The model used to estimate pallet life in the durability section of PDS is a composite of several computed "factors" which are intended to reflect the impact of design characteristics on pallet durability. The objective of this study was to evaluate the reliability of the estimates of joint performance and the resulting estimates of pallet life relative to the estimated joint performance. A series of delayed fastener axial withdrawal tests were performed on a wide range of pallet fasteners to evaluate the estimates of joint separation resistance that are used in the computation of the F ( 1) factor, the factor for joint separation resistance perpendicular to the pallet deck. This data, in addition to data obtained from previous studies, suggested that the model underestimated the delayed withdrawal performance of threaded nails. An improved relationship was derived for helically threaded, twisted square wire and annularly threaded nails which had the additional advantage of being sensitive to lumber moisture content both at the time of joint assembly and at the time of joint testing. Both the original and the improved relationships were found to grossly overpredict the withdrawal performance of plain shank nails and staples. A series of pallet corner drop tests were performed to evaluate the reliability of the estimates of joint torsional shear resistance that used in the computation of the F(2) factor, the factor for joint separation resistance parallel to the pallet deck. The pallets tested varied by lumber species, number of fastener couples, and fastener stiffness as measured by the MIBANT bend angle. The observed affect of changes in fastener stiffness on pallet diagonal rigidity was found to be accurately reflected in the computed F(2) values. The observed affect of changes in the number of fastener couples on pallet diagonal rigidity was overpredicted in the computed F(2) values. The observed affect of changes in the lumber specific gravity on pallet diagonal rigidity appeared to be overpredicted in the computed F(2) values but this might be due to the fact that the measured pallet distortions were adjusted to account for differences in pallet weights. Pallet weight is specific gravity dependent and adjusting pallet distortion by weight may have reduced the observed affect of specific gravity. It was not possible to statistically confirm a relationship between the estimates of pallet durability relative to pallet diagonal rigidity and observed pallet life. However, such a relationship appears likely. Also, the estimates of pallet durability were found to be conservative. / M.S.

This thesis contains the results of Phase-1 of a project funded by Ford Motor Company. The objective is to study the feasibility of Acousto-Ultrasonics (AU) as a nondestructive technique for assuring the quality of adhesively bonded sheet-metal used for automobiles. Other nondestructive (NDT) techniques were also applied viz., ultrasonics. radiography and thermography to supplement and verify the results of the AU technique. The AU Technique demonstrated the best results in terms of its sensitivity to the variations in the properties of the interface. Regions having kissing bonds or regions lacking adhesive were easily identified by this technique. These regions contribute to the mixed mode failure. A bond quality (BQ) model is suggested to take into account the mixed mode failure. Destructive testing results show fairly consistent correlation of BQ values with the breaking strength of the adhesive joint failing in mixed mode failure. The BQ values were calculated from the SWF (stress wave factor) values generated by the AU technique. No correlation was observed between the SWF values and the breaking strengths of the bonds failing cohesively. Cohesive failures occur at higher loads than those for mixed mode failures. These are, of course, governed by the maximum possible strength of a joint. More work needs to be done to develop a better way to analyze signals for differentiating total cohesive failure, at least for academic interest. The results strongly suggest the potential of this technique for quantitative evaluation of such types of bonding. Automation of this technique can be developed for application on the assembly line of the motor-car industry. Future work to make this technique more efficient and sensitive is suggested. / Master of Science

No description available.

No description available.

A two-dimensional finite-element computational procedure is developed for the accurate analysis of the strains and stresses in adhesively bonded joints. The large displacements and rotations experienced by the adherends and the adhesive are taken into account by invoking the updated Lagrangian description of motion. The adhesive layer is modeled using Schapery's nonlinear single integral constitutive law for uniaxial and multiaxial states of stress. Effect of temperature and stress level on the viscoelastic response is taken into account by a nonlinear shift factor definition. Penetrant sorption is accounted for by a nonlinear Fickean diffusion model in which the diffusion coefficient is dependent on the penetrant concentration and the dilatational strain. A delayed failure criterion based on the Reiner-Weisenberg failure theory has also been implemented in the finite element code. The applicability of the proposed models is demonstrated by several numerical examples. / Doctor of Philosophy

