A study aimed at determining the thermal deformation response and thermal buckling loads of rectangular grid-stiffened composite panels is presented. Two edge conditions are considered for the panel, one in which all panel edges are free to deform, and another when all the edges are restrained. In the first case panel deformations due to a uniformly distributed thermal load are analyzed. In the latter case, thermal loads causing buckling failure due to the suppressed in-plane deformations are determined. The panel is composed of a skin and a network of stiffeners, which are all made of the same graphite-epoxy composite material. Kirchhoff's Theory is used to determine the pre-buckling deformations and load distributions of the composite laminates for a panel with free to deform edges. To illustrate both the in-plane and out-of-plane deformations of plate structures under uniform thermal loads, two thermal coefficient vectors, thermal expansion and thermal bending coefficient vectors are introduced. Linear panel buckling analysis performed by assuming a linear undeformed prebuckling state. Rayleigh-Ritz Method, which utilizes minimization of the total energy of a structure to determine the buckling loads, is used to govern the buckling analysis of composite laminates forming the panel. Lagrange Multiplier Method is used along with the Rayleigh-Ritz Method to enforce the deformation continuity constraints at discrete locations along the skin and stiffener interface. As a result, graphical and numerical presentations of the effects of skin and stiffener laminate stacking sequences on the thermal deformations and on the thermal buckling load of the grid-stiffened panel are given. / Master of Science

This thesis investigates the effects of damage characteristics on residual compressive strength (RCS) of 4-mm thick preconditioned carbon/epoxy quasi-isotropic panels through the study of their compressive behaviour. Results of 2-mm thick preconditioned panels mostly from a previous study are also analysed. The preconditions of varying sizes include impact damage, quasi-static damage, single and multiple artificial delaminations of circular and elliptical shapes embedded at different through-the-thickness (TTT) locations, hemispherical-shaped domes of different curvature and depth and open holes. The mechanisms of impact damage and the characteristics of energy absorption were dependent on panel thickness and incident kinetic energy (IKE). A damage threshold for compressive strength (CS) reduction was found at 455-mm2 and 1257 mm2 for 2- and 4-mm thick panels, respectively. Panels affected by the presence of internal delaminations followed a sequence of prebuckling, local and global buckling (mode I) and postbuckling (mode II) in both the longitudinal and transverse directions. Their compressive failure was related to mode I to II transition. Possibility of delamination propagation was examined using response characteristics on the basis of the sequences. Evidence of delamination propagation was found only in panels with large damages and was not sensitive to RCS. For low and intermediate IKEs the effect of impact damage could be simulated with a single delamination (2-mm thick panels) and 3 delaminations of medium size (4-mm thick panels). For high IKEs, the additional effect of local curvature change was significant. The combined effect of delamination number, size and curvature change determines the RCSs. It was demonstrated that the present method of embedding artificial delaminations proves to be very useful for studying RCS of impact-damaged panels via the establishment of response characteristics and their links to the effects of the preconditions on them. This thesis also presents two analytical models, one for deflection of transversely loaded panels and the other one for the prediction of compressive strength retention factor (CSRF) based on the correlation between the ratio of maximum transverse force to initial threshold force and the CSRF, observed experimentally in thick panels.

The desire of builders and architects of maximum transparency and homogeneous surfaces in glass façades and glass structures extends to interior all-glass applications such as glass partitions or all-glass doors. In conventional glass systems the interconnections are performed by eye-catching fittings and clamping details that reduce the transparency and disturb the aesthetics. Novel glass–plastic-composite panels show a significantly reduced self-weight by composition of a polymer polymethylmethacrylate (PMMA) interlayer core and cover layers of thin glass. The innovative composites show high structural performance with optical properties of conventional glass. The panels allow for a direct connection into the thick PMMA interlayer core with the supporting structure or other panels. Such an integrated connection design reduces stress concentrations and allows for the development of small and unobtrusive fittings. Different integrated connections for the glass–plastic-composite panels have been designed and investigated. This article presents an experimental study on different connections, such as mechanically fastened and adhesively integrated, tested under tensile loading. Based on video analyses, crack progressions and failure mechanisms are evaluated and discussed in detail. The tests investigate temperature effects as well as the influence of the interlayer core thickness and glass type of the cover layers in varying build-ups. The comprehensive evaluation includes a description of the mechanical load-bearing behaviour in form of load versus displacement graphs as well as an investigation of crack progression and failure mechanisms for the final assessment. The results from this experimental study elucidate the structural characteristics of integrated connections in glass–plastic-composite panels under tensile loading and represent a basis for the ongoing development of real application fittings.