Abstract
Sensors for structural health monitoring (SHM) need to be permanently integrated on structures and withstand the harsh service environments, which has been a big challenge for the application of SHM in aircrafts. This paper focuses on the durability of flexible eddy current array (FECA) sensors in harsh service environments of aircrafts, including vibration environment and several typical exposed environments. First, a kind of FECA sensor is illustrated and its integration method is proposed. Moreover, in order to study the durability of the sensor in vibration environment, the modal analysis is performed by the finite element method. According to the simulation results, the durability experiment in vibration environment is carried out under the fourth order vibration mode, which makes the sensor suffer the harshest vibration loads. During the vibration experiment, output signals of the sensor keep stable and the sensor is well bonded to the structure, which shows the integrated sensor has high durability in vibration environment. Finally, the durability of integrated sensors is separately tested in three exposed environments, including salt fog corrosion environment, fluid immersion environment, as well as hygrothermal and ultraviolet-radiation environment. After these environmental exposure experiments, all sensors are well bonded to structures and can effectively monitor fatigue cracks, which shows great durability. Therefore, FECA sensors can survive in harsh service environments of aircrafts, which provides important support for the engineering applications of FECA sensors.
Highlights
Sensors for structural health monitoring (SHM) need to be permanently integrated on structures and withstand the harsh service environments, which has been a big challenge for the application of SHM in aircrafts
Compared with other related researches, the innovation of this paper is to propose an integration method of the flexible eddy current array (FECA) sensor and study the durability of FECA sensors in vibration environment and several typical exposed environments for the first time, which provides important support for the engineering applications of FECA sensors
During the use of the aircraft structure, sensors are exposed to a variety of exposure environments, which will adversely affect the normal operation of FECA sensors, such as sealant aging and failure, metal corrosion, insulation failure, etc
Summary
In the use of aircraft structure, airflow and engine working can cause structural vibration. This area is in a state of reciprocating bending, and the frequency reaches 1005 times a second Under such a large deformation and high frequency change state, the adhesion between the sensor and the specimen is very likely to fail. The frequency sweep is completed at an excitation magnitude of 0.8 g, and the resonance frequency of the specimen in the fourth order vibration mode is 1055 Hz. the blue curved band region with zero displacement of the specimen in the fourth-order mode always exists during the experiments. During the formal experiment, the vibration frequency is set to 1055 Hz, and excitation magnitude gradually increases from 0.8 to 8 g At this moment, the cycle counting start and signals from the FECA sensor are www.nature.com/scientificreports/ Figure 10. It shows that the integrated sensor has high durability in vibration environment and can effectively resist the impact of the vibration environment
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