Withdrawal Resistance Research Articles

Effect of blowing agent concentration on rigid polyurethane foam and the properties of foam-core particleboard

ABSTRACT In this research, a sandwich panel with particleboard as surface layers and rigid polyurethane (PU) foam as core layers (foam-core particleboard) was produced with a one-step in situ foaming process. The effects of hydrofluorocarbon concentration as the blowing agent (BA) on the foam features and physical and mechanical properties of the produced panels were investigated. Typical micrograph of the rigid PU foam showed well-defined closed cells of spherical and polyhedral shapes. It was shown that the number of fractured cells in the foam structure was increased with the addition of BA in the amount of more than 4.5%. The results showed that the bending strength and internal bond values significantly raised with increasing BA concentration up to 6%. Screw withdrawal resistance from the face and thickness swelling were not significantly changed while the BA concentration varied. Edge screw withdrawal resistance and water absorption were drastically decreased when the blowing agent concentration was raised in the whole studied range. ABBREVIATIONS: PU: polyurethane; OH: hydroxyl; PO: polyol; ISO: isocyanate; BA: blowing agent; PMDI: polymeric methylene diphenyl diisocyanate; BS: bending strength; IB: internal bond; SWR: screw withdrawal resistance; TS: thickness swelling; WA: water absorption

Improving density estimation in large cross-section timber from existing structures optimizing the number of non-destructive measurements

Abstract The density of 45 structural Salzmann pine timber pieces with nominal dimensions of 150 × 200 × 5000 mm3 from an existing 18th century structure was estimated using the following non-destructive methods: needle penetration resistance (NPR), screw withdrawal resistance (SWR) and drilling chips extraction (DCE). Non-destructive testing (NDT) measurements were correlated with actual and apparent density (considering a rectangular cross-section instead of the actual profile). Ten non-destructive measurements were taken in each specimen with each device. The best results were obtained with DCE and the poorest with NPR. The increase of the determination coefficient obtained by increasing the number of measurements did not show a great improvement from the fifth to the tenth measurement: r2 = 0.12–0.65 for one reading, 0.35–0.77 for five readings and 0.42–0.76 for ten readings, depending on the device. Because density varies along pieces, three accumulated measurement sequences along them were analyzed to correlate better with the minimum number of readings: Linear (LM), End to Centre (ECM) and Centre to End (CEM) methods. CEM was the most effective sequence, giving higher r2 than the others. In practical work involving the in-situ estimation of density it is recommended that a minimum of 3 or 4 measurements using CEM be performed.

Comparison of blockboards with core layers made of kiri (Paulownia spp.) and of spruce (Picea abies) regarding mechanical properties

In this study, kiri wood (Paulownia spp.) is assessed as potential core layer material for blockboards. Blockboards with core layers made of kiri and spruce (Picea abies) were produced using Anthocephalus cadamba as crossband veneer and beech (Fagus sylvatica) as face veneer. With spruce as core layer material, higher values for bending strength and modulus of elasticity, tested in grain direction, and screw withdrawal resistance were obtained. In return, blockboards with kiri as core layer material were 31% lighter and showed a more homogeneous core layer material with regard to density.

Solutions to reduce moisture driven backout and improve withdrawal strength of nailplates: experimental investigations

