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|Title:||Fatigue and Fracture of the FRP-Wood Interface: Experimental Characterization and Performance Limits|
|Committee Chair:||Roberto A. Lopez-Anido, Assistant Professor of Civil Engineering|
|Committee Members:||Douglas J. Gardner, Professor, Wood Science and Technology; Eric Landis, Associate Professor of Civil Engineering; Lech Muszynski, Assistant Scientist, Wood Science and Technology|
|Subjects:||Composite materials; Fiber reinforced plastics|
|Date of Defense:||2003|
A performance-based material evaluation methodology was developed to qualify FRP composite reinforcement bonded to glulam structural members for highway bridge applications. The objectives of this thesis are: a) to implement and correlate two methods to evaluate the fatigue and fracture performance of FRP-wood interfaces with associated performance limits; and b) to provide data and recommendations necessary to develop performance-based material specifications. The first method is based on evaluating the apparent shear strength in a single-lap shear test by fatigue tension loading. The second method is based on evaluating the interface fracture toughness in Mode I or opening-mode using fracture mechanics. ASTM standard test procedures were identified as the basis for each method. However, these test procedures had to be modified and adapted for FRP-wood interfaces. The research approach combined experimental techniques, data reduction methods and analytical tools. A laminating press was designed and calibrated for timedependent effects to fabricate the test samples. Two material systems that passed adhesive screening tests were evaluated: E-glasslurethane pultruded composite sheet with urethane adhesive (material system B) and E-glasslepoxy composite sheet by continuous lamination with epoxy adhesive (material system C). The fatigue performance of FRPwood interfaces using a single-lap shear configuration was characterized by modifying ASTM D2339 standard test procedure. A fatigue performance-based evaluation criteria and associated limits were proposed. It was shown that material system C had higher apparent shear strength and better fatigue resistance than system B. Quality bonding was observed for both material systems in terms of high percentage of wood failure. Finite Element Analysis (FEA) was performed on a model simulating single lap shear specimens loaded in tension to analyze the peeling and shear stress distributions in the overlap area. The Mode I fracture toughness of FRP composite and wood bonded interfaces was evaluated using flat double-cantilever beam (DCB) specimens. ASTM standard test procedure D5528 for unidirectional FRP composites was modified to characterize hybrid FRP-wood materials. Crack lengths and crack opening displacements were monitored during the experiments using a CCD digital camera system with digital image correlation. An important simplification was realized with flat DCB geometry with respect to other methods based on tapered specimens. Three data reduction methods were applied to compute interlaminar fracture toughness: modified beam theory, compliance calibration and shear corrected compliance. The three methods provided similar fracture toughness values. It was found that Mode I fracture toughness of material system C (epoxy adhesive) was significantly higher than that of material system B (urethane adhesive). It was demonstrated that this fracture method could be used to quantitatively discriminate and evaluate FRP-wood bonded material systems.
Hong, Yong, University of Maine, CEE2003-002