An intelligent sensor system for monitoring fatigue damage in welded steel components

A sensor and data storage system that monitors fatigue damage in load-bearing steel components is described. The sensor is a thin steel sheet measuring 50 × 20 mm, with a pre-crack in its centre. It is fixed next to a welded joint on the component under test. It follows the component's flexions in service and begins to fatigue, thereby lengthening its crack. Crack length is measured using a simple circuit and is recorded using a microcontroller. This is achieved by laying electrically conductive tracks on the sensor in a direction perpendicular to that of the crack. They are connected to the microcontroller's analogue to digital converter via resistors in a potential divider arrangement. When the crack propagates past a track, it breaks its continuity, thereby changing the network's output voltage. The crack length is represented by the analogue voltage recorded. The microcontroller is configured to operate in low power mode, waking up at predetermined intervals to read the sensor. In this way, it consumes very little current and can operate over many years. The data are stored in memory and can be remotely downloaded from a distance of up to 30 m using Bluetooth™ technology, to a PC. It can then be analysed to predict the component's useful life.