Micro-Macro Modeling of the External Strengthening of Concrete with Fiber Reinforced Polymer: Phase I, II, and III

摘要

The issue of moisture diffusion in composite materials is important because of its associated problem of freeze and thaw. The volumetric expansion of water when it freezes to form ice results in stress concentrations at the inclusion tip that may synergistically interact with the residual tensile stresses in a laminate at low temperatures to initiate a crack. In addition, understanding the long-term effect of daily and/or seasonal freeze-thaw cycling on crack growth is of vital importance for structural durability. A theoretical framework for the calculation of the stress intensity factor, KI, of a preexisting crack in a composite structure due to the phase transition of trapped moisture. The constrained volume expansion of trapped moisture is postulated to be the crack driving force. The principle of minimum strain energy is employed to calculate the elastic field within an orthotropic laminate containing an idealized elliptic inclusion in the form of ice. It is postulated that a slender elliptical inclusion can be used to approximate the stress field at the crack face, which can be used to calculate the stress intensity factor for the crack. The model developed as above, is verified. The verification is based on comparisons of the stresses in an elliptic elastic inclusion and the stress intensity factor with a special isotropy and with finite element analysis for the case of orthotropy. The results indicate that the stress state in a slender elliptic elastic inclusion can be used to approximate the stress field at the crack tip, which could subsequently be adopted to determine the stress intensity factor. Analyses of the delamination and fatigue life prediction for freeze-thaw cycling are provided as specific applications of the model.