Wood Failure Research Articles

Adhesive bonding of 3D-printed ABS parts and wood

Additive manufacturing, also known as 3D printing technology, has experienced massive growth in the last decade. Instead of printing the entire product, 3D printing can be used to produce only the most complex parts, which are then combined with simple, non-printed parts from other materials to make the final product. In addition to mechanical connections, adhesive bonding is most commonly used to combine printed parts with other elements. In this study, the influence of 3D-printing parameters on the bond shear strength of 3D-printed Acrylonitrile-butadiene-styrene copolymer parts bonded to beech wood was investigated. Three printing settings with different layer thicknesses (0.39, 0.19, 0.09 mm) and a posttreatment method that utilized acetone vapour were used. The three different adhesives applied were commercial one-component polyurethane adhesive, hot melt adhesive for edge bonding, and a two-component polyurethane adhesive. The results show that the type of adhesive had the biggest influence on the strength of the bond. The highest bond strength was achieved using a two-component polyurethane adhesive. The type of failure (failure in wood, plastic, adhesive, or cohesive failure) depended greatly on the type of adhesive and thickness of the printed layer.

Feasibility of manufacturing cross-laminated timber using fast-grown small diameter eucalyptus lumbers

Eucalyptus is one of the most important plantation species in South China. Alternate applications of plantation grown hardwood such as eucalyptus need to be developed due to decreased demands of fibers for pulp and paper industry. The feasibility of manufacturing three-layer cross-laminated timber (CLT) using fast-grown small diameter eucalyptus wood (Eucalyptus urophylla×Eucalyptus grandis) was evaluated in this study. L9 (33) orthogonal tests with three factors and three levels were adopted to study the effects of adhesive spread rate, pressure, and pressing time duration on the block shear strength (BSS), wood failure percentage (WFP), and rate of delamination (RD) of CLT via block shear tests and cyclic delamination tests. The results indicated that the optimal pressing parameters were adhesive spread rate of 160g/m2, pressing pressure of 0.8MPa, and pressing time duration of 200min with one-component polyurethane adhesive used. The values of modulus of elasticity (MOE) and modulus of rupture (MOR) in the major and minor strength directions of CLT were 11,466MPa, 24.5MPa, 681MPa, and 8.6MPa, respectively. The values of transverse shear moduli and interlaminar shear strength in the major and minor strength directions of CLT were 91.8MPa, 1.3MPa, 241.6MPa, and 0.5MPa, respectively. The mechanical properties of eucalyptus CLT were equivalent to those of commercially available softwood CLT. These results indicate CLT panels manufactured from fast-grown small diameter eucalyptus lumber is promising for structural applications.

SHEAR STRENGTH IN THE GLUE LINE OF Eucalyptus sp. AND Pinus sp.WOOD

ABSTRACT To evaluate the adhesive efficiency on the union of glued joints in a particular temperature and humidity conditions for a specified time the adhesive must be submitted to specific load tests, such as shear in the glue line. The objective of this study was to evaluate the shear strength in the glue line of Eucalyptus sp and Pinus sp.woods. Five adhesives (castor oil, sodium silicate, modified silicate, , PVA and resorcinol-formaldehyde), three weights (150 g/m2, 200 g/m2, and 250 g/m2) and two species (Eucalyptus sp. and Pinus sp.) of wood were used. Twelve specimens were obtained from each repetition per treatment, corresponding to 108 specimens that were conditioned at a temperature of 23 ± 1°C and relative humidity of 50 ± 2%. The interaction between the weight and type of adhesive was significant for the shear strength in the glue line of eucalyptus wood. However, no interaction between the weight and the adhesive was found for pinus, only the isolated from the adhesive effect. Chemical bonds originated in the polymerization of resorcinol-formaldehyde adhesives and castor bi-component conferred upon these adhesives the greatest resistance in the glue line. Castor and resorcinol-formaldehyde adhesives showed the highest shear strength values in the line of glue and wood failure. Castor adhesive presented satisfactory performance for bonding of eucalyptus and pine woods.

High Bonding Temperatures Greatly Improve Soy Adhesive Wet Strength.

