtained with bending specimens bent at a moisture content of at least 16% and quarter- or semi-quartersawn. The number of rejected specimens increased slightly when HF bending was used. Single-stage predrying of oak to a final MC of 8% resulted in a high rejection rate (>70%) regardless of drying technique. The acceptance rate was higher for less stiff specimens where the ratio of ultrasonic velocity in the straight (vS) and bent region (vB) was less than 0.5 (vB/vS).

Deflection determination of composite wood bending elements reinforced with cylindrical polymer composite dowels

Introduction. At the present time, environmental and logistical problems of the construction of prefabricated and temporary bridge structures are relevant. It is possible to create new constructive solutions based on renewable and recyclable materials to meet the requirements of load-bearing capacity and durability. The aim of the research is to study the operation of dowels in a composite structure and to find the dependence of deflections on the number and material of nagels.
 Materials and methods. A wooden composite beam combined with polymer composite dowels is proposed as a modern structural solution. There are a number of issues that cast doubt on the feasibility of building modified wooden structures. One of them requires studying how the polymer composite and wood work together: whether the combination of materials will lead to improved mechanical properties compared with classical solutions. The samples of dowel joints with polymer-composite reinforcement have been tested, the load-carrying ability of such a joint has been estimated, and the deformations of composite beams with a varying number of dowels have been studied using the LIRA-SAPR software package.
 Results. On the basis of normative calculations of dowel load-carrying ability and verification in the second group ofthe limiting states the equation allowing to specify the required number of dowels under the existing deflections was derived.
 Conclusions. Calculation of deflections of bendable elements have a large number of necessary specifications, but do not take into account the presence of additional reinforcing parts, such as dowels. With the help of the work done the dependence has been obtained which can be implemented in the existing normative calculations to better describe the performance of a real structure.

Čimbenici koji utječu na proces savijanja cjelovitog drva

The effect of temperature and moisture on the behaviour of solid wood is a well-known fact that directly affects wood creep as well. Wood creep includes three types of behaviour, such as viscoelastic creep, mechano-sorptive creep, and pseudo-creep and recovery. All these types can occur simultaneously, and it is sometimes complicated for researchers to isolate or distinct one from another. This paper presents a review of literature on wood rheology and creep properties, as well as factors that influence them, mainly time, temperature, and moisture content. The study of the viscoelasticity and wood creep is very important for gaining knowledge to be applied in solid wood bending.

Experimental Study on the Bending and Shear Behaviors of Chinese Paulownia Wood at Elevated Temperatures.

Chinese Paulownia wood has been extensively used in the construction of timber buildings and lightweight sandwich structures. However, the bending and shear behaviors at elevated temperatures were not well understood. A total of 162 specimens were tested to investigate the bending, tangential shear, and radial shear performances of Chinese Paulownia wood under temperatures from 20 to 220 °C. It was found that the bending specimens exhibited ductile failure due to the progressive damage after reaching the peak load, while the tangential and radial shear specimens exhibited brittle shear failure along the shear plane. The elevated temperatures had limited effects on the failure modes. Under the same temperature, the retention rate of the modulus of elasticity is significantly higher than that of the modulus of rupture. Moreover, the bending strength, tangential shear strength, and radial shear strength generally and nonlinearly decreased with the increasing temperature. The EN 1995-1-2 design curve for the shear strength of wood at elevated temperatures is conservative for both the tangential and radial shear specimens. However, the design curve may not be adopted to estimate the tangential shear strength at temperatures higher than 220 °C.

RESEARCH PROGRESS OF SOLID WOOD BENDING SOFTENING TECHNOLOGY. REVIEW

The softening process of wood bending has a very important influence on theperformance, forming shape, and yield of bentwood. The paper reviewed the typical softening processes in solid wood bending by analyzing the various softening mechanism and softening processes. Themain influencing factors of the softening technology on the bending properties were summarized based on the comparative analysisof the related research progress of wood softening. In view of the lack of systematic analyses of the cost and environmental factors associated with the softening process, this paper goes in detail analyzing themajor softening technologies with comprehensive comparisonof the economic and environmental advantages and disadvantages.The paper also draws light on thedevelopment trends of softening technology that can be implemented in wood industry which can hence improve the added value of wood. Under the background of green development, the authors believe that the softening technology should not only benefit theeconomic efficiency but also meet the social needs of low-carbon and environment-friendly.

