RU2042942C1 - Electroacoustic hardness gauge - Google Patents

Abstract

FIELD: inspection of materials. SUBSTANCE: electroacoustic hardness gauge has rod with indenter, piezoexciter and piezoreceiver mounted on rod and connected correspondingly to generator of oscillations and unit for processing and recording of signals. Unit is manufactured in the form of electron phase meter and computer which computes hardness of material with allowance for measured phase of signal. Indicators of testing results are connected across output of computer. EFFECT: improved authenticity of hardness measurements. 3 cl, 1 dwg

Description

 The invention relates to a testing technique for non-destructive testing of the physicomechanical properties of materials, primarily microhardness of products, by pressing an indenter into the test surface.

 Known portable hardness tester [1] which contains an electro-acoustic rod transducer of controlled impedance with an indenter at the working end and an electronic circuit of the original design. The principle of operation of the hardness tester is based on the dependence of the frequency of self-oscillations of the loaded electro-acoustic transducer on the mechanical reactance of the controlled surface of the products.

 The main disadvantage of the known hardness tester is the low measurement accuracy due to the weakly expressed dependence of the self-oscillation frequency on the active component of the controlled impedance, i.e. from the microhardness of the product in the contact zone.

Amplitude-dependent hardness testers have a higher sensitivity of the electro-acoustic transducer to the hardness parameter of the controlled products [2]
They use an inversely proportional relationship between the value of the active part of the controlled impedance in the zone of contact with the indenter and the amplitude of its velocity fluctuations at the resonant frequency. Moreover, the amplitude of the test oscillation excitation force applied to the indenter is kept constant. Under these conditions, the amplitude of the vibrational velocity of the loaded indenter is determined by the quality factor of the system, which in turn depends on the microhardness of the contact zone of the hardness gage sensor with the controlled surface.

 A disadvantage of the known method of solidometry and a device for its implementation is the nonlinear effect on the results of measuring the hardness of the elastic modulus of the controlled materials. In order to reduce this effect, the complex design of the sensor of the electro-acoustic hardness transducer is used, which has a high quality factor at the resonant frequency of self-oscillations. This reduces the manufacturability and efficiency of the use of hardness testers for precision and destructive control of the hardness of materials.

 In addition, the known solution does not provide control of the modulus of elasticity of products and measure the hardness of materials with previously unknown elastic properties. Finally, the amplitude-dependent microhardness measurement method has a narrow measurement range due to the limited dynamic range of the controlled amplitudes of the vibrational velocity. When the measured amplitudes decrease below the permissible value (for example, when controlling the boundary values of hardness at the edges of the working range), self-oscillations are disrupted due to the imbalance of phases and amplitudes of the self-oscillating system of the converter.

 The closest to the proposed technical essence and the obtained effect is a hardness tester [3] which is based on the well-known phase-dependent method for measuring hardness and contains an electro-acoustic rod transducer with structurally combined piezoelectric exciter and vibration receiver, as well as an electronic circuit. The transducer is made in the housing and contains a rod with an indenter at the working end, an interaction spring between the rod and the housing, and a piezoelectric vibration exciter mounted on the rod with one common and two separate electrodes. The electronic circuit contains a phase meter connected to its inputs to the piezoelectric electrodes, one of the inputs of which is connected to the output of a high-frequency oscillation generator, the control input of which is connected to the first output of the control unit, the first input of which is connected to the output of the phase meter, and a drive is connected between the second input and output of the control unit indenter mechanism.

 The hardness tester registers the phase shift between the harmonic signals of the exciting self-oscillation of the force indenter and its vibrational velocity in the mode loaded on the controlled product. The hardness of the products is determined on the basis of the measured phase shift according to empirically obtained results of preliminary calibration on samples with known rheological properties.

