SU1483328A1 - Device for determining material hardness - Google Patents

Abstract

The invention relates to the study of the mechanical properties of materials, in particular to the determination of hardness by applying a single shock force. The purpose of the invention is to improve the accuracy and performance of measurements by assessing the hardness of the extreme value of the second derivative of the shock acceleration of the striker. The implementation of such an assessment is carried out by a device containing two series-connected differentiators in the measuring path. 2 Il.

Description

one

The invention relates to the study of the mechanical properties of materials, in particular to the determination of hardness by applying a single shock force.

The purpose of the invention is to improve the accuracy and performance of measurements.

Fig. 01 shows graphs of the change in the temporal characteristics of the shock acceleration and its derivatives; Fig 2 is a block diagram of the proposed device,

The device comprises a guide tube 1, a striker 2 with an indenter 3, a piezo-accelerometer 4 fixed on the striker 2, connected in series to a matching amplifier 5, whose input is connected to a piezo accelerometer 4, a low-pass filter 6, the first 7 and second 8 differentiators, a peak detector 9, an analog-to-digital converter 10, a decoder 11 and a digital indicator 12, and a comparator 13, whose input is connected to the output of the second differentiator 8, and the output to the control input of the analog-digital converter 10.

The device works as follows.

When the striker 2 collides with the product, the piezo-accelerometer 4 produces a signal proportional to the shock acceleration. In the course of the impact, under the action of the penetrating striker 2, the material first experiences elastic ,. and then plastic deformations. Changes in the mechanical stress-strain state of a material in

The contact zone is caused by changes in the nature of the force interaction of the striker with the material, which leads to changes in the shape of the fronts of the shock acceleration pulse a (t) (Fig. 1, a). The change in the nature of the force interaction is most pronounced on the signal, proportional to the second derivative of the shock acceleration, which has two clearly pronounced extremes at the stage of insertion of the striker into the material. The magnitudes of both (extremes are related linearly to the hardness of the material

H1) KPGT Ј “-P

where K gh - proportionality coefficient.

To implement the described hardness evaluation using pulse parameters a (t), the signal from the piezo accelerometer 4 passes through the matching amplifier 5 and the low-pass filter 6 (Fig. 1a), in the first differentiator 7 is converted into a signal proportional to the sharpness of the striker movement ( figure 2, b). The second differentiator 8 generates a signal proportional to the second derivative of the shock acceleration (FIG. 2, c). The extreme value of this signal, which is linearly related to the hardness of the material, is allocated by the peak detector 9 and is fed to one of the inputs of the analog-digital converter 10, the control input of which receives a voltage pulse from the comparator 13 at the moment when the voltage of the second signal production483328 "

water from the acceleration at the input of the comparator 13 will exceed the set threshold value (figure 2, d). Analog-to-digital converter 10 converts the signal from peak detector 9 into a digital code that, when passed through a decoder 11, is displayed on a digital indicator 12 in terms of the hardness of the material.

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Claims (1)

Invention Formula A device for determining the hardness of materials containing a guide tube, a head with an indenter, a piezo accelerometer ,. fixed on the striker connected in series matching amplifier, the input of which is connected to a pie-zaxaxometer, filter low pass and first differentiator, second differentiator, peak detector, analog-to-digital converter, the signal input of which Connected to a peak detector, a comparator and a digital indicator, characterized in that, in order to improve the accuracy and performance of measurements, it equipped with a decoder, the input of which is connected to the output of the analog-digital converter, and the output - to the input of the digital indicator, the input of the second differentiator is connected to the output the first differentiator, and the output - with the inputs of the peak detector and comparator, the output of which is connected to. control input of the analog-to-digital converter. but Am f five figure 1 Fsh.g