Timber trusses, typically manufactured from timber members connected by nailplates, are widely used in the domestic housing market. Their use is however limited to indoor environments. The exposure of timber trusses to environments where the timber experiences high amounts of moisture content (MC) variations causes the nailplates to be driven out from the surface of the timber, a phenomenon commonly referred to as “backout”. As part of a collaborative project between the industry, Griffith University and Queensland Department of Agriculture and Fisheries (DAF), this paper aims at investigating solutions to both prevent backout of the nailplates and increase their withdrawal resistance under large MC variations. The nailplate teeth were redesigned following (1) a mechanical approach consisting of redesigning the tooth profile and allowing the nails to resist the withdrawal force by both friction and mechanical action and (2) the application of an adhesive to a redesigned tooth profile, allowing the adhesive to penetrate the timber with the nail. The efficiency of the new designs was experimentally assessed using single teeth (representative of nailplate teeth) with respect (1) to their ability to resist backout resulting from accelerated MC cycles and (2) their quasi-static withdrawal resistance after increasing numbers of moisture cycles. Results showed that the proposed mechanical designs reduced the backout by up to 50% when compared to currently used tooth designs. The application of an adhesive prevented moisture driven backout. The newly investigated tooth designs resulted in higher withdrawal strengths to currently used nails. It was identified that subjecting the nails to only one moisture cycle reduced the withdrawal resistance of currently used and glued teeth by up to 60% while the withdrawal resistance of the proposed mechanical designs was not affected by the number of cycles.

Functional Assessment of Particleboards Made of Apple and Plum Orchard Pruning

Three-layered composite materials consisting in wood-chips bonded by a resin (particleboard) were successfully produced from two by-products: plum and apple tree branches, waste biomass produced after orchard pruning; a third particleboard was made from an industrial softwood blend as a reference. After collecting the branches, the raw materials were characterized in matters of density, bark content and bulk density of particles. Various physical and mechanical properties were assessed in accordance with European Standards for wood-based panels, namely thickness swelling, water absorption, modulus of rupture, modulus of elasticity, internal bonding strength, screw withdrawal resistance, as well as density profile and machining properties during milling and drilling. Modulus of rupture was 14.4 ± 1.2 N mm−2 for plum-based panels and 12.8 ± 2.3 N mm−2 for apple-based panels, while modulus of elasticity was 2576 ± 140 N mm−2 for plum-based panels and 2432 ± 345 N mm−2, which fulfills the mechanical requirements for panels of furniture production and interior equipment purposes which of this kind of materials is modulus of rupture of 11 N mm−2 and modulus of elasticity of 1600 N mm−2. The results showed in general, a good performance of the composite materials elaborated from waste biomass, thus offering a potential revalorization of a rather undervalued by-product.Graphical

Effect of a Polymer Additive on Properties of Creosote-Treated Wood

Abstract The potential for using a low molecular weight polyethylene (PE) polymer to improve the properties of creosote-treated wood was evaluated on samples of six different wood species. Samples were impregnated with creosote alone or amended with the PE additive and then tested to failure in third-point loading to determine modulus of elasticity and modulus of rupture. Samples were then subjected to three soak–dry cycles to assess the impact of moisture uptake on fastener performance or water repellency. The presence of the PE was associated with lower preservative retentions, but had no significant effect on modulus of elasticity, modulus of rupture, water repellency, or fastener withdrawal resistance. The results suggest that the additive limited preservative uptake, but did not improve any of the wood properties evaluated.

In-situ density estimation by four nondestructive techniques on Norway spruce from built-in wood structures

AbstractNeedle penetration resistance (NPR), screw withdrawal resistance (SWR), core drilling (CD) and drilling chips extraction (DCE) are nondestructive and semi-destructive techniques used to estimate density in timber structures. In most of the previous studies, these techniques were tested in clear sawn timber and clear specimens. The goal of the present paper is to study the relationship between density and these techniques by means of five different devices in whole pieces of timber from built-in engineering structures, which are from 12 4.5-m long structural timber joists of Norway spruce from a 19thcentury building in Barcelona (Catalonia, Spain). Although determination coefficients (R2) for density estimation models were lower than those from clear timber, the results obtained confirmed that these four techniques are suitable forin-situdensity estimation of woods in buildings. The best results were obtained by CD (the bigger the bit, the higher the correlation), followed by DCE, and SWR. The worst correlation was found for NPR devices, but the results could be probably improved with more measurements.