 The prototype provides high speed due to the inertialess nature of establishing phase relationships between these signals during measurements. The process of controlling the hardness of products is easily automated due to the direct coupling of the measuring circuit with the actuator drive of the sensor. Together, these two circumstances contribute to ensuring high performance solidometry on the principle basis of the prototype, for example, as part of robotic complexes for controlling the quality of production of products.

 The disadvantage of the prototype is the need for preliminary calibration of the conversion characteristics of the hardness tester for samples with known hardness and elastic modulus and the absence of an analytical relationship for extrapolating the transfer characteristics of the hardness tester to calibration points.

 The disadvantage is the narrow range of hardness control due to phase restrictions on the stable self-excitation of the oscillations of the Converter. In addition, the range of hardness tester’s performance is also limited by the amplitude dependence of the indenter vibrational velocity on the rheological properties of the controlled materials. All this makes it difficult to balance the phases and amplitudes of the self-oscillating system of the hardness transducer and limits the range of controlled mechanical reactance of the products.

 Finally, the disadvantage of the prototype is the fundamental impossibility of simultaneously controlling the reactive component (elastic modulus) of the tested materials and / or controlling the hardness of products with previously unknown elastic properties (unknown elastic modulus).

 The purpose of the invention is to increase accuracy and expand the range of measurement of hardness of materials with any, including a previously unknown elastic modulus, to enable simultaneous measurement of hardness and elastic modulus of controlled materials and to increase the operational reliability of the hardness tester by eliminating disruptions in the self-oscillating process when the indenter is loaded onto products with prototype values controlled rheological parameters.

 The goal is achieved by the fact that the known hardness tester comprising an electro-acoustic transducer housing, a rod with an indenter, a spring interacting between the housing and the rod, a piezoelectric receiver and a vibration exciter installed on the rod, having one common ground electrode and two separate exciter and vibration electrodes connected by its inputs to these electrodes a phase meter whose output is connected to the first input of the control unit, the first output of which is connected to the control input of the generator , the output of which is connected to the piezoelectric electrode of the oscillation exciter, the actuator of the indenter drive, connected between the second input and output of the control unit, is additionally equipped with a calculator, first and second indicators, a single vibrator and an amplitude detector, the input of which is connected to the electrode of the piezoelectric receiver of oscillations, and the output to the third the input of the control unit and the first output of the calculator, the second input of which is connected to the output of the generator, the third with the output of the phase meter, and the first and second outputs of the calculator with unified respectively with said first and second indicator, the first output of the calculator is also connected to the monostable control input, an information input of which is connected to the control input of the generator, and the output to the input of the calculator synchronization.

 The goal is achieved by the fact that the generator of high-frequency oscillations is made in the form of a self-oscillator of a harmonic signal of constant frequency.

 In addition, the goal is achieved by the fact that the one-shot is made in such a way that the duration of the impedance of the delay of the information signal generated by it is inversely proportional to the voltage at its control input.

 The invention is illustrated in the drawing, which shows a diagram of a hardness tester.

 Electro-acoustic hardness tester contains a sensor in the composition of the rod 1 with an indenter 2 at the working end and a spring 3 interacting between the rod 1 and the housing 4 of the sensor. On the rod 1 are mounted a piezoelectric pickup exciter 5 of acoustic vibrations made with separate electrodes of the receiver and exciter and a common grounding electrode. The electronic circuit of the hardness tester contains a phasometer 6 connected to its inputs to the exciter-exciter 5, the input of the piezoelectric exciter of which is connected to the output of the generator 7, and the input of the piezoelectric receiver to the input of the amplitude detector 8. The first and third inputs of the control unit 9 are connected to the outputs of the phase meter 6 and the amplitude detector 8, and the actuator 10 of the indenter drive is connected between the second input and output of block 9. Moreover, the first output of block 9 is connected to the control input of generator 7 and the information input of one brother 11, the output of which is connected to the synchronization input of computing unit 12. The first, second and third inputs of block 12 are connected respectively to the outputs of the amplitude detector 8, generator 7 and phase meter 6, and the first and second outputs of block 12, respectively, to the first 13 and second 14 indicators . Moreover, the first output of block 12 is also connected to the control input of the single-shot 11. The controlled product 15.

