Viscoelastic embedment behaviour of dowels and screws in timber under in-service vibration

Dowel and screw connections in timber structures behave nonlinearly, even at loads which would be experienced in a structure in normal service. They exhibit hysteresis and creep as a result of both the viscoelastic behaviour of the timber itself and the frictional interaction between the timber and connecting elements, and stress concentrations are created which behave plastically, even at loads well below the nominal yield force of the connection. A fundamental process in the load transfer through such a connection is the embedment of the connector into the timber that surrounds it, and the frictional, nonlinear and time-dependent properties in that process are investigated here. A simple rheological model, a combination of Kelvin–Voigt viscoelastic elements, was fitted to the measured response of a block of timber in embedment by a plain dowel or screw. Experiments were performed in which an oscillating force was applied to the screw or dowel, representative of in-service vibration in a timber structure. The effects of plasticity and viscoelasticity were quantified by comparing equivalent linear stiffnesses for an oscillating load, a short-term change in static load, and an initial static loading. The results showed a stiffness, on average, 3.8 times higher under oscillating load than under initial static loading with the same peak force. By quantifying and modelling viscoelastic behaviour in timber around a connector, this work contributes to the development of damping and stiffness models for joints under oscillating load. Such models could be used to determine the contribution of connections to the dynamic response of long spans and tall buildings in timber.     

Polycyclic aromatic hydrocarbons in meat smoked with different types of wood

The influence of the wood used for the smoking of meat on the formation of polycyclic aromatic hydrocarbons (PAH) has been studied. Ten types of wood and charcoal were used for preparation of smoked meat samples. The analytical sample preparation method implied extraction of PAH with cyclohexane, liquid–liquid extraction with N,N-dimethylformamide/water, back extraction with cyclohexane, followed by clean-up on silica solid phase extraction (SPE) column and quantification by gas chromatography–mass spectrometry. It was found that the type of wood has a significant influence on the amount of PAH in smoked meat. The samples smoked with apple-tree and alder contained the smallest PAH concentrations. The samples smoked with spruce had the highest concentrations of PAH. The difference in content of benzo[a]pyrene (from 6.04 till 35.07 μg/kg) and total PAH (from 47.94 till 470.91 μg/kg) indicates that choice of wood for smoking is one of the critical parameter to be controlled in order to diminish the contamination of food products.     

Sound insulation of walls using wood insulation mat and plywood jointed with a combination of adhesive tape and wood dowels

In this study sound insulation of walls was evaluated using wood insulation mat and plywood jointed with a combination of adhesive tape and wood dowels. Building of actual wall assembly test specimens and evaluating their sound insulation revealed that the sound transmission loss for jointing using a combination of adhesive tape and wood dowels was considerably higher than that using nails, for middle and high frequency ranges of 2 kHz and above. When comparing heat-insulating materials (sound-absorbing materials), the test specimen using high-density glass wool had greater sound insulation than the specimen using low-density materials, and the specimen using wooden heat-insulating/sound-absorbing materials showed roughly the same properties as glass wool of 20 % higher density. When the sound insulation for impact sounds of the experimental specimen (joined with adhesive tape and using wooden heat-insulating/sound-absorbing materials) was compared to a specimen with a typical composition (joined with nails and using glass wool), the former proved to have better sound insulation, by approximately 10 dB for light impact sounds between 400 and 800 Hz and approximately 5 dB for higher frequencies. For heavy impact sounds, the experimental specimen displayed a greater sound insulation for all frequencies, by 5–10 dB at frequencies of around 100 Hz and of 400 Hz and above.     

Determination of shearing stiffness parameters to design multi-layer spruce beams using welding-through wood dowels

This paper presents a methodology to characterize the secant shearing stiffness of welding-through wood dowels used in multi-layer spruce beams. Welding-through wood dowel’s stiffness behaviour as well as isostatic multi-layer beams’ behaviour were investigated experimentally. These elements are made by a specifically designed machine to guarantee repeatability. A model of finite elements was developed to reproduce the bending behaviour of the beams tested from non-linear connection behaviour. This model is then used to study the influence of parameters such as: layer number, spacing of dowels, load type (concentrated or distributed), strength class and beam span. After a sensibility analysis, a parameterized regression model allows to obtain k _ser and k _u fastener secant stiffness in compliance with EN 1995-1 standard to design multi-layer beams in an elastic analytical model way. This model is based on the work by Kreuzinger (1999).     

