Piezoelectric ceramic stack driven impact press-in test method and test system thereof

Abstract

The invention discloses a piezoelectric ceramic stack driven impact press-in test method and a test system thereof. According to the invention, a piezoelectric ceramic stack is used as a drive, a sample is carried on a displacement table, measurement parameters in an impact press-in test are monitored through a force sensor and a displacement sensor, a computer is used for realizing accurate control and subsequent processing and analysis of the measurement parameters, and the whole test adopts electric control actuation; the device is simple in structure and convenient to operate and control, the pressure head can be accurately controlled to be impacted and pressed into the surface of a sample at a certain speed, and the maximum press-in load and the maximum press-in depth in the impact press-in process can be estimated according to the maximum output displacement of the pressure head under the free condition; compared with other impact press-in tests, the impact press-in test method has the advantages that the safety and the stability are well guaranteed, and the impact press-in test method has great application potential.

Description

Technical Field

[0001] The invention belongs to the field of detection and measurement, and in particular relates to an impact press-in test method driven by a piezoelectric ceramic stack and a test system thereof. Background Art

[0002] In the fields of aviation equipment, energy and power, core components are often used under complex and harsh impact load conditions, such as aircraft engine turbine blades and hypersonic vehicles, bird strikes on civil airliners, and impact damage to photovoltaic glass. Therefore, testing the material mechanical properties of core components under impact conditions is of great significance to improving their working stability, durability, and applicability under impact conditions.

[0003] For core components, the service environment is very complex and harsh, and their preparation is usually cumbersome and expensive. Traditional material mechanical properties testing technology requires cutting enough samples from the raw materials or target devices, and then machining them to obtain standard specimens whose size and shape meet the test requirements. The load is transferred to the specimen using a fixture to make it bear the force as a whole, and it usually needs to be loaded to the plastic deformation stage or even fracture. Although traditional material mechanical properties testing technology is relatively mature, due to its macroscopic, holistic, and destructive testing characteristics, core components are difficult to meet the requirements of such material mechanical properties testing. Therefore, smaller-scale instrumented pressing technology has gradually come into people's view.

[0004] Instrumented indentation technology can test target samples at the micro-nano scale. It is an emerging material mechanical properties testing technology with a wide range of application prospects. With its micro-area and non-destructive testing characteristics, it solves the unavoidable testing problems of traditional material mechanical properties testing technology and can efficiently test the mechanical properties of small-scale materials or precious core devices. The impact indentation test is based on instrumented indentation technology and is driven by electromagnetic-piezoelectric coupling, air gun or pendulum to achieve the impact of the indenter on the sample surface. However, the above-mentioned driving methods still have problems in terms of control accuracy, operation difficulty and test safety that need to be improved. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention proposes a piezoelectric ceramic stack-driven impact pressing test method and a test system thereof, which completely adopts the piezoelectric ceramic stack as the drive, places the sample on a displacement table, monitors the measurement parameters during the impact pressing process through force sensors and displacement sensors, uses a computer to achieve precise control and subsequent processing and analysis of the measurement parameters, and the entire test process adopts electronic control actuation.

[0006] An object of the present invention is to provide a piezoelectric ceramic stack driven impact indentation testing method.

[0007] The piezoelectric ceramic stack driven impact indentation test method of the present invention comprises the following steps:

[0008] 1) Build an impact press-in test system:

[0009] One end of the piezoelectric ceramic stack is fixed on the frame, and the other end is fixedly connected to the pressure rod. The displacement direction of the piezoelectric ceramic stack is collinear with the pressure rod. The pressure rod is equipped with a displacement sensor and a force sensor. The other end of the pressure rod is equipped with a pressure head. The sample is mounted on the displacement table, and the surface of the sample is perpendicular to the pressure rod.

[0010] The piezoelectric ceramic stack is connected to a power source; the force sensor and the displacement sensor are respectively connected to an information collector; the displacement stage is connected to a digital control system; the information collector and the digital control system are respectively connected to a computer;

[0011] 2) According to the maximum output displacement U of the pressure head under free conditions f Estimated maximum indentation load F max and maximum penetration depth

[0012] h max , maximum press load F max and maximum penetration depth h max The maximum output displacement U of the pressure head under free conditions f

[0013] satisfy:

[0014]

[0015] Among them, E S and E C are the elastic modulus of the sample and the indenter, t and H are the thickness of the sample and the indenter, respectively. A

[0016] is the stiffness of the piezoelectric ceramic stack; according to the maximum output displacement U of the indenter under free conditions f , the maximum indentation load F in the impact indentation test can be estimated using the above formula max and maximum penetration depth h max ; Based on the estimated maximum penetration depth h max and maximum indentation load F max , get the indentation load and indentation depth range of the impact indentation test, and then judge whether it meets the impact indentation test requirements. If the range is too large, adjust the test parameters and re-estimate according to the above formula until the impact indentation test requirements are met to ensure the feasibility and safety of the test; 3) The computer controls the position of the sample to be moved by the translation stage through the digital control system, so that the sample is placed under the indenter; 4) The power supply sends an excitation voltage to the piezoelectric ceramic stack, and the excitation voltage excites the piezoelectric ceramic stack to move, thereby driving the indenter

[0017] Impact the sample; control the displacement of the piezoelectric ceramic stack by adjusting the electrical signal of the excitation voltage, thereby controlling the impact speed of the indenter, and realize the impact indentation test by driving the indenter with voltage; the electrical signal of the excitation voltage is divided into three stages: voltage rising stage, voltage constant stage and voltage falling stage;

[0018] The displacement of the piezoelectric ceramic stack is proportional to the excitation voltage. The maximum output displacement of the piezoelectric ceramic stack is ΔL. max :

[0019] ΔL max =nd 33 U max

[0020] Among them, U max is the maximum excitation voltage, n is the number of single-layer piezoelectric ceramic sheets in the piezoelectric ceramic stack, d 33 is the piezoelectric coefficient of the polarized piezoelectric ceramic in three directions;