Soy wood adhesive bond strengths reported in different literature studies are difficult to compare because a variety of temperatures and other conditions have been used for the bonding and testing step. Some reports have indicated bond strengths are sensitive to bonding temperature, but the reason(s) for this has not been intensively investigated. Although these prior studies differ in other ways (such as type of soy, wood species, and test method), the effect of bonding temperature has not been clearly examined, which is important for focusing commercial applications. A tensile shear test using two-parallel-ply veneer specimens with smooth maple was used to measure both the dry and wet cohesive strength of soy adhesives. Although the soy adhesives gave very good strengths and dry wood failure, they often have low wood failure and shear strengths under wet conditions when bonded at 120 °C. However, wet strength greatly increased as the bonding temperature increased (120, 150 and 180 °C) for these two-ply tests with. This study examined the use of different types of soys (flours, concentrates and isolates) and different bonding temperatures and bonding conditions to evacuate several possible mechanisms for this temperature sensitivity, with coalescence being the most likely.

Effects of surface modification methods on mechanical and interfacial properties of high-density polyethylene-bonded wood veneer composites

To improve interfacial adhesion between wood veneer and high-density polyethylene (HDPE) film, wood veneer was thermally modified in an oven or chemically modified by vinyltrimethoxysilane. The wood veneers were used to prepare plastic-bonded wood composites (PBWC) in a flat-press process using HDPE films as adhesives. The results showed that both modifications reduced veneer hydrophilicity and led to enhancement in shear strength, wood failure, and water resistance of the resulting PBWC. The thermal treatment significantly decreased the storage modulus close to 130 °C (the melting temperature of plastic). Thermal-treated wood veneer maintains mechanical interlocking for bonding and veneer strength which then declined under thermal treatment due to hemicellulose degradation and cellulose de-polymerization. In the silane-treated PBWC, enhanced interlocking and a stronger bonding structure resulted from the reaction between the silane-treated veneer and HDPE. This strong bonding structure allowed thermal stability improvement demonstrated by high modulus and low tanδ values. However, the strength of silane-treated PBWC was still much lower than thermosetting resin-bonded composites at higher temperatures due to the melting behavior of thermoplastic polymer, precluding its use in certain applications.

The effect of soda bagasse lignin modified by ionic liquids on properties of the urea–formaldehyde resin as a wood adhesive

ABSTRACT The aim of this research was to investigate the influence of lignin modified by ionic liquids on physical and mechanical properties of plywood panels bonded with the urea–formaldehyde (UF) resin. For this purpose, soda bagasse lignin was modified by the 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) ionic liquid and then the various contents of unmodified and modified lignins (10, 15, and 20%) were added at pH=7 instead of second urea during the UF resin synthesis. The physicochemical properties of the prepared resins as well as the water absorption, shear strength, and formaldehyde emission of the plywood panels made with these adhesives were measured according to standard methods. According to Fourier Transform Infrared (FTIR) Spectrometry, by treatment of lignin, the C=O, C–C, and C–H bonds decrease while the content of the C–N bond dramatically increases. Based on the finding of this research, the performance of soda bagasse lignin in UF resins dramatically improves by modification by ILs; as the resins with modified lignin yielded lower formaldehyde emission and water absorption when compared to those made from unmodified lignin and commercial UF adhesives, respectively. The shear strength as well as wood failure percentages are lower for the panels produced with modified lignin than for the panels produced with UF resins alone.

Influence of different types of reinforcements on the embedment behavior of steel dowels in wood

In this study, dowel displacement-embedment stress relationships for different types, numbers and positions of reinforcements were experimentally investigated using a half-hole embedment test setup. Tests were performed parallel to the grain and in compression. Screws with a full or partial thread at different positions below the dowel and oriented strand board, plywood and nail plates on the loaded surfaces of the specimens, served as reinforcements. Test results underline their potential for an increased ductility of dowel-type connections. Comparison of reinforced and unreinforced specimens suggests premature failure of the unreinforced wood and consequently, an underestimation of the embedment strength as it is subsequently used in the design of dowel connections using the European yield model. This was supported by the investigation of cracks on the surface of the specimens visualized by means of a full-field deformation measurement system. It could be demonstrated that the strength in the embedment test even further increases if the reinforcement elements actively contribute to the load transfer. This property however cannot be considered as embedment strength, but represents the strength of a connection system. Test data is compared to the design equation in Eurocode 5.