Influence of fungal decay by different basidiomycetes on the structural integrity of Norway spruce wood

The potential influence of diverse decay patterns caused by different brown rot causing basidiomycetes on the structural integrity of wood was investigated. Therefore, decayed Norway spruce (Picea abies Karst.) specimens representing a wide range of mass loss, caused by four different brown-rot fungi and one white-rot fungus, were applied to a high-energy multiple impact (HEMI)-test series. The relationship between the resistance to impact milling (RIM) and the mass loss by fungal decay could be subdivided into three areas: 1. Prior to measurable mass loss, a strength reduction was detectable due to the depolymerisation of wood cell wall components. 2. Between 0 and 25–30% mass loss, RIM decreased with increasing mass loss. 3. Above 30% mass loss, RIM increased again due to gluing effects of the fungal mycelium. The influence of the different brown rot fungi on the structural integrity of the wood differed slightly, but partly significantly.     

Influence of different wood flour fractions on the mechanical properties of injection molded WPC with cellulose propionate

This research investigated the effect of different fractions of commercial wood flour (Type c100 from JRS, Germany) on mechanical and physical properties of wood-polymer composites (WPC). The fractions were named regarding the mean lengths of their particles in µm; 80, 130, 255, 405 and 485. The composite samples were manufactured with 30 wt% of wood flour fractions of all five groups as well as the not fractionated flour, and 70 wt% of cellulose propionate (CP). The melt mass-flow rate (MFR) of the different granules, tensile strength, and modulus of elasticity, flexural strength, flexural modulus and the impact strength of the injection molded specimens as well as the water uptake were determined in this study. WPCs with the specific size range used in this investigation exhibited improved strength and modulus of elasticity in tensile and flexural tests, compared to pure CP. Using fraction 255, the mechanical properties increased the most. Tensile strength rose by 28 and 13% compared to CP and to WPC with the not fractioned wood powder, respectively. Fraction 255 increased flexural strength by 33 and 5% compared to CP and WPC with the not fractioned flour. The MFR (tested at 190 °C with 7.16 kg) of WPC_255 is the lowest with 2.3 g/10 min. Composites with the smallest particles showed the least water uptake.     

Effects of milking stall dimensions on behavior of dairy cows during milking in different milking parlor types

Dairy cow body size has increased over time because of breeding selection for higher milk yield, but milking stall dimensions have never been adjusted and are based on the practical experience of milking-machine manufacturers and advisory institutions. Narrow, limited milking stall dimensions might lead to behavioral changes during milking due to lack of comfort. The aim of this study was to examine the current space allowance in milking stalls on dairy farms and assess the effect of space allowance on cow behavior during milking. On 15 Swiss dairy farms, we measured clear milking stall dimensions and cow body dimensions. We calculated space ratios for length (SR_length) and width (SR_width) by dividing the milking stall length or width by cow body length or belly width, respectively. When the space ratio was >1, we assumed that the body length or width of cow was smaller than the milking stall length or width. On each farm, 10 healthy cows were chosen for behavioral observation during 1 evening milking. We recorded rumination, elimination, and latency to enter the milking stall by direct observation. Hind leg activity was recorded using acceleration loggers. Data were analyzed using general linear mixed-effects models with farm as a random effect. Due to a strong collinearity between SR_width and SR_length, we chose SR_length for further analysis, because it is based on skeletal characteristics. The SR_length was smallest in side-by-side parlors (1.07 ± 0.01) and largest in tandem parlors (1.18 ± 0.01). More cows had a tendency to ruminate with increasing SR_length (odds ratio: 1.8). None of hind leg activity, maximum peaks of hind leg accelerations, or latency to enter the milking stall were significantly affected by SR_length. Latency to enter the milking stall was longer for group milking parlors (side-by-side: 44.0 ± 3.2 s; herringbone: 34.3 ± 2.9 s) than for tandem parlors (19.0 ± 2.7 s). Milking parlor type had no effect on hind leg activity, maximum peaks of hind leg accelerations or rumination. The SR_length affected rumination behavior to some extent, indicating that cow comfort was positively affected by larger milking stall length. Because cow comfort is important for good milking performance, further investigations of milking stall dimensions for cow comfort and thus welfare are needed. Furthermore, the results showed that parlor type affected cow behavior, irrespective of SR_length, making future research necessary to identify the factors leading to this effect of parlor type.     

