Fracture and Damage Mechanics V

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Authors: Cheol Woo Park, Jong Sung Sim, Tai Sik Lee
Abstract: This study investigates the punching shear strength of concrete bridge decks strengthened with various fiber reinforced polymer (FRP) materials, carbon fiber sheet (CFS), glass fiber sheet (GFS) and carbon fiber grid (CFG). This study performed fatigue loading tests on the strengthened bridge decks with different fatigue loading levels. Based on the experimental results, a damage index was determined considering the damage mechanics and was applied to the plastic punching shear strength model for the evaluation of the punching shear strength with respect to the number of fatigue loading cycles. The developed model seems to successfully estimate the punching shear strength of damaged bridge decks with sufficient reliability. It is anticipated, therefore, that the developed model may help improving the design of strengthening of damaged bridge deck panels.
Authors: R. Kabir, Alfred Cornec, Wolfgang Brocks
Abstract: Quasi-brittle fracture of fully lamellar two phase (α2+γ)TiAl is investigated both experimentally and numerically. Fracture tests are conducted at room temperature, which fail in a quasi-brittle and unstable manner but exhibit significant variations in crack initiation and propagation prior to unstable failure. Fractographic investigations are performed which elucidate the micromechanical causes of the macroscopic behaviour. The observed deformation and fracture behaviours of the specimens are simulated by a finite element model containing cohesive elements for modelling the material separation. In order to capture the scatter of the macroscopic behaviour, a stochastic approach is chosen, in which local variations of cohesive parameters are taken into account. The model can describe and explain the physical phenomena of the specific material.
Authors: Chiara Colombo, Mario Guagliano, Laura Vergani
Authors: Cheol Woo Park, Jong Sung Sim, Sung Jae Park
Abstract: Various types and forms of FRP materials have been applied for structural strengthening of reinforced concrete (RC) beams. When CFRP plates are used, however, a premature failure used to occur before strengthening effect appears adequately. This is primarily due to the rip-off of CFRP plate attached on RC beams. Despite of numerous studies on the rip-off failure of externally strengthened RC beams, the failure mechanism is not clearly explained yet. Investigations from the literatures have shown that the rip-off failure is dependant on vertical and shear stresses at the level of main reinforcements in RC beams. This study suggests an analytical model to investigate the ripoff failure load based on the stresses at the level of main reinforcements. The proposed model is relatively simple and produces very comparable results to the test data. Therefore, it is anticipated that the proposed model can be successfully used to provide further information on the rip-off failure mechanisms and its prevention.

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