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Effect of Pre-Strained CFRP Composite Patch on Cracked Steel Plates

HESHAM EL-EMAM, ALAA ELSISI, HANI SALM, MOHAMED SELEEM and HOSSAM SALLAM

Abstract


Externally bonding carbon fiber reinforced polymer (CFRP) patches to the damaged elements to arrest the crack propagation can be used to extend the fatigue life of steel bridges. In this paper, a numerical study was performed to highlight the effect of bonded pre-stressed composite patches on the fracture parameters, such as stress intensity factors, crack tip opening displacement and the plastic zone. A threedimensional finite element model of the double sided CFRP patch-strengthened specimen is used to study the fracture behavior of an inclined edge crack under different combinations of loading modes I and II. The influence of different prestrain levels, 0.058, 0.1, and 0.2% on the fracture parameters are also investigated. It is found that the introduction of a compressive stress by pre-tensioning of the CFRP patch prior to bonding produced a significant reduction of up to 70% in SIFs for different crack lengths, which led to increasing the remaining fatigue life of the steel member. For a given level of pre-stressing, the SIF obtained is zero until a specific level of the external applied stress is reached. The pretension of the composite patch developed crack closure mechanism, which reduced the crack tip opening displacement and plastic zone size by 42% and 80% respectively for a/w=0.3 at 0.2% prestrain level. Based on these results, the pre-strain level needed to accomplish a complete crack arrest can be predicted using the crack length/plate width ratio (a/W) and the fatigue load.

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