[0021] a) In the voltage rising stage, the excitation voltage reaches the maximum excitation voltage U within the rising stage time Δt1 max This stage is the impact indentation process of the impact indentation test; the speed of the piezoelectric ceramic stack is the impact speed of the indenter v in satisfy:

[0022]

[0023] Among them, Δt1 is the rising phase time of the excitation voltage; the speed v of the piezoelectric ceramic stack is in The speed of the pressure head is controlled by the power supply to adjust the electric signal of the excitation voltage, and the rising phase time of the excitation voltage is set so that the rising phase time Δt1 of the excitation voltage can quickly reach the maximum excitation voltage U of the kilovolt level within the microsecond level. max , the driving pressure head has a greater impact speed, thus meeting the high speed requirement of the impact press-in test;

[0024] The excitation voltage drives the piezoelectric ceramic stack in the voltage rising stage, and the output current I of the power supply satisfies:

[0025]

[0026] Wherein, C is the capacitance of the piezoelectric ceramic stack; the output current I of the power supply is calculated by the above formula. If the output current of the power supply is less than the rated current of the power supply, the speed required for the impact test can be achieved within the rated current; if the output current of the power supply is greater than the rated current of the power supply, the test conditions are changed and the output current I of the power supply is recalculated according to the above formula until the output current is less than the rated current of the power supply;

[0027] b) In the constant voltage stage, the excitation voltage maintains the maximum value U max The constant stage time is Δt2, at which time the piezoelectric ceramic stack does not deform, and the displacement output of the piezoelectric ceramic stack maintains the maximum output displacement ΔL of the piezoelectric ceramic stack. max This stage is the load-keeping process of the impact press-in test.

[0028] c) In the voltage drop stage, the excitation voltage is reduced from the maximum value U max The displacement of the piezoelectric ceramic stack is gradually reduced to 0 during the descending period Δt3. max Gradually decreases to 0. This stage is the unloading process of the impact test. According to the electrical signal of the excitation voltage in the constant voltage stage and the voltage drop stage, the holding time of the piezoelectric ceramic stack at the maximum displacement output and the retraction speed v are obtained. out ;

[0029] By regulating the voltage value and action time of the electric signal of the excitation voltage in the voltage rising stage, the voltage constant stage and the voltage falling stage, the impact pressing process, the load holding process and the unloading process of the indenter in the impact pressing test are controlled respectively;

[0030] 5) The force sensor and displacement sensor obtain force signals and displacement signals respectively, which are collected by the information collector, transmitted to the digital control system to be converted into digital signals, and transmitted to the computer; the computer performs automatic control of the test and subsequent processing and analysis.

[0031] Among them, in step 2), by adjusting the electrical signal of the excitation voltage of the power supply and combining the displacement output characteristics of the piezoelectric ceramic stack, the maximum output displacement U of the indenter under free conditions is obtained. f ; The displacement directions of the pressure head and the piezoelectric ceramic stack are the same, so the displacement output of the piezoelectric ceramic stack is the same as the displacement output of the pressure head.

[0032] For the indentation test, the indentation depth and indentation load need to meet the set conditions. The indentation depth cannot account for too large a proportion of the sample thickness and must be smaller than the set range, for example, less than one tenth. The indentation load must be prevented from being too large to ensure that the indenter is not damaged due to excessive load. If the conditions are not met, the type and material of the indenter or the model of the piezoelectric ceramic stack should be changed, and the maximum indentation load and indentation depth should be re-estimated to meet the test conditions.

[0033] The range of the indentation load and indentation depth of the impact indentation test needs to meet the requirements of the impact indentation test. If the indentation load and indentation depth are too large, it will not be suitable for subsequent analysis, and may even cause problems that make the test impossible, and it may not be what the tester wants to see; if the range of the indentation load and indentation depth is too large, the model, size and material of the indenter, the thickness of the sample or the model of the piezoelectric ceramic stack should be adjusted, and the calculation should be repeated until the requirements of the impact indentation test are met. The adjusted test parameters are one or more of the model, size and material of the indenter, the thickness of the sample, and the model of the piezoelectric ceramic stack.

[0034] In step 4), the power supply itself has the function of adjusting the excitation voltage signal and can input the electrical signal of the excitation voltage to the piezoelectric ceramic stack; or the power supply is connected to an analog-to-digital converter, and the analog-to-digital converter is connected to a computer, and the computer controls the electrical signal of the excitation voltage input by the power supply to the piezoelectric ceramic stack through the analog-to-digital converter.

[0035] In step 4) a), if the output current is greater than the rated current of the power supply, the test condition is changed to replace the power supply to increase the rated current of the power supply or to select a capacitor of a piezoelectric ceramic stack with a smaller capacitance.

[0036] The rising phase time Δt1 of the excitation voltage ranges from 0.1ms to 10ms, and the maximum excitation voltage U max The range is between 100V and 1000V.

[0037] Another object of the present invention is to provide a piezoelectric ceramic stack driven impact indentation testing system.

[0038] The piezoelectric ceramic stack-driven impact indentation test system of the present invention comprises: a translation platform, a sample, a pressure head, a force sensor, a displacement sensor, a pressure rod, a piezoelectric ceramic stack, a frame, a power supply, an information collector, a digital control system and a computer; wherein one end of the piezoelectric ceramic stack is fixed on the frame, and the other end is fixedly connected to the pressure rod, and the displacement direction of the piezoelectric ceramic stack is collinear with the pressure rod; a displacement sensor and a force sensor are mounted on the pressure rod; a pressure head is mounted on the other end of the pressure rod; the sample is mounted on the translation platform, and the surface of the sample is perpendicular to the pressure rod; the piezoelectric ceramic stack is connected to the power supply; the force sensor and the displacement sensor are respectively connected to the information collector; the translation platform is connected to the digital control system; the information collector and the digital control system are respectively connected to the computer; the computer controls the translation platform to move the position of the sample through the digital control system , so that the sample is placed under the pressure head; the power supply sends an excitation voltage to the piezoelectric ceramic stack, and the excitation voltage excites the piezoelectric ceramic stack to move, thereby driving the pressure head to impact the sample; the displacement of the piezoelectric ceramic stack is controlled by adjusting the electrical signal of the excitation voltage, thereby controlling the impact speed of the pressure head, and realizing the impact pressure test by driving the pressure head through voltage; by regulating the voltage value and action time of the electrical signal of the excitation voltage in the voltage rising stage, the voltage constant stage and the lower voltage drop stage, the impact pressure process, the load holding process and the unloading process of the pressure head of the impact pressure test are controlled respectively; the force sensor and the displacement sensor obtain the force signal and the displacement signal respectively, which are collected by the information collector, transmitted to the digital control system to be converted into digital signals, and transmitted to the computer; the computer performs automatic control, subsequent processing and analysis on the test.

