Papers by Author: Xin Jun Wu

Abstract: Cables are used as critical structure components for suspended and cable-stayed bridges. It has been recently increased the need for inspection methods to assess the conditions of the cables due to owners concern about the operability and safety of such aging structures. An alternative technique is being developed in this paper. The magnetostrictive guided wave technology is used to test broken wires. The suitability of this method is studied through application tests on experimental setups, lab-made cables with simulated broken wires and field test. Test Results indicate that this technique can detect two broken wires away exceeding two meters and propagating over one hundred meters. It is a promising method for nondestructive testing of bridge cables.

Abstract: Prestressing strands are widely used in civil structures. The health monitoring of the strands is an important factor in evaluating the structural safety. This paper aims to improve the detection sensitivity of the guided wave technique in strands by wavelet processing. Groove defects with different depths are cut in the wire and detected by magnetostrictive sensors. The wavelet threshold method is employed to denoise the signals. In this study, the suitable thresholds are related to the median value of the coefficients. Results show that defects above 3.6% cross section loss can be found after this processing. Moreover, the amplitudes of the defect signals are related to the defect depths, which can be used to size the defects.

Abstract: Corrosion of prestressing strands is a main durability issue for prestressing structures. In general, the corrosion zones of strands are hidden in structures which lead to be hardly inspected by traditional methods. An instrument for detecting the non visible corrosion of prestressing strands using magnetostrictive guided waves is provided. The instrument is described in detail. The workflow to detect the strands is provided. Field trials and laboratory experiments show that the information of position, length and amount of the corrosion can be obtained from the data. The instrument provides support for ensuring the safety of prestressing structures.

Abstract: Pulsed eddy current (PEC) technique has been successfully used for measuring wall thinning of carbon steel equipments without removal of the insulation. In field applications, the probe performance decreases in presence of ferromagnetic claddings. This paper presents a method based on saturation magnetization to solve this problem. The main principle of this method is to weaken the magnetic shielding effect of the cladding by magnetizing it to saturation. A U-shaped magnetizer is designed to realize this method. Contrast experiments are performed on a Q235 steel plate covered by a galvanized steel cladding. The experiment results show that the thickness measurement range and lift-off range are increased by applying this method to the common PEC probe.