Adhesively bonded joints have been investigated for several decades. In most analytical studies, the Bernoulli-Euler beam theory is employed to describe the behaviour of adherends. In the current work, three analytical models are developed for adhesively bonded joints using the Timoshenko beam theory for elastic material and a Bernoulli-Euler beam model for viscoelastic materials. One model is for the peeling test of an adhesively bonded joint, which is described using a Timoshenko beam on an elastic foundation. The adherend is considered as a Timoshenko beam, while the adhesive is taken to be a linearly elastic foundation. Three cases are considered: (1) only the normal stress is acting (mode I); (2) only the transverse shear stress is present (mode II); and (3) the normal and shear stresses co-exist (mode III) in the adhesive. The governing equations are derived in terms of the displacement and rotational angle of the adherend in each case. Analytical solutions are obtained for the displacements, rotational angle, and stresses. Numerical results are presented to show the trends of the displacements and rotational angle changing with geometrical and loading conditions. In the second model, the peeling test of an adhesively bonded joint is represented using a viscoelastic Bernoulli-Euler beam on an elastic foundation. The adherend is considered as a viscoelastic Bernoulli-Euler beam, while the adhesive is taken to be a linearly elastic foundation. Two cases under different stress history are considered: (1) only the normal stress is acting (mode I); and (2) only the transverse shear stress is present (mode II). The governing equations are derived in terms of the displacements. Analytical solutions are obtained for the displacements. The numerical results show that the deflection increases as time and temperature increase. The third model is developed using a symmetric composite adhesively bonded joint. The constitutive and kinematic relations of the adherends are derived based on the Timoshenko beam theory, and the governing equations are obtained for the normal and shear stresses in the adhesive layer. The numerical results are presented to reveal the normal and shear stresses in the adhesive.

Rivets are widely used as a means of fastening in airframe construction industry. There are various types of riveted joints on an aircraft fuselage or on a helicopter body. Among the other types of fasteners riveted joints are preferred in such applications due to / their permanence after installation and their economical advantages. In a riveted joint, it is known that residual stresses are present as a result of the installation process. Furthermore, during the flight of an aircraft, the fuselage is loaded in one cycle and such cycles are repeated throughout the service life. As a result, the panels and the rivets are subjected to fatigue type loading. The integrity of the joint must be maintained against this combination of service loads and the residual stresses. Hence, the riveting process parameters which influence the residual stresses are utmost critical in terms of fatigue life of the hole body. In this study it is aimed to obtain an accurate numerical model of a single-lap riveted joint which is widely used in airframes. 2-D axisymmetrical and 3-D numerical models are generated using commercial finite element code ABAQUS/CAE and subsequent parametric studies are carried out on these models. The Results of both models are compared with those found in the literature. Clearance between hole and rivet shank is selected as the primary parameter to be inspected. The effects of hole clearance on the final residual stress field are examined on 2-D and 3D models. Furthermore, a through the thickness, crack on the inner panel which is initiated after installation is modeled. The crack is perpendicular to the direction of loading. It is placed to the residual tensile stress zone that surrounds the rivet hole. Hence, the effects of residual stresses are also taken into account. For a riveted joint subjected to fatigue loading, such a macroscopic crack could eventually form. In this thesis, stress intensity factors (SIF&rsquo / s) for this crack are calculated for various parameters such as clearance and crack length. These can be utilized in a subsequent fatigue crack growth analysis as the initial values or they can be used in a fracture analysis, to predict unstable crack growth due to overload (i.e. crack linking).

Meniscus is a fibrocartilaginous tissue which plays an important role in joint stability, lubrication, and load bearing and transmission. Meniscal tears are commonly encountered in sports activities, or caused by degeneration of the cartilage with ageing. They lead to pain, loss of work, disturbed biomechanics of the knee and inability to walk or even move the legs. As the meniscal tissue is avascular in the inner portion, injury to this part does not heal by itself, and therefore treatments are needed. In some cases when complex tears occur, the tissue cannot be successfully treated with the conventional methods. Tissue engineering appears to be a promising alternative to treat such complex tears. It includes the application of cells on scaffolds (or cell carriers), and provision of bioactive agents to the site of injury in order to regenerate the damaged tissue. The cells and the bioactive agents are involved in the synthesis of the new tissue, while the scaffold acts as a support to guide the cells until the new tissue is formed, and it is slowly absorbed by the body leaving the new tissue behind. Thus, a natural tissue is generated at the end. Few studies have been reported on the tissue engineering of meniscus, but neither of them was able to completely mimic the meniscus structure, nor could they succeed in constructing scaffolds with sufficiently high tensile properties. In the current in vitro study, a novel 3D construct was proposed, in which the natural tissue is perfectly mimicked. The 3D construct consisted of aligned collagen fibers embedded within a foam network which stabilizes the structure. The foam was prepared by freezing a polymer solution with a certain concentration, and lyophilizing it. Aligned fibers were aimed to improve the tensile properties. The construct was impregnated in alginate gel, which was then crosslinked, to improve the compressive properties. The foam was prepared from (poly(L-lactic acid)/poly(lactic-co-glycolic acid) (PLLA/PLGA) solutions of various concentrations (2%, 2.5%, 3%, and 4% w/v) and at different freezing temperatures (-20oC or -80oC) to select the best preparation condition. After analysis of the microstructure and mechanical properties, foams prepared from 3% polymer solution frozen at -20oC were found to be the most appropriate for use as scaffold for the 3D construct, since they had large pores, high and interconnected porosity, as well as high mechanical strength. The 3D constructs were seeded with human meniscus cells and incubated for 21 days. Cell behavior on the constructs was examined. Cell attachment and proliferation was found to be better with the constructs not coated with alginate. However, the constructs coated with alginate demonstrated higher compressive strength. It was also found that incorporation of collagen fibers significantly improved the tensile properties. All the constructs were shown to lead to the production of extracellular components specific for fibrocartilages, and thus it was concluded that they were promising for use in meniscal replacement.