[0039] The translation stage adopts a three-dimensional piezoelectric translation stage.

[0040] The piezoelectric ceramic stack includes a plurality of identical single-layer piezoelectric ceramic sheets and electrodes, wherein the electrodes include a positive electrode and a negative electrode; wherein the plurality of single-layer piezoelectric ceramic sheets are stacked, an electrode is arranged between two adjacent single-layer piezoelectric ceramic sheets, and the polarities of the two adjacent electrodes are opposite, so that the polarization directions of the piezoelectric ceramics PZT of the adjacent single-layer piezoelectric ceramic sheets are opposite.

[0041] Advantages of the present invention:

[0042] The present invention adopts a piezoelectric ceramic stack as a drive, places a sample on a displacement table, monitors the measurement parameters in the impact press-in test through a force sensor and a displacement sensor, uses a computer to achieve precise control and subsequent processing and analysis of the measurement parameters, and the entire test process adopts electronic control actuation; the present invention has a simple structure and is easy to operate, and can accurately control the indenter to impact and press into the sample surface at a certain speed, and according to the maximum output displacement of the indenter under free conditions, the maximum indentation load and the maximum indentation depth of the impact press-in test can be estimated; compared with other impact press-in tests, the present invention has good safety and stability, and is an impact press-in test method with great application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A schematic diagram of an embodiment of a piezoelectric ceramic stack driven impact indentation testing system of the present invention;

[0044] Figure 2 A schematic diagram of a simplified mechanical model of an indenter of an impact indentation testing system driven by a piezoelectric ceramic stack of the present invention;

[0045] Figure 3 A schematic diagram of an indenter of an embodiment of a piezoelectric ceramic stack driven impact indentation testing system of the present invention;

[0046] Figure 4 A predicted diagram of the maximum output displacement of a steel sample of an embodiment of the piezoelectric ceramic stack driven impact indentation testing system of the present invention;

[0047] Figure 5 A predicted diagram of the maximum output displacement of a magnesium sample of an embodiment of the piezoelectric ceramic stack driven impact indentation testing system of the present invention;

[0048] Figure 6 A schematic diagram of a piezoelectric ceramic stack of an embodiment of the impact indentation test system driven by a piezoelectric ceramic stack of the present invention, wherein (a) is an exploded view and (b) is an overall connection relationship diagram;

[0049] Figure 7 A schematic diagram of an electrical signal of an excitation voltage of an embodiment of a piezoelectric ceramic stack driven impact indentation test method of the present invention;

[0050] Figure 8 A schematic diagram of the electrical signal control of the excitation voltage of an embodiment of the impact indentation test method driven by the piezoelectric ceramic stack of the present invention;

[0051] Fig. 9 This is a graph of the impact indentation load-depth curve obtained for an embodiment of the piezoelectric ceramic stack driven impact indentation test method of the present invention. DETAILED DESCRIPTION

[0052] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0053] like Figure 1 As shown, the piezoelectric ceramic stack driven impact indentation test method of this embodiment includes the following steps:

[0054] 1) Build an impact press-in test system:

[0055] One end of the piezoelectric ceramic stack is fixed on the frame, and the other end is fixedly connected to the pressure rod. The displacement direction of the piezoelectric ceramic stack is collinear with the pressure rod. A displacement sensor and a force sensor are mounted on the pressure rod. The outer shell of the displacement sensor is fixedly connected to the frame, the inner rod of the displacement sensor is connected to the pressure rod, and the upper and lower surfaces of the force sensor are connected to the pressure rod. A pressure head is installed on the other end of the pressure rod. The sample is mounted on the displacement table. The displacement table adopts a three-dimensional piezoelectric displacement table, including three displacement axes of X, Y and Z. The sample is mounted on the Z axis of the displacement table, and the surface of the sample is perpendicular to the pressure rod.

[0056] The piezoelectric ceramic stack is connected to a power source; the force sensor and the displacement sensor are respectively connected to an information collector; the displacement stage is connected to a digital control system; and the information collector and the digital control system are respectively connected to a computer.

[0057] 2) Estimate the maximum penetration depth h max and maximum indentation load F max :

[0058] In traditional impact indentation tests, a pendulum, weight, air gun, etc. are usually used to drive the indenter, giving it a large initial velocity so that it impacts and presses into the specimen. Although the indenter can impact the specimen at a large velocity, this type of test makes it difficult to control the indentation depth and indentation load generated during the test, and may even damage the specimen or indenter due to excessive impact velocity.

[0059] In the present invention, the piezoelectric ceramic stack is completely adopted as the driving device. Since the piezoelectric ceramic stack itself has the advantages of self-limiting displacement and precise control, the present invention can solve this problem well. On the basis of the mechanical model, the maximum pressing load and the maximum pressing depth in the impact pressing process can be estimated according to the maximum output displacement of the piezoelectric ceramic stack under free conditions, and the feasibility and safety of the test are guaranteed.

[0060] Since the piezoelectric ceramic stack drives the indenter through displacement output, the maximum indentation load will be generated when the indenter reaches the maximum indentation depth. Therefore, a simplified mechanical model is established based on the free condition and the maximum indentation depth, such as Figure 2 The middle of Figure 2 is the free output situation, at which the maximum output displacement with the pressure head is Uf , Figure 2 The right side shows the limit of the indentation during the impact indentation process, at which the maximum indentation depth h max Next, the test system is simplified in combination with the output characteristics of the piezoelectric ceramic stack, and the impact pressing process is analyzed.

