SU896568A1 - Method and device for detecting developing cracks - Google Patents

Description

(54) METHOD OF DETECTING DEVELOPING

DEFECTS AND DEVICE FOR ITS IMPLEMENTATION

The invention relates to non-destructive testing and can be used to control the quality of materials and products using acoustic emission. A known method of detecting developing defects is that they receive signals of actual emission, amplify them, compare amplitudes of signals with a given detection threshold, and envelope the detected signals of the REED, a device for implementing this method that contains series-connected transducers, an amplifier, and a peak detector. and amplitude discriminator units for measuring and recording acoustic emission parameters pj The disadvantage of this method and device is insufficient The reliability of the detection of several simultaneously developing defects in the product. The closest in technical essence to the invention is a method for detecting developing defects, namely, loading a product, receiving acoustic emission signals, at various points on the product surface, amplifying and detecting signals, setting a detection threshold and when the amplitude of the signal exceeds the detection threshold separately register signals from each reception point 1; The closest in technical essence to the invention is a device comprising several channels for receiving signals Emission, each of which consists of series-connected converters, an amplifier, a peak detector, an adjustable threshold circuit and a recorder. The disadvantage of these methods and devices is that when a high intensity acoustic emission signals occur, there is a loss of useful information, and a high level of noise limits the scope of application of the method and device data. The purpose of the invention is to reduce information loss and expand the scope of application. This goal is achieved by mixing the detected signals from all reception points, delaying the mixed signal and setting a detection threshold for it. The device is equipped with a signal mixer connected to the outputs of peak detectors of each channel, a delay circuit, the output of which is connected to the second inputs of adjustable threshold circuits, and an initial threshold setting circuit, the output of which is connected to the mixer input. The drawing shows a block diagram of a device for implementing the method. The device contains several channels for receiving acoustic emission signals, each of which consists of a series-connected transducer 1, amplifier 2, peak detector 3, adjustable horn circuit 4 and recorder 5, mixer 6, whose inputs are connected to the outputs of peak detectors 3 of each channel, 7 delays, the input of which is connected to the output of the mixer 6, and the output to the second inputs of the adjustable threshold circuits, and the initial setting threshold schemes 8, the output of which is connected to the input of the mixer 6. The device operates after dukndim.

Acoustic emission signals are received by transducers 1 at various points on the surface of the product, amplified by amplifiers 2, and fed to a peak detector 3, where the envelope signal is highlighted.

The iododetected signal is fed to the input of adjustable threshold circuits 4 of each channel, in which the current value of the voltage of the signal envelope is compared with the varying value of the detection threshold.

Claims (2)

1. A method for detecting developing defects, consisting in loading the products, receiving acoustic emission signals at various points on the surface of the product, amplifying and detecting the signals, setting the detection threshold, and when the amplitude of the detection signal exceeds the detection threshold, signals from each receiving point differing from that, in order to reduce, in case of exceeding this value, they go to the corresponding recorders 5. The detected signals from the peak detectors go to the mixer 6, where they are mixed and generated signal varying threshold. This signal is delayed in delay circuit 7 by a time equal to the rise time of the leading edge of the signal envelope. The voltage from the output of the delay circuit 7 is fed to the second inputs of the adjustable threshold circuits 4 of each channel, which ensures that only the channel that received the signal goes first to the recorder 5. Scheme 8 of the initial threshold setting provides the initial voltage for detecting the signal at mixer 6. The constant time of the peak detectors 3 is chosen such that the varying voltage of the trigger threshold after one acoustic emission event does not reach the initial threshold setting until the reverberation of this signal ends control object. In the presence of a continuous interfering signal, the threshold level rises above the level of the interfering signal, thus excluding the possibility of its registration. Thus, the proposed method for detecting developing defects and the device for its implementation reduce information loss and expand the scope of application due to the possibility of monitoring products under conditions of continuous acoustic interference. Claim 58 for loss of information and extension of application, mix the detected signals from all reception points, delay the mixed signal and set its detection threshold. 2. An apparatus for carrying out the method of claim 1, comprising several channels for receiving acoustic emission signals, each of which consists of a series-connected transducer, amplifier, peak detector, adjustable threshold circuit, and recorder, is so that it is equipped with 8 connected to the outputs of the peak detectors of each channel of the signal mixer, a delay circuit whose output is connected to the second inputs of adjustable threshold circuits, and a threshold initial setting circuit whose output is connected to input mixer. Sources of information taken into account during the examination 1.Greshnikov V.A., Drobot Yu.V. Acoustic emission. Publishing of standards. M., 1976, p. 91. 2. US patent JP 3822586, cl. G 01 N 29/04, 1974 (prototype).