ASSESSMENT IN BENDING AND SHEAR STRENGTH OF GLUED LAMINATED TIMBER USING SELECTED MALAYSIAN TROPICAL HARDWOOD AS ALTERNATIVE TO TIMBER RAILWAY SLEEPERS

This paper presents a pilot study on bending and shear strength of glued laminated (glulam) timber using selected tropical timber namely, Kekatong (Cynometra spp.) and Melagangai (Potoxylon melagangai) as an alternative for timber railway sleepers. Selected timbers were manufactured in accordance with MS758:2001 and the bending test was conducted according to ASTM D198:2013. The shear test for glue line integrity was performed to observe the bond performance in glulam accordance to MS758:2001.The results showed both species can be used as structural members since the bending strength obtained from the laboratory work is greater than the allowable bending strength. In terms of the percentage of wood failure, the bonding characteristics of both glulam satisfied the bonding requirement stipulated in the standard and have the potential to be used as glulam timber railway sleepers.

Influence of orientation and number of layers on the elastic response and failure modes on CLT floors: modeling and parameter studies

In the present paper, the bending behavior of Cross Laminated Timber panels is investigated by means of the linear elastic exact solution from Pagano (1970, 1969). The resulting stresses are the input for a wood failure criterion, which can point out the first-crack load and the respective dominant failure mode. Heterogeneous layers are modeled as equivalent and homogeneous layers. This simplified and deterministic modeling gives results in good agreement with a reference experimental test. A comparison is made with respect to the panel’s global stiffness and failure stages within the apparent elastic stage. Finally, parameter studies are carried out, in order to quantify CLT limitations and advantages. The effect of varying properties such as the panel’s slenderness, orientation of transverse layers and number of layers for a fixed total thickness are investigated.

Shear strength of furfurylated, N-methylol melamine and thermally modified wood bonded with three conventional adhesives

ABSTRACTThe shear strength of furfurylated, N-methylol melamine (NMM) and thermally modified wood bonded with emulsion polymer isocyanate, polyvinyl acetate (PVAc), and polyurethane (PU) adhesives was examined. Furfurylation and NMM modification of Scots pine had a significant negative effect on the bonding strength with all adhesives irrespective of the treatment intensity. The obtained low-shear strength values were related to the brittle nature of the wood after modifications rather to the failure of the bondline. PVAc showed a better bonding performance with both furfurylated and NMM modified wood while the combination of furfurylated wood and PU gave the highest reduction in bonding strength (47–51%). Shear strength also decreased significantly after thermal modification in both Scots pine (36–56%) and beech (34–48%) with all adhesives. With the exception of thermally modified beech samples bonded with PU, bondline was found to be the weakest link in thermally modified wood as it was revealed by the wood failure surfaces. Bondline thickness and effective penetration of adhesives did not relate to the shear strength of all modified wood materials. The lower shear strength of modified wood could be attributed to other factors, such as the reduced chemical bonding or mechanical interlocking of adhesives, and the reduced strength of brittle modified wood substrate.

New design approach for controlling brittle failure modes of small-dowel-type connections in Cross-laminated Timber (CLT)

The introduction of Cross-laminated Timber (CLT) as an engineered timber product has played a significant role in considerable progress of timber construction in recent years. Extensive research has been conducted in Europe and more recently in Canada to evaluate the fastening capacity of different types of fasteners in CLT. While ductile capacities calculated using the yield limit equations are quite reliable for fastener resistance in connections, however, they do not take into account the possible brittle failure mode of the connection which could be the governing failure mode in multi-fastener joints. Therefore, a stiffness-based design approach which has already been developed by the authors and verified in LVL, glulam and lumber has been adapted to determine the block-tear out resistance of connections in CLT by considering the effect of perpendicular layers. The comparison between the test results on riveted connections conducted at the University of Auckland (UoA) and the Karlsruhe Institute of Technology (KIT) and the predictions using the new model and the one developed for uniformly layered timber products show that the proposed model provides higher predictive accuracy and can be used as a design provision to control the brittle failure of wood in CLT connections.