[0061] To simplify the estimation process, consider the case where the inclination angle α = 60°, when the indenter is at the maximum penetration depth h max When Figure 3 As shown, the contact area of ​​the pressure head at this time is calculated:

[0062]

[0063] For the specimen and the indenter, the equivalent contact stiffness is calculated based on the knowledge of contact mechanics:

[0064]

[0065] Where K S and K In are the equivalent contact stiffness of the specimen and the indenter, E S and E C are the elastic modulus of the sample and the indenter, respectively, t and H are the thickness of the sample and the indenter, respectively. S is the contact area when the indenter is at the maximum indentation depth. The stiffness of the piezoelectric ceramic stack is recorded as K A .

[0066] based on Figure 2 The simplified mechanical model shown in the figure considers the free output of the indenter and the maximum penetration depth of the indenter. According to the relationship between displacement and stiffness, we get:

[0067]

[0068] where F max It is the maximum penetration load generated when the indenter is at the maximum penetration depth.

[0069] According to the maximum output displacement U of the pressure head under free conditions f Estimated maximum indentation load F max and maximum penetration depth h max , maximum press load F max and maximum penetration depth h max The maximum output displacement U of the pressure head under free conditions f satisfy:

[0070]

[0071] Among them, E S and E Care the elastic modulus of the sample and the indenter, t and H are the thickness of the sample and the indenter, respectively. A is the stiffness of the piezoelectric ceramic stack; according to the maximum output displacement U of the indenter under free conditions f , the maximum indentation load F in the impact indentation test can be estimated using the above formula max and maximum penetration depth h max , according to the estimated maximum penetration depth h max and maximum indentation load F max , the indentation load and indentation depth range of the impact indentation test are obtained, and then it is determined whether the impact indentation test requirements are met. If the parameter range is too large, one or more of the models of the indenter, test piece and piezoelectric ceramic stack are adjusted, and the estimation is re-performed according to the above formula until the impact indentation test requirements are met to ensure the feasibility and safety of the test.

[0072] A simplified mechanical model is used to analyze the impact indentation process. Therefore, when the test conditions change, the relationship between the parameters will become more complicated. For example, using a Vickers indenter as the indenter for the impact indentation test will make the calculation of the contact area more complicated. However, this method and analysis process can still be carried out, and finally the contact area can be obtained.

[0073] U f With F max and h max The relationship between.

[0074] Next, we will take a specific test as an example to illustrate this method. The rated voltage of the piezoelectric ceramic stack is 1000V, the maximum output displacement is 100μm, and the stiffness K A The model is 35N / μm; the indenter is made of diamond material with an elastic modulus of 220GPa and a thickness of 3mm; steel and magnesium are selected as sample materials respectively, and the sample thickness is 1mm.

[0075] First, the steel sample was tested and estimated. By adjusting the excitation voltage signal, the maximum output displacement of the indenter under free conditions was 20 μm. According to the above analysis method, Figure 4 The prediction results are shown.

[0076] according to Figure 4 In the prediction graph, find U f The maximum indentation load F corresponding to 20 μm max and maximum penetration depth

[0077] h max .Depend on Figure 4 It can be seen that when the piezoelectric stack output displacement is small, the maximum penetration depth (h max ) and the free displacement of the piezoelectric stack output (Uf ) is very close, such as Figure 4 As shown in the figure, when the free displacement of the piezoelectric stack is 20 μm, the maximum indentation depth is 19.71 μm. This is because the contact area of ​​the conical indenter is very small during the initial indentation, and the stiffness of the indenter and the sample is much smaller than that of the piezoelectric stack.

[0078] In order to test the situation of large indentation depth, the indentation test of magnesium sample with small elastic modulus was estimated. By adjusting the excitation voltage signal, the maximum output displacement of the indenter under free condition was 100 μm. According to the same analysis method as above, the following is obtained: Figure 5 The prediction results are shown.

[0079] from Figure 5 It can be seen that as the output displacement of the piezoelectric stack increases, the maximum indentation depth also gradually increases, but the deviation between them also gradually increases. When the output displacement of the piezoelectric stack reaches 100μm, the maximum indentation depth is only 91.64μm. This is because when the indentation depth increases, the indentation contact area and contact stiffness will increase sharply. When the contact stiffness of the sample cannot be ignored compared with the stiffness of the piezoelectric stack, as the indentation force increases, the output displacement of the piezoelectric stack will decrease accordingly.

[0080] Although the above analysis is only for the ideal conical indenter, in fact, similar analysis can be done for indenters of other shapes. In addition to the flat indenter, for all other indenters with pointed tips, a general conclusion is that as the indentation depth increases, the indentation force will also increase, and the output displacement of the piezoelectric stack will decrease accordingly. This avoids the problem of excessive indentation force. At the same time, according to the above method, as long as the free output displacement of the piezoelectric stack is given, the maximum indentation depth and indentation force can be estimated, thereby effectively controlling the impact indentation process.

[0081] The method of the present invention can effectively predict the maximum pressing load and maximum pressing depth during the impact pressing process.

[0082] A simplified mechanical model is established to analyze the indenter, piezoelectric ceramic stack, and test piece at the maximum indentation depth, and the maximum indentation load and maximum indentation depth of the indenter are estimated by the maximum output displacement of the indenter under free conditions. This overcomes the problem that traditional impact tests can only control the impact velocity but not the indentation process, and greatly ensures the safety and feasibility of impact indentation tests.

[0083] 3) The computer controls the translation stage to move the position of the sample through a digital control system so that the sample is placed under the pressure head.