 Electro-acoustic hardness tester works as follows.

From the output of the generator 7, the test frequency ω _{about the} amplitude F _o through the piezoelectric exciter electrode 5, the acoustic rod 1 and indenter 2 acts on the controlled product 15. In contrast to the prototype, the test frequency ω _{о is} chosen constant and independent of the controlled mechanical impedance.

 The reaction of the indenter 2 loaded onto the controlled product in the form of a signal proportional to its vibrational velocity is obtained at the electrode of the piezoelectric receiver 5. The phase shift between the harmonic excitation signals of the indenter 2 and its reaction is measured by a phase meter 6 connected between the electrodes of the piezoelectric element 5.

The control of the drive 10 of the indenter 2 is carried out similarly as in the prototype. Before the contact of the surface of the controlled product 15 with the indenter 2 occurs, its rapprochement is carried out at a small amplitude of the test force from the output of the generator 7 with a frequency of ω _about . At the moment of contact, due to a change in the quality factor of the oscillating system with the indenter 2 loaded on the product, the control unit 9 generates a signal to the actuator 10 about the loading movement of the sensor by the value Δ X by the signal from the output of the phasemeter 6, which ensures the normal pressure of the indenter 2 due to compression of the spring 3. In addition In addition, a control signal is generated to the generator 7, switching it into a measurement mode with a nominal amplitude of the test force F _o frequency ω _o .

 Additionally, in the invention, the amplitude of the vibrational speed of the indenter 2 is measured. For this, an amplitude detector 8 is connected to the piezo receiver 5. At the moment of indenter 2 contacting the surface of the controlled product 15 due to a change in the quality factor of the oscillating system of the electro-acoustic hardness sensor, in addition to the indicated jump in the phase shift of the measuring signals, the amplitude changes vibrational speed. This change serves as an additional criterion for determining the moment of contact.

 The signal from the output of the detector 8 is fed to an additional input of the control unit 9 in order to increase the reliability of the identification of the contact and enable the drive program 10 of the indenter 2 according to the described scheme.

In addition, the amplitude of the vibrational velocity V measured in the detector 8 _{in the} indenter 2 in the loaded mode is one of the arguments for determining the desired hardness and elastic modulus of the controlled products. The required parameters also depend on the phase shift φ _x measured in the phasemeter 6 between the excitation signals and the indenter response to the test effect on the amplitude F _о and frequency ω _{о of the} test signal from the output of the generator 7.

Thus, at the informational first, second, and third inputs of the computing unit 12, measuring signals are generated that are proportional to the amplitude of the vibrational velocity Vv of the indenter 2 loaded onto the controlled product from the output of the amplitude detector 8, the amplitude F _o and the frequency ω _{о of the} test signal of the indenter 2 from the generator output 7, the phase shift φ _x between the harmonic signals of the indenter 2 excitation and its vibrational velocity from the output of the phasemeter 6. These intermediate transformation parameters are arguments for determining the desired microhardness R _x and elastic modulus E _{x of the} controlled material. The analytical dependence connecting them (transformation algorithm) is obtained as follows.

The exciting acoustic rod test harmonic signal is described by the expression
_{F (t) F o ˙ sin} ω o˙ t, ( 1) where F _o, ω _o amplitude and frequency of the test signal.

