SU1054673A2 - Capacitance transducer for gauging length of fatigue crack - Google Patents

Description

110 The invention relates to a measuring technique, namely, methods for monitoring the state of the surface of parts made of conductive structural materials, rials, and can be used to study fatigue cracks of complex configuration. According to the main author. St. A ff 669181 is known for a capacitive sensor for measuring the length of a fatigue crack, comprising an insulating substrate and a comb plate placed on the substrate. The teeth of the plate are made of different widths, monotonously varying over the length of the plate C 3: However, this sensor does not allow to determine the coordinate of the point of origin of the branching crack, since the change in capacitance it characterizes only the length and direction of crack development. The purpose of the invention is to determine the coordinates of a point of origin of a branched crack. The goal is achieved by the fact that a capacitive sensor for measuring the length of a fatigue crack is provided with a jumper connecting the ends of the comb plate and a second output terminal placed on this jumper. This makes it possible, along with the change in the length of the fatigue crack, to determine the coordinates of the origin of the branch of the crack. Figure 1 shows the proposed sensor, a General view; figure 2 is the same, a longitudinal section; FIG. 3 shows a block scheme of the measuring system to which the sensor is connected during operation; in fig. - time diagram of the sensor capacitance change; Figure 5 is the same, changes in its resistance. A capacitive sensor for measuring the length of a fatigue crack contains 732. an insulating substrate 1 and a conductive lining 2 placed on the substrate 1. Teeth 3 lining 2 are of different widths, monotonically varying along the length of the lining, the 06 plate has a current lead, the second current lead 5. placed on jumper 6 The sensor works as follows. Before starting the test, a sensor is glued onto the part 7 and is connected to the input of the measuring system containing the switch 8, which connects the wires from the terminals t and 5 and from. the test part 7 having current output 9. sensor capacitance meter 10 relative to part 7 and sensor resistance meter 11. The outputs of the meters 10 and 11 are connected to the recorder 12. In the process of growth, the fracture crosses the teeth 3 of the plates 2 and breaks them, the total resistance of the sensor changes. The capacitance of the sensor is constant. In the case of a branched crack, it is closest to the point; The origin of the tooth 3 is broken in two places (Fig. 3). as a result, the section of the tooth between the cracks is no longer electrically connected to the lining 2, and the sensor capacitance decreases. FIG. and 5 points corresponding to this event are marked with an asterisk. Thus, the moment of the first sensor capacitance change indicates the time at which the split cracks originated, and the resistance of the sensor between the current leads L and 5 measured at the same time corresponds to the point's coordinate. Using the proposed sensor to control branch cracks will allow you to easily and reliably investigate the fatigue processes of welds, parts made of composite materials, and other elements operating in difficult operating conditions.

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Claims (1)

CAPACITIVE SENSOR FOR MEASURING LENGTH OF FATIGUE CRACK on ed. St. N ¹ 669181 |