[0084] 4) Voltage driven indenter impact test:

[0085] like Figure 6 As shown, the piezoelectric ceramic stack includes a plurality of identical single-layer piezoelectric ceramic sheets and electrodes, wherein the electrodes include a positive electrode and a negative electrode; wherein the plurality of single-layer piezoelectric ceramic sheets are stacked, an electrode is arranged between two adjacent single-layer piezoelectric ceramic sheets, and the polarities of the two adjacent electrodes are opposite, so that the polarization directions of the piezoelectric ceramics PZT of the adjacent single-layer piezoelectric ceramic sheets are opposite; P and h E are the thickness of a single-layer piezoelectric ceramic sheet and electrode, respectively; l is the total length of the piezoelectric ceramic stack; a and b are the characteristic dimensions of the cross section of the piezoelectric ceramic stack; and 3 is the characteristic direction along the length of the piezoelectric ceramic stack.

[0086] The working state of the piezoelectric ceramic stack is described by the first-order piezoelectric equation (type d). Considering the stacking mode and working state of the piezoelectric ceramic stack, the material properties of the piezoelectric ceramic sheet after polarization, etc., the first-order piezoelectric equation is simplified.

[0087] For a single-layer piezoelectric ceramic sheet, in the polarization direction, i.e., the 3-direction, there is the following relationship:

[0088] x3=d 33 E3

[0089] Where x3 is the strain of the single-layer piezoelectric ceramic in the three directions, E3 is the electric field generated by the positive and negative electrodes in the three directions, and formula (1) shows that when a certain electric field strength E3 is applied in the three directions of the single-layer piezoelectric ceramic, a unidirectional strain x3 is obtained that is linearly related to the electric field strength. Figure 6 As shown in (a), a single-layer piezoelectric ceramic sheet is stacked with positive and negative electrodes. A power supply and positive and negative electrodes are used to generate an excitation voltage U at both ends of the single-layer piezoelectric ceramic sheet, thereby obtaining an electric field strength E3 acting in the direction of the single-layer piezoelectric ceramic sheet 3. Combining the thickness of the single-layer piezoelectric ceramic sheet with formula (1), its displacement is calculated:

[0090]

[0091] Δl=h P x3=h P d 33 E3=d 33 U

[0092] In order to generate a larger displacement under the control of the same driving power supply, considering the relationship between the electric field direction generated by the positive and negative electrodes and the polarization direction of the single-layer piezoelectric ceramic sheet, according to Figure 6 (a) The stacking method shown will use d 33 The polarized single-layer piezoelectric ceramic sheets and the positive and negative electrodes are stacked together periodically according to a regular pattern, and the following is obtained: Figure 6(b) shows the overall structure of the piezoelectric ceramic stack. Since the positive electrode and the negative electrode are connected in parallel to each layer of piezoelectric ceramic sheets, which is equivalent to the parallel connection of capacitors, the voltage excitation of each layer of piezoelectric ceramic sheets is the same; the piezoelectric ceramic sheets of each layer are stacked together in a mechanical series manner, and the displacement of each layer of piezoelectric ceramic sheets is superimposed and output, thereby obtaining the piezoelectric ceramic stack.

[0093] Displacement output characteristics of the electroceramic stack in the free state:

[0094] ΔL=nΔl=nd 33 U

[0095] Wherein, n is the number of single-layer piezoelectric ceramic sheets in the piezoelectric ceramic stack. By means of the above formula, the power supply excitation voltage is adjusted to control the total displacement output ΔL of the piezoelectric ceramic stack in the free state.

[0096] It can be seen from the above formula that the displacement output of the piezoelectric ceramic stack has a linear relationship with the excitation voltage, so the displacement output of the piezoelectric ceramic stack is controlled by adjusting the electrical signal of the excitation voltage. Based on the above theory, the test method proposed in the present invention is completely driven by voltage. Compared with other driving methods, the operation is simpler and the control is more precise. In addition, since the output displacement of the piezoelectric ceramic stack is self-limiting, the safety of the impact test is also guaranteed. Here, the method is described in detail.

[0097] The power supply sends an excitation voltage to the piezoelectric ceramic stack, which excites the piezoelectric ceramic stack to move, thereby driving the indenter to impact the sample; the displacement of the piezoelectric ceramic stack is controlled by adjusting the electrical signal of the excitation voltage, thereby controlling the impact speed of the indenter, and the impact indentation test is realized by driving the indenter with voltage; the electrical signal of the excitation voltage is divided into three stages, such as Figure 7 As shown: OA segment during voltage rising phase, AB segment during voltage constant phase and BC segment during voltage falling phase;

[0098] The OA stage is the rising stage of the excitation voltage. The electrical signal of the excitation voltage is set so that the excitation voltage quickly reaches its maximum value U in a short time. max Since the response speed of the piezoelectric ceramic stack is extremely fast, its response time is extremely short compared to the voltage action time and can be ignored. Therefore, no matter how the electrical signal of the excitation voltage changes, the above formula is valid, that is, the excitation voltage and the displacement output of the piezoelectric ceramic stack maintain a linear relationship, and the acceleration process of the piezoelectric ceramic stack can also be ignored. When the excitation voltage reaches the maximum value U max When , the maximum output displacement of the piezoelectric ceramic stack is:

[0099] ΔL max =nd 33 U max

[0100] Among them, U max is the maximum excitation voltage, n is the number of single-layer piezoelectric ceramic sheets in the piezoelectric ceramic stack, d 33 is the piezoelectric coefficient of the polarized piezoelectric ceramic in three directions;

[0101] Considering the action time of the electric signal of the excitation voltage in the rising stage, the speed of the piezoelectric ceramic stack is the impact speed v of the indenter. in satisfy:

[0102]

[0103] Among them, Δt1 is the rising phase time of the excitation voltage; the speed v of the piezoelectric ceramic stack is in The speed of the pressure head is controlled by the power supply to adjust the electric signal of the excitation voltage, and the rising phase time of the excitation voltage is set so that the rising phase time Δt1 of the excitation voltage can quickly reach the maximum excitation voltage U of the kilovolt level within the microsecond level. max , the driving pressure head has a greater impact speed, thereby meeting the high speed requirement of the impact press-in test. This stage is the impact press-in process of the impact press-in test.