In the preliminary design stage of a car body, targets are first set on the performance characteristics of the overall body and its components using optimization and engineering judgment. Then designers try to design the components to meet the determined performance targets and keep the weight low using empirical, trial-and-error procedures. This process usually yields poor results because it is difficult to find a good design that satisfies the targets using trial-and-error and there might even be no feasible design that meets the targets. To improve the current design process, we need tools to link the performance targets and the physical design parameters. A methodology is presented for developing two such tools for design guidance of joints in car bodies. The first tool predicts the performance characteristics of a given joint fast (at a fraction of a second). The second finds a joint design that meets given performance targets and satisfies packaging and manufacturing constraints. These tools can be viewed as translators that translate the design parameters defining the geometry of a joint into performance characteristics of that joint and vice-versa. The methodology for developing the first translator involves parameterization of a joint, identification of packaging, manufacturing and styling constraints, and establishment of a neural network and a response surface polynomial to predict the performance of a given joint fast (at a fraction of a second). The neural network is trained using results from finite element analysis of several joint designs. The second translator is an optimizer that finds the joint with the smallest mass that meets given performance targets and satisfies packaging, manufacturing and styling constraints. The methodology is demonstrated on a joint of an actual car. / Ph. D.

This study investigates the structural integrity of hydrofoils under three scenarios: regular boating, turning, and collision with an underwater obstacle. To analyse the forces acting on the hydrofoil, calculations were performed and simulations were conducted in SolidWorks using a CAD model of the hydrofoil.The simulations reveal that the weld between the struts and the wing undergoes plastic deformation during both regular boating and turning. This deformation is particularly problematic during turning, as the forces on the weld increase significantly. Under the collision scenario, the bolts at the breakpoint fail before critical damage occurs to the components above.The results highlight the weakness of the weld and the need for a redesign of the hydrofoil to eliminate it. An alternative fastening method, such as bolted joints with watertight sealing, should be considered.

The purpose of the proposed research is to evaluate the mechanical response of stitched T-joints under tension, bending, and combined tensile-flexure loading. The use of fiber-reinforced polymer matrix composites has increased in primary load-bearing structures due to their many attributes, such as their high strength and stiffness-to-weight ratio, and tailorability. Composite T-joints are often used in aerospace, marine, and wind turbine structures to provide load connectivity between orthogonal components, such as stiffeners to skins. However, one of the main drawbacks of polymer matrix composites is their low interlaminar strength, which can lead to delamination when subjected to out-of-plane loads. Techniques such as braiding, knitting, stitching, tufting, and z-pinning have been used to reinforce T-joints in the through-thickness direction. Most research has been focused on the tensile or bending behavior of T-joints, although these joints are often subjected to a combination of tensile and bending loads in service. A few experimental and analytical studies have been conducted on the mechanical response under combined tensile-flexure loading conditions, but no studies have been conducted on stitched T-joints. In this study, mechanical tests of 3D stitched and unstitched T-joints under tension, bending, and combined tensile-flexure were conducted, and the ultimate load, displacement, and absorbed energy were obtained. The average displacement at total failure under tension, bending, and combined tensile-flexure loading conditions for the stitched specimens were found to be 34%, 51%, and 24% greater, respectively, when compared to their unstitched counterparts. Similarly, the average absorbed energy for stitched specimens is 58%, 82%, and 51% greater under tension, bending, and combined tensile-flexure loading conditions. The failure surfaces of stitched and unstitched T-joints were analyzed using an optical microscope, and areas of interest, such as resin-rich regions, stitches, and different damage types, were identified. Furthermore, the skin-flange interface fracture surface of the combined loading T-joint specimens were analyzed using a scanning electron microscope. Significant differences in the fracture surface indicated varying degrees of mixed-mode loading conditions within a specimen for all specimen types. A numerical analysis of a stitched double cantilever beam specimen was conducted to evaluate smeared cohesive laws to represent stitched regions. Overall, stitching results in improved damage tolerance in T-joints subjected to various loading conditions.

