Finite element analysis of stress and strain distributions in mortise and loose tenon furniture joints

We studied the effect of loose tenon dimensions on stress and strain distributions in T-shaped mortise and loose tenon （M＆amp;LT） furni-ture joints under uniaxial bending loads, and determined the effects of loose tenon length （30, 45, 60, and 90 mm） and loose tenon thickness （6 and 8 mm） on bending moment capacity of M＆amp;LT joints constructed with polyvinyl acetate （PVAc） adhesive. Stress and strain distributions in joint elements were then estimated for each joint using ANSYS finite element （FE） software. The bending moment capacity of joints increased significantly with thickness and length of the tenon. Based on the FE analysis results, under uniaxial bending, the highest shear stress values were obtained in the middle parts of the tenon, while the highest shear elastic strain values were estimated in glue lines between the tenon sur-faces and walls of the mortise. Shear stress and shear elastic strain values in joint elements generally increased with tenon dimensions and corre-sponding bending moment capacities. There was consistency between predicted maximum shear stress values and failure modes of the joints.     

椭圆榫T型构件接合强度影响因素研究

以北美鹅掌楸为基材,探究椭圆榫T型构件接合强度的影响因素。采用单因素试验探究涂胶量、陈放天数对椭圆榫抗拔强度的影响;采用正交试验探究榫眼深度、长度和宽度三个因素对椭圆榫抗弯强度的影响。结果表明:涂胶量对椭圆榫T型构件抗拔强度的影响非常显著,陈放天数的影响比较显著。榫眼宽度是影响椭圆榫T型构件抗弯强度的主要因素,榫眼深度和长度次之,而深度的影响大于长度。     

典型直榫梁柱节点在现代木结构中的应用研究

基于Abaqus有限元分析,对不同榫长的实木榫卯连接梁柱节点和榫长为75 mm的不同层数的正交胶合木(CLT)榫卯连接梁柱节点进行数值模拟,分析其受力状态并提取荷载-位移曲线,与使用金属连接件连接的梁柱节点承载力进行对比,探究将榫卯连接应用在现代木结构中的理论依据。研究表明:竖向荷载作用下,榫长75 mm的榫卯连接梁柱节点承载能力处于M8和M10螺栓连接梁柱节点的理论承载力之间;当榫长增大时,节点的最大承载力逐渐提高,榫长150 mm的榫卯节点承载力已经略微超过M12螺栓连接时的理论承载强度,说明榫卯连接梁柱节点在承载能力上可以满足现代木结构建筑的使用要求。由于榫卯节点的承载力主要受到顺纹抗压强度的影响,因此相比于实木连接榫卯节点,CLT榫卯节点的承载力无显著提高。     

Experimental and numerical investigations on adhesively bonded timber joints

Adhesively bonding of timber structural elements provides new opportunities as it is well adapted for the anisotropic and fibrous nature of the material. Experimental and numerical investigations were carried out on adhesively bonded full-scale double-lap joints composed of timber adherends (spruce) and adhesive layers. The influence of different geometric parameters and adhesives on the joint strength was studied. The investigated geometric parameters were the thickness of the adhesive layer (0.5–2.0?mm), the overlap length (40–280?mm), and the ductility of the adhesive (using three different adhesives). It was found that the joint strength was independent of the adhesive layer thickness (for the thickness range investigated) that the joint strength increased with the overlap length up to an apparent maximum of approximately 200?mm and that strength was almost independent of the adhesive stiffness. The numerical investigation was in good agreement with the experimental results and allows for the model to be used for strength prediction of the investigated joints.     

Effect of moisture content of members on mechanical properties of timber joints

To investigate the effect of moisture content (MC) of members on the mechanical properties of timber joints, bending tests of precut joints and shear tests of dowel-type joints were carried out using timbers of Japanese cedar (Cryptomeria japonica D. Don) with three moisture conditions: green, kiln-dried with a MC target of 15%, and over-kiln-dried with a MC target of 5%. For the bending test, timbers were processed with a precut processing machine into “koshikake-ari” (a kind of dovetail joint) and “koshikake-kama” (a kind of mortise and tenon joint). A pair of members was jointed together without mechanical fasteners. Bolts (diameter = 12 mm) and nails (diameter = 2.45 mm) were used as dowels in the shear test. Bolted joints were constructed with one bolt and two metal side plates. Two nails and two metal side plates were used for the nailed joint. For precut joints, no clear effect of MC was recognized on maximum moment and initial stiffness. The maximum strength of mechanical joints assembled with kiln-dried wood was changed by the degree of drying. Stiffness of the joints assembled with kiln-dried specimens was larger than that of the joints assembled with green specimens.Part of this study was presented at the 7th International IUFRO Wood Drying Conference, Tsukuba, July 2001     