[0104] According to the above formula, the speed of the piezoelectric ceramic stack can be controlled by adjusting the electrical signal of the excitation voltage in the upper stage. However, for a power supply, the maximum speed of the piezoelectric ceramic stack that can be achieved is limited. Since the piezoelectric ceramic stack is essentially a capacitor, if you want to drive the piezoelectric ceramic stack through the OA segment of the excitation voltage signal, the output current I of the power supply needs to be: The excitation voltage drives the piezoelectric ceramic stack in the voltage rising stage, and the output current I of the power supply needs to satisfy:

[0105]

[0106] The capacitance of the piezoelectric ceramic stack is usually much larger than the built-in capacitance of the power supply, and the excitation voltage is linearly related to time, so the above equation is simplified here:

[0107]

[0108] Wherein, C is the capacitance of the piezoelectric ceramic stack; the output current I of the power supply is calculated by the above formula. If the output current is less than the rated current of the power supply, the speed required for the impact test can be achieved within the rated current; if the output current is greater than the rated current of the power supply, replace the power supply, increase the rated current of the power supply by replacing the power supply, or select a capacitor of the piezoelectric ceramic stack with smaller capacitance, and recalculate the output current I of the power supply according to the above formula until the output current is less than the rated current of the power supply.

[0109] The above formula shows that if we want to use the voltage rising phase of the excitation voltage signal to drive the piezoelectric ceramic stack at a speed v in To produce deformation, the output current of the power supply needs to be I. Therefore, the rated current of the power supply limits the waveform of the excitation voltage in the rising stage, and the speed of the piezoelectric ceramic stack is also the maximum at this time.

[0110] In the constant voltage stage, the excitation voltage remains constant at the maximum value, and the constant stage time is Δt2. At this time, the piezoelectric ceramic stack does not deform, and the displacement output of the piezoelectric ceramic stack maintains the maximum output displacement ΔL of the piezoelectric ceramic stack. max This stage is the load-keeping process of the impact press-in test.

[0111] In the voltage drop stage, the excitation voltage is reduced from the maximum value U max The displacement of the piezoelectric ceramic stack is gradually reduced to 0 during the descending period Δt3. max Gradually decreases to 0. This stage is the unloading process of the impact test. According to the electrical signal of the excitation voltage in the constant voltage stage and the voltage drop stage, the holding time of the piezoelectric ceramic stack at the maximum displacement output and the retraction speed v are obtained. out ;

[0112] By regulating the voltage value and action time of the electrical signal of the excitation voltage in the voltage rising stage, the voltage constant stage and the voltage falling stage, the impact pressing process, the load holding process and the unloading process of the impact pressing test are controlled respectively.

[0113] Next, we will take a specific instrument device as an example to illustrate the impact indentation test driven by the piezoelectric ceramic stack based on the above principle. A high-power output power supply with a rated voltage of 2000V and a rated current (DC) of 400mA is used. The capacitance of the piezoelectric ceramic stack is 200nF, the rated voltage is 1000V, and the maximum stroke is 100μm. In the actual impact indentation test, the indenter is driven by the piezoelectric ceramic stack and pressed into the sample surface at a certain impact speed. Therefore, the displacement of the indenter and the piezoelectric ceramic stack is the same. To avoid ambiguity, the displacement in the following text refers to the displacement of the indenter. Secondly, for the impact test, the impact indentation process is the most critical. The duration of the indenter staying in the sample and gradually withdrawing from the sample is relatively long, and the speed of withdrawing from the sample is also relatively slow. Therefore, in this example, the impact indentation process is mainly described. When the sample is a soft material, in this case, it can be considered that the indenter can reach the maximum output displacement of the piezoelectric ceramic stack, that is, the maximum indentation depth, but the indentation load generated during the indentation process is also small. As the hardness of the sample material gradually increases, the indentation depth of the indenter will gradually decrease, but the indentation load during the process will also increase. Therefore, the following mainly describes the limit case of the indentation process, that is, the case with the maximum indentation depth.

[0114] Use as Figure 8 When the maximum excitation voltage applied is 1000V, according to the parameters of the piezoelectric ceramic stack, the maximum indentation depth of the indenter is 100μm. According to the impact velocity formula of the indenter:

[0115]

[0116] Since the capacitance of the piezoelectric ceramic stack is 200nF, according to the output current formula of the power supply:

[0117]

[0118] It can be seen that the output current of the power supply just reaches the rated value to meet the demand, so the indenter impacts the sample surface at a speed of 200mm / s, and this speed is the maximum impact speed that the indenter can reach. If you want to further increase the maximum impact speed, you need to adjust the parameters of the instrument.

[0119] By adjusting the electrical signal of the excitation voltage, the maximum value of the excitation voltage is reduced to 500V. According to the linear relationship between the displacement output of the piezoelectric ceramic stack and the excitation voltage, the maximum indentation depth of the indenter is 50μm, and the action time remains unchanged. The calculation method is the same as the above process, and then:

[0120]

[0121] It can be seen that under this excitation voltage signal, the impact speed and maximum penetration depth of the indenter are reduced, the required power supply output current is also reduced, and the power supply meets this output condition.

[0122] The stages in which the excitation current remains constant and decreases continuously correspond to the process in which the indenter stays in the sample and gradually withdraws from the sample surface. Compared with the impact pressing process of the indenter, these two processes last longer and the speed of the indenter is slower, so the control is also simpler.

[0123] Through the above examples, we know that within the rated current range of the power supply, by regulating the electrical signal of the excitation voltage, controlling the impact speed and maximum indentation depth of the indenter in the impact indentation test, the impact indentation test at a preset speed can be completed. Therefore, compared with other driving modes, the impact indentation test method proposed in the present invention realizes complete electric control braking, which is more convenient to operate and more precise to control. And under the condition that the specimen is a soft material, the indenter reaches the maximum output displacement of the piezoelectric ceramic stack, that is, there is a maximum indentation depth, but as the hardness of the specimen increases, the indentation depth of the indenter also decreases continuously, but the indentation load generated in the process will increase, which also shows that the displacement of the piezoelectric ceramic stack is self-limiting, ensuring the safety of the test at a larger impact speed.