Influence of novel retail lighting on the quality of coffee cream in different types of packaging

The degradation of coffee cream quality, in different packaging and exposed to different lamps, was evaluated. Coffee cream is often retailed in packaging highly permeable to light and oxygen with high surface-to-volume ratio; therefore, riboflavin-containing coffee cream is sensitive to photooxidative reactions. Light-emitting diodes (LEDs) or sodium vapour lamps show lower emissions in the critical range for riboflavin-containing products, creating less excitation energy for riboflavin compared with fluorescent lamps. Parameters investigated were the oxygen content and the hexanal concentration in the packaging, as well as riboflavin degradation. The impact on these quality attributes was shown to be higher for coffee cream packaged in light- and oxygen-permeable packaging and when exposed to fluorescent lamps. The quality of dark-stored references was not affected during storage indicating light-induced quality deterioration. The application of LEDs or sodium vapour lamps proved able to maintain the quality of light exposed coffee cream for a longer time.     

72A帘线钢不同连续冷却条件下基体相变行为研究

采用Formastor-FII全自动相变仪对72A帘线钢盘条进行连续冷却试验,采用膨胀法测得钢的临界相变点。对不同冷却速度下的试样,用光学显微镜观察试样组织,用显微硬度仪测定维氏硬度,根据测定的相变点绘出试验钢72A静态CCT曲线。结果表明,最佳冷却速度不超过15℃/s,可得到珠光体和索氏体,避免产生马氏体,有利于改善盘条的拉拔加工性能。     

Shear properties of metal-free wooden load-bearing walls using plywood jointed with a combination of adhesive tape and wood dowels

In this study, the potential of wood-only (metal-free) load-bearing walls was proposed and tested based on the idea of using the same type of material throughout wherever possible while improving basic properties such as strength, sound insulation, and heat insulation. Specifically, a technique was tested of combining pressure sensitive adhesive tape and wood dowels in place of nails for load-bearing structures with panel reinforcement represented by wood-frame construction. For this paper, its strength was evaluated by conducting in-plane shear tests, which revealed that the initial rigidity and maximum load of the proposed test specimens were greater than that of specimens using nails for jointing. However, the shear load factor, which is calculated based on some strength parameters and which forms the foundation of housing strength design, was slightly lower than that of the nail-jointed specimen. This was because there was a large decline in post-collapse resistance and a lower calculated absorbed energy caused by brittleness. The early detachment of panels was also revealed as a problem in the tests.     

Influence of different types of protein on in vitro availability of intrinsic and extrinsic iron and zinc

The influence of beef, pork and soy proteins on intrinsic and extrinsic iron and zinc in vitro availability was investigated, by measuring mineral dialysability. Intrinsic iron dialysability (percentage of iron dialysed) was similar in the animal proteins and higher than that from soy protein isolate (P<0·001). Intrinsic zinc dialysability from pork protein was statistically (P<0·001) higher than that from other proteins studied. Beef and soy proteins do not differ in their percentages of zinc availability. The effect on the extrinsic iron availability was different among the three proteins studied, but not on the extrinsic zinc availability. The composition of amino acids and/or the small peptides produced during the digestion process of the protein can modify the iron, and probably the zinc, availability. The inorganic zinc addition (10 μg ml⁻¹) reduced the non-haem and extrinsic iron availability, while it did not affect the haem iron availability. At the concentrations used in this study (10 μg ml⁻¹) a decrease of zinc dialysability caused by the inorganic iron addition was not observed. ©1997 SCI     

Influence of chemical modification of wood on the crystallisation of polypropylene

The mechanical properties of wood/polypropylene composites depend strongly on interfacial adhesion between components. However, the application of chemical modification to improve compatibility can influence the supermolecular structure of polypropylene matrix. The experimental material comprised two most common Polish timber species pine wood (Pinus silvestris L.) as a softwood species and beech wood (Fagus silvatica L.) as a hardwood species. The size of wood sawdust ranged from 0.5 to 1.0 mm. Three different types of wood/PP mixture were prepared: (1) PP – untreated wood, (2) PP – NaOH treated wood and (3) PP – esterified wood with maleic anhydride. In this work, the kinetic parameters of crystallization of PP by differential scanning calorimetry were investigated. It is interesting that crystallisation of PP depends on the kind of wood. The chemical treatment of wood caused changes of crystal conversion and half crystallisation time of polypropylene matrix.     