Effect of surface layers compressibility and face-to-core-layer ratio on the properties of lightweight hybrid panels

ABSTRACTThe hybridisation of wood-based panels has gained interest in recent years. Lightweight hybrid panels consisting of wood fibres as faces and a mixture of wood particles with expandable polystyrene (EPS) granules as core layer were manufactured in this study. The effects of initial compression and different face-to-core-layer weight ratios were investigated. Results showed that both variables significantly influence panel properties. The initial compression enhanced the surface layer quality while negatively affecting the core layer. Adding EPS influenced the core layer quality, which improved the panel properties. The weight ratio of the face-to-core-layer also enhanced the bending properties and thickness swelling. The internal bond was weakened by increasing the face-to-core-layer ratio.Abbreviations: WBPs: wood-based panels; EPS: expandable polystyrene; MOR: modulus of rupture; MOE: modulus of elasticity; IB: internal bond; SS: surface soundness; SWR: screw withdrawal resistance; TS: thickness swelling; WA: water absorption

Effects of recycled fiber content on the properties of medium density fiberboard

The large global production quantity of medium-density fiberboard (MDF) creates equal quantities of waste MDF, which consequently requires research on the recycling of MDF. This work was conducted to study the effect of recycled fiber (RF) content on the recycling properties of MDF. After pretreating waste MDF, a refiner and hammer were used to isolate refiner RFs (RRFs) and hammer mill RFs (HRFs) from two softwood species. This work also characterized the physical, chemical, and morphological features of RFs and virgin fibers (VFs). RRF and HRF contents of 0, 5, 10, 20, 30, 50, and 100% were used to fabricate recycled MDF (rMDF) panels. All RFs had shorter fiber lengths and higher fines contents than VFs had. The presence of N from urea–formaldehyde resins was confirmed by multiple analyses; more N was distributed in RFs than in VFs. The highest internal bonding (IB) strength of the rMDF occurred at 10% RF, regardless of isolation method and wood species; IB strength decreased afterward. The mechanical properties, including modulus of rupture, modulus of elasticity, and screw withdrawal resistance of rMDF, showed behaviors similar to the IB strength with increasing RF content. However, the thickness swelling, water absorption, and formaldehyde emission of rMDF samples decreased with increasing RF content. Statistical analysis indicates that the minimum of 10% RFs can be used to replace VFs without diminishing the properties of rMDF. The improved properties of rMDF were ascribed to the reinforcing effects of RFs covered with cured resins.

Effects of peeling and steam-heating treatment on mechanical properties and dimensional stability of oriented Phyllostachys makinoi and Phyllostachys pubescens scrimber boards

Epidermal peeling treatment (EPT) and steam-heating treatment (SHT) are two popular pretreatments for bamboo processing. This study examined the effects of EPT and SHT on strength properties, profile density distribution, internal bond strength (IB), rate of springback, nail withdrawal resistance, and dimensional stability of oriented bamboo scrimber board (OBSB) made of moso bamboo (Phyllostachys pubescens Mazel) and makino bamboo (P. makinoi Hayata) strips. Results obtained using non-destructive testing (NDT) revealed that EPT for moso bamboo in the processing of OBSB caused lower ultrasonic-wave velocity (Vu) and dynamic modulus of elasticity (DMOEu) parallel to the fiber direction, but higher Vu and DMOEu perpendicular to the fiber direction. However, EPT slightly affected variations in modulus of elasticity (MOE) and modulus of rupture (MOR) of moso bamboo. In contrast, the effects of SHT on Vu and DMOEu were inconsistent and insignificant among the OBSB samples. On the other hands, SHT caused increasing in MOE and MOR of OBSB, but leads to decrease in MOE and MOR of OBSB comprising bamboo strips after EPT. Both EPT and SHT contributed to more uniform profile densities in OBSB and had a positive impact on nail withdrawal resistance. EPT increased IB of moso bamboo and SHT enhanced IB of makino bamboo with epidermis only. Bamboo strips after SHT resulted in significant decrease in water absorption of all OBSB specimens. Reduction in swelling as a result of SHT not only improved the dimensional stability of OBSB but also enhanced strength.

