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Lastabtragende Klebverbindungen stellen im Konstruktiven Glasbau einen wesentlichen Forschungsgegenstand der vergangenen Jahre dar. Getrieben von gestalterischen Gesichtspunkten sind dabei die transparenten Klebstoffe von besonderem wissenschaftlichem und wirtschaftlichem Interesse. Die vorliegende Arbeit widmet sich ausschließlich der Klebstoffgruppe der zweikomponentigen Epoxidharze, da diese im Konstruktiven Glasbau bisher kaum Beachtung finden. Detaillierte Informationen zu den Eigenschaften und zum Verhalten fehlen fast vollständig und werden innerhalb der vorliegenden Arbeit geschaffen. Die durchgeführten Untersuchungen gliedern sich in die Untersuchungen zur Wahl eines geeigneten Epoxidharzes, in die Untersuchungen der Verarbeitungsbedingungen und in die Charakterisierung der optimierten Klebverbindung. Ferner wurden auch konstruktive Maßnahmen zum Schutz der Klebschicht in die Untersuchungen eingebunden. Innerhalb des Untersuchungsprogramms wurde großer Wert auf eine ausgewogene Gewichtung unterschiedlicher Kriterien gelegt. In die engere Auswahl kamen acht Epoxidharzklebstoffe, die grundlegend untersucht und analysiert wurden. Im Ergebnis konnte ein vielversprechender Klebstoff ausgewählt werden. Die weiterführenden Untersuchungen zu den Verarbeitungsbedingungen hatten die Optimierung des Eigenschaftsprofils zum Ziel. Sowohl die thermische Stabilität des Klebstoffs als auch das Anfangs- und das Restbruchverhalten der Glas-Metall-Verbindungen konnten nennenswert verbessert werden. Ebenso wurde die Wirksamkeit der konstruktiven Schutzmaßnahmen erfolgreich nachgewiesen. Aus den Ergebnissen und deren Wertung konnten abschließend Handlungsempfehlungen für den Einsatz transparenter Epoxidharze in Glastragwerken abgeleitet werden. Die sich nach den eigenen Untersuchungen ergebenden, weiteren offenen wissenschaftlichen Fragestellungen und deren zugehöriger Forschungsbedarf werden am Ende ebenfalls erörtert.

Fracture mechanics is an effective approach for characterizing material resistance to interfacial failure and for making interface reliability predictions. Because interfacial bond integrity is a major concern for performance and reliability, the need to evaluate the fracture and delamination resistance of an interface under different environmental conditions is very important. This study investigates the effects of temperature, solution chemistry and environmental preconditioning, in several solutions on the durability of silicon/epoxy and glass/epoxy systems. A series of experiments was conducted using wedge test specimens to investigate the adhesion performance of the systems subjected to a range of environmental conditions. Both silicon and glass systems were relatively insensitive to temperature over a range of 22-60°C, but strongly accelerated by temperatures above 60°C, depending on the environmental chemistry and nature of the adhesive system used. Silicon/commercial epoxy specimens were subjected to preconditioning in deionized (DI) water and more aggressive solution mixtures prior to wedge insertion to study the effect of prior environmental exposure time on the system. The wedge test data from preconditioned specimens were compared with standard wedge test results and the system was insensitive to preconditioning in DI water but was affected significantly by preconditioning in aggressive environments. Plots describing - G (crack velocity versus applied strain energy release rate) characteristics for a particular set of environmental conditions are presented and a comparison is made for different environmental conditions to quantify the subcritical debonding behavior of systems studied. A kinetic model to characterize subcritical debonding of adhesives for microelectronic applications is also proposed based on molecular interactions between epoxy and a silane coupling agent at the interface and linear elastic fracture mechanics, which could help predict long-term deterioration of interfacial adhesion. / Master of Science

The damage development and strength of ply-level scaled carbon/epoxy composite laminates having stacking sequence of [+Tn/-Tn/902n]s where constraint ply angle, T, was 0, 15, 30, 45, 60, and 75 degrees, and size was scaled as n=1,2,3, and 4, is reported in Part I. X-radiography was used to monitor damage developments. First-ply failure stress, and tensile strength were recorded. First-ply failure of the midplane 90 deg. plies depended on the stiffness of constraint plies, and size. All 24 cases were predicted using Zhang's shear-lag model and data generated from cross-ply tests. Laminate strength was controlled by the initiation of a triangular-shaped local delamination of the surface angle plies. This delamination was predicted using O'Brien's strain energy release rate model for delamination of surface angle plies. For each ply angle, the smallest laminate was used to predict delamination (and strength) of the other sizes. The in-situ tensile strength of the 0 deg. plies within different cross-ply, and quasi-isotropic laminates of varying size and stacking sequence is reported in Part II. No size effect was observed in the strength of 0 deg. plies for those lay-ups having failure confined to the gauge section. Laminates exhibiting a size-strength relationship, had grip region failures for the larger sizes. A statistically significant set of 3-point bend tests of unidirectional beams were used to provide parameters for a Weibull model, to re-examine relationship between ultimate strength of 0 deg. plies and specimen volume. The maximum stress in the 0 deg. plies in bending, and the tensile strength of the 0 deg. plies (from valid tests only) was the same. Weibull theory predicted loss of strength which was not observed in the experiments. An effort to model the durability and life of quasi-isotropic E-glass/913 epoxy composite laminates under steady load and in an acidic environment is reported in Part III. Stress-rupture tests of unidirectional coupons immersed in a weak hydrochloric acid solution was conducted to determine their stress-life response. Creep tests were conducted on unidirectional coupons parallel and transverse to the fibers, and on ±45°. layups to characterize the lamina stress- and time-dependent compliances. These data were used in a composite stress-rupture life model, based on the critical element modeling philosophy of Reifsnider, to predict the life of two ply-level thickness-scaled quasi-isotropic laminates. / Ph. D.