Tests for outdoor window profiles: 90° mortise tenon corner joints strength assessment

The research focuses on the assessment of the performances of glued laminated wood corner joints for outdoor window profiles applications, proposing a methodology to appreciate the strength of 90° tenon mortise corner joints. The rationale relies on the potential damage (i.e. breaking of the frame) that can be caused by poor glueing processes and/or typology of adhesives. There is a number of standards for assessment of wood-adhesive bonds for outdoor windows; however, there is a lack of specific standards related to glueing assessment for outdoor wood frames, which can take into account all the factors influencing the glueing quality. The proposed methodology was tested on red oak window profiles. A commercially available polyvinyl acetate-based adhesive was used for corner joints. Bending strength of 90° tenon mortise corner joints was measured and compared with maximum admissible loads on the frame to limit its deformations within admissible ranges. The test results show that the 90° tenon mortise corner joints strength exceeds the admissible load to preserve the functionality of the frame. In order to appreciate the influence of conditioning processes on adhesion, shear strength tests of the flatwise glued joint samples (bond lines of lamellae) were carried out after different conditioning processes.     

Bending moment resistance of dowel corner joints in case-type furniture under diagonal compression load

We investigated bending moment resistance under diagonal compression load of corner doweled joints with plywood members. Joint members were made of 11-ply hardwood plywood of 19 mm thickness. Dowels were fabricated of Beech and Hornbeam species. Their diameters(6, 8 and 10 mm) and depths of penetration(9, 13 and 17 mm) in joint members were chosen variables in our experiment. By increasing the connector's diameter from 6 to 8 mm, the bending moment resistance under diagonal compressive load was increased, while it decreased when the diameter was increased from 8 to 10 mm. The bending moment resistance under diagonal compressive load was increased by increasing the dowel's depth of penetration. Joints made with dowels of Beech had higher resistance than dowels of Hornbeam. Highest resisting moment(45.18 N·m) was recorded for joints assembled with 8 mm Beech dowels penetrating 17 mm into joint members Lowest resisting moment(13.35 N·m) was recorded for joints assembled with 6 mm Hornbeam dowels and penetrating 9 mm into joint members.     

Bending moment resistance of corner joints constructed with spline under diagonal tension and compression

We determined the effects of the penetration depth and spline material and composite material type as well as joining method on bending moment resistance under diagonal compression and tension in common wood panel structures. Composite materials were laminated medium density fiberboard (MDF) and particle board. Joining methods were buttand miter types. Spline materials were high density fiber board (HDF).The penetration depths of plywood, wood (Carpinus betolus) and splinewere 8, 11 and 14 mm. The results showed that in both diagonal compression and tension, MDF joints are stronger than particle board joints,and the bending moment resistance under compression is higher compared with that in tension. The highest bending moment resistance under tension was shown in MDF, butt joined using plywood spline with 8 mm penetration depth, whereas under compression bending moment resistance was seen in MDF, miter joined with the HDF spline of 14 mm penetration depth.     

Prediction of bending stiffness and moment carrying capacity of sugi cross-laminated timber

Cross-laminated timber (CLT) panels consist of several layers of lumber stacked crosswise and glued together on their faces. Prototype sugi CLT floor panels were manufactured and bending tests were carried out under the different parameters of lumber modulus of elasticity (MOE), number of layers, thickness of lumber and thickness of CLT panels. On the basis of above tests, bending stiffness and moment carrying capacity were predicted by Monte Carlo method. MOE of lumber was measured by using grading machine and tensile strength of lumber was assumed to be 60 % of bending strength based on the obtained bending test. Bending stiffness EI of CLT panels could be estimated by adopting composite theory and equivalent section area. Experimental moment carrying capacity showed 12 % higher value than the calculated moment carrying capacity by average lumber failure method, and also showed 45 % higher value than the calculated moment carrying capacity by minimum lumber failure method due to the reinforcement of the outer layer by the neighboring cross layer.     

Evaluating the strength of finger-jointed lumber of Gmelina arborea in Costa Rica

