A fatigue detecting sensor that enables easy and precise estimation of fatigue damage of machines and structures was developed, based on the crack growth characteristics of metal. The sensor is composed of a metal foil with a single edge notch and a base metal foil. The two metal foils are bonded at the both far ends. The sensor is attached with an adhesive to the surface of structural member which is subjected to cyclic loads. The fatigue damage of the member is detected as the fatigue crack initiation from the notch tip of the sensor. The fatigue crack growth rate is independent of the crack length. The metal foil of the sensor is given pre-tension, so the sensor has stable crack growth characteristics independent of the average strain. The crack growth length is measured in a certain period after the installation. The length is converted to the fatigue damage of the member during the sampling period of sensor installation. Since no measuring instrument and signal wiring is necessary, the diagnosis procedure becomes easy and the cost for structural health monitoring could be reduced. With such small size of the sensor as conventional strain gages, the pin-pointed application of the sensor to the hot spot of structural stress concentration, where is important for the fatigue strength estimation of welded structures, is possible. Therefore, precise fatigue remaining life assessment could be carried out. Sensors with several strain ranges were developed, so application to vast strain range is possible. Even such a small strain range as 1/10000 is able to be detected. The sensors have been applied to various products like steel bridges, rolling stocks, ships, etc.

Bridge Engineering 163 Issue BE1Remaining life estimation by fatigue damage sensor Nihei et al.

The performance of an engine valve encapsulating sodium in the hollow was analyzed theoretically. Hollow valves are occasionally used due to the light weight to enhance efficiency and maximum rotation speed. Further, hollow valves encapsulating sodium in the hollow have been practically applied so that the heat transfer of the hollow valve is improved. However, there are little report on the performance of the sodium encapsulated engine valve quantitatively. In the present study, the heat transfer characteristics of a hollow valve and a sodium encapsulated valve were analyzed in comparison to a solid valve, by finite element method (FEM). As a result, the maximum temperature of the sodium encapsulated valve was lower by 413 or 115 than that of the hollow valve or the solid valve. Therefore, it has been concluded that the enhancement of efficiency and maximum rotation speed is possible without decreasing in the thermal performance by replacing the conventional solid or hollow valve to the sodium encapsulating valves.

SummaryThe characteristics of Fatigue Damage Sensors (FDS) that are in use for fatigue life estimation of monitoring structural members in ship structures are discussed in order to improve prediction accuracy of estimated fatigue life exposed to random wave loads such as storms under various loading conditions peculiar to ship structures. Coefficients affected by loading histories against constant amplitude loading and mean stress levels are introduced for the estimation procedure using FDSs and confirmed by a series of fatigue testing and numerical simulations. This newly proposed fatigue life estimation procedure using obtained coefficients is checked by comparison results of fatigue test for large size structural model on which FDSs and strain gauges are provided simultaneously and to which random loads by assumption of storm patterns are applied under various mean stress levels.

We examined the deterioration of a tie pad material in relation to its dynamic fatigue when inserted between ties and rails. For the purpose of this investigation, we measured the tackifying and cracking phenomena of natural vulcanized rubbers by Demattia Flexing Machine. As the result, we found that the cracking phenomena appeared on the tension side of the test pieces and tackifying phenomena did on the compression side. We confirmed that it was very important to choose the most effective antioxidant under repetition of dynamic deformation.