[0124] By regulating the excitation voltage signal, changing its maximum value and the corresponding time of different stages, the indenter is pressed into the sample surface at a certain speed and an impact indentation test is completed. In this process, the indentation load and indentation depth during the indentation process are measured by force sensors and displacement sensors, and the measurement parameters of the sensors are recorded, processed and analyzed using data acquisition cards and computer systems. The iconic result is the indentation load-depth curve of impact indentation, such as Fig. 9 shown.

[0125] Fig. 9 In the figure, the horizontal axis is the indentation depth h, and the vertical axis is the indentation load F. O is the starting point, at which the indenter has the maximum speed; at point A, the indenter reaches the maximum indentation depth, at which point the speed of the indenter is 0; at point B, the indenter exits the sample surface, and the speed at which the indenter exits the sample is slower than the impact speed.

[0126] pass Fig. 9 The indentation load-depth curve shown in the figure describes the impact indentation test in which the indenter impacts the surface of the sample at a preset speed. The OA and AB segments of the curve are analyzed by the model analysis method to obtain the dynamic mechanical performance parameters of the material. For example, the Oliver-Pharr analysis method is used to analyze the AB segment to obtain the dynamic elastic modulus E of the sample.

[0127] 5) The force sensor and displacement sensor collect force signals and displacement signals respectively, which are collected by the information collector, transmitted to the digital control system to be converted into digital signals, and transmitted to the computer; the computer performs automatic control of the test and subsequent processing and analysis.

[0128] The present invention innovatively adopts piezoelectric ceramic stack as a driving module, inputs a specific voltage signal to the piezoelectric ceramic stack, realizes the pressure head to impact and press into the sample surface at a certain speed, uses force sensors and displacement sensors to monitor parameters, and controls the test process through a computer and performs subsequent processing and analysis. Compared with other impact press-in test methods, the advantages and novelties of the test method proposed by the present invention are: it completely adopts the piezoelectric ceramic stack for driving, gives full play to its advantages such as large stroke, fast response and simple regulation, so that the pressure head is pressed into the sample surface at a preset impact speed; the piezoelectric ceramic stack itself has displacement self-limiting property, and the impact press-in process regulation is more convenient, which greatly improves the operational stability and safety of the impact press-in test; the piezoelectric ceramic stack and the three-dimensional piezoelectric displacement stage of the present invention are both electrically controlled, so compared with the impact press-in test using different driving modes, the overall structure of the test system designed by the present invention is simple, easy to operate and precisely controlled, and a computer control system can be expanded on this basis to further improve the automation and convenience of the method.

[0129] Finally, it should be noted that the purpose of publishing the embodiments is to help further understand the present invention, but those skilled in the art can understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments, and the scope of protection claimed by the present invention shall be subject to the scope defined in the claims.

Claims

1. A piezoelectric ceramic stack driven impact indentation test method, characterized in that: The impact press-in test method comprises the following steps: 1) Build an impact press-in test system: One end of the piezoelectric ceramic stack is fixed on the frame, and the other end is fixedly connected to the pressure rod. The displacement direction of the piezoelectric ceramic stack is collinear with the pressure rod. The pressure rod is equipped with a displacement sensor and a force sensor. A pressure head is installed at the other end of the pressure rod. The sample is placed on the translation table, and the surface of the sample and the pressure rod are perpendicular to each other; The piezoelectric ceramic stack is connected to a power source; the force sensor and the displacement sensor are respectively connected to an information collector; the displacement stage is connected to a digital control system; the information collector and the digital control system are respectively connected to a computer; 2) According to the maximum output displacement U of the pressure head under free conditions f Estimated maximum indentation load F max and maximum penetration depth h max , maximum press load F max and maximum penetration depth h max The maximum output displacement U of the pressure head under free conditions f satisfy: Among them, E S and E C are the elastic modulus of the sample and the indenter, t and H are the thickness of the sample and the indenter, respectively. A is the stiffness of the piezoelectric ceramic stack; according to the maximum output displacement U of the indenter under free conditions f , the maximum indentation load F in the impact indentation test can be estimated using the above formula max and maximum penetration depth h max ; Based on the estimated maximum penetration depth h max and maximum indentation load F max , get the indentation load and indentation depth range of the impact indentation test, and then judge whether it meets the impact indentation test requirements. If the range is too large, adjust the test parameters and re-estimate according to the above formula until the impact indentation test requirements are met to ensure the feasibility and safety of the test; 3) The computer controls the translation stage to move the position of the sample through a digital control system so that the sample is placed under the pressure head; 4) The power supply sends an excitation voltage to the piezoelectric ceramic stack, and the excitation voltage excites the piezoelectric ceramic stack to move, thereby driving the indenter to impact the sample; the displacement of the piezoelectric ceramic stack is controlled by adjusting the electrical signal of the excitation voltage, thereby controlling the impact speed of the indenter, and the impact indentation test is realized by driving the indenter with voltage; the electrical signal of the excitation voltage is divided into three stages: a voltage rising stage, a voltage constant stage, and a voltage falling stage; The displacement of the piezoelectric ceramic stack is proportional to the excitation voltage. The maximum output displacement of the piezoelectric ceramic stack is ΔL. max : ΔL max =nd 33 U max Among them, U max is the maximum excitation voltage, n is the number of single-layer piezoelectric ceramic sheets in the piezoelectric ceramic stack, d 33 is the piezoelectric coefficient of the polarized piezoelectric ceramic in three directions; a) In the voltage rising stage, the excitation voltage reaches the maximum excitation voltage U within the rising stage time Δt1 max This stage is the impact indentation process of the impact indentation test; the speed of the piezoelectric ceramic stack is the impact speed of the indenter v in satisfy: Among them, Δt1 is the rising phase time of the excitation voltage; the speed v of the piezoelectric ceramic stack is in The speed of the pressure head is controlled by the power supply to adjust the electric signal of the excitation voltage, and the rising phase time of the excitation voltage is set so that the rising phase time Δt1 of the excitation voltage can quickly reach the maximum excitation voltage U of the kilovolt level within the microsecond level. max , the driving head has a greater impact speed, thus meeting the high speed requirement of the impact press-in test; The excitation voltage drives the piezoelectric ceramic stack in the voltage rising stage, and the output current I of the power supply satisfies: Wherein, C is the capacitance of the piezoelectric ceramic stack; the output current I of the power supply is calculated by the above formula. If the output current of the power supply is less than the rated current of the power supply, the speed required for the impact test can be achieved within the rated current; if the output current of the power supply is greater than the rated current of the power supply, the test conditions are changed and the output current I of the power supply is recalculated according to the above formula until the output current is less than the rated current of the power supply; b) In the constant voltage stage, the excitation voltage maintains the maximum value U max The constant stage time is Δt2, at which time the piezoelectric ceramic stack does not deform, and the displacement output of the piezoelectric ceramic stack maintains the maximum output displacement ΔL of the piezoelectric ceramic stack. max This stage is the load-keeping process of the impact press-in test. c) In the voltage drop stage, the excitation voltage is reduced from the maximum value U max The displacement of the piezoelectric ceramic stack is gradually reduced to 0 during the descending period Δt3. max Gradually decreases to 0. This stage is the unloading process of the impact press-in test. According to the electrical signal of the excitation voltage in the constant voltage stage and the voltage drop stage, the holding time of the piezoelectric ceramic stack at the maximum displacement output and the retraction speed v are obtained. out ; By regulating the voltage value and action time of the electric signal of the excitation voltage in the voltage rising stage, the voltage constant stage and the voltage falling stage, the impact pressing process, the load holding process and the unloading process of the indenter in the impact pressing test are controlled respectively; 5) The force sensor and displacement sensor obtain force signals and displacement signals respectively, which are collected by the information collector, transmitted to the digital control system to be converted into digital signals, and transmitted to the computer; the computer performs automatic control of the test and subsequent processing and analysis.

