BS EN 4859:2019 pdf free.Aerospace series – Sensor based clamp load determination / high tensile bolts – Technical specification.
3.1 thin film ultrasonic transducer this kind of transducer applied to one of the two a bolt ends converts an electrical pulse in an ultrasonic wave travelling through the bolt body and transforms the reflected ultrasonic wave back into an electrical echo signal; the thereby used physical principles are the piezoelectric effect and its reversion
3.2 sputtering PVD (physical vapour deposition) process to apply thin films onto a substrate; under vacuum and by means of physical methods the base material becomes transformed into the gas phase; the condensing particles form the target layer on the substrate; sputtering is used to apply thin film ultrasonic transducer on bolts
3.3 clamp load needed axial force in a bolt to secure a save operation in a bolted joint
4 Clamp load measurements on bolts
4.1 Configuration of thin film transducer based sensor bolts Three layers coated onto the top of the bolt (a) form an ultrasonic thin film transducer. Applied in a vacuum process the transducer becomes a permanent part of the bolt (see Figure 1). The transducer consists of a piezoelectric thin film (b), followed by a protection layer (c) and an electrode metallization (d). Figure 2 shows different sensor bolts equipped with a thin film transducer.
The ultrasonic clamp load determination in sensor bolts is based on the pulse echo method. This technique works similar to systems like sonar or ultrasonic based material testing.
The thin film transducer placed at one of the bolt ends receives an alternating current (AC) pulse. The transducer follows the change of the electrical voltage by changing its length. The coupling of the transducer with the bolts surface leads to an ultrasonic wave travelling through the bolt. The ultrasonic waves are reflected by the opposite side of the bolt and travel back in direction of the transducer (see Figure 3). There, an echo signal can be detected. The transducer works as both, as sender and receiver. 1t is the time period between pulse sending and receiving the echo.
BS EN 4859 pdf download.