Physical-mechanical properties and bonding quality of heat treated poplar (I-214 clone) and ceiba plywood

Abstract: The present paper investigates the physical and mechanical modifications of both poplar (I-214 clone) and ceiba veneers and plywood after heat treatments of different intensities (5 and 7 % of dry mass losses). Plywood panels were glued before and after heat treatment with urea-formaldehyde (UF) and melamine-urea-formaldehyde (MUF) resins. In order to assess the treatments’ effects on both the wood and the glues, the dry mass, the density, the bending strength, the Young’s modulus and the bonding quality were measured before and after heat treatment. The results of the different treatments were compared as well. Results showed that the loss in cell wall polymers due to the heat treatment caused a significant reduction of the equilibrium moisture content of the samples. From a mechanical point of view the treatment resulted in an important reduction of strength and in a small reduction of stiffness. Bonding quality as well as mechanical properties were widely affected by the heat treatment. The different intensities of the treatments (the treatment range was up to 5% and 7% of dry mass loss) did not show significant differences for most of the features assessed. The mechanical performance as well as the bonding quality of treated samples suggested that veneers should be glued after heat treatment. Apparent cohesive wood failure showed that different degradations affect wood and glues with a prominent effect on the glues for UF resins and a prominent effect on the wood for MUF resins.

PROPRIEDADES FÍSICO-MECÂNICAS DE PAINÉIS DE LÂMINAS PARALELAS REFORÇADOS COM PRFV

http://dx.doi.org/10.5902/1980509819676O objetivo desta pesquisa foi avaliar as propriedades físico-mecânicas de painéis de lâminas paralelas (LVL) com camadas de Polímeros Reforçados de Fibra de Vidro (PRFV) impregnadas com dois tipos de matrizes. Primeiramente foi realizada a fabricação dos painéis LVL com nove camadas de lâminas de madeira unidas com resina à base de fenol-formaldeído na gramatura de 190 g/m2 em linha simples. Posteriormente, foi feita a aplicação do reforço de fibra de vidro impregnado com resinas epóxi ou poliéster isoftálica com NPG. Os tratamentos consistiram na aplicação de uma a quatro camadas de fibra de vidro impregnadas com resina epóxi ou isoftálica, totalizando 21 painéis. As propriedades avaliadas foram a massa específica, o teor de umidade, a flexão estática na posição flatwise e egdewise e a resistência ao cisalhamento na linha de cola. Em flexão estática na posição flatwise, uma camada de PRFV, em tratamentos com resina epóxi e isoftálica, foi suficiente para influenciar o módulo de elasticidade (MOE), enquanto para o módulo de ruptura (MOR), duas camadas de PRFV foram necessárias para tratamentos com resina isoftálica e uma camada para tratamentos com resina epóxi. Na posição edgewise, os valores de MOE e do MOR se mantiveram estáveis após a aplicação de duas camadas de PRFV. A resina epóxi apresentou maior resistência ao cisalhamento e maior percentual de falhas na madeira, enquanto a resina isoftálica, apesar de apresentar valores de resistência similares à fenólica, não apresentou boa adesão à madeira, representada pelo baixo percentual de falhas na madeira. Portanto, a aplicação de uma camada de PRFV com resina epóxi na posição de tração seria o suficiente para melhorar as qualidades mecânicas (flexão estática e cisalhamento) dos painéis LVL fabricados com lâminas de madeira de pinus unidas com fenol-formaldeído.

