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The X-ray CT method was applied to evaluate micro-damage -namely, deterioration of concrete specimens under cyclic uniaxial loading tests. The μ-focus X-ray CT scanner was used. Concrete cylinders with a diameter of 50 mm and a length of 100 mm were prepared as specimens. Cyclic uniaxial loading tests were conducted on the specimens. The X-ray CT images of the specimens were taken at the loading level 0, 60, 70, 80 and 90 percent of their uniaxial compressive strength. For three dimensional CT images of the specimen, the Three Dimensional Medial Axis Analysis (3DMA) method was applied to evaluate porosity and width, length, persistence of cracks which represent deterioration of the specimen. As the results, slight micro-fracturing occurs until a loading level R = 60%, and starts to increase at R of 60% to 70%. The cracking occurs in a part of the mortar near boundary between aggregate and mortar, and the crack links to another crack with increasing loading level. The degree of cracking varies according to the position dependent on the final apparent fracture surface of the specimen. It is concluded that the X-ray CT method with 3DMA is effective for not only evaluating the state of micro-cracking within the specimen, but also estimating the process of deterioration of the specimen with an increasing loading level.

Conventional eddy current testing (ECT) using a pickup coil probe is widely employed for the detection of structural cracks. However, the inspection of conventional ECT for steel structures is difficult because of the magnetic noise caused by the nonuniform permeability of steel. To combat this challenge, we have developed a small magnetic sensor probe with a dual-channel tunneling magnetoresistance sensor that is capable of reducing magnetic noise. Applying this probe to a complicated component of steel structures—such as the welds joining a U-shaped rib and deck plate together—requires the reduction of signal fluctuation caused by the distance (liftoff) variations between the sensor probe and the subject. In this study, the fundamental crack signal and the liftoff signal were investigated with the dual-channel sensor. The results showed that the liftoff signals could be reduced and differentiated from the crack signals by the differential parameters of the dual-channel sensor. In addition, we proposed an extraction technique for the crack signal using the Lissajous curve of the differential parameters. The extraction technique could be applied to the inspections not only for flat plates but also for welded angles to detect cracks without the influence of the liftoff signal.

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ABSTRACT:In recent years, the world has seen many natural disasters such as earthquakes, floods, and tsunamis. In particular, Japan experienced a very bad flood that damaged many bridges in Sayo, Shiso and Mimasaka along several branched rivers of the Chigusa and Ibo rivers in 2009. We need to develop a new rescue structure to survive such disasters. We have to consider how to recover a damaged structure or how to rebuild a new type of rescue system as soon as possible after a disaster occurs because time is of the essence when trying to save lives. To this end, we have created an optimum deployable bridge based on an origami folding structure determined by computer analysis. Such computer analysis based on origami is a skill that is useful for making new designs for light structures or achieving high stiffness in mechanics. We wish to use this computing skill to help people recover from natural disasters. To design a new emergency bridge called MobilebridgeTM we have originally created an optimization truss by computing mechanics. We realize that it is necessary to develop this Mobilebridge as soon as possible to be ready for the next natural disaster.

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