Composite Patch Configuration and Prestraining Effect on Crack Tip Deformation and Plastic Zone for Inclined Cracks

Bonding a composite patch to a cracked steel section is an efficient technique to reinforce cracked members or to delay fatigue crack growth in the structural elements. In this paper, a numerical study was performed to highlight the effect of bonded prestressed composite patches on the fracture parameters, such as crack tip opening displacement and the plastic zone. A three-dimensional finite element model of the double sided strengthened specimen is used to study the fracture behavior of an inclined edge crack under different combinations of modes I and II loading conditions. The influence of the pretension level, patch stiffness ratio, and fiber orientation on the crack tip opening displacement and plastic zone are also investigated. The introduction of a compressive stress by pretensioning of the composite patch prior to bonding produces a significant reduction in the crack tip opening displacement and plastic zone. This pretensioning reduces the crack tip driving force and subsequently reduces the fatigue crack growth rate, which increases the fatigue life of the structural member. Furthermore, the increase in the patch stiffness ratio reduces the amount of plastic zone and opening displacement at the crack tip. The effectiveness of the fiber orientation in the composite patch depends primarily on the loading directions and crack inclination angle.