Preliminary evaluation of a density-based lumber grading method for hem-fir CLT manufacturing

European Journal of Wood and Wood Products - In the manufacturing process of cross-laminated timber (CLT), lumber selection and grading are essential steps for the quality control of CLT. In this...     

Cost optimization of cross-laminated timber panels in one-way bending

European Journal of Wood and Wood Products - For the purposes of structural design, cross-laminated timber (CLT) panels are typically chosen from tables detailing standardized layups. While this is...     

Moisture induced stresses in cross laminated timber (CLT) made from hydrothermally modified wood

European Journal of Wood and Wood Products - In the current research work, moisture gradients and moisture induced stresses (MiS) were investigated in cross laminated timber (CLT) bearing...     

Testing the durability of timber above ground: evaluation of different test methods

A large number of studies on the decay performance of wood in outdoor exposure have been conducted in the past. However, no test methodology for wooden components exposed above ground reflecting the variety of different loads has been established so far. Many test protocols were modified in different ways throughout the years and results were often published only in an encoded or incomplete way. This makes it difficult to obtain comparable results to work on a comprehensive above-ground test methodology. Therefore, a comparative study on moisture performance and the resulting decay response was conducted. Five different wood species were exposed according to 24 different test methods representing a wide range of different exposure situations including in- and on-ground exposure. After three years of exposure the moisture load as well as decay development differed between the test methods and tested materials. Different parameters were identified influencing the moisture performance of wood in the respective test set-ups and finally an attempt was made to set up a test methodology providing sets of test methods for differently severe applications within use class 3.1 and 3.2 as defined in the European standard EN 335 (2013).     

Probabilistic models for the withdrawal behavior of single self-tapping screws in the narrow face of cross laminated timber (CLT)

Cross laminated timber (CLT) and self-tapping screws have strongly dominated the latest developments in timber engineering. Although knowledge of connection techniques in traditional light-frame structures can be applied to solid timber constructions with CLT, there are some product specifics requiring additional attention; for example in positioning of fasteners, differentiation in the side face and narrow face of the panels and the influence of potential gaps. The load–displacement behaviour of single, axially-loaded self-tapping screws positioned in the narrow face of CLT and failing in withdrawal was investigated. For the first time a multivariate probabilistic model was formulated together with models relating the parameters with the thread-fibre angle and the density. Different types and widths of gaps, initial slip and / or delayed stiffening as well as softening after exceeding of the maximum load can be considered. Beyond the scope of this contribution, the probabilistic model is seen as a worthwhile basis for investigations into the withdrawal behaviour of primary axially loaded, compact groups of screws positioned in timber products and subjected to withdrawal failure.     

Prediction of strength and stiffness of concentrated compressive load applied to the narrow face of cross-laminated timber

European Journal of Wood and Wood Products - The behavior of the concentrated compressive load applied to the narrow face of cross-laminated timber (CLT) panels is an essential parameter in the...     

The long-term evaluation of FRPs bonded to timber

This research investigated the long-term environmental effects on bond strength at the interface between fiber- reinforced polymers (FRPs) and timber. A total of 581 timber specimens were bonded with seven types of FRP sheets (unidirectional and bidirectional glass, carbon, aramid, and hybrids) using a wet lay-up technique. The specimens were exposed to acidic, alkaline, fresh water, and sea water solutions with pH of 2.5, 7, 7.25, 10, and 12.5 for 1, 3, 6, 9, and 12 months. A chamber was also used to simulate ultraviolet radiation after 6 months. A series of single-lap shear tests were then conducted to determine the interfacial bond strength reduction. The results showed that bidirectional carbon and glass FRP sheets demonstrated better bond strength as compared to unidirectional carbon and glass FRP sheets in most cases after exposure to the chemical solutions and ultraviolet radiation. Moreover, acidic and sea water solutions, respectively, had the most and the least effects on the reduction of bonds at the interface between hybrid FRPs and timber. Meanwhile, bidirectional aramid FRPs showed high deterioration in the interfacial bond strength under the effect of water and alkaline (pH 12.5) solutions. Finally, the failure modes on timber substrates were explored and classified.     

Effect of excessive pretreatment of pine timber with CCA wood preservatives on the bond quality of PRF and TRF wood adhesives

The phenol-resorcinol-formaldehyde adhesive is suitable for use at all levels of CCA retention that were tested. Due to changes in retention during treatment, best results are obtained if the glue-spread rate is kept above the standard of 200 g/m², or control measures are taken to prevent the glue-spread from dropping below this level. The tannin-resorcinol-formaldehyde adhesive, without modification, unlike its performance in the manufacture of plywood, appears from these tests to be less suitable for use on treated timber from the view point of lowered percentage of wood failure.     

Use of electronic nose and trained sensory panel in the evaluation of tomato quality

In this paper the performances of an electronic nose based on metalloporphyrin‐coated quartz microbalance sensors and of an experienced panel of seven human assessors in the evaluation of gases derived from degradation reactions in tomatoes are presented and discussed. The performances are measured in terms of the capability of both systems to distinguish between samples of different quality coming from conventional and organic production systems. The study deals with the application of pattern recognition techniques based on either multivariate statistical methods (PCA, GPA) or artificial neural networks using a self‐organising map (SOM). The response pattern of the sensor array and the sensory data are analysed and compared using these methods. Similarities in the classification of the data by electronic nose and human sensory profiling are found. © 2000 Society of Chemical Industry     

人造极性能和质量缺陷的无损检测技术

较为详细地介绍了目前人造板无损检测技术的主要方法和基本原理,以及在生产中的应用.     

鳜鱼肌肉品质评价的初步研究

以7尾健康成年鳜鱼(体重383g±12·6g)为实验对象,测定鱼肉品质的相关指标,包括:肌肉水分含量、脂肪含量、胶原蛋白含量、肌肉pH、电导率、滴水损失、肌肉渗出性损失、肌纤维直径、肌肉质构。结果表明,鳜鱼肌肉水分含量为78·93%±0·61%,脂肪含量为1·59%±0·47%,胶原蛋白含量为0·98%±0·12%,肌肉pH为(6·00±0·16),鱼体垂直电导率为(1·93±0·69)S,鱼体水平电导率为(5·60±0·36)S,滴水损失为10·48%±2·69%,肌肉渗出性损失为32·92%±1·71%,肌纤维直径为(107·36±11·17)μm;在肌肉质构指标中,硬度为(716·73±136·35)g,弹性为(0·86±0·04),凝聚性为(0·53±0·05),黏性为(369·82±79·59),咀嚼力为(317·61±77·41)g,回复力为(0·36±0·02)。在上述指标中,鳜鱼肌纤维直径(Y)与肌肉硬度(X)呈显著负相关(P0·05):Y=-9·6397X2+596·83X-8181·5(R2=0·968);肌肉脂肪含量(Y)与硬度(X)之间呈显著负相关(P0·05):Y=(2×106)X2-88589X+1764·2(R2=0·878);肌肉咀嚼力(Y)与pH(X)呈极显著正相关(P0·01):Y=1853X2-21274X+61286(R2=0·928)。本研究表明,肌纤维直径、脂肪含量、肌肉pH等是评价鳜鱼肌肉品质的重要指标。