Microstructural analysis to understand the strength of teak wood using experimental methods

Teak wood is a widely used material for construction applications. However, microstructural and micromechanical behavior is still unknown. This study aims to determine the micromechanical properties of teak wood using an experimental study. For strength prediction, tensile, bending, and compressive testing has been performed on micro samples of teak wood at different loading rates, i.e., 1 mm/min, 0.5 mm/min, and 0.25 mm/min. The scanning electron microscopic (SEM) technique has been adopted for microstructural analysis, and nanoindentation proceeded for local properties. This study shows that the mean value of ultimate tensile, bending, and compressive strength of teak wood is 71.15 MPa, 59.72 MPa, and 39.36 MPa, respectively, at a 1 mm/min loading rate. The tensile and compressive strength decreases with decreasing loading rate, showing direct dependence on loading rate. In contrast, the bending strength does not relate to the loading rate. Therefore, we cannot directly compare the loading rate and bending strength results. Using the SEM technique, the fracture patterns of samples have been studied. Nanoindentation of specimens shows that the cell wall plays a more crucial role in forming good mechanical properties than the material present inside the cell wall.

Triethanolamine impregnation/steam synergistic softening of teakwood to improve bending properties and its mechanism

ABSTRACT Solid wood bending component has good mechanical properties and unique artistic characteristics. To investigate bending properties of solid wood and its mechanism, this paper has conducted the studies of softening and bending teakwood which is chosen as raw material, vacuum impregnation was carried out with environmentally friendly triethanolamine (TEA), sodium chloride (NaCl) and sodium dodecyl benzene sulfonate (SDBS) as compound softening solution, and the wood was softened with superheated steam as the medium. The results show that the infiltration of softening solution can increase the content of O and N elements in the wood and form C-NH2 and C–N bonds with C element. When the concentration of softening solution is 15%(m/m), the wood presents the best bending property, and the bending coefficient can reach 1/9.24, which is 20.48% higher than that of the untreated wood, and the qualification rate of bending components is increased to 85%. After drying and shaping, compression strength parallel to grain and bending strength increased by 22.91% and 20.82%, as well the indentation modulus and hardness of the cell wall increased by 16.70% and 21.45%, respectively. Meanwhile, the wet swelling rate and chord length change rate decreased by 51.39% and 3.37%.

Robotic zip-bending of wood structures with programmable curvature

Standard wood bending approachesrely either on heavy industrial processes optimized for repeatability or on crafting techniques that are mostly intended for the production of small-scale products. Contemporary research focuses on digital fabrication methods to overcome geometrical limitations and automate freeform wood construction without the need for highly specialized craftsmanship. The presented research focuses on robotic zip-bending to achieve custom curved wood elements with structural properties. The technique uses kerfing patterns applied to two layers of planar wood elements to achieve a zipped composite with precomputed bending and twisting behaviour. The article describes the entire workflow from initial material studies to the realization of a robotically-made 1:1 structural installation. The involved methods, such as mechanical testing, geometrical form-finding, structural FEA simulation, CNC robot programming, and 3D scanning, are described with extensive qualitative analysis and quantitative data. The work demonstrates robotic zip-bending’s structural and geometrical capabilities for prospective applications in the construction industry, including suggestions for future research developments.

Predictive model of the modulus of elasticity in static bending (MOE) of larch wood based on gray relation analysis (GRA) and gene expression programming (GEP)

To accurately evaluate the modulus of elasticity in static bending (MOE) of wooden components in ancient timberwork buildings under the “minimum intervention principle,” the nondestructive testing of physical and mechanical properties were conducted on larch. Using moisture content (MC), density (ρ), the stress wave propagation velocity ( ), the modulus of elasticity in dynamic bending (Ed), the rotational resistance value of the drilling needle (fdrill), and the resistance value of the feeding needle (ffeed) as the main parameters, the correlation between several parameters and MOE was firstly calculated using the Gray Relation Analysis (GRA) and ranked according to the strength of the correlation. Six combinations were selected according to the ranking, and the Gene Expression Programming algorithm (GEP) was used to build models for predicting MOE. The results showed that the correlation between several parameters and MOE was good (between 0.5 and 0.8), and the prediction model established with combination 6 was the best, which indicated that the prediction model established based on GRA-GEP algorithm had a certain feasibility and effectiveness, and the combined effect of the six parameters to evaluate the MOE of wooden components of ancient buildings was better in the field inspection.

Furfural-based resin for modifying birch wood properties

Furfural (F) cannot be easily polymerized like furfuryl alcohol, but it is an aldehyde that can react with urea (U) to make a polymeric network. The possibility of preparing F/U polymer along with an acidic catalyzer (maleic anhydride; M) was evaluated as a means to improve some selected properties of birch (Betula pendula) wood. The F+U/M resin was introduced into the wood with a double treatment technology. The first step involved dilution of F in water and methanol, and the second step was immersion in a U/M aqueous solution. The color of treated wood was darkened after resin curing from brown to a spectrum of black depending on the amount of loaded resin. The 60 to 80% of materials were converted to a non-leachable polymer based on the different formulations. The water absorption and volumetric swelling of the treated samples decreased with an increase in weight percent gain (WPG). The analysis of mechanical strength showed that treatment with F + U/M reduced to some extent the hardness and the impact bending of wood, while modulus of rupture, modulus of elasticity, and compression parallel to the grain with WPG were increased. The exposure of the samples to the accelerated weathering showed noticeable changes in color and roughness.