Withdrawal Resistance and Failure Mode of Semi-Circular Wooden Composite with Different Fasteners

Wooden Composite is assembled with semi-circular waste wood by fastener, in order to provide local Indonesian affordable construction components potentially. Considering wooden composite, the withdrawal resistance affect the shear resistance ability under short-term lateral load, therefore withdrawal test is carried out in this study. The withdrawal test shows that steel nail and self-tapping screw work properly to attach each specimen when considering the assembly of wood composite. The observation results indicate different types of fasteners affect the test result significantly. For the fasteners connected with hardwood, the test result shows higher withdrawal resistance than softwood, both using self-tapping screw and steel nail. Based on the test results, there are 3 main failure modes that is concluded, which are fastener failure, material failure, and conditional failure. The test result of self–tapping screw also shows that this kind of fastener is able to withstand 3.5 times stronger than steel nail.

Influence of moisture content on the results of penetration and withdrawal resistance measurements on softwoods

Abstract Needle penetration resistance (NPR) and screw withdrawal resistance (SWR) are widely used techniques for density estimation of woods integrated in timber structures. The moisture content (MC) influences these measurements and correction coefficients are needed to ensure the accuracy of results. The goal of the present paper was to scrutinize the relation between NPR and SWR measurements and MC in case of radiata pine, Scots pine, Salzmann pine, and maritime pine usually used in wood constructions, from which 25 specimens from each species were probed. The specimen’s MC ranged from 65.1 to 8.3%. Results show that NPR depth has a positive linear relationship with MC while the SWR force a negative one below the fiber saturation point (FSP). Above the FSP, the MC influence is less pronounced and less regular. MC correction factors of measurements below the FSP are proposed for the species studied.

Screw Withdrawal Resistance and Surface Soundness of Three-Layer Fiberboard Having Coarse Fibers in Core Layer

Screw Withdrawal Resistance and Surface Soundness of Three-Layer Fiberboard Having Coarse Fibers in Core Layer

백합나무를 이용하여 제조한 3층 파티클보드와 배향성 스트랜드보드(OSB)의 물성에 관한 연구

본 연구에서는 주요 조림수종으로 선정된 백합나무를 이용하여 파티클보드(PB)와 배향성 스트랜드보드(OSB)를 제조하여 보드 원료로서의 가능성을 확인하였다. 두께 15 mm, 밀도 <TEX>$0.7g/cm^3$</TEX>의 파티클보드와 두께 10 mm, 밀도 <TEX>$0.65g/cm^3$</TEX>의 OSB를 제조하였으며, 파티클보드 공장에서 상용하고 있는 <TEX>$E_1$</TEX> 등급의 요소 폼알데하이드 수지와 왁스, 경화제를 첨가하여 실제 생산, 유통하는 보드제품과 최대한 유사하게 제작조건을 맞추었다. 제조된 보드의 품질시험 결과, PB의 경우, 평균두께 15.8 mm, 평균밀도 <TEX>$0.71g/cm^3$</TEX>, 함수율은 5.8% 기준에 적합하였다. 휨강도는 KS 규격(KS F 3104)의 13형 이상(<TEX>$13.0N/mm^2$</TEX> 이상), 박리강도는 18형 이상(<TEX>$0.3N/mm^2$</TEX> 이상), 나사못 유지력은 평면에서는 18형 이상(700 N 이상), 측면 15형 이상(300 N 이상)의 품질을 만족시켰다. 그러나 휨강도가 박리강도, 나사못유지력에 비해서 낮은 강도를 나타내는데 이것은 파티클 길이/두께의 비율(Slenderness ratio)이 영향을 미친 것으로 판단된다. OSB의 경우, 평균두께 10.7 mm, 평균밀도 <TEX>$0.68g/cm^3$</TEX>, 함수율은 6.3%로 KS F 3104 기준에 적합하였으며, 휨강도 18형 이상(<TEX>$18.0N/mm^2$</TEX> 이상), 나사못유지력 18형 이상(700 N 이상), 박리강도 13형 이상(<TEX>$0.20N/mm^2$</TEX> 이상)의 품질을 만족시켰다. This study was conducted to investigate a potential of Yellow poplar (Liriodendron tulipifera L.) as a raw material for the manufacturing of particleboard (PB) and oriented strandboard (OSB). PB panels were prepared at the parameters of <TEX>$0.7g/cm^3$</TEX> density, 15 mm thickness, three-layer, <TEX>$E_1$</TEX> grade urea-formaldehyde (UF) resin, emulsion wax, and hardener. OSB panels were manufactured with a density of <TEX>$0.65g/cm^3$</TEX>, thickness of 10 mm, and <TEX>$E_1$</TEX> grade of UF resin. Particle size of the face layer of PB was 20~80 mesh with 7~9% moisture content (MC), while that of core-layer was 3~20 mesh with 3~5% MC, which was similar to the production condition of commercial PB. As a result, the manufactured PB panels with 15.8 mm thickness, <TEX>$0.7g/cm^3$</TEX> density, and 5.8% MC satisfied the requirement of bending strength of 15 type PB of Korean Industrial Standard (KS F 3104). Both internal bonding (IB) strength and surface screw withdrawal resistance also satisfied the requirement of 18 type PB of the standard. But, the edge screw withdrawal resistance satisfied the requirement of 15 type PB of the standard. These differences in properties could be due to the slenderness ratio of raw particles. In case of OSB panels with 10.7 mm thickness, <TEX>$0.68g/cm^3$</TEX> density, and 5.8% MC satisfied all the requirements of bending strength, screw withdrawal resistance, and IB strength of 18 type PB of the standard. These results suggest that Yellow poplar wood has a good potential as a raw material for the production of PB and OSB.

