RU2190831C2 - Process of manufacture of transducers controlling cyclic deformation - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: process can be used to measure deformation and stress on surface of parts of machines subject to cyclic loading. Process consists in exposure of foil of plastic homogeneous material, electrolytic copper, for instance, under constant stress amplitude σ_t to number of cycles Nt found by formulas

D = (1+C)σ_A+(1-C)K/N_A, C = σ_A/σ_Bg, where σ_A, N_A are stress amplitude and number of loading cycles under which response of transducers is required; K, σ_RO, I_g, σ_Bg are parameters of calibration dependence of initial foil: K is proportionality factor; σ_RO is fatigue limit of material of part; I_g is value of injury of material of part under which reaction of foil emerges; σ_Bg is analog of ultimate strength of material of foil. Then foil is cut into separate elements used as transducers. EFFECT: enhanced sensitivity of transducers. 2 dwg

Description

 The invention relates to measuring equipment and can be used to measure strains and stresses on the surface of machine parts subjected to cyclic loading, as well as the degree of fatigue damage of machine parts.

 A known method of manufacturing sensors for monitoring cyclic deformations, the principle of which is based on a comparison of their state after cyclic loading on the test object and calibration samples, which allows for dark spots appearing on the surface of the sensors to control deformations based on 0.05-0.01 mm and for structural changes - based on 0.003-0.005 mm.

The method consists in the fact that a metal plate, for example of stainless steel, is subjected to galvanic copper plating for 20 minutes in an alkaline bath containing 23 g of CuCN, 30 g of NaCN and 10 g of Na ₂ CO ₃ per liter of water at an electrolyte temperature of +30 ^o С , voltage on the bath 0.35 V and current density 6 A / m ² . Then, galvanic copper plating is carried out for 15 minutes in an acid bath containing 250 g of CuSO ₄ • 5H ₂ O, 80 g of H ₂ SO ₄ per liter of water at a bath voltage of 0.5 V and a current density of 300 A / m ² . Then remove the resulting foil and cut it into individual elements used as sensors.

The sensor is glued onto the surface of a calibration sample, for example with a conical working part, which experiences deformations cyclically changing in time and known in magnitude. According to the results of these tests, a calibration relationship is established between the number of cycles before the appearance of the sensor reaction and the amplitude of the existing deformation. (The most simple response of the sensor is estimated by the moment the first “dark spots” appear.)
Other sensors stick to the surface of the test piece, which experiences cyclically varying loads, and also determine the number of cycles before the reaction of the sensor at the test points. As a result, using the calibration dependence, determine the magnitude and nature of the distribution of deformations and stresses on the surface of the part. (Okubo Hajime. Determination of stresses by galvanic copper plating. - Moscow: Mashinostroenie, 1969, pp. 16-41).

 The use of the galvanic method of producing foil under strictly constant conditions and the manufacture of sensors (both for calibration and measurements) by cutting the foil into parts ensures the invariability of the properties of the sensors and the accuracy of the measurements.

 The disadvantage of this method is the low sensitivity of the sensor (which leads to a longer test duration), the inability to control the properties of the sensors, the narrow range of manifestations of the reaction of the sensors, the high complexity and complexity of the method, the instability of the reaction of the sensors in the form of dark spots (ibid., P. 17, 38) .

A known method of manufacturing sensors for monitoring cyclic deformations, namely, that the metal plate is subjected to galvanic copper plating at room temperature, first for 1 min at a current density of 600 A / m ² , then for 10 min at a current density of 250 A / m ² , and the electrolyte contains 280-300 g of CuSO ₄ • 5H ₂ O and 85-90 g of H ₂ SO ₄ per liter of water, the resulting coating is removed and cut into individual elements used as sensors (ed. certificate 1032328).

 A distinctive feature of this analogue is that copper plating is carried out only in an acidic electrolyte. As a result, the manufacturing method is simplified (by eliminating the operation of copper plating in an alkaline environment with toxic components), the sensitivity of the sensors is increased by an average of 15%, and the stability of the appearance of dark spots is ensured.

 The disadvantages of this method are the low sensitivity of the sensors, the lack of the possibility of its regulation, the narrowness of the range of measured voltages.

As a prototype, a method of manufacturing sensors by galvanic copper plating for controlling cyclic deformations was selected, which consists in the fact that the metal plate is subjected to galvanic copper plating in an electrolyte containing 125-250 g / l CuSO ₄ • 5H ₂ O and 20-70 g / l H ₂ SO ₄ , at a current density of 100 A / m ² to the maximum cathodic diffusion density and a temperature of 3-40 ^o C to obtain a coating with a thickness of 5-30 microns, remove the coating from the plate and cut it into pieces (ed. Certificate. 1191730) .

 A distinctive feature of the prototype is a wide range of changes in the copper plating modes, as a result, the sensitivity of the sensors increases by another 5-35% and it becomes possible to manufacture sensors with different levels of sensitivity.

 The method selected as a prototype has the following disadvantages. The sensitivity of the sensors remains low, which requires extensive testing, and the range of sensitivity is narrow.