) задержки распространения акустической волны в пересчете к известной длине стержня. При этом в операторной форме выражение (2) на основании известного преобразования Лапласса можно записать в виде
F_x(p)=F

(3) где Р оператор Лапласса.At the point of contact of the indenter with the controlled material due to the finite propagation time of acoustic vibrations in the rod, a phase delay Δφ _{of the} test signal is observed. In addition, the attenuation of the acoustic wave with a time constant α _о occurs in the rod. This is described by the expression
F _x (t) F _o ˙e ^-α o ^t ˙sin (ω _o ˙t Δφ _o ). (2)
In an unloaded acoustic rod without losses, i.e. when α _о 0, which is satisfied by real acoustic hardness transducers, the phase delay Δφ _о has a constant value determined by the acoustic length of the rod and the speed of propagation of vibrations in it. For a rod of a certain length made of a material with known density and acoustic resistance, the phase constant Δφ _о at a fixed frequency ω _{о of the} test signal in a more convenient form for analysis can be expressed in terms of the time constant τ _хо (

) the propagation delay of the acoustic wave in terms of the known length of the rod. Moreover, in operator form, expression (2) based on the well-known Laplace transform can be written as
F _x (p) = F

(3) where P is the Laplace operator.

The constant for each acoustic rod parameter τ _хо (or the corresponding constant phase delay Δφ _о ) can be obtained analytically. However, as will be shown below, using this parameter it is simple and sufficient to calibrate the sensor when setting up the hardness tester.

(4) где Z_х полное сопротивление контролируемого импеданса;
R_х его активная составляющая (контролируемая твердость);
E_х модуль упругости контролируемого материала;
М_о колебательная масса подвижной системы преобразователя твердости;
ω_о угловая тестовая частота.The controlled mechanical impedance is complex and is described by the expression
Z _x (j · ω _o ) = R _x + j · ω _o · M _o +

(4) where Z _{x is the} impedance of the controlled impedance;
R _x its active component (controlled hardness);
E _x modulus of elasticity of the controlled material;
M _{about the} vibrational mass of the movable system of the hardness Converter;
ω _о angular test frequency.

(5)
На основании известного соотношения, колебательную скорость нагруженного на контролируемое изделие индентора определим как отношение возбуждающей индентор тестовой силы и полному реактору контролируемого изделия по формуле
v_x(P)

(6) где λ_x=

(7)
диссипативный коэффициент затухания колебательной энергии преобразователя на активном сопротивлении (твердости) контролируемого импеданса;
ω_x

(8)
собственная резонансная частота колебаний преобразователя твердости;
ω_E

(9)
частота реактивного резонанса преобразователя твердости.In operational form (4) is written as
Z _x (P) = M

(5)
Based on the known relation, the vibrational speed of the indenter loaded on the controlled product is defined as the ratio of the test force exciting the indenter to the complete reactor of the controlled product according to the formula
v _x (P)

(6) where λ _x =

(7)
dissipative attenuation coefficient of the vibrational energy of the converter on the active resistance (hardness) of the controlled impedance;
ω _x

(8)
natural resonant frequency of oscillation of the hardness transducer;
ω _E

(nine)
hardness transducer resonance frequency.

A_o·e

sin(ω_xt+α_x)+B_o·sin(ω_ot+φ_x)

(10)
Как видно из (10), возбужденные во внедренном инденторе акустические колебания носят сложный гармонический характер и состоят из двух составляющих. Во-первых, это затухающие с постоянной времени λ_xколебания на собственной резонансной частоте ω_х преобразователя, во-вторых, это незатухающие вынужденные колебания на тестовой частоте ω_о генератора 7 возбуждения твердомера. Учитывая, что затухающая составляющая колебательной скорости индентора с амплитудой Ао стремится к нулю и через интервал времени
T_изм ≥

(11) после возбуждения индентора тестовой частотой ω_о становится пренебрежимо малой, информационный сигнал колебательной скорости в установившемся режиме переходного процесса в инденторе можно записать в виде
v_x.уст(t)

B_o·sin(ω_ot+φ_x)
(12)
Здесь параметры амплитуды В_о и фазы φ_х имеют следующие значения, полученные на основании справочных данных
B_o=

(13)
φ_x -arctg

+ arctg

2

-Δφ_o+arctg

2

(14)
При этом амплитуда установившегося значения колебательной скорости при условии (11) и ее фазовый параметр будут равны соответственно
V_B