2. The impact indentation test method according to claim 1, characterized in that: In step 2), the maximum output displacement U of the indenter under free conditions is obtained by adjusting the electrical signal of the excitation voltage of the power supply and combining the displacement output characteristics of the piezoelectric ceramic stack. f ; The displacement directions of the pressure head and the piezoelectric ceramic stack are the same, so the displacement output of the piezoelectric ceramic stack is the same as the displacement output of the pressure head.

3. The impact indentation test method according to claim 1, characterized in that: In step 2), if the range is too large, the test parameters to be adjusted are one or more of the type, size and material of the indenter, the thickness of the sample, and the type of the piezoelectric ceramic stack.

4. The impact press-in test method according to claim 1, characterized in that: In step 4), the power supply itself has the function of adjusting the excitation voltage signal and can input the electrical signal of the excitation voltage to the piezoelectric ceramic stack; or the power supply is connected to an analog-to-digital converter, and the analog-to-digital converter is connected to a computer, and the computer controls the electrical signal of the excitation voltage input by the power supply to the piezoelectric ceramic stack through the analog-to-digital converter.

5. The impact indentation test method according to claim 1, characterized in that: In step 4) a), if the output current is greater than the rated current of the power supply, the test condition is changed to replace the power supply to increase the rated current of the power supply or to select a capacitor of a piezoelectric ceramic stack with a smaller capacitance.

6. The impact indentation test method according to claim 1, characterized in that: In step 4) a), the rising phase time Δt1 of the excitation voltage ranges from 0.1ms to 10ms, and the maximum excitation voltage U max The range is between 100V and 1000V.

7. A piezoelectric ceramic stack driven impact indentation test system, characterized in that: The impact indentation test system comprises: a translation table, a sample, a pressure head, a force sensor, a displacement sensor, a pressure rod, a piezoelectric ceramic stack, a frame, a power supply, an information collector, a digital control system and a computer; wherein one end of the piezoelectric ceramic stack is fixed on the frame, and the other end is fixedly connected to the pressure rod, and the displacement direction of the piezoelectric ceramic stack is in line with the pressure rod; the pressure rod is equipped with a displacement sensor and a force sensor; the other end of the pressure rod is equipped with a pressure head; the sample is mounted on the translation table, and the surface of the sample is perpendicular to the pressure rod; the piezoelectric ceramic stack is connected to the power supply; the force sensor and the displacement sensor are respectively connected to the information collector; the translation table is connected to the digital control system; the information collector and the digital control system are respectively connected to the computer; the computer controls the translation table to move the sample through the digital control system so that the sample is placed The power supply sends an excitation voltage to the piezoelectric ceramic stack, and the excitation voltage excites the piezoelectric ceramic stack to displace, thereby driving the indenter to impact the sample; the displacement of the piezoelectric ceramic stack is controlled by adjusting the electrical signal of the excitation voltage, thereby controlling the impact speed of the indenter, and realizing the impact indentation test by driving the indenter through voltage; the impact indentation process, the load holding process and the unloading process of the indenter in the impact indentation test are controlled respectively by regulating the voltage value and the action time of the electrical signal of the excitation voltage in the voltage rising stage, the voltage constant stage and the lower voltage drop stage; the force sensor and the displacement sensor obtain the force signal and the displacement signal respectively, which are collected by the information collector, transmitted to the digital control system to be converted into digital signals, and transmitted to the computer; the computer performs automatic control, subsequent processing and analysis on the test.

8. The impact press-in test system according to claim 7, characterized in that: The displacement stage adopts a three-dimensional piezoelectric displacement stage.

9. The impact press-in test system according to claim 7, characterized in that: The piezoelectric ceramic stack includes a plurality of identical single-layer piezoelectric ceramic sheets and electrodes, wherein the electrodes include a positive electrode and a negative electrode; wherein the plurality of single-layer piezoelectric ceramic sheets are stacked, an electrode is arranged between two adjacent single-layer piezoelectric ceramic sheets, and the polarities of the two adjacent electrodes are opposite, so that the polarization directions of the piezoelectric ceramics of the adjacent single-layer piezoelectric ceramic sheets are opposite.

Images