Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 220-230). Also available via the Internet

Thesis (Ph.D.)--University of California, San Francisco, 2004. / Bibliography: leaves 108-116. Also available online.

published_or_final_version / abstract / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

The aim of this study has been to investigate the possibilities to identify lack of glue in finger joints by checking different non-destructive techniques. Specifically, this study puts emphasis on finding a method suitable for an automated and fast industry production line of home furnishing products. The methods investigated are of three main varieties: Sound/vibration Thermography Tomography The most promising method was the high-power ultrasound thermography. This method is fast and reliable, but more research is needed. It is necessary to find out if the thermography waves can penetrate deep enough. Another possible method is computed tomography. This method can take a lot of time, but the speed of scanning depends on the accuracy demanded. / Uppgiften har varit att granska möjligheterna att identifiera bristfälliga trälimningar eller helt avsaknad av lim i fingerskarvar med hjälp av olika metoder som inte förstör materialet, NDT (non-destructive testing). Undersökningen syftar speciellt till att finna en metod som är anpassad till ett effektivt produktionsflöde i industrin. Det måste där med vara en metod som med stor snabbhet kan hitta eventuella fel på produkterna. De metoder som mer omfattande har granskats är ljud/vibration, termografi och tomografi. Den metod som visat sig mest lovande är high-power ultrasound thermography. Tester måste dock utföras för att säkerställa att metoden är passande för ändamålet. Framför allt om de termografiska vågorna tränger in tillräckligt djupt. En annan möjlighet är datortomografi. Denna metod kan vara tidskrävande, men skanningshastigheten beror på hur noggrant mätresultat som erfordras. Här finns också en säkerhetsaspekt som måste beaktas, eftersom röntgenstrålar används.

published_or_final_version / abstract / toc / Mechanical Engineering / Master / Master of Philosophy

Mechanical strength in wood has always been compromised due to the complex behaviours of the material when interfered with moisture and heat. These factors has always limited the use of the material. However, the will of using more sustainable materials such as wood has contributed to a wider use of the material and several new ways that lead to improvement. Several of these methods emphasizes the joining of two wood components together endwise, where finger-joints are the most commonly used method. Several studies regarding how well finger-joints can withstand external load has been made over the years. However, many of these studies focuses on geometrical properties or strength varying in different species. This study focuses on how relative humidity and temperature affects mechanical strength in finger-jointed wood products. There were beliefs before the research started that increasing temperature would affect mechanical strength greatly. However, it turned out to only affect the mechanical strength marginally, and that relative humidity was the largest contributor to decreasing tolerance levels. It is important to notify that mechanical strength seemed to be directly affected to moisture content (MC), which is a result of an interactive relationship with both temperature and RH. It was particularly MC-levels above 9.2% that showed a decrease in mechanical strength. This research also focused on estimating the relative MOR per cross-section in varying conditions. This method could be used to better understand to which degree hygroscopic factors affects mechanical strength relative to the glued-surface area between finger-joints. Even though the findings in this study indicates that there seems to be possible to estimate strength in regards to relative MOR per cross-section, the results were not sufficient to be viewed as scientifically proof. The findings could however be used as ground for future studies.

Finger movements in the sagittal plane mainly consist of flexion and extension about the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints. The purpose of this study was to develop a biomedical finger model and to validate it by comparing finger strength and muscular forces in static exertions, which predicated from the model and measured in experiments. Two kinematic finger models were developed: one was with the assumption of constant tendon moment arms, and the other was with the assumption of non-constant tendon moment arms. Equations of static equilibrium were derived for these finger models using the principle of virtual work. Equations of static equilibrium for the finger models were indeterminate since only three equations were available for five unknown variables (forces). By reducing the number of variables based on information in the literature on muscular activities in finger movements, the amounts of force which muscles exerted to maintain static equilibrium against an external load were computed from the equilibrium equations. The muscular forces were expressed mathematically as functions of finger positions, tendon moment arms, lengths of phalanges, and the magnitude and direction of external load. Equations of muscular forces were used to predict external finger strength and to compute internal muscular forces in static exertions against an external load. Computer simulations were performed to compute finger strengths and muscular forces at various finger positions and directions of force exertions. For this, finger positions were controlled, and lengths of phalanges were measured. Experiments were performed to measure finger strengths and muscular activity levels in submaximal contractions. Muscular activity levels were estimated by ratios of standardized EMG amplitude to exerted force. Measurements were taken in combinations of four finger positions and four directions of force exertions. Validation of the biomechanical finger models was done by comparing the results of computer simulations and experiments. Significant differences were found between the predicted and measured finger strengths. However, the trends of finger strengths with respect to finger positions were similar in both the predicted and measured. Trends of variations in predicted and measured muscular activity levels were not different from each other. These findings indicate that the finger models and the procedure to predict finger strengths and muscular forces were correctly developed. / Ph. D.