(15)
tg(φ_x+Δφ_o)=tgη_x=2

(16)
Подставляя значения для ω_Е ² ω _о ² из (16) в (15) получим
V_B

sinη_x
(17) откуда в окончательном виде алгоритм измерения твердости запишем в виде
R_x

sinη_x (18)
Модуль упругости Ех контролируемого материала при этом определим на основании (9) и 16
E_x=M_o·ω $\genfrac{}{}{0ex}{}{\text{2}}{\text{o}}$ +

cosη_x (19)
Таким образом, выявлено, что контролируемая микротвердость изделия R_x в зоне нагруженного контакта с индентором электроакустического преобразователя оказывается пропорциональной произведению амплитуды тестовой силы F_о, возбуждающей в инденторе колебания на частоте ω_о на синус угла фазового сдвига η_х между гармоническими сигналами этой тестовой силы и реакцией индентора на тестовое возбуждение в виде его колебательной скорости, и обратно пропорциональна амплитуде V_в этой скорости в установившемся режиме, т.е. через интервал времени Т_измустановления режимов колебания согласно (11). При этом амплитуда V_воказывается независимой от акустической длины стержня преобразователя и времени τ_хо задержки в нем распространения волны тестовых колебаний. Упомянутый параметр τ_хо косвенно участвует в алгоритме преобразователя (18) в виде зависимого от него начального фазового сдвига Δφ_о незащемленного индентора согласно (14). Последний измеряют в режиме холостого хода ненагруженного индентора и учитывают при определении аргумента η_x на основании (16).The inverse Laplace transform for expression (6) makes it possible to determine the vibrational velocity of the electro-acoustic hardness transducer loaded in a controlled impedance in a temporal form in the form
v _x (t)

A _o · e

sin (ω _x t + α _x ) + B _o sin (ω _o t + φ _x )

(10)
As can be seen from (10), the acoustic vibrations excited in the indenter introduced are of a complex harmonic nature and consist of two components. Firstly, these are oscillations damped with a time constant λ _x at the natural resonant frequency ω _{x of the} transducer, and secondly, these are undamped forced oscillations at a test frequency ω _{о of} a hardness tester excitation generator 7. Considering that the damped component of the indenter vibrational velocity with amplitude A0 tends to zero even after a time interval
T _meas ≥

(11) after the indenter is excited, the test frequency ω _о becomes negligible, the information signal of the vibrational velocity in the steady state transient in the indenter can be written as
v _x.ust (t)

B _o sin (ω _o t + φ _x )
(12)
Here the parameters of the amplitude In _about and phase φ _x have the following values, obtained on the basis of reference data
B _o =

(13)
φ _x -arctg

+ arctg

2

-Δφ _o + arctg

2

(fourteen)
In this case, the amplitude of the steady-state value of the vibrational velocity under condition (11) and its phase parameter will be equal, respectively
V _b

(fifteen)
tg (φ _x + Δφ _o ) = tgη _x = 2

(sixteen)
Substituting the values for ω _Е ² ω _о ² from (16) in (15) we obtain
V _b

sinη _x
(17) whence in the final form we write the hardness measurement algorithm in the form
R _x

sinη _x (18)
The elastic modulus Ex of the controlled material is determined on the basis of (9) and 16
E _x = M _o $\genfrac{}{}{0ex}{}{\text{2}}{\text{o}}$ +

cosη _x (19)
Thus, it was found that the controlled microhardness of the product R _x in the zone of loaded contact with the indenter of the electro-acoustic transducer is proportional to the product of the amplitude of the test force F _о , exciting in the indenter oscillations at a frequency ω _о by the sine of the phase shift angle η _x between the harmonic signals of this test force and the indenter response to test excitation in the form of its vibrational velocity, and is inversely proportional to the amplitude V _at this speed in the steady state, i.e. through the time interval T _ism establishing the modes of oscillation according to (11). In this case, the amplitude V _in is independent of the acoustic length of the transducer rod and the time τ _{xo of the} delay in it of the propagation of the wave of test oscillations. The mentioned parameter τ _{х0 is} indirectly involved in the algorithm of the transducer (18) in the form of an initial phase shift Δφ _{о of an} unshielded indenter dependent on it according to (14). The latter is measured in the idle mode of an unloaded indenter and taken into account when determining the argument η _x based on (16).