The use of finger-jointed lumber of Gmelina arborea (gmelina) for the production of glue-laminated beams is becoming more important to the wood industry in Costa Rica. At the request of the local wood industry, two different kinds of adhesives, thermoplastic polyvinyl emulsion (catalyzed PVA) and 1-part polyurethane adhesive (PU) were tested on finger joints of gmelina wood and their strength properties compared under dry, boiled, and saturated conditions. The results showed that under the boiled and saturated conditions, the PVA adhesive exhibited low tensile strength and poor distribution of failures while PU showed much more promise. Based on our preliminary results, the PU adhesive can be successfully used for finger-joint boards of gmelina. Palabras clave: Adhesivos, Melina, Modos de falla, Vigas laminadas Resumen. El uso de la madera unida con juntas de dedo (finger-jointed) para la producción de vigas laminadas-encoladas está tomando mayor importancia en la industria maderera de Costa Rica. Atendiendo la solicitud de la industria, sobre la calidad de los finger joints de la madera de melina, se ensayaron dos tipos diferentes de adhesivos, una emulsión de polivinilo catalizado (thermoplastic polyvinyl emulsion, catalizado, PVA) y un adhesivo de poliuretano (polyurethane adhesive, PU) de un componente, para comparar sus características de resistencia bajo condiciones secas, de ebullición y de saturación. Los resultados muestran que bajo condiciones de ebullición y saturación, el adhesivo PVA tiene una baja resistencia a la tensión y una deficiente distribución de fallas, mientras que el PU mostró resultados mucho más prometedores. Basados en los resultados preliminares, el adhesivo PU puede ser utilizado exitosamente para unir las tablas de melina con juntas de dedo.     

单板/HDF复合木地板的制造工艺与产品性能研究

单板/高密度纤维板(HDF)复合木地板结合了实木地板和浸渍纸层压木质地板的优点,是地板产业发展的新方向之一。文中以12mm厚HDF为基材、复合意杨单板,试制了"耐磨纸-单板-HDF基材-平衡纸"四层结构地板用复合板材。研究了不同单板厚度、胶黏剂种类(聚氨酯-PU,脲醛树脂-UF)及涂布量对板材翘曲度、吸水厚度膨胀率、内结合强度及机加工性能的影响。结果表明:1)单板与HDF复合制造木地板是可行的;2)复合木地板的翘曲度随单板厚度和施胶量的提高而递增,最高可达约0.6%;3)贴面采用聚氨酯胶黏剂,产品性能优于脲醛树脂胶合板材,但冷压周期偏长。推荐工艺条件为:单板1.2mm,PU或UF胶黏剂均可,涂布量控制在100g/m~2左右。     

木框斜角榫接合性能研究

在木家具结构设计中,特别是具有中国传统家具风格的实木家具结构设计中,木框角部斜角榫接合强度是人们既关注又无法回避的问题。抗拉强度和抗弯强度是衡量木框斜角榫接合性能高低的两个重要指标。笔者对三种常用的、易于机械加工的斜角榫接合试件的强度(抗拉强度,抗弯强度)进行了实验测定,并从各个方面对其进行比较、分析。研究结果表明:斜角榫接合形式,胶黏剂种类,加压时间等各个因子都不同程度地影响着木框角部接合的整体结构性能。单肩斜角明榫接合效果最好。     

非胶合条件下松木直角榫卯接合的抗拉力

通过拉伸试验研究了非胶合状态下,木材直角榫卯构件配合间隙、榫头长度和榫卯纹理方向等参数,对榫卯连接节点抗拉力的影响.结果表明:木材直角榫卯构件在拉伸过程中的抗拉力-行程曲线可分为2段,即快速线性上升和近似直线缓慢下降段;在一定范围内,构件抗拉力随着过盈配合公差的增加、榫头长度的延长而提高;同等条件下,榫卯纹理方向一致时的抗拉力要高于榫卯纹理方向直交时.     

Numerical analysis of furniture constructions

Summary Trying to rationalize principles of furniture design and construction whose objective function is minimization of material use and maximization of the strength of elements and construction nodes, a research project was undertaken with the objective to work out, write and test the effectiveness of a program designed for rigidity-strength analysis of furniture side frames constructions. The program provides results of computation of values of cross section forces, node translocations and dimensions of connectors (dowels or tenons) in selected places of connection of component elements. It was found that tenon connections in constructions of chair side frames ensure sufficient strength and rigidity of the system and maintain optimal dimensions of cross sections of component elements. Dowel connections can replace tenon joints reaching the same strength, but the areas of cross sections of the elements to be joined will have to increase from 18 to 45%. The strength of connections and their dimensions do not constitute the function of the position of the connecting member in the chair and the rigidity of the chair side frame depends directly on the position of the connecting member and increases as the position of this element is lowered. The developed computer program allows accurate, rapid and multiple rigidity-strength analysis of furniture frame constructions made of wood.     