即食豆腐脑中盐类凝固剂包埋的研究

研究了盐类凝固剂的不同包埋比例对即食豆腐脑的凝胶强度、失水率及感官评定得分的影响。试验结果表明,对盐类凝固剂进行包埋,有利于盐类凝固剂分散均匀,可在一定程度上延缓大豆蛋白与盐类凝固剂的作用,有利于形成比较均匀的凝胶。盐类凝固剂∶麦芽糊精为1∶3时,所得的即食豆腐脑产品较好。     

Influence of ageing on mechanical properties of wood to wood bonding with wheat flour glue

Earlier research into native wheat flour for wood to wood bonding showed excellent bonding properties comparable to synthetic adhesives, but no data about ageing behaviour is available. Short and long term effects on mechanical properties were analysed by lap joint testing and modified DCB-specimens. Results showed no significant reduction in bonding properties, but a trend to lower adhesive strength after 12 months of storage was noticeable. Changes in wheat polymers were observed by means of DSC and FTIR-ATR. Soluble degradation products of starch were analysed by GC-FID after methanolysis and derivatisation. FTIR measurements indicated changes in the structure of starch, but no appreciable alteration of proteins. Investigations by DSC showed increasing crystallinity during 3 months of storage. After 6 months more degradation products were detected. Results indicated that hydrolysis of starch is responsible for a moderate decrease of bonding performance; wheat proteins seem to be less affected.     

不同二次蒸馏方式对浓香型白酒中氨基甲酸乙酯去除率的影响

我国白酒通常采用甑桶一次蒸馏方式,不进行二次蒸馏。采用壶式蒸馏、常压蒸馏及减压蒸馏对浓香型原酒进行二次蒸馏,研究不同二次蒸馏方式对氨基甲酸乙酯(EC)去除率的影响。结果表明,采用适当的掐头去尾方法能够获得EC浓度较原酒低的二次蒸馏酒,EC大量存在于酒尾及残液中。壶式蒸馏时的EC相对去除率最高(92.76%),其次是减压蒸馏(89.55%)、常压蒸馏(81.46%)。慢火壶式蒸馏酒的EC浓度略低于快火,快、慢火壶式蒸馏对EC的去除无明显差异。二次蒸馏对不同EC浓度(233.33~1 162.94μg/L)的原酒均能达到较好的去除效果,EC相对去除率在89.91%~92.76%。壶式蒸馏过程中EC浓度随着酒精度的降低而呈现先下降后平稳再上升的趋势,二次蒸馏掐头去尾工艺能有效降低白酒中EC的含量。壶式蒸馏过程前期的EC主要来源于酒中本来存在的EC,而蒸馏过程后期的EC可能来自于氰化物等前体物质的转化。     

Effects of different pretreatment processes on viscose fabrics in different types and properties

Abstract

In this study, the effects of different pretreatment processes on the properties of viscose fabrics (sulphur content, whiteness degree, weft yarn breaking force, crystallinity and fiber surface) and on the color efficiency and repeatability of the prints have been investigated. For this purpose, viscose fabrics obtained from different sources and containing different amounts of sulphur were causticized, bleached, and reductive-washed. After impregnation with urea, fabrics were printed with two reactive dyestuffs having the same reactivity, but different molecular sizes. Color values of both dyes were measured and fastness was tested and compared in order to observe the effects of different pretreatment processes. Different methods of sulphur analysis were also investigated and tested to determine the sulphur content of the fibres. Among these methods, the lead acetate method, which is a subjective evaluation system, has been selected as the most appropriate for practical working conditions of the plants, and a sulphur scale was formed according to this method. Accuracy of the scale was also confirmed by elemental analysis (CHNS–O) method.     

On the tribological properties of extremely different wood materials

Three different woods (lignum vitae; black fiber palm; spruce) were investigated regarding their friction and wear properties under abrasion and sliding. For the abrasive wear against silicon carbide paper, the palm wood gave the lowest removal of material, especially under an orientation of the black fibers normal to the contact region (on R–T-plane in R-direction). At the same time, this material had the highest anisotropy. Slightly less abrasion resistant was lignum vitae, whereas spruce was most easily abraded. This can be considered as an indication that spruce can easily be machined. Under sliding conditions against smooth steel, a similar tendency, but at much lower wear rates compared to abrasion, was found. The relatively high coefficient of friction under dry sliding allows the use of these woods as friction materials, for example in brakes. Additional lubrication of the two best woods, lignum vitae and black fiber palm, by soaked sunflower oil brought the coefficient of friction to a much lower level, so that the use of these woods as bearing materials in various applications is promising.