Effect Of Temperature And Loading Rate On Bond Characteristics Between FRP Sheet And Steel Plate

FRP strengthening steel structures and structure members has gained great interest in recent years. To make this strengthening method can be widely used in the local engineering, it must ensure that FRP sheet and steel plate have enough good bonding performance. Besides, engineering structures may be su ffered from dynamic loadings including explosion, earthquake and impact. What’s more, due to the natural environment of the engineering are not the same in different regions, it possibly be subjected to elevated temperature and cold temperature in the engi neering structures. The aforementioned effect factors(individual effect or coupling effect) can significantly affect the interface bonding performance between FRP sheet and steel plate. As a consequence, it is attractive to especially investigate the bond ing performance of FRP/steel single-lap joints under various dynamic loadings and test temperatures. The primary objective of this research is summarized as follows:(1) Three types of FRP/steel single-lap joints are tested under different dynamic loading speeds(0.625, 1.25, 2.5, 5.0 m/s), by means of a MTS servo-hydraulic high-rate testing machine. The experimental results of test samples include bond stress-displacement curves, bond strength, interfacial fracture energy and shear stiffness. Results show that both bond strength and shear stiffness of BFRP/steel single-lap joints increase with the increasing loading speed. But the mechanical properties of CFRP/steel single-lap joints and GFRP/steel single-lap joints are not sensitive to loading speed. The general rule is that the bond strength of specimens reaches a maximum value at the loading speed of 1.25 m/s, when the loading speed is more than or less than 1.25 m/s, the average bond strength of samples is decreased. The failure modes are also observed. Overall, most specimens show adhesive/steel interface failure and mixed failure mode under dynamic tensile loads. It shows that different loading speeds have no significant effect on the failure mode of the specimens.(2) Three types of FRP/steel single-lap joints are tested under different temperatures(-25, 0, 50, 100 ?C). It reveals that the mechanical properties of the specimens show a remarkable temperature effect. When the temperature increases from-25 to 50 ?C, the bond strength of BFRP/steel sin gle lap joint and GFRP/steel single lap joint increases with the increasing temperature. However, the bond strength decrease from 50 to 100 ?C. Besides, for CFRP/steel single lap joints, the bond strength increase in the range of-25 to 0 ?C, then decrease to 25 ?C, but when the temperature is increased to the 50 ?C, bond strength continues to rise, and the last hot temperature(100 ?C) enable the bond strength decrease again. In addition, the temperature has an effect on the failure mode of the samples. Th e typical failure mode in most specimens at low temperature(-25 and 0 ?C) is adhesive/steel interface failure, and most samples show mixed failure mode at 50 ?C, whereas the failure mode turn to adhesive/FRP interface failure at the elevated temperature( 100 ?C).DIC method can effectively analyze the full strain field of FRP in the overlapping areas and the failure process of the specimens. The longitudinal strain distribution of FRP in the overlapping areas are non-uniform under dynamic load. At the bottom of bonded area, longitudinal strain starts to localize. As the time increases, the localization zone continues to grow and propagate toward the interior bonded area. Finally, the failure of specimens initiate from the edge of the adhesive layer. The change rule of strain contour of the specimen along the time is influenced by high temperature. It indicates that high temperature make the adhesive stress of the specimen re-distribute.