D = (1+C)σ_A+(1-C)K/N_A,
C = σ_A/σ_Bg,
где σ_A, N_A - амплитуда напряжения и число циклов нагружения, при которых требуется появление реакции датчиков;
K, σ_RO, П_g, σ_Bg - параметры калибровочной зависимости исходной фольги (К - коэффициент пропорциональности: σ_RO - предел выносливости материала детали; П_g - величина поврежденности материала детали, при которой появляется реакция фольги: σ_Bg - аналог предела прочности материала фольги).To increase the sensitivity of the sensor to cyclic deformations, expand the range of sensitivity and control it, which ultimately leads to a decrease in the test duration, a foil of a plastic homogeneous material, for example, copper electrolytic, before cutting it into individual elements used as sensors, subjected to cyclic deformation at a constant amplitude of stresses σ _t to the number of cycles N _t , determined by the formulas

D = (1 + C) σ _A + (1-C) K / N _A ,
C = σ _A / σ _Bg ,
where σ _A , N _A is the amplitude of the voltage and the number of loading cycles at which the appearance of the reaction of the sensors is required;
K, σ _RO , П _g , σ _Bg are the parameters of the calibration dependence of the initial foil (K is the proportionality coefficient: σ _RO is the endurance limit of the material of the part; P _g is the amount of damage to the material of the part at which the foil reaction appears: σ _Bg is an analog of the tensile strength foil material).

 In FIG. 1 shows a diagram of the installation for implementing the method: figure 2 - calibration curves of sensors manufactured by the prototype method and the proposed method.

 The installation contains a sample 1, on the working part of which a piece of foil 2 is fixed. The sample is installed in the clamping collets 3 and 4 of the headstock 5 and 6 and is loaded through the earrings 7 and 8 with the load 9. The collets are mounted in the headstock bearings for rotation. The electric motor 10 provides rotation of the sample, and the counter 11 captures the number of revolutions.

 The method is as follows. In a known manner receive foil 2 with a thickness of 5-30 microns. This can be a copper galvanic foil or a foil of another plastic homogeneous material (aluminum, nickel, etc.).

A piece in the form of a strip is cut from the foil and glued to a calibration sample with a conical working part. (Samples are made of the same material as the test piece.) Using clamping collets 3 and 4, sample 1 is fixed in headstock 5 and 6 and load 9 is applied through the earrings 7 and 8. In this case, the middle part of the sample experiences a clean bend (the amount of bending moment M = P • a / 2, where P is the weight of the load 9, taking into account the weight of the devices), and the upper fibers of the sample are compressed, the lower ones are stretched. The foil element glued onto the sample also experiences the same deformations. Emerging with maximal normal stress at any cross section of the sample equal to σ = M / W, where W = pD ^3/32, d - diameter of the cross section. Thus, on a sample with a conical working part, the stresses vary along the length depending on d.

 The electric motor 11, rotating the sample, provides alternate passage of the foil material through the zones of tension and compression with a symmetric (sinusoidal) cycle of voltage change. Stopping the engine periodically inspects the foil to measure the diameter of the largest cross section of the sample to which the reaction has spread. Based on the measurement results, a calibration dependence is built between the amplitude and the number of cycles of alternating stresses at which the foil reaction manifests itself on the investigated structural part (curve 1 in figure 2). To implement the method, a fatigue testing machine MUI-6000 can be used.

где K, σ_Ro, П_g, σ_Bg - параметры, определяемые известными способами аппроксимации (Сызранцев В. Н., Лобрынько А.В. Методы прогнозирования долговечности деталей по показаниям датчиков деформаций интегрального типа: Учебное пособие. - Курган: КМИ, 1993, с.49-54):
К - коэффициент пропорциональности;
σ_Ro - предел выносливости материала детали;
П_g - величина поврежденности материала детали, при которой появляется реакция фольги;
σ_Bg - аналог предела прочности материала фольги.The resulting calibration dependence is described by a mathematical expression of the form

where K, σ _Ro , П _g , σ _Bg are the parameters determined by known approximation methods (Syzrantsev V.N., Lobrynko A.V. Methods for predicting the durability of parts according to the readings of strain gauges of the integral type: Textbook. - Kurgan: KMI, 1993 , p. 49-54):
K is the coefficient of proportionality;
σ _Ro is the endurance limit of the material of the part;
P _g - the amount of damage to the material of the part at which the foil reaction appears;
σ _Bg is an analogue of the tensile strength of the foil material.