BENDING CHARACTERISTICS OF LAMINATED WOOD COMPOSITES CONSTRUCTED WITH BLACK PINE WOOD AND ARAMID FIBER REINFORCED FABRIC

The aim of this study was to determine the 4-point bending strength and modulus of elasticity in bending of Black pine wood laminated materials reinforced with aramid fiber was bonded using epoxy or polyurethane glues separately. The samples were prepared in accordance with the TS 5497 EN 408 (2006). The results of the study determined that the highest value for static bending strength was found in the laminated wood samples (83.94 N.mm-2) that were prepared using inter-layer aramid fiber reinforced polymer (AFRP) and epoxy glue. The highest value of modulus of elasticity in bending was found in the samples prepared with inter-layer epoxy and AFRP (10311.62 N.mm-2). It was observed that the samples parallel to the glue line of the laminated material showed higher performance compared to those perpendicular to the glue line. The data obtained as a result of this study demonstrated that aramid fiber reinforced Black pine wood laminated materials can be used in the building industry as building materials.

Phase change material impregnated wood for passive thermal management of timber buildings

The Scots pine (Pinus sylvestris L.) sapwood was impregnated with the eutectic mixture of capric acid (CA) and stearic acid (SA) as phase change material (PCM) via vacuum process for passive thermoregulation in timber buildings. The hygroscopic properties, mechanical properties, thermal energy storage (TES) characteristics and lab-scale thermo-regulative performance of wood/CA-SA composite were evaluated. The produced composite from PCM was morphologically and physico-chemically characterized by SEM, FT-IR and XRD analysis. Thermal energy storage (TES) properties, cycling chemical/thermal reliability, and thermal degradation stability of the produced composite were determined by TG/DTA and DSC analysis. The hygroscopic tests revealed that the wood/CA-SA composite showed low water absorption (WA) and high anti-swelling efficiency (ASE) after 264 hours in water. Wood treatment with CA-SA increased the bending and compression strength of wood. TG/DTA data demonstrated that the wood/CA-SA composite left higher residue of 10.31% at 800°C than that of wood with 6.87%. The DSC measurements showed that the obtained wood/CA-SA composite had a good TES capacity of about 94 J/g at 23.94°C. The cycling DSC results confirmed the eutectic PCM in wood indicated high chemical stability and storage/release reliability even though it was run 600 times melt/freeze. According to thermal performance test, the wood/CA-SA composite has ability of storing excess heat in the environment and preventing the heat flow to the environment. It can be concluded that the fabricated wood/CA-SA composite can be used for indoor temperature regulation and energy saving in timber buildings.

A Comparison of the Loading Direction for Bending Strength with Different Wood Measurement Surfaces Using Near-Infrared Spectroscopy

Wood is widely used throughout society for building resources and paper. To further expand wood’s use in the wood industry, we tested the bending strength properties of wood and certified its internal quality by using near-infrared spectroscopy (NIRS). In this study, the relationship between bending strength and loading direction was compared by changing the light acquisition point of wood surfaces to elucidate the anisotropy of the wood using NIRS. The two loading directions were defined by using a bending test as the radial section and the tangential section. Two light acquisition points with NIRS were also defined by a bending test as the loading position (the compression surface) and the opposite surface (the tensile surface), and a comparison was made between the prediction accuracy of the wood’s mechanical strength properties obtained via a bending test using two pieces of light acquisition data. The strength properties of the wood bending tests were the elastic modulus in bending (Eb), the bending strength (Fb) and density (DEN). Cryptomeria japonica was prepared and cut into a final size of 20 mm × 20 mm × 320 mm. Near-infrared (NIR) spectra were obtained from the compression force side and the tensile force side (calculating these averages), and a partial-least-squares regression (PLSR) was performed for the regression analysis. In the NIR measurement position, the best calibration results of the PLSR were the averaged data between the side undergoing the compression force and that undergoing the tensile force. Comparing the two loading directions, the result for the radial section was slightly superior to that of the tangential section. The radial section showed a good relationship between the spectra acquisition position and the arrangement of the wood’s structure. The estimation accuracy of bending strength properties differed depending on the location where the NIR spectra acquisition was performed.

