Visual strength grading of Argentinean Eucalyptus grandis

The present paper reports the results of an investigation regarding the design of a method for visually grading sawn timber of Argentinean Eucalyptus grandis. An empirical research project with four samples of beams and one sample of boards subjected to bending, one sample of boards subjected to tension and one sample of specimens subjected to compression, was carried out. The results obtained with specimens in structural sizes show the influence of the more important strength and stiffness reducing growth characteristics and allow to analyse different strength, stiffness and density profiles in comparison with the international strength class system established in the European standard EN 338. The research also reveals particularities for this timber species as the high ratio of modulus of elasticity and strength to density, in comparison with other deciduous species, among others.

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Visuelle Festigkeitssortierung von Eucalyptus grandis aus ArgentinienFestigkeits-, Steifigkeits- und Rohdichteprofile und zugehörige Grenzwerte der Sortierparameter

Zusammenfassung Dieser Beitrag fasst die Ergebnisse einer Studie zusammen, in der die Möglichkeiten einer visuellen Festigkeitssortierung von Eucalyptus grandis aus Argentinien untersucht wurden. Die Untersuchung umfasste vier Teilstichproben mit Kanthölzern und eine Teilstichprobe mit Brettern in Biegeversuchen und jeweils eine Teilstichprobe mit Zug- bzw. Druckprüfkörpern. Die Ergebnisse der Versuche mit Prüfkörpern in Bauholzabmessungen zeigen den Einfluss der wichtigsten visuellen Sortierparameter und erlauben die Einteilung von Bauholz aus Eucalyptus grandis in unterschiedliche Festigkeitsklassen nach EN 338. Die vorliegende Studie zeigt darüber hinaus besondere Eigenschaften dieser Laubholzart wie das hohe Verhältnis von Elastizitätsmodul und Festigkeit zur Rohdichte.

     

Embedding strength in joints of fast-growing Argentinean Eucalyptus grandis with dowel-type fasteners. Analysis according to the criterion adopted by European standards

The present paper reports on the results of an investigation regarding the determination of the embedding strength of sawn timber of Argentinean Eucalyptus grandis with dowel-type fasteners. The importance of accurately knowing this property has increased with the increasing demand for this material for structural purposes. An empirical research project with 294 specimens prepared for testing under the embedding action of rigid fasteners (nail, bolt and dowel) was carried out according to the procedures prescribed in EN 383 (2007). The results showed no significant influence of pre-drilling on the embedding strength for nailed joints, which is not in line with the European experience and the corresponding criterion adopted by the Eurocode?5 (2005). The characteristic values of the embedding strength estimated based on the timber density and by applying the corresponding equation from the Eurocode?5 (2005) for bolted joints were 45% and 176% greater than those obtained in this project for the specimens loaded parallel and perpendicular to the grain, respectively, and similar percentages were found for dowelled joints (45% and 126%). These results showed that the reliability of structural design may be strongly affected if the embedding strength of this timber species is estimated by following the procedures adopted by the Eurocode?5 (2005) for dowel-type connections.     

Effectiveness of fundamental resonant frequency for determining the elastic properties of Argentinean Eucalyptus grandis in structural sizes

The present paper reports the results of an investigation regarding the elastic properties of Argentinean Eucalyptus grandis by the dynamic method of measuring the fundamental frequencies of vibration. It aims at scrutinising how that method is suitable to this timber species. For this purpose an empirical research project with one sample of boards and four samples of beams in structural sizes exhibiting a wide range of variation in quality was carried out. The results give evidence of the effectiveness of this method for determining the elastic properties for Argentinean Eucalyptus grandis in different sizes, and that it is reliable for pieces of high quality as well as for those containing important strength and stiffness reducing factors, such as the presence of pith, among others.     

Machine strength grading of Argentinean<Emphasis Type="Italic"> Eucalyptus grandis</Emphasis>

The present paper reports the results of an investigation regarding the possibility of machine strength grading sawn timber of Argentinean Eucalyptus grandis. In order to assess the usefulness of each parameter for predicting the mechanical properties of this timber species, and to propose strength, stiffness and density profiles, an empirical research project with four samples of beams and one sample of boards subjected to bending, and another sample of boards subjected to tension parallel to the grain, was carried out. The results obtained with specimens in structural sizes reveal the more important single and combined parameters for machine strength grading this timber species, and allow to analyse strength, stiffness and density profiles in comparison with the international strength class system established in the European standard EN 338.     

Load-carrying capacity of timber-to-timber joints of fast-growing Argentinean Eucalyptus grandis with nails of small diameter laterally loaded in double shear: analysis according to the criterion adopted by European standards

The present paper reports the results of an investigation regarding the study of the load-carrying capacity of connections with nails of small diameter pneumatically driven in timber-to-timber joints of fast-growing Argentinean Eucalyptus grandis. The effectiveness of the equations provided by Eurocode 5 for calculating the lateral load-carrying capacity of these joints was checked for the specimens exhibiting the geometrical parameters adopted by the European design rule and also for those with reduced spacing and end distances. A failure mode presenting features common to both j and k types of failure according to the criterion of the European design rule confirmed that the plastic hinges could be developed before brittle failure due to splitting or block shear occurred, even if the specimens present reduced spacing and end distances. The load-slip curves confirmed ductile behaviour for all cases. The empirical results showed that the structural design is situated on the conservative side if the equations adopted by Eurocode 5 are applied to the analysed connections when the spacing and end distances recommended by this design rule are used. The results also showed that the joint area may be decreased by up to 31 % in relation to that corresponding to the recommended spacing and end distances without reducing the load-bearing capacity below the characteristic value determined according to the European design rule.     