A feasibility study of using two-component polyurethane adhesive in constructing wooden structures

This investigation was conducted to determine the feasibility of using a two-component polyurethane （PUR） adhesive, with special waterproof properties, in constructing wooden structures. We designed and conducted tests to compare the shear strength and adhesion performance of PUR with polyvinyl acetate （PVAc） adhesive on block-shear specimens constructed of oriental beech （Fagus orientalis L.）, fir （Abies alba Mill.）, poplar （Populus deltoides Bartr.）, white oak （Quercus alba L.）, sycamore （Platanus orientalis L.） and white walnut （Juglans cinerea L.）. The values of the percentage of wood failure were also determined in specimens constructed with each adhesive. The highest shear strength values of both adhesives were obtained in specimens constructed of beech, while the lowest shear strength values were obtained in fir and poplar specimens. Average shear strength of the PUR adhesive was 16.5% higher than that of the PVAc adhesive. Specimens constructed of fir, poplar and sycamore were characterised by the highest percentages of wood failure, whereas the lowest average percentages of wood failure were obtained in beech and oak specimens. With the exception of oak specimens, there was no statistically significant difference between percentage of wood failure among the PUR and PVAc adhesives. Generally, the PUR adhesive showed an acceptable adhesion performance on wood materials used in our study.     

木家具常用榫结构受力分析与计算

家具的结实与稳定程度,一直是用户选购家具时所考虑的主要因素,同时也是衡量家具质量优劣的主要标准．对家具几种常用的、易受损坏的榫接合形式在承载荷过程中所受的各类力进行了分析;并在此基础上给出了对所受各类力进行量化计算的数学模型     

重组竹家具椭圆榫接合性能研究

通过试验探讨重组竹家具椭圆榫接合性能的影响因素,研究榫头宽度方向与厚度方向的配合尺寸对抗拉强度的影响,以及榫头宽度对椭圆榫抗弯矩强度的影响,得出重组竹椭圆榫接合强度的变化规律;并通过比较表明,重组竹椭圆榫的抗弯矩强度要远高于普通实木椭圆榫。     

Measurement of bending properties of wood by compression bending tests

We measured Young's modulus, proportional limit stress, and bending strength by the compression bending test and examined the applicability of the testing method by comparing it with conventional bending test methods. Long columns of todomatsu (Japanese fir,Abies sachalinensis Fr. Schmidt) with various length/thickness ratios were the specimens. A compressive load was axially applied to the specimen supported with pin ends. Young's modulus, the proportional limit stress, and the bending strength were obtained from the load-loading point displacement and load-strains at the outer surfaces until the occurrence of bending failure. Four-point bending tests were also conducted, and the bending properties obtained were compared with the corresponding properties obtained by the compression bending tests. Based on the experimental results, we believe that when the stress-strain relation is measured by the load-loading point displacement relation using specimens whose length/thickness ratio is large enough, the bending properties can be obtained properly using the compression bending test.     

Cutting force variability as a consequence of exchangeable cleavage fracture and compressive breakdown of wood tissue

In the present study, the conditions of chip propagation or fracture in orthogonal oblique cutting of beech wood (Fagus silvatica) in the 90°–0° direction for a type-I chip has been investigated. The force required for orthogonal wood cutting is pronouncedly variable, which is the consequence of exchangeable different ways of material breakdown. The chip formation process is discontinuous because of interrupted splitting of the material in front of the cutting tool. A 10-mm-thick specimen was cut at a rake angle of 31° and 42° with chip thicknesses ranging from 0.1 to 0.3?mm. The chip segment length increased with the chip thickness. A chip of varying length and thickness was modelled using the finite element method. For each case, the bending or compressive stress in the chip and the stress intensity factor at the crack tip was calculated. The segment length of the chip can be calculated by taking into account the condition that a crack propagates when the stress intensity factor K _I at the crack tip equals the critical stress intensity factor K _IC, and the bending or compressive stress σ _x in the chip is smaller than the strength σ _u . Good agreement between the calculated and the measured values was observed. The chip segment length can change considerably already with small changes in the bending strength and critical stress intensity factor. This large sensitivity is also confirmed by the fluctuation of the measured chip segment lengths by as much as 400%.     

Effect of knife wear on finger-joint strength of silver fir (Abies alba) wood

Abstract

This study was carried out to determine the effect of knife wear, as measured in hours of use, on the finger-joint strength of silver fir wood (Abies alba), bonded with polyurethane (PU) and polyvinyl acetate (PVAc) adhesives. Wood samples were collected after 1, 32 and 64 h of knife wear. Results showed that as knife wear increased, bending strength or modulus of rupture (MOR) of the finger-jointed samples was reduced by 11.1% (PVAc) to 21.2% (PU) after 32 h of knife wear, and by 19.6% (PVAc) to 27.6% (PU) after 64 h of knife wear, whereas modulus of elasticity (MOE) of the finger-jointed samples was reduced by 10.5% (PVAc) to 12.5% (PU) after 32 h of knife wear, and by 11.7% (PVAc) to 10.0% (PU) after 64 h of knife wear. Tension strength of the finger-jointed samples was reduced by 2.1% (PVAc) to 1.5% (PU) after 32 h of knife wear, and by 5.4% (PVAc) to 16.0% (PU) after 64 h of knife wear.