The effects of different variables on the screw withdrawal strength of plywood

Aim of study: The purpose of this study is to investigate the effect of the pilot-hole, screw type, screwing direction, water retention and adhesive on the screw pull resistance of the plywood. Material and Methods : Two types of screws, 3.5 mm and 4 mm in diameter, were used in the study. The supplied 18 mm thick plywood is sized to 50 mm x 50 mm according to TS EN 13446 standards. The pilot-holes were drilled so that 80% of the screw diameter would be used. After the polyvinyl acetate (PVAc) and polyurethane (PU) adhesives were injected into the pilot-holes, screwing was carried out perpendicularly and horizontally to the surface of the sample. Half of the samples were immersed in water for 2 hours before the screw withdrawal test. The results of the tests were interpreted by statistical analysis. Main results: When examining the results, all of the pilot-hole drilled samples showed higher screw withdrawal resistance than the pilot-hole drilled samples. It was also found that the screw withdrawal resistance perpendicular to the surface is higher than that parallel to the surface. When the glue applied pilot-hole specimens were examined, the PU specimens showed higher screw withdrawal strength than the PVAc specimens. A lower screw withdrawal strength was determined when samples were immersed in water. It was also found that as the screw diameter increases, the screw withdrawal strength increases. Research highlights: In is concluded that applying PU in pilot-holes before driving screw in significantly affected screw holding performance in plywood.

Effect of Panel Density and Resin Content on Properties of Medium Density Fiberboard

This study was conducted to evaluate the effect of panel density and resin content on properties of medium density fiberboard (MDF) to obtain some insights on MDF properties as a function of panel density and resin content. MDF panels with different panel densities such as 650, 700, 750 and 800 kg/m3 were manufactured by adjusting the amount of wood fibers in the mat forming. MDF panels were also fabricated by spraying 8, 10, 12, and 14% of urea-formaldehyde (UF) resins onto wood fibers in a drum-type mechanical blender to fabricate MDF panels with a target density of 650 kg/m3. As the panel density and resin content increased, the internal bonding (IB) strength of MDF panel consistently increased. Modulus of rupture (MOR), modulus of elasticity (MOE) and screw withdrawal resistance (SWR) had a similar trend to the IB strength. In physical properties, thickness swelling (TS) and water absorption (WA) decreased with an increase in both panel density and resin content. In addition, the formaldehyde emission (FE) which increased as the panel density and resin content became greater. In overall, the panel density of MDF had more significant effect than the resin content in all properties of MDF panels, indicating that it was better to adjust the panel density rather than the resin content for MDF manufacture.

