The durability of flexible eddy current array (FECA) sensors in harsh service environments

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.

Seismic Behavior of Reinforced Concrete Frame Joints in Coastal Atmosphere

The study aims to research the influence of salt fog corrosion cycles on seismic performance of reinforced concrete (RC) frame beam-column joints in coastal atmosphere. Based on low cyclic loading tests of six RC frame beam-column joint specimens, this study analyses the failure patterns, hysteresis loops, load carrying capacity, displacement, backbone curves, and energy dissipation capacity of corrosion-damaged RC frame beam-column joints. The effect of salt fog corrosion cycles and axial compression ratios are tested repeatedly. The results show that with the same level of axial compression of the frame joint specimens, as the increase of salt fog cycles, the strength, ductility, energy dissipation, bearing capacity, and deformation capacity of joints degenerated to different degrees． When the corrosion level is the same, the stiffness degradation appeared to be more apparent as the increase of axial compression ratio. Then, the behavior degeneration rule of the RC frame beam-column joints is analyzed and formed according to the results of the test; the degeneration restoring force models of corroded RC frame beam-column joints is formed and verified based on Clough’s three-line degenerate restoring force model and the introduction to cyclic degeneration index. The results show that the restoring force model can better describe the hysteresis characteristics of the beam-column joints of corroded RC frames. The research is a theoretical reference for the seismic analysis of the RC frame structure affected by coastal atmospheric environment.

Corrosion Resistance Testing of the Galvanized Sheet Metal Braze Welding Joints

The joining of the galvanized sheet is normally difficult to be done with classical methods, requiring special attention to the specific problems involved during the welding process. This paper presents the development of the joint technology by Cold Metal Transfer (CMT) of galvanized steel sheet using as filler material a CuSi wire electrode. The salt fog corrosion test was made to certify anticorrosive protection of the galvanized sheet metal joints. This test revealed a minimal deterioration of the galvanized zinc coating during welding and also confirms that using adequate technology galvanized steel can be weld without affected anticorrosive protection of the zinc layer.Experimental researches include optimization of the welding technology using CMT concept; technical skill development solutions of the joints; elaboration and implementation of laboratory advanced technology; experimentation and demonstration of technology functionality by obtaining of braze welded joints corrosion resistant.