Joint attention, a crucial component in interaction and an important milestone in human development, has drawn a lot of attention from the robotics community recently. Robotics researchers have studied and implemented joint attention for robots for the purposes of achieving natural human-robot interaction and facilitating social learning. Most previous work on the realization of joint attention in the robotics community has focused only on responding to joint attention and/or initiating joint attention. Responding to joint attention is the ability to follow another's direction of gaze and gestures in order to share common experience. Initiating joint attention is the ability to manipulate another's attention to a focus of interest in order to share experience. A third important component of joint attention is ensuring, where by the initiator ensures that the responders has changed their attention. However, to the best of our knowledge, there is no work explicitly addressing the ability for a robot to ensure that joint attention is reached by interacting agents. We refer to this ability as ensuring joint attention and recognize its importance in human-robot interaction. We propose a computational model of joint attention consisting of three parts: responding to joint attention, initiating joint attention, and ensuring joint attention. This modular decomposition is supported by psychological findings and matches the developmental timeline of humans. Infants start with the skill of following a caregiver's gaze, and then they exhibit imperative and declarative pointing gestures to get a caregiver's attention. Importantly, as they aged and social skills matured, initiating actions often come with an ensuring behavior that is to look back and forth between the caregiver and the referred object to see if the caregiver is paying attention to the referential object. We conducted two experiments to investigate joint attention in human-robot interaction. The first experiment explored effects of responding to joint attention. We hypothesize that humans will find that robots responding to joint attention are more transparent, more competent, and more socially interactive. Transparency helps people understand a robot's intention, facilitating a better human-robot interaction, and positive perception of a robot improves the human-robot relationship. Our hypotheses were supported by quantitative data, results from questionnaire, and behavioral observations. The second experiment studied the importance of ensuring joint attention. The results confirmed our hypotheses that robots that ensure joint attention yield better performance in interactive human-robot tasks and that ensuring joint attention behaviors are perceived as natural behaviors by humans. The findings suggest that social robots should use ensuring joint attention behaviors.

Ziel der Arbeiten ist die Entwicklung von Verbindungsgeometrien für ebene, textilbewehrte Betonbauteile auf Basis der Klebtechnik. Zur Charakterisierung des Tragverhaltens geeigneter Verbindungen werden umfangreiche experimentelle Verbunduntersuchungen auf Garn- und Bauteilebene durchgeführt. Mit den so gestalteten Verbindungen mit nachträglichem Verguss lassen sich die Referenzlasten des ungestörten Bauteils erreichen, wobei eine weitere Optimierung der Klebung zur Gewährleistung einer vereinfachten Herstellbarkeit und eines reproduzierbaren Versagensverhaltens anzustreben ist.

The Interstate Highway System plays a vital role in our economic development by providing a continuous corridor for transporting goods and services. Currently, there is a need for repair and expansion of the existing highways, which include all bridges along its path. Because of the high demand for the highway system, repair and expansion must occur rapidly and efficiently. In recent years, precast bridge deck systems have become an efficient way to reduce construction time during repair. This thesis presents the experimental research of the behavior of the U-Bar joint detail used in precast bridge deck systems. This detail consists of staggered reinforcement extending beyond the precast deck portion into the joint. Six specimens utilizing the U-Bar detail were constructed and tested. Three specimens were tested in flexure to simulate the forces applied in a longitudinal deck joint, while three specimens were tested in pure tension to simulate the forces experienced in a transverse deck joint located over an interior pier. A tight 180° bend at 3db was desired in order to minimize the thickness of the deck. To achieve this tight bend, deformed wire reinforcement was chosen for the U-Bar detail due to the favorable material properties of deformed wire reinforcement. The purpose of the testing was to determine if the joint details could generate a precast deck system that could emulate the monolithic cast-in-place deck systems already in use. For monolithic behavior in a precast deck system, the joints must be able transfer shear, tension and moments. In this research, the joint overlap length was the most dominant variable, and should not be less than 152.4 mm (6”). The precast bridge deck joint should consist of high strength concrete with f’c of at least 68.9 MPa (10 ksi). The longitudinal reinforcement spacing should be no greater than 152.4 mm (6”).

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 182-188). Also available on the Internet.

Thèse doctorat : Génie des Matériaux : Villeurbanne, INSA : 2004. / Titre provenant de l'écran-titre. Bibliogr. à la fin de chaque chapitre.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains ix, 80 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 75-80).

Thesis (M.S.) -- Mississippi State University. Department of Forest Products. / Title from title screen. Includes bibliographical references.