CCF300/5228A aero composite stiffened panels achieved absorbing saturation in hygrothermal condition (70 C distilled water), whose absorbing process followed the Fick law. Many debonding and gaps of matrix to fibers could be observed after hygrothermal exposure by scanning electron microscope (SEM). Compressive experiments were conducted on unaged and aged composite stiffened panels. Failure modes of the two types of specimens are quite similar with several major ways, including the debonding and fracture of stiffeners together with the splitting and ripping of panel. Buckling patterns for both types of specimens are similar and characterized by buckling of panels between stiffeners and buckling of the middle two stiffeners. However, the bending direction of buckling mid-panel for aged specimens is opposite to that of the unaged at same position panel, which shows that hygrothermal condition influences the bending direction of buckling mid-panels seriously. There still exists a post-buckling process for aged specimens under axial compression, whose average buckling load and failure load decrease by 3.1% and 22.2% respectively, comparing to that of unaged specimens.
Aluminum alloy 2024-T4 specimens were exposed to atmosphere for 7, 12, and 20 years, respectively, to study long-term corrosion in a coastal environment. One-directional corrosion region and cross-directional corrosion region were defined according to corrosion characters. The statistical regularities, surface appearance, corrosion products, and cross-sectional morphology of both regions were investigated. It was found that the minimum remaining thicknesses of each region can be described by a normal distribution and linearly decrease as the exposure time is increased from 7 to 20 years. The corrosion pits, chlorine ions, and interlinked inner pits are promoting exfoliation, and the alloyÕs corrosion susceptibility along the long transverse direction is strongly location dependent due to the restrictions imposed by the side material.
Flexible eddy current array sensor has the characteristics of flexibility and light weight. It has a wide application prospect for surface crack monitoring of metal structures. In order to solve the problem of low sensitivity of crack identification of traditional flexible eddy current array sensor, the methods of changing the spacing between the excitation coil and the sensing coil (SES) of the sensor and pasting the permalloy film on one side of the sensor are adopted to improve the sensitivity of crack identification. Firstly, a finite element model is established to analyze the influence of the permalloy film on the eddy current density on the surface of the specimen and the influence of the SES on the sensitivity of crack identification of the sensor. The simulation results show that when the SES increases from 0.1 mm to 0.4 mm, the sensitivity of the three sensing coils of the sensor to crack identification increases by 144.96%, 181.63% and 136.36%, respectively. And the sensitivity of the sensor to crack identification is improved when the permalloy film is stuck on the upper surface of the sensor, which is up to 81.88%. Then, the experimental results show that when the SES increases from 0.1 mm to 0.4 mm, the sensitivity of the three sensing coils to crack identification increases by 114.68%, 161.66% and 131.24%, respectively. The sensitivity of the sensor to crack identification is increased by 68.21% when the permalloy film is pasted on the surface of the sensor. The error between simulation results and experimental results is introduced by lift-off. The research results can be used to improve the sensitivity of crack identification.
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