D = (1+C)σ_A+(1-C)K/N_A,
C = σ_A/σ_Bg,
Исходя из возможностей имеющейся установки (фиг.1) и временных ограничений назначают величину амплитуды напряжений σ_t, при которой будет осуществляться циклическое деформирование фольги (в общем случае σ_t может быть не равно σ_A). Необходимое число циклов деформаций вычисляется по формуле

Фольгу наклеивают, например клеем марки Циакрин 30, на образец с цилиндрической рабочей частью. Устанавливают образец 1 на описанную выше установку, и нагружают числом циклов N_t под действием груза 9, величина которого вычисляется по приведенным выше формулам исходя из величины

Единственным отличием процесса по сравнению с описанным выше состоит в том, что максимальные нормальные напряжения во всех поперечных сечениях образца (в пределах его цилиндрической рабочей части) равны. Следовательно, равные деформации испытывают и все точки материала фольги 2.Analyzing the calibration dependence, one chooses the magnitude of the amplitude σ _A and the number of cycles N _{A of} alternating voltages at which one would like to observe the manifestation of the reaction on the sensor, but at which the reaction on the initial foil is not yet manifested. (These values are selected, for example, based on preliminary calculations of the test structure for strength and the time allotted for testing.)
According to the selected values of σ _A and N _A , the damage value is calculated

D = (1 + C) σ _A + (1-C) K / N _A ,
C = σ _A / σ _Bg ,
Based on the capabilities of the existing installation (Fig. 1) and time constraints, the magnitude of the stress amplitude σ _t is assigned at which cyclic deformation of the foil will take place (in the general case, σ _t may not be equal to σ _A ). The required number of deformation cycles is calculated by the formula

The foil is glued, for example with glue brand Tsiakrin 30, on a sample with a cylindrical working part. Set the sample 1 to the installation described above, and load the number of cycles N _t under the action of the load 9, the value of which is calculated according to the above formulas based on the value

The only difference between the process compared to the one described above is that the maximum normal stresses in all cross sections of the sample (within its cylindrical working part) are equal. Therefore, equal points are experienced by all points of the material of the foil 2.

 Then the foil is soaked with acetone, removed from the sample and cut into individual elements used as sensors.

 The reaction on such a sensor will manifest itself even with fewer loading cycles. Obviously, the more preliminary the foil was used up (the greater the level of stresses and the number of cycles), the faster the reaction of the sensors will appear, the more sensitive they will be.

где К=28,4•10⁶; σ_Ro = 274,76 МПа; П_g=0,2201; σ_Bg = 275,9 МПа.
Кривая 2 на фиг.2 представляет собой калибровочную зависимость датчиков, изготовленных по предлагаемому способу. Она получена из условия ее прохождения через точку А с координатами σ_A = 200 МПа. N_A =3875 циклов. Эффект проявляется через, примерно, в 6 раз меньшее число циклов. При этом из приведенных выше формул находим П^*=0,06198 и, чтобы получить такую характеристику датчика, например при σ_t = 210 МПа, надо циклически деформировать исходную фольгу 10⁴ циклов.An example of the use of the proposed method is presented in figure 2 in the form of graphs of the relationship between the voltage amplitude and the number of cycles until the first dark spots appear. Curve 1 is obtained by mathematical description of the calibration dependence of the sensors made by the prototype method of electrolytic copper foil and tested on samples of steel 45:

where K = 28.4 • 10 ⁶ ; σ _Ro = 274.76 MPa; P _g = 0.2201; σ _Bg = 275.9 MPa.
Curve 2 in figure 2 represents the calibration dependence of the sensors manufactured by the proposed method. It is obtained from the condition of its passage through point A with coordinates σ _A = 200 MPa. N _A = 3875 cycles. The effect is manifested through an approximately 6 times smaller number of cycles. Moreover, from the above formulas we find P ^* = 0.06198 and in order to obtain such a characteristic of the sensor, for example, at σ _t = 210 MPa, it is necessary to cyclically deform the initial foil 10 ⁴ cycles.

Таким образом, предварительное циклическое деформирование материала фольги позволяет существенно и до нужных пределов повысить чувствительность изготавливаемых из нее датчиков. Достигаемый эффект расширяет область использования датчиков для контроля циклических деформаций, снижает продолжительность усталостных испытаний. Простота и технологичность способа создает благоприятные условия для его широкого применения в исследовательской практике.To establish the calibration dependence of the obtained sensors (curve 2) use the expression

Thus, preliminary cyclic deformation of the foil material allows significantly and to the necessary limits to increase the sensitivity of the sensors made from it. The achieved effect expands the field of use of sensors for monitoring cyclic deformations and reduces the duration of fatigue tests. The simplicity and manufacturability of the method creates favorable conditions for its widespread use in research practice.

Claims (1)

A method of manufacturing sensors for monitoring cyclic deformations, namely, that the foil is made of a homogeneous plastic material, for example, copper electrolytic, is cut into individual elements used as sensors, characterized in that the foil is subjected to cyclic deformation at a constant voltage amplitude σ _t up to the number of cycles N _t defined by the formulas

D = (1 + C) σ _A + (1-C) K / N _A ,
C = σ _A / σ _Bg ,
where σ _A , N _A is the amplitude of the voltage and the number of loading cycles at which the appearance of the reaction of the sensors is required;
K, σ _RO , P _g , σ _Bg - parameters of the calibration dependence of the initial foil: K - coefficient of proportionality; σ _RO is the endurance limit of the material of the part; P _g - the amount of damage to the material of the part at which the foil reaction appears; σ _Bg is an analogue of the tensile strength of the foil material.

Images