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

钢和其他金属结构在反复载荷下容易开裂。各种类型的载荷，如波浪、机械振动、风致振动、交通或其他循环载荷，可以在这些金属结构的关键位置诱导裂纹的逐渐形成和增长。容易开裂的结构存在于许多领域，包括工业设施、制造业、化学加工、海洋和近海结构、船舶、管道、运输基础设施和与能源相关的基础设施。目前修复这些裂缝的技术通常需要焊接或螺栓连接。这需要使用重型设备，但在进入场地受限的情况下，这可能是不可行的。此外，这些操作可能会由于产生热量和火花（在某些情况下可能导致爆炸）或由于噪音而导致结构的服务中断，这可能会对居住者产生不利影响。该项目将通过引入一种无需使用重型设备、不需要焊接或螺栓连接的修复技术来解决这些缺点。碳纤维增强聚合物（CFRP）复合材料贴片可以粘结在裂纹钢结构表面以弥合裂纹，从而减小裂纹尖端附近的应力范围，提高裂纹构件的疲劳寿命。这些补丁的好处可以通过对补丁进行预应力来增加，这样它们就会在裂缝尖端附近和裂缝前缘之前产生压应力。然而，目前对这些复合贴片进行预应力的技术通常需要使用笨重的固定装置和坚硬的反应框架，这在实验室应用中可能是可行的，但在现场是不切实际的。提出的研究利用形状记忆合金（SMA）钢丝的形状记忆效应来实现这种预应力效应。通过抑制预拉伸SMA钢丝的热致收缩，并使用碳纤维弥合裂纹，所提出的SMA/CFRP补片可以显着提高裂纹钢元件的疲劳寿命。该技术具有明显的优势，不需要使用重型设备，因此可以安装在交通不便的地方。此外，由于安装不需要焊接或以其他方式产生火花、高温或明火，因此可以在有限或不中断服务的情况下实施。

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.