It is a common method to strengthen the damaged RC structures with bonded steel plates. At present the ultimate bearing ca- pacity of RC structures strengthened with bonded steel plates is calculated mostly using the theory based on the test. Four beams, including one reference beam, two strengthened concrete beams in primary force and secondary force respectively, and one strengthened concrete beam which was not anchored enough, were tested under four-point bending (4PB) in order to get the data of strain of longitudinal bars, bonded bottom steel plate in tension and deflection of beams in the middle span. The experimental program was supported by a three-dimensioned finite analysis using ABAQUS. At the end of experiments and finite analysis, it is concluded that the investing strengthening technique can significantly improve the load-carrying capacity and the phenomenon of stress concentration at the end of interface, as well as the damage at interface, can be well simulated with cohesive element provided by ABAQUS.
The rigid body limit equilibrium method （LEM） and the nonlinear finite element method （NFEM） are often used in the analysis of anti-sliding stability of gravity dam. But LEM cannot reflect the process of progressive instability and mechanical mecha- nism on failure for rock mass while NFEM is difficult to use to solve the displacement discontinuity of weak structural plane. Combining the research with Xiangjiaba Hydropower Station project, the analysis of anti-sliding stability for segment 12# of the dam has been carried out using interface stress element method （ISEM）. The results can reflect the most dangerous location, the scope and distribution of failure zone in weak structural plane, and present the process of progressive failure in dam foun- dation as well as the safety coefficient of possible sliding body. These achievements provide an important technical reference for dam foundation treatment measures. The computational results show that ISEM can naturally describe discontinuous de- formation of rock mass such as dislocation, openness and sliding. Besides, this method is characterized by good adaptability, convenient calculation and high compatibility, thus it is regarded as an effective way to make an analysis of anti-sliding stabil- ity of gravity dam
An experimental investigation on the mechanical mechanisms of fatigue micro-crack initiation and propagation of a nickel-based superalloy is presented. By coupling digital image correlation method and scanning electron microscope, the fatigue residual strain distribution at the grain scale has been obtained. The results showed that there is a trend of accumulation for the residual strain. Micro-cracks are more likely to initiate in or near the areas with particularly large residual strain, and propagate along the large-strain paths.
Dong Lei 1 Kefeng Wang Qing Zhang Pizhong Qiao (State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China) (College of Mechanics and Materials, Hohai University, Nanjing 210098, China)
Based on the framework of the extended finite element method (XFEM), the enriched exponent discontinuous function is modified properly by introducing the rigidity ratio of two sides materials of interface crack, and the portion integral scheme is adopted for interface elements containing two materials. To embody the singularity of the crack tip, the triangle function is introduced directly. What’s more, the maximum loop stress fracture criterion is adopted to determine the extension direction in extended material domains, and the true extension distance for each load step is determined by reducing or increasing half the current trial extension distance until the equivalent stress intensity factor reaches the type I fracture toughness of material. Finally, with the improved XFEM, the interface crack propagation in a cantilever deep beam and concrete gravity dam are simulated without re-meshing respectively and their failure modes are also analyzed.