Mechanical and physical screw withdrawal properties behavior of agglomerated panels reinforced with coir and pejibaye fibers

ABSTRACTThe screw withdrawal resistance and the mechanical behavior of agglomerated panels reinforced with coir and pejibaye fibers were evaluated using through and non-through screw withdrawal tests. Widespread commercially materials, such as Pinus solid wood, Medium Density Fiberboard (MDF) and plywood, were also tested in order to compare the behavior and results obtained with the lignocellulosic-reinforced agglomerated panels. Among the conventional materials tested, the highest maximum withdrawal load/thickness ratio was measured in solid wood. Panels reinforced with natural fibers showed lower withdrawal resistance than conventional materials. However, panels reinforced with coir fibers reached about 74% of the maximum strength achieved by MDF samples. Panels reinforced with pejibaye showed the worst mechanical performance. Hybridization between pejibaye and coir fibers resulted, however, in a performance improvement of approximately 50% in the maximum withdrawal load comparing with panels reinforced only with pejibaye fibers. The behavior along screw withdrawal was analyzed and could be split into four different steps. Each of these steps was correlated to the screw withdrawal rate, and also with the interactions between the material and the screw. The mechanisms involved in each step are presented and discussed.

Withdrawal resistance of screws in structural composite lumber made of poplar (Populus deltoides)

Withdrawal resistance of screws on face, edge and end directions of oriented strand lumber (OSL), laminated veneer lumber (LVL) and plywood made out of poplar (Populus deltoides) were experimentally evaluated. Two types of screws, namely, drywall screw and sheet metal screw in two different diameters (4 and 5mm) were evaluated. The results obtained were compared with those of solid poplar wood and the failure modes of specimens were visually examined. Test results showed that: (1) OSL joints were stronger than same joints constructed of LVL, plywood and poplar wood; (2) screw diameter positively influenced on withdrawal resistance, and its effects on withdrawal load were more influenced by root diameter of the screws and grain direction; (3) due to increased root diameter, sheet metal screw had significantly higher withdrawal resistance than drywall screw; (4) perpendicular to the grain direction (face and edge) were higher compared to the results for the parallel to the grain direction (end). However, there was no significant difference between OSL and poplar wood for maximum withdrawal resistance when the screw is either inserted in the edge or end-grain surface withdrawal directions; (5) the experimental results of failure modes included the plug shear failure around the screw of end direction, a rolling shear failure or tension axial stresses perpendicular to the grain of edge direction and splitting failure of the superficial fiber layer of the block of face direction.

SCREW AND NAIL HOLDING PROPERTIES OF PLYWOOD PANELS REINFORCED WITH GLASS FIBER FABRIC

ABSTRACT In this study, plywood and reinforced plywood with glass fiber fabric were produced with rotary peeled poplar veneers using phenol formaldehyde adhesive. Screw and nail holding tests were conducted to obtain the characteristics of the plywood and reinforced plywood boards. One control group and three different test groups were used. The effects of glass fiber fabric on the screw direct withdrawal, screw-head pull-through, and lateral nail resistance were determined. The results of the tests indicated that the reinforced plywood’s resistances to direct withdrawal of the screw, screw-head pull-through, and lateral nail resistance were significantly higher than those of the unreinforced plywood. In addition, reinforcement of the plywood boards provided longer displacement at maximum load.

Determination of Screw Withdrawal Resistance of Some Heat-Treated Wood Species

Determination of Screw Withdrawal Resistance of Some Heat-Treated Wood Species