Le programme de recherche développé dans le cadre de cette thèse a pour principal objectif de concevoir, réaliser et valider une méthodologie d'étude des effets du vieillissement des interfaces collées, basée sur l'utilisation d'un dispositif de fluage innovant pouvant être couplé à un vieillissement hygrothermique. Celui-ci reprend la configuration classique de joint à double recouvrement mais permet de solliciter sous charge constante l'assemblage collé béton/composite. Il présente de plus certaines spécificités (zones de joint non sollicitées, compatibilité avec une machine d'essai à simple recouvrement existante,...) qui permettent de recueillir un grand nombre de résultat expérimentaux complémentaires. En premier lieux, nos travaux présentent une synthèse bibliographique retraçant le contexte du renforcement par composites collés et précisant les principaux mécanismes physico-chimiques susceptibles d'affecter la durabilité des adhésifs. Le manuscrit décrit ensuite les travaux expérimentaux menés pour étudier le comportement mécanique et physico-chimique des deux adhésifs sélectionnés pour la réalisation des joints collés béton/composites. Finalement, une approche prédictive basée sur i) des tests de fluage thermo-stimulés, ii) sur l'application du Principe de Superposition Temps-Température et iii) sur l'utilisation du modèle rhéologique de Burger, a permis de proposer un modèle de fluage non linéaire pour chacun des deux systèmes de colle. La seconde partie des travaux expérimentaux concerne la conception et la validation d'un dispositif innovant destiné à la caractérisation du comportement en fluage des interfaces collées béton/composite. Un élément important du cahier des charges de ce dispositif était d'en limiter l'encombrement, de sorte qu'il soit possible de tester plusieurs corps d'épreuve dans une chambre climatique au volume réduit, en vue d'étudier les effets synergiques du fluage et du vieillissement environnemental sur la durabilité des joints collés. Dans ce contexte, un prototype capable de solliciter en fluage trois corps d'épreuves à double recouvrement réalisés avec le procédé de renforcement Sika®Carbodur®S et connectés sur un unique circuit hydraulique, a été conçu et réalisé. Les résultats issus du prototype ont permis de le valider, en vérifiant notamment le maintient dans le temps de la charge appliquée, et le comportement symétrique des corps d'épreuve à double recouvrement. Le comportement mécanique des interfaces collées s'est révélé répétable, symétrique et conforme aux diverses modélisations réalisées, soit en calculant la réponse instantanée de l'interface au moyen d'un logiciel aux Eléments Finis (E.F.) ou à partir du modèle analytique de Volkersen, soit en calculant la réponse différée de l'interface en intégrant le modèle de fluage non linéaire de l'adhésif identifié précédemment dans le calcul aux E.F.. La dernière partie des travaux présentés dans le manuscrit concerne la réalisation d'un banc complet de fluage impliquant 14 corps d'épreuves à double recouvrement. Ces corps d'épreuve sont réalisés pour moitié avec le système de renforcement Sika®Carbodur®S et pour l'autre moitié avec le système Compodex. Le banc de fluage est installé dans la salle de vieillissement hygrothermique du Département Laboratoire d'Autun (40°C ; 95% H.R.). Tous les corps d'épreuves sont sollicités en fluage par un système de chargement alimenté par un circuit hydraulique similaire à celui utilisé pour le prototype, mais complété par une centrale hydraulique régulant la pression à partir de la mesure d'un capteur de pression. Pour compléter ces caractérisations sur interfaces collées, des essais de vieillissement sont également menés sur des éprouvettes d'adhésifs massiques stockées dans la salle climatique, certaines d'entre elles étant simultanément soumises à des sollicitations de fluage / The main objective of the present research is to design, realize and validate a methodology for studying ageing of bonded interfaces, based on the development of an innovative experimental creep device that can be coupled to hydrothermal aging. This device is based on the double-lap joint shear test configuration and enables to apply a constant load to the bonded assembly. In addition, this device combines other complementary features (unsolicited bonded joint zones, compatibility with an existing single lap shear test machine ...) that allows collecting useful complementary data. First, our work presents a literature review outlining the context of strengthening by bonded composite and specifying the main physicochemical mechanisms that may affect the durability of adhesive joints. Then, the manuscript describes the experimental characterizations carried out to assess both mechanical and physicochemical behaviors of the two adhesives selected for this study and which will be used to bond the composite on RC specimens in a later stage. Finally, a predictive approach based on i) thermo-stimulated creep tests, ii) on the application of the Time-Temperature-Superposition Principle and iii) on the use of the Burger's rheological model, allowed us to propose a non-linear creep model for each of the two adhesive systems. The second part of the experimental work is devoted to the design and validation of an innovative device for characterizing the creep behavior of concrete / composite adhesively bonded interfaces. An important requirement in the specifications was to reduce the size of the experimental device, so that several test specimens could be installed in a climatic room of limited volume, in order to study the synergistic effects of creep and hydrothermal ageing on the joint durability. In this line, a prototype involving three double-shear test-specimens loaded by flat jacks actuated by a centralized hydraulic system, was designed and realized (test-specimens were prepared using the Sika®Carbodur® S strengthening system). Collected data made it possible to validate the creep setup, by checking the constancy of the applied load over time, and the symmetrical behavior of the double lap shear test bodies. The mechanical behavior of the bonded interfaces was found to be repeatable, symmetrical and in a fair agreement with numerical and analytical modeling, done either by calculating the instantaneous response of the interface using a finite element (FE) approach and the analytical Völkersen's model, or by simulating the delayed creep response of the interface using a FE model in which the non-linear creep behavior of the adhesive layer had been implemented. The last chapter of the manuscript presents the realization of a full-scale creep setup involving fourteen double lap test specimens. Half of the test specimens were strengthened with Sika®Carbodur ® S and the other half with Compodex® C12 reinforcing composite system. This creep setup was installed in the climatic room of the Département Laboratoire d'Autun (40°C, 95% R.H.). Test specimens are creep loaded thanks to flat jacks powered by a hydraulic system similar to that used in the prototype, but supplemented by an electronic station that ensures pressure regulation in the circuit, based on the measurements of a pressure sensor. Beside these characterizations of bonded interfaces, complementary tests are also conducted on samples of the buk adhesive material stored in the climatic room, some of these samples being simultaneously subjected to creep loading

