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Theoretical and experimental analysis of adhesive composite joints
Polymer matrix composites are used in repair of aerospace structures. Adhesively bonded composite patches are capable of minimizing balance and clearance problems on control surfaces and can be readily formed to complex aircraft contours. Reinforcement in a patch can be tailored to suit the loading configuration and to minimize undesirable stiffness increase. Adhesive joining is also attractive for future technologies of integrated manufacturing of large composite structures. One problem impeding wider use of adhesive joints is lack of understanding of their fatigue behavior and lack of reliable methods of fatigue life prediction. The objective of this dissertation was systematic analysis of static and fatigue behavior of joints of a variety of configurations and development of fundamentals of fatigue life prediction. ^ Behavior of adhesive lap joints with delaminated adherends of arbitrary lay-ups was analyzed first. Variations of the strain energy release rate with delamination size in the joints with unidirectional and cross-ply adherends were calculated and analyzed based on a modified analytical model and geometrically linear and non-linear finite element (FE) analyses. Effects of delamination location and size on the strain energy release rates under different loads were evaluated and compared with experimental observations of crack growth in joints with embedded delaminations. The critical strain energy release rates for the delamination propagation were obtained for the first time from in-situ observations. ^ Static and fatigue analysis of double cantilever beam (DCB), end notch flexure (ENF), and crack lap shear (CLS) specimens was performed next. A mixed mode fatigue fracture model was developed and verified on fatigue crack propagation in adhesive lap joints. A method of life prediction for joints of arbitrary configurations was proposed and demonstrated on the lap joints with embedded cracks. Simultaneous propagation of the bond crack and delamination crack was also analyzed. ^ A comprehensive acoustic emission (AE) analysis of mixed mode fatigue fracture of joints was performed. Pattern recognition analysis was used to classify the AE signals from different fracture tests. Dynamic FE modeling was used to simulate the signals from different fracture micromechanisms. Scattered AE signals were simulated numerically for the first time and analyzed using pattern recognition method. The results correlated well with the experimental data. A new method of nondestructive evaluation of the loading mode mixity in joints under fatigue was formulated. (Abstract shortened by UMI.)^
Applied Mechanics|Engineering, Mechanical
Qin, Minghao, "Theoretical and experimental analysis of adhesive composite joints" (2003). ETD collection for University of Nebraska - Lincoln. AAI3116602.