Guided wave tomography has shown great potential for quantitative nondestructive evaluation in structural health monitoring. An improved simultaneous iterative reconstruction technique (SIRT) combining genetic algorithm (GA) is presented in order to improve image quality of guided wave tomography. The simulated reconstructed images of flawed plate and pipe using usual SIRT and improved SIRT methods have been compared quantitatively and qualitatively.
The fracture properties of the thermo-setting materials of epoxy asphalt mixture were evaluated based on J-integral concept and ultimate strength and compared to that of HMA with thermo-plastic binder materials. Totally 60 specimens cored from SGC with different notches were tested with SCB test under a temperature of -10°C and 20°C. The experimental results reveals that epoxy asphalt mixture has a super higher resistance of fracture at low temperature than thermo-plastic HMA due to its super high tensile strength and flexibility, and the influences of temperature on the fracture resistance of EAM is not so significant as that of thermo-plastic HMA. Good repeatability of SCB test results indicates the capability of the SCB test to be useful for measuring the fracture toughness of epoxy asphalt mixture.
The detection of localized defects such as cracks and corrosion in pipes using guided waves has been shown to be an effective nondestructive evaluation technique for structural health monitoring (SHM). Cross borehole tomography in seismology is introduced into the guided wave inspection of a pipe when the pipe is considered as an unwrapped plate. Guided waves propagating in pipe with a crack defect are simulated using the finite element model and the arrival times for the fastest modes are extracted and sent to the tomographic algorithm. The tomographic reconstruction is based on the simultaneous iterative reconstruction technique (SIRT). For some cylindrical shell geometries such as stacked storage tanks, access to the entire circumference of the structure could be impractical or even impossible, three different image fusion techniques are used to enhance the image equality reconstructed from the incomplete datasets. The results show that the defect is more pronounced after imaging fusion.
Signal enhancement of ultrasonic guided waves is studied using time reversal technique. The defect in pipe is detected by activating single mode guided waves L(0,2) at the center frequency of 70 kHz. Time-reversal technique is used to further enhance the defect detection capability. A method to identify the defect is described on a finite element model. Numerical results show that the time reversal technique has the ability to evidently enhance the amplitude of damage reflected wave and improve the detection efficiency of defect.
A newly developed skid resistance measurement system ViaFriction is studied, which can detect the skid resistance under conditions with a variable slip rate, just like the braking process with an anti-lock braking system (ABS). Until now there is still no evaluation framework on the testing results from this test system. In the scope of this paper, the impact from the temperature of the ambient air, the road surface, the tire and the water for the test as well as the influence of the driving speed of the test vehicle on the testing results of the ViaFriction was identified and transferred to a correction function. This total correction algorithm for the measurement results of the ViaFriction allows a comparative analysis of the friction coefficients at different speeds and under different testing temperatures.
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