In addition, it was found that the elastic modulus E _{x of the} controlled material is determined by relation (19) independently and simultaneously with the measurement of hardness R _x as a function of the same information arguments (parameters): phase η _x , amplitude V _in and test amplitude F _о at t ≥T _edited in accordance with (11). In this case, the elastic modulus E _x according to (19) is additionally determined by the selected value of the constant test frequency ω _about indenter excitation. This is due to the reactive nature of the elastic component of the resistance of the controlled complex impedance.

The device of the proposed hardness tester implements the algorithm (18) and (19) in the computing unit 12 (Fig. 1). The amplitude of the vibrational velocity V _in goes to the first input of the calculator 12 from the output of the amplitude detector 8, the test amplitudes F _about and the frequency ω _about to the second input 12 from the output of the generator 7, and the measured phase angle η _x between the information signals to the third input 12 from the output phase meter 6. Moreover, to determine the information phase η _x taking into account φ _x and Δφ _{about the} latter is previously measured at idle of the hardness transducer and stored in the calculator 12 for subsequent accounting in each of the measurements based on (16).

In addition, the control input of the calculator 12 receives a synchronization pulse of the measurement time from the output of the one-shot 11. The delay of this pulse relative to the start of measurement (the moment of indenter penetration into the product, determined by the second output of the control unit 9) is selected on the basis of condition (11) inversely to the dissonant coefficient λ _x so that the transition process of establishing the amplitude of the vibrational velocity is completed by the time the information parameters are measured at any hardness, i.e. inversely proportional to the measured hardness R _x (see 7 and 11). For this, the delay time of the one-shot 11 is provided inversely proportional to the voltage at its control input, which in turn is proportional to the current value of the measured hardness R _x at the first output of the computing unit 12. From the same output, the voltage proportional to the controlled microhardness R _{x of the} product, calculated on the basis of the algorithm (18) in block 12, it goes to the first indicator 13. The second indicator 14 from the second output of the calculator 12 receives the results of determining the elastic modulus E _x by the formula (19).

Claims (3)

 1. ELECTRO-ACOUSTIC SOLIDOMETER, comprising an electro-acoustic transducer housing, a rod with an indenter, a spring interacting between the housing and the rod, a piezoelectric exciter and a receiver installed on the rod, having one common and two separate exciter and oscillation electrodes, a phase meter connected to the electrodes by their inputs, an output which is connected to the first input of the control unit, the first output of which is connected to the control input of the generator, the output of which is connected to the piez electrode excitation oscillator, indenter actuator actuator, connected between the second input and output of the control unit, characterized in that the hardness tester is additionally equipped with a calculator, first and second indicators, a single vibrator and an amplitude detector, the input of which is connected to the electrode of the oscillation piezoelectric receiver, and the output to the third input of the unit control and the first input of the computer, the second input of which is connected to the output of the generator, the third with the output of the phase meter, and the first and second outputs of the computer are connected respectively with the first and second indicators, and the first output of the computer is also connected to the control output of a single-shot, the information input of which is connected to the control input of the generator, and the output to the input of the synchronization of the computer.  2. The hardness gage according to claim 1, characterized in that the generator is made in the form of a self-oscillator of a harmonic signal of constant frequency.  3. The hardness gage according to claim 1, characterized in that the one-shot is made in such a way that the delay time of the input pulse in it is inversely proportional to the voltage at its control input.

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