SU1744586A2 - Acoustic method of measuring microhardness - Google Patents

Abstract

The invention relates to the technique of controlling materials and products, can be used to determine the hardness and internal friction of the surface layer of materials and products and is an improvement of the basic invention according to the authors. St. Ns 1231430. The purpose of the invention is to increase the information content by additionally determining the equivalent loss resistance caused by internal friction in the local zone of the surface layer of the material. Acoustic method for measuring microhardness according to ed. St. isfe 1231430 consists in the additional determination of the equivalent loss resistance of the indenter before implantation, measuring the frequencies of the indenter's own resonance before and after implantation in the test sample, the difference between which determines the actual area of the indenter-contact area of the test sample. The j junction surface of the contact determines the mechanical loss of the acoustic system due to the acoustic emission of the indenter into the sample, taking into account which the equivalent resistance is obtained, which are rfjyc-induced by internal friction in the local zone of the surface layer. 2 ill., 1 tab.

Description

The invention relates to the technique of controlling materials and products, can be used to determine the hardness and internal friction of the surface layer of materials and products and is an improvement of the acoustic method of measuring microhardness according to the author. St. No. 1231430.

The purpose of the invention is to increase the information content by determining the equivalent loss resistance caused by internal friction in the local zone of the surface layer of the material,

FIG. 1 shows a block diagram of a device implementing the method; Fig. 2 illustrates the construction of an acoustic sensor.

A device that implements an acoustic method for measuring microhardness contains a PMT-3 microhardness meter (not shown), an acoustic sensor, and an acoustic sensor measuring unit.

The acoustic sensor contains a magnetostriction rod 1, which is fixed at one end to the load mass 2 of the rod, and the other end ends with an indenter 3. The exciter coil 4 is attached to the lower end of the weight 2 of the load rod, and the piezoelectric transducer 5 is attached to the upper end. Acoustic system formed by a magnetostrictive rod 1, an indenter 3, a mass of 2 load rod, excitation coil 4 and piezo

00

The transducer 5 is assembled into a single rigid unit and secured in the glass 6, which is placed in the housing 7 of the acoustic sensor so that the walls of the glass 6 at three points touch the plastic stops 8, adjusted by screws 9. The glass 6 with the speaker system is attached to the screw 10 the core 11 of the solenoid of the load mechanism, into the upper part of which the rod 12 is screwed, and through the washer 13 is suspended on the compensation spring 14, which with its lower end rests on the adjusting nut 15 screwed on the cover 16 of the acoustic housing 7 and yes chica. In the annular recess of the cover 16, a supporting and guide rod 12 of a nylon washer 17 is installed with a guide lug. The coil 18 of the solenoid is bolted 19 to the cover 16. On the upper part of the washer 13 weights 20 are mounted. The housing 7 of the acoustic sensor is attached to the upper bracket 21 of the PMT-3 microhardness tester loading mechanism. The magnetostrictive rod 1 with the indenter 3 passes through the hole in the hollow rod 22 of the PMT-3 microhardness meter indenter mechanism for balancing. The hollow rod 22 has a mounting screw 23. The measuring unit contains a power amplifier 24, a measuring amplifier 25, an indicator 26, a spectrum analyzer 27, a frequency meter 28.

The method is implemented as follows.

The test sample is fixed on the microscope stage so that the sample surface under study is parallel to the working plane of the stage. The stage of the microscope is turned to the extreme right position until it stops. Macro and microscrews move the microscope tube to focus the sample surface on focus. By rotating the micrometric screws of the microscope stage, the place required for measuring the microhardness is set. The stage is turned counterclockwise until it stops. The selected load on the indenter 3, depending on the hardness of the test material, is created by changing the coil 18 of the solenoid or by installing the weight 20 on the top of the washer 13. Rotate the mounting screw 23 to release the indenter 3 with the magnetostrictive rod 1 from the hollow rod 22.

Then, in a spherical indenter 3, resonant oscillations are excited by an oscillator formed by a piezoelectric transducer 5, a feedback amplifier 24 and a drive coil 4. The amplitude of oscillation of the indenter 3 is controlled by the voltage Vi from the piezoelectric transducer 5 using a measuring amplifier 25 and indicator 26. Spectrum analyzer 27 and frequency meter 28 measure the resonant frequency fi of the acoustic system consisting of the indenter 3, magnetostriction rod 1, excitation coil 4, mass 2 loads and a piezo transducer 5, as well as

bandwidth AF of an equivalent resonant circuit (Fig. 2), which determine the equivalent loss resistance g0 of an unloaded acoustic system according to the formula

 ,

where L is equivalent to the inductance of the equivalent resonant circuit.

Further, the acoustic system is pressed with a constant force to the test sample with an indenter 3. The introduction of the indenter 3 into the test sample causes the acoustic system parameters to change: the resonant frequency determined by the reactive part of the contact zone impedance

the indenter 3 is the test sample, and the quality factor determined by the active part of the impedance of the contact zone indenter 3 is the test sample.

Current feedback covering

the power amplifier 24 maintains a constant current in the excitation coil 4 and, therefore, the driving force applied to the speaker system. Under these conditions, the oscillation amplitude of the indenter

3, recorded by the indicator 26 in the form of a voltage U2, is proportional to the quality factor of the speaker system. Since the quality factor of the speaker system depends on the active component

the impedance of the contact area, which in turn is determined by the contact area and, consequently, the microhardness of the sample, indicator 26, the scale of which is calibrated in units of hardness, shows

microhardness of the sample.

Frequency meter 28 is measured by the changed value of the resonance frequency fa of the acoustic system and the change Af (f2-fi) is determined. which is proportional to Voi where VST is the area of the contact zone, indenter 3 is the test sample. By calibrating the instrument with an optical microscope of the PMT-3 microhardness meter, the area value Sk is determined from the change in frequency Af. Then calculate the equivalent resistance of the losses, due to internal friction in the local zone of the surface layer, according to the formula

r AU

 1/2

where AU Ui-U2; Ui and U2 - respectively, the voltage of the resonant oscillations of the unloaded acoustic system and after the introduction of the indenter 3 into the sample

rn Sk vJoF HA + / # B), 2V2a

BUT

AT

lg (1 -v} V1 + V 2V202

/

lg (1 -v) V1 + v 2ttfa

St

VSK (

a2 R

where /, E, v, O are, respectively, density, Young's modulus, Poisson’s ratio and shear wave velocity for the sample material; R is the radius of the spherical indenter; - dimensionless constants depending on the Poisson ratio, determined by the table.

In addition, the obtained information on the internal friction in the local zone of the sample material, which is an important mechanical characteristic of the structure and state of the material, provides studies of the distribution of the stress of the surface layers, adhesion

0

five

0

five

multilayer structures, phenomena of fatigue and other material properties caused by dislocation friction and its structure.

Claims (1)

The invention of the acoustic method of measuring microhardness by author. St. NS 1231430, characterized in that, in order to increase the information content, the equivalent loss resistance g 0 of the oscillating indenter before implantation is additionally determined, the frequencies of the indenter's own resonances are measured before and after the implantation, the actual area of the indenter-sample contact area is determined by the difference in measured frequencies , according to which the equivalent resistance hp of mechanical losses due to the acoustic waves emitted by the indenter into the sample is calculated, and the equivalent resistance rm sweat is determined p due to internal friction in the local zone of the surface layer, according to the formula AU Rm r0 U2 -HP thirty where AU Ui-U2; Ui and U2 are, respectively, the voltage of the resonant oscillations of the indenter before and after penetration into the sample.