Failure of structures is often preceded by localized damages in critical regions. For concrete structures, damage occurs in the form of cracking. A point sensor (e.g., a small strain gauge) intersecting a crack is heavily stretched and may therefore break and lose its functionality at an early stage of the damage process. On the other hand, a sensor that happens to be between two cracks may not capture the cracking (and hence the damage) at all. The goal of this project is to develop a long gauge length sensor based on the optical fiber, which can obtain the average strain over a relatively large region (within which damage has occurred). An inclined fiber is embedded inside a strain hardening cementitious composite (SHCC) plate. When the SHCC is under tensile strain, multiple cracks will form, leading to increasing bending loss of the fiber at the cracks. With the plate cast into the critical zone of a structural member, the measurement of the optical loss of the fiber after overloading (e.g., due to an earthquake or unexpected impact) can reflect the strain and damage in the zone. Under service loading, fine cracks may also form along the sensor, but these cracks may self-heal when moisture is available. We expect the sensor to have different response under dynamic loading for unhealed cracks (with fibers deforming within the cracks) and healed ones (where the cracks are close). The sensor can hence serve an additional purpose to monitor the occurrence of self-healing, which is important for long-term durability.
The student will be involved in the fabrication of sensors, its installation into structural members and testing to verify sensor performance.
Students will learn about optical sensor design, instrumentation for optical sensing as well as the basic behavior of strain hardening cementitious composites.