Albizia richardiana King & Prain as a raw material for ply and particleboard

Woods of Albizia richardiana has been studied for assessing the suitability for plywood and particleboard manufacture. It was found that 1.5 mm thick smooth and figured veneer can be peeled and dried easily. Three-ply plywood were made using veneer of this species bonded with liquid urea formaldehyde glue of 50% solid content extended with wheat flour and catalyzed (ammonium chloride) with 2% hardener under the three specific pressures, viz,1.05 N/mm2, 1.40 N/mm2, 1.76 N/mm2 in three replications at 6 minute press time and 120°C press temperature. Dry and wet shear test were conducted on the sample and their shear load at failure per unit area and percentage of wood failure were determined. 1.05 N/mm2 pressure for the manufacture of plywood was found to be the best. The physical and mechanical properties of Albizia richardiana wood particleboard were studied. The particleboards were tested for determining the strength and dimensional stability. The tensile strength 0.56N/mm2 passed the British and German standard specification, bending strength (modulus of rupture10.80N/mm2) was found nearest to Indian Standard but low German and British standard specification.

Tensile Strength, Elasticity and Cracking Character of Softwood Tissues

Wood tensile strength in longitudinal direction depends on wood density and structure. Growth rings in wood consist of earlywood and latewood which differ greatly in their properties. Latewood is denser, less porous and more resistant to tension along the fiber compared earlywod. The ratio of latewood and earlywood is different for each type of wood species and also depends on growing conditions, climate and etc. The study is aimed to evaluate the tensile strength, elasticity and cracking character of Lithuanian-grown softwood tissues, depending on the wood species, tissue width and latewood ratio in the sample. For the study three species of wood (spruce, pine and larch) were chosen. Samples were cut with the microtome, tissues cross-sectional area of about 0.15-0.50 mm2. The ratio of latewood and earlywood was evaluated using microscope. Wood tissue tensile strength was tested in the tensile machine with a feed rate of 0.2 mm/min. Research results showed that the highest tensile strength was obtained for larch wood samples, while the spruce wood most tended to deformation. Ir was determined that the tensile strength and elasticity of wood are highly influenced by wood microstructure and earlywood and latewood ratio in the sample. Also the wood microstructure and failure mechanism of the samples were evaluated. DOI: http://dx.doi.org/10.5755/j01.ms.21.2.6881

Wet adhesion durability improvement of polyurethane wood adhesives with primer

Southern yellow pine and Douglas fir were glued with two different 1C PUR adhesives and evaluated by means of the vacuum-pressure and delamination tests according to the Canadian Standard CSA O112.9 and the European Standard EN 391, method B, respectively. By using a water-based primer before application of the adhesive, wet wood failure percentage and delamination resistance of the polyurethane adhesives dramatically increased compared to matched samples glued under the same conditions without primer. Standard requirements were achieved when primer was used.

Peeling and Gluing Study of Khaya anthotheca for Ply and Particle Board

Logs of Khaya anthotheca wood has been studied for assessing the suitability of plywood and particleboard manufacture. It was found that 1.5 mm thick smooth and figured veneer can be made and dried easily. Three-ply plywood were made using veneer of this species bonded with liquid urea formaldehyde glue of 50% solid content extended with wheat flour and catalyzed (ammonium chloride) with 2% hardener under the specific pressures, viz, 1.05 N/mm2, 1.40 N/mm2, 1.76 N/mm2 in three replications at 6 minute press time and 120°C press temperature. Dry and wet shear test were conducted on the sample and their shear load at failure per unit area and percentage of wood failure were determined. 1.05 N/mm2 pressure for the manufacture of ply wood was found to be the best. The physical and mechanical properties of K.anthotheca particleboard were studied. The particleboards were tested for determining the strength and dimensional stability. The tensile strength (internal bond strength 0.68 N/mm2) passed the German and British standard specifications; bending strength (modules of rupture 11.25 N/mm2) passed the Indian Standard but did not pass the German and British standard specifications.