O presente trabalho consiste basicamente num estudo experimental de juntas híbridas metal-compósito unidas mecanicamente por fixadores. Foram analisadas juntas fabricadas através de uma chapa metálica de titânio unida a uma placa em compósito de fibra de carbono e resina epóxi por fixadores de monel. As juntas avaliadas são juntas simples (\"single lap joint\"), ou seja, as mesmas foram submetidas ao simples cisalhamento. Antes, porém, dos ensaios das juntas, foram fabricados corpos-de-prova (CDPs) do compósito seguindo as especificações das normas ASTM D3039 e ASTM D3518. Os ensaios de tração e cisalhamento dos CDPs de compósito possibilitaram a determinação de propriedades mecânicas, bem como de valores de resistência. Sob posse das propriedades e resistência média, foram executadas simulações computacionais via Método dos Elementos Finitos com o intuito de prever o comportamento mecânico das juntas a serem ensaiadas seguindo a norma ASTM D5961 e, assim, delinear estratégias para os ensaios. Os ensaios das juntas foram realizados, possibilitando assim a avaliação do comportamento mecânico de juntas híbridas e de seus mecanismos de falha. Por fim, as conclusões e as perspectivas para trabalhos futuros foram apresentadas. / This work consists on an experimental investigation of hybrid joints (metal-composite) joined by fasteners. For this work, hybrid joints of titanium joined to composite (carbon fiber with epoxy resin) by monel fasteners were manufactured. Only single lap joints were investigated. However, before manufacturing specimens of joints, composite specimens were tested following the ASTM D3039 e ASTM D3518. The tensile and shear tests provided the mechanical properties and strength values of the composite. Finite element analyses of the hybrid joints were carried out, using average mechanical properties and strength values. These simulations followed the specifications of ASTM D5961 in order to predict the mechanical behavior of the joints during the experimental tests, as well as, provide a good strategy for the test setup. The experimental tests were carried out, observing the mechanical behavior and failure mechanisms of the hybrid joints. Finally, the conclusions and perspective of future works were showed.