MARBOWL: increasing the fun experience of shooting marbles

This paper focuses on the old school game of shooting marbles. We investigate which aspects of this tangible game make it popular and show how experienced fun can increase by elaborating such aspects through an iterative design process. A questionnaire and field study, tailored to the user group of primary school children aged 9–12 years old, revealed that aspects within areas of physical control, surface of the playground, opponent, and stakes of the game had the biggest influence on the fun experience of shooting marbles. A gameflow model and fun toolkit were used to improve the game in these respective areas. This resulted in a moving marble hole entitled Marbowl: a tangible marble game that augments existing game aspects such as timing, distance, surface, and other physical and environmental influences. A working prototype was field tested with 24 children at a primary school. Results show that different gameflow areas like concentration needed, playability, difficulty to win the game, and amount of challenge, increased in a positive way. Together these findings concluded that compared with the original marble game, children experienced a higher level of fun while playing with Marbowl.     

Relationship between timber quality and the influence of moisture content above fibre saturation on mechanical properties in beams of fast-growing Argentinean Eucalyptus grandis

The present paper reports on the results of an investigation regarding the relationship between timber quality and the influence of moisture content above fibre saturation on bending strength and stiffness in structural-sized beams of fast-growing Argentinean Eucalyptus grandis. An empirical research project with a sample containing 96 pairs of structural-sized beams (seasoned and unseasoned) was carried out. Results showed that the influence of moisture content on mechanical properties was related to timber quality and it increased with timber quality but this relationship did not clearly emerge from the results obtained by visually strength grading the sample with the most important strength and stiffness reducing growth characteristic (the presence of pith), whereas it was better revealed by machine grading the sample with the most important single parameter (modulus of elasticity). Results also showed that decisions related to structural design with timber of high quality exposed to service class 3 according to European standards or installed near fibre saturation are situated on the unsafe side if the strength and stiffness values are obtained by multiplying those corresponding to seasoned timber by a constant factor representing the average behaviour of this material. Even though this average behaviour compared relatively well with the results obtained by applying the criteria adopted by standards of overseas and Latin-American countries, which do not consider timber quality for this purpose, the reliability required by structural design accounts for the convenience of taking into account the relationship between timber quality and the influence of moisture on mechanical properties where timber of high quality is concerned.     

Creep in beams of Argentinean Eucalyptus grandis loaded in unseasoned state

This paper reports the results of an investigation of creep in beams of Argentinean Eucalyptus grandis loaded in unseasoned state and allowed to dry under load. An empirical research project with a sample containing 15 structural-sized beams subjected to long-term loading was carried out. The results allow to compare the creep behaviour of these beams with previous data reported for structural-sized beams of this timber species loaded in dry condition and also with those reported for other species. The effectiveness of the criteria adopted by standards of overseas and Latin-American countries for calculating the creep deflections in unseasoned beams of this timber species under a long-term loading is analysed.     

Ti–Cu–Ni shape memory bulk metallic glass composites

New Ti–Cu–Ni shape memory bulk metallic glass composites were obtained by carefully controlling the cooling rate upon quenching. This allows for the formation of a metastable microstructure consisting mainly of ductile, spherical martensitic Ti(Ni,Cu) precipitates embedded in an amorphous matrix also containing a small volume fraction of TiCu and Ti₂Cu precipitates. These composites exhibit large ductility and high strength combined with a strong work-hardening behaviour. A deformation mechanism is proposed with the help of experimental observations and finite-element simulation. The simulation results demonstrate that stress concentrations occur around the precipitates, which promotes a heterogeneous stress distribution and the formation of multiple shear bands. Additionally, different transformation temperatures were observed for martensitic precipitates depending on whether they are completely or partially embedded in the amorphous matrix.     

Microstructural Evolution and Mechanical Behaviour of Metastable Cu-Zr-Co Alloys

Three different Cu-Zr-Co alloys, namely Cu40Zr37.5Co22.5, Cu42.5Zr45Co12.5 and Cu49Zr49Co2, were obtained by rapid cooling. The microstructure and phase formation of as-cast rods with diameters of 2 mm are compared with those of the respective ingots. An increasing Co content stabilises the B2 CuZr phase and leads to the precipitation of a ternary Cu-Zr-Co phase. The variation of the cooling rate affects the size of the B2 dendrites as well as the volume fraction and the morphology of the interdendritic phases. The mechanical properties were determined in compression and all alloys show a certain plastic deformability despite the presence of several binary and ternary intermetallic phases. The deformation mechanisms are discussed on the basis of the microstructures and the constituent phases.