Detection of wood failure by image processing method: influence of algorithm, adhesive and wood species

Wood failure percentage (WFP) is an important index for evaluating the bond strength of plywood. Currently, the method used for detecting WFP is visual inspection, which lacks efficiency. In order to improve it, image processing methods are applied to wood failure detection. The present study used thresholding and K-means clustering algorithms in wood failure detection, and four kinds of plywood were manufactured to analyze the influences of wood species and adhesive. Results show that the detection by K-means clustering method is more accurate than thresholding method; it could better correlate with visual inspection results, while the detection results by thresholding method could not reflect the fluctuation of visual inspection results with types of plywood. Moreover, both analyses of the influence of adhesive and wood species show that thresholding method based detection results are more affected by adhesive color, veneer color and permeability of poplar and eucalyptus veneer (mean absolute error compared with visual inspection: PF-Eucalyptus: 15.77 %; PF-Poplar: 25.42 %; UF-Eucalyptus: 30.55 %; UF-Poplar: 21.48 %); whereas K-means clustering method based detection results show no significant change as adhesive and wood species varies (PF-Eucalyptus: 11.07 %; PF-Poplar: 10.22 %; UF-Eucalyptus: 14.77 %; UF-Poplar: 8.50 %). It can be concluded that K-means clustering method has better compatibility for different adhesive and wood species in wood failure detection.

Influence of Welding Time on Tensile-Shear Strength of Linear Friction Welded Birch (Betula pendula L.) Wood

The purpose of this work was to determine the optimal welding time for linear friction welding of birch (Betula pendula L.) wood while keeping the other parameters constant and at similar levels compared to other species in a similar density range. Specimens with dimensions of 20 × 5 × 150 mm3 were welded together, and the influence of welding time (2.5, 3.0, 3.5, and 4.0 s) on the mechanical properties of the specimens was determined. The studies included a tensile-shear strength test as well as visual estimation of wood failure percentage (WFP). Additionally, X-ray microtomographic imaging was used to investigate and characterise the bond line properties as a non-destructive testing method. The highest mean tensile-shear strength, 7.9 MPa, was reached with a welding time of 3.5 s. Generally, all four result groups showed high, yet decreasing proportional standard deviations as the welding time increased. X-ray microtomographic images and analysis express the heterogeneity of the weld line clearly as well. According to the averaged group-wise results, WFP and tensile-shear strength correlated positively with an R2 of 0.93. An extrapolation of WFP to 65% totals a tensile-shear strength of 10.6 MPa, corresponding to four common adhesive bonds determined for beech.

RESISTÊNCIA AO CISALHAMENTO DAS JUNTAS ADESIVAS PRODUZIDAS COM TRÊS DIFERENTES ESPÉCIES DE MADEIRAS E ADESIVOS VINÍLICOS PARA APLICAÇÕES NÃO ESTRUTURAIS

Os adesivos utilizados na colagem de madeiras para aplicações não estruturais normalmente contêm uma emulsão de poli(acetato de vinila) (PVAc) estabilizada com poli(álcool vinílico) e alguns aditivos. A ligação adesiva formada com essa classe de adesivo é pobre quando exposta à umidade e à temperatura. Nesse contexto, a classificação prévia dos adesivos utilizados para aplicações não estruturais, com resistência à umidade e à temperatura, é muito importante para a qualidade e durabilidade das juntas adesivas. Neste trabalho, foi estudada a influência de três espécies de madeiras (Fagus sylvatica L., Mimosa scabrella Bentham e Micropholis cf. venulosa Mart. & Eichler) na resistência ao cisalhamento das juntas adesivas preparadas com três adesivos vinílicos, sintetizados com diferentes concentrações do N-butoximetilacrilamida (NBMA). Os ensaios de resistência ao cisalhamento, na linha de colagem, foram realizados sob diferentes ciclos de acondicionamento das juntas adesivas. Os resultados indicaram que há diferenças significativas na resistência de colagem das juntas adesivas e na porcentagem de falha na madeira provocada, tanto pela espécie de madeira quanto pelo tipo de adesivo utilizado. Os adesivos produzidos foram classificados de acordo com a classe de durabilidade, após várias etapas de acondicionamento. Os valores mais altos de resistência ao cisalhamento foram observados nas juntas coladas com as madeiras de Micropholis cf. venulosa Mart. & Eichler e Fagus sylvatica L., com o adesivo AD-3. O menor valor de resistência ao cisalhamento foi observado nas juntas adesivas preparadas com a madeira da espécie Mimosa scabrella Bentham. A madeira Micropholis cf. venulosa Mart. & Eichler mostrou-se mais adequada para a substituição da madeira Fagus sylvatica L.