I-CORPS Teams: SMA/FRP Patches for Repair of Metallic Structures

University Of Houston, Houston TX

Investigators

Abstract

Steel and other metallic structures may be susceptible to cracking when subjected to repeated loading. Various types of loads, such as waves, vibrations due to machinery, wind-induced vibrations, traffic or other cyclic loads, can induce gradual formation and growth of cracks at critical locations in these metallic structures. Structures that are susceptible to be cracking can be found in many sectors including industrial facilities, manufacturing, chemical processing, marine and off-shore structures and vessels, pipelines, transportation infrastructure, and energy-related infrastructure. Current techniques to repair these cracks typically require welding or bolting. This requires the use of heavy equipment, which may not be feasible when access to the site is limited. Further, these operations may require a disruption of service of the structure due to the formation of heat and sparks (which could lead to explosion in some cases) or due to noise, which could adversely affect occupants. This project will address these shortcomings by introducing a repair technique that can be implemented without the use of heavy equipment and which does not require welding or bolting. Carbon fiber reinforced polymer (CFRP) composite patches can be bonded to the surface of cracked steel structures to bridge the cracks, thereby reducing the stress range near the crack tip and increasing the fatigue life of the cracked element. The benefit of these patches can be increased by prestressing the patches, such that they induce compressive stresses near the crack tip and ahead of the crack front. However, current techniques to prestress these composite patches typically require the use of cumbersome and heavy fixtures and a stiff reaction frame, which may be feasible in laboratory applications but impractical in the field. The proposed study exploits the so-called shape memory effect of shape memory alloy (SMA) wires to achieve this prestressing effect. By restraining the thermally induced contraction of prestrained SMA wires and using carbon fibers to bridge the crack, the proposed SMA/CFRP patches can substantially increase the fatigue life of cracked steel elements. This technology has the distinct advantages that it does not require the use of heavy equipment, and therefore can be installed in locations where access is limited. Further, since the installation does not require welding or otherwise generate sparks, high heat, or open flames, it can be implemented with limited or no disruption of service.