Flow-induced vibration plays a positive role on heat transfer enhancement. Meanwhile, it is also a negative factor for fatigue strength. Satisfying the fatigue strength is the primary prerequisite for heat transfer enhancement. This paper numerically studied the flow-induced vibration of planar elastic tube bundle based on a two-way fluid-structure interaction (FSI) calculation. The numerical calculation involved the unsteady, three-dimensional incompressible governing equations solved with finite volume approach and the dynamic balance equation of planar elastic tube bundle solved with finite element method combined with dynamic mesh scheme. The numerical approach was verified by comparing with the published experimental results. Then the vibration trajectory, deformation and stress contour of planar elastic tube bundle were all studied. Results show that the combined movement of planar elastic tube bundle represents the agitation from inside to outside. The vibration of out-of-plane is the main vibration form with the typically sinusoidal behavior because the magnitude of displacement along the out-of-plane direction is the 100 times than the value of in-plane direction. The dangerous point locates in the innermost tube where the equivalent stress can be utilized to study the multiaxial fatigue of planar elastic tube bundle due to the alternating stress concentration. In the velocity range of 0.2-3 m/s, it is inferred that the vibration amplitude plays a role on the stress response and the stress amplitude is susceptible to the fluid velocity. This research paves a way for studying the fatigue strength of planar elastic tube bundle by flow-induced vibration.

The micromechanical properties of the steel-fiber-reinforced cementitious composites with different water-binder ratios and silica fume contents were studied by nanoindentation. The elastic modulus, indentation hardness, total input energy, and ratio of the elastic deformation energy to the total input energy were analyzed in the interfacial transition zone (ITZ) and the cement matrix. The results show that with the reduction of water-binder ratio in the range of 0.18–0.24, the elastic modulus, indentation hardness, elastic deformation capacity, and energy dissipation capacity increased in the ITZ and cement matrix, and the increase of the ITZ was greater than that of the matrix, yet the ITZ did not disappear. With the increase of silica fume content in the range of 0–30%, the weak ITZ was gradually strengthened or even disappeared. In terms of obtaining the stronger ITZ, adding silica fume is more effective than reducing the water-binder ratio. When the water-binder ratio was high at 0.24, large silica fume contents (30%) had significant effects on enhancing the micromechanical properties of the ITZ and matrix. At a low water-binder ratio of 0.18, large silica fume contents (30%) enhanced the micromechanical properties of the ITZ while degrading those of the cement matrix.