INFLUENCE OF FATIGUE ON BENDING OF Pinus caribaea WOOD

ABSTRACT This research aimed to evaluate the effect of the number of fatigue cycles (NC, 0 – reference, 450, 4500, 45000, and 90000) for frequencies (Fr) of oscillation equal to 0.5 and 1.0 Hz on the modulus of elasticity (Em) and operating stress (σm) in the static bending of Pinus caribaea wood. Em and σm were determined taking into account three specimens (SPEC) manufactured for reference condition and another three for each of the four NC levels and each Fr level, resulting in 27 SPEC. Sixty experimental determinations were obtained, being the approximate total time of sample exposure to fatigue of 350 hours. The same specimens used to determine Em and σm for the reference condition were also used (via non-destructive tests) to obtain these properties for all fatigue cycles. The frequency and number of cycles significantly influenced both investigated properties. Reductions in Em and σm values were observed after 45000 cycles. The progressive increase in the number of fatigue cycles caused more marked reductions in mechanical properties when compared to the increase in the frequency of oscillation.

Deadman anchoring design for cable logging: a new approach

Cable yarding is still a common system for transporting wood in steep terrain. In the Pacific Northwest, United States, and other regions of high-productivity forestry, reduced rotation ages for harvest have resulted in a lack of large stumps to serve as anchors for cable-yarding systems. One of the most common anchoring alternatives to stumps is buried deadman anchors. Conventional design of this system has been limited to simplified charts that account for soil resistance, as well as both shear and bending resistance, of the deadman, which is typically a buried log. However, these charts are limited to larger deadman anchors of only Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), which are likely not readily available in modern operations. Thus, revised, simplified design charts are proposed that consider a variety of different soil failure mechanisms, as well as several different wood types and bending conditions. An updated approach provides a quantitative perspective towards safe anchoring in modern forest operations.

Index for Wood Bending Shapes

家具部材の曲げ木製造において，近年増加している不良現象への対策が課題となるいま，樹種の選定基準になる物性や，曲げ木可能な材厚（s）と曲げ半径（r）の相関のような形状基準が求められている。本研究では蒸煮直後の木材を押し型曲げ試験に供して，樹種別の材特性と曲げたわみ量の関係を検討した。押し型曲げ試験で引張側側面に割れが多数見られたため，縦引張試験から破壊ひずみの限界 （εt（Max）） を算出した。また，木材にベンディングバンドを沿わせて曲げることで材上端部から中立軸までの距離（t）が長くなることを確認した。本実験結果から，引張試験の破壊ひずみを判断指標とする条件式 （s-t） / （r + t） < εt（Max） が有用であることを提案する。 なお，押し型曲げ試験の結果が良好であった条件でこの関係が満たされていたことを確認した。

Lignocellulosic materials modification and engineering in relation to viscoelastic perspectives

By 2010, only 52% or 94 million ha of the total land area in Indonesia was forested. Therefore, we should develop forest plantation with fast growing species, or better efficiency and quality improvement for the utilization of forest products. The conventional method of fabricating curved wooden products is to cut wooden beams into a curved wood, and to connect them for the expected curve shape. However, the disadvantages of this conventional woodworking process are wasting of wood raw materials, decreasing the wood strength due to fiber cutting, and reducing the beauty of wood fiber direction. These problems can be overcomed by bending solid wood, as well as curving laminated veneer lumber (LVL). The bending method of solid wood requires special technique and equipment compared to curving method of LVL. The development of commercial products is required to understand basic knowledge of wood bending. This paper deals with lignocellulosic materials modification and engineering in relation to viscoelastic perspectives; describing viscoelastic property of wood and other lignocellulosic materials, and development of furnitures and bicycle frames from LVL curves. It is expected that more modified and engineered products can be made from lignocellulosic materials based on the knowledge of their viscoelastic properties.

Effect of Bio-based Adhesive on Tensile Strength and Bending of Balsa Wood Adhesive Joint

The aim of this study was to determine the effect of adhesive on tensile strength and bending strength of adhesive joints on balsa wood by varying the type of bio-based adhesive. The use of bio-based adhesive is very potential both as a substitute for synthetic-based adhesive. In this research, adhesive joint was applied using a specimen of balsa wood which was connected with bio-based adhesive which was varied, namely bio-based adhesive from rubber tree sap, sap of jackfruit tree and sap of breadfruit tree. In this study, tensile testing and bending testing were conducted to determine the tensile strength and bending of balsa wood that has been connected using bio-based adhesive variations. The results of the research show that the variation of bio-based adhesive can affect the strength of the structure of balsa wood which is done by adhesive joints because in the variation of bio-based adhesive has different adhesive characteristics so that the binding ability between bio-based adhesive surfaces is different. Fault analysis was carried out after tensile and bending tests to see the effect of bio-based adhesive variations on balsa wood. It is evident that the results of tensile testing on rubber tree sap bio-based adhesive were 28,193 MPa, on jackfruit sap bio-based adhesive was 19,93 MPa and on breadfruit tree bio-based adhesive sap was 15,963 MPa. While the results of bending testing amounted to 23.58 MPa for bio-based adhesive rubber tree sap, on 23.45 MPa for bio-based adhesive sap and breadfruit tree sap at 19.18 MPa.