Une étude de faisabilité de poutres en bois lamellé-collé a été menée en Guyane Française en utilisant les essences locales. Le but est de déterminer les paramètres de collage assurant la bonne résistance mécanique des assemblages par lamellation et par aboutage, nécessaires à la fabrication de poutres en bois lamellé-collé en climat tropical. Trois essences de bois abondantes de différentes densités ont été sélectionnées. Les adhésifs de types Mélamine-Urée-Formol et Résorcinol-Phénol-Formol ont été utilisées. Les paramètres de collage considérés sont : le grammage, le temps d’assemblage fermé et la pression.En utilisant les normes Européennes, plusieurs campagnes de tests ont été conduites sur des échantillons normalisés. Concernant le collage par lamellation, des tests élémentaires de délamination et de cisaillement des joints de colle ont été réalisés. Le test de délamination consiste en deux cycles d’immersion dans l’eau sous pression et de séchage, il induit de sévères variations d’humidité du bois susceptibles de créer des ouvertures des joints de colles. Le collage par aboutage est réalisé sur des poutres normalisées aboutées. Les entures sont obtenues grâce à un outillage standard communément utilisé pour les résineux. Les résultats ont mis en évidence l’influence des propriétés du bois et des paramètres de collage sur la résistance du joint et la résistance mécanique du produit. En effet, les paramètres du bois, tels que la densité, la rétractibilité et l’imprégnation, ont une forte influence sur le collage, en particulier sur la pression et le grammage nécessaires à la production d’un produit commercialisable. Il apparait qu’un bois de densité moyenne et poreux nécessite un grammage et une pression élevés comparé à un bois de densité élevée qui nécessite des valeurs moindres. Aussi, l’influence d’autres paramètres de fabrication, tels que le rabotage, l’encollage double face et simple face ainsi que l’épaisseur des lamelles, a été établie. Par contre il semblerait que le matériel communément utilisé pour l’aboutage des résineux n’est pas adapté aux feuillus tropicaux. En final, des paramètres de collage ont été validés pour la fabrication de lamellé-collé endémique en Guyane Française et une étude du coût de production d’une poutre lamellé-collé standard a identifié les conditions économiques d’une fabrication en Guyane Française. / A feasibility study of glued-laminated timber beams was carried out in French Guiana using local wood species. The aim of the study was to evaluate the gluing parameters that could ensure good mechanical properties for the manufactured glued-laminated beams in tropical climates. Three abundant wood species with different specific gravity were selected for the study. Melamine-Urea-Formaldehyde and Resorcinol-Phenol-Formaldehyde resins were used for gluing. The three gluing parameters considered are: adhesive spread rate, closing assembly time and gluing pressure.Using European standards, several laboratory tests were performed on normalized samples. The evaluation of a successful lamella’s gluing was done by using elementary tests of delamination and shearing. A delamination test consists of two cycles of water immersion at high pressure and drying which induces severe hygroscopic variation in wood thus causing joints opening. The finger-joints are made using a standard tool usually used for cutting softwoods. The performed tests revealed the influence of wood properties and the gluing parameters on the joint resistance and the mechanical properties of the product. Results show that wood properties such as specific gravity, shrinkage coefficient, and permeation, have a high degree of influence on the gluing step especially on the gluing pressure and on the adhesive spread rate needed to produce a commercial product. Furthermore, wood with medium specific gravity needs more adhesive and more pressure than the one with high specific gravity. Additionally, the effects of other manufacturing parameters, such as planning, double or simple side glue spreading and lamellae thicknesses, on the glue joint resistance were demonstrated. Finally, the common tools used for softwoods are not adapted to making the finger joints with tropical hardwoods.In conclusion, optimal gluing parameters for manufacturing glued-laminated timber beams in French Guiana were established and an economical study using standard glued-laminated timber beams revealed the economic conditions under which a successful manufacturing of these local beams can be implemented in French Guiana.

Les produits structuraux (poutres, poteaux…etc) en bois de hêtre reconstitué par collage, notamment le Bois Massif Reconstitué (BMR) présentent un fort potentiel tant au niveau de la performance mécanique que de la ressource disponible par comparaison aux essences résineuses. Par ailleurs, les normes européennes actuelles sont rédigées pour les essences résineuses et l’usage du bois de hêtre en structures est limité à la classe de service 1 et aux produits d’intérieur et d’ameublement. Le marché français montre une forte augmentation de l’importation de produits structuraux en bois reconstitué par collage, principalement d’Allemagne et d’Autriche. Au-delà du potentiel de résistance mécanique du hêtre, son utilisation comme bois d’œuvre contribuera positivement au bilan carbone pour l’environnement, par la réduction des transports des bois d’importation. Cependant, pour un usage structural, les produits en hêtre reconstitué par collage nécessitent de passer par une évaluation de leur performance, notamment la fiabilité des aboutages. Cette thèse présente une méthodologie expérimentale et numérique permettant l’analyse du comportement mécanique des poutres en BMR. La démarche a été appliquée avec succès dans le cadre de poutres constituées de 2 à 3 lamelles avec ou sans aboutages. Dans ce contexte, nous avons également réalisé une étude paramétrique pour étudier l’influence de plusieurs paramètres sur la résistance des aboutages. En fin, nous avons formulé le problème d’optimisation de la géométrie de l’enture multiple afin d’augmenter la résistance des aboutages et donc la résistance globale des poutres en BMR / Nowadays, adhesively reconstituted products made of beech timber appear to be of increasing interest for structural purposes due to its high strength/stiffness properties as compared to the most soft-wood species. Furthermore, beech timber is not recognized by most standards for structural uses and restricted to service class 1 and only the furniture, interior joinery and do-it-yourself sectors are still the major users. The French market shows great increasing imports of adhesively reconstituted structural products from Germany and Austria. Moreover, the use of local species, like beech, for the production of reconstituted structural elements could be better for the carbon balance, since it reduces import transportation. However, despite the high mechanical performance of beech timber, adhesively reconstituted products need to meet some requirements, such as the performance of finger-joints. This thesis presents experimental and numerical approaches to deal with the mechanical behaviour of adhesively reconstituted beech beams, for structural purposes. Two-layer and three-layer beams with or without finger-joints have been considered and successfully studied. In addition, a parametrical study has been undertaken to study the influence of several parameters on the mechanical resistance of finger-joints. We, finally, proposed an optimization of the finger-jointing geometry in order to increase the resistance of finger-joints