A device and method for measuring the bulk modulus of a viscoelastic material based on electrical measurements

Abstract

The present application belongs to the field of material testing, and particularly relates to a viscoelastic material bulk modulus measuring device and method based on an electric measuring method, wherein the measuring device comprises a pressure tank and a viscoelastic material testing support; the viscoelastic material testing support comprises a fixing frame and a plurality of sets of deformation testing clamps; the deformation testing clamp comprises a fixed elastic sheet, a testing elastic sheet and a clamp block, the fixed elastic sheet is provided with a hollow slot in the middle, the testing elastic sheet is arranged through the hollow slot, and the fixed elastic sheet and the testing elastic sheet are perpendicular to each other, a strain gauge is pasted on the testing elastic sheet, adjacent one end of the fixed elastic sheet and the testing elastic sheet is fixedly arranged on the fixing frame, and adjacent the other end is fixedly arranged on the clamp block, and the clamp block is provided with an abutting rod perpendicular to the arrangement direction of the testing elastic sheet. The present application realizes direct and high signal-to-noise ratio measurement of the bulk strain of the viscoelastic material under a hydrostatic pressure environment by precisely isolating non-measurement direction interference through the double elastic sheet structure of the fixed elastic sheet and the testing elastic sheet of the deformation testing clamp.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of material testing, and particularly relates to a viscoelastic material bulk modulus measuring device and method based on electrical measurement method. BACKGROUND

[0002] Propellant grain is a kind of particle reinforced composite material, and its mechanical properties are time-dependent, and the material properties will degrade with the extension of storage time. At present, the integrity evaluation of propellant grain mainly relies on numerical simulation analysis, and the bulk modulus is an important material parameter in the simulation calculation of the structural integrity of propellant grain.

[0003] The existing bulk modulus measurement techniques usually include indirect calculation, unidirectional compression test and three-directional confining test, but all have some problems, which are as follows:

[0004] Indirect calculation theory: Since it is difficult to directly and accurately measure the bulk modulus, the bulk modulus parameter of propellant material is currently obtained by the relationship between the tensile modulus, Poisson's ratio and the bulk modulus in the isotropic linear elasticity theory, and is represented by the tensile modulus and Poisson's ratio measured by the test. Since the tensile modulus and Poisson's ratio are obtained by the test respectively, the cumulative error of the bulk modulus obtained by numerical iteration will naturally increase. This principle is based on the assumption of isotropy of the material, and is not applicable to many anisotropic or tension-compression different materials (such as polymers, composites, etc.). The propellant material is a viscoelastic material, and its bulk modulus, Young's modulus and Poisson's ratio are all functions of time. In addition, the tensile and compressive properties of the propellant material are quite different, so the bulk modulus of the propellant material obtained from the above formula is quite different from the actual situation, and cannot meet the needs of accurate analysis and calculation of the mechanical response of the engine grain. Therefore, it is necessary to study the test theory of the bulk modulus, establish the test method of the bulk modulus of the propellant material, and accurately measure the bulk modulus of the propellant material.

[0005] Elastomer unidirectional compression test: the traditional elastomer bulk modulus test method (Chinese patent "CN202111041242.1 Elastomer bulk modulus test device and method") is based on the isotropic linear elasticity assumption, and uses the uniaxial compression test with radial constraint to calculate the bulk modulus, which is not applicable to the bulk modulus measurement of viscoelastic materials. Because the viscoelastic material does not conform to the linear elasticity assumption, and the bulk modulus of the viscoelastic material is time-dependent, the mechanical properties of the viscoelastic material need to be measured by creep or relaxation test to obtain the curve of the change of the mechanical properties with time, and the traditional elastomer compression test cannot meet the requirements.

[0006] Three-direction confining pressure test: In the three-direction confining pressure test device, hydraulic oil is usually used as the pressure transmission medium. The traditional oil pressure volume modulus test device (such as a piston type sealing tank) applies pressure to the high-pressure sealing tank piston, measures the volume change in the container, although the structure is simple, but there are problems of poor sealing, deformation of the metal container itself, and additional volume change caused by the compression of the pressure medium, so the measured volume change may not be the volume change of the test piece, and the precision is not enough. The current way to handle the error of the oil pressure device is to do a contrast empty load test or place a calibration test of an equal volume of stainless steel block. The algebraic difference between the liquid intake data obtained during the loaded test and the liquid intake data under the empty load condition is used as the actual liquid intake data. The corresponding relationship between the actual liquid intake data and the pressure is used to determine the material volume modulus (Chinese patent "CN202010218902.8 A testing system and method for testing the isostatic pressure strength and volume modulus"). However, this processing method cannot completely eliminate the system error of the oil pressure device, such as poor sealing, and each pressure needs to be tested to exclude the influence of medium liquid compression and container deformation, which is complex and time-consuming. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a simple structure based on the electrical measurement method for accurately measuring the volume modulus of viscoelastic materials.

[0008] The present application provides a viscoelastic material volume modulus measurement device based on an electrical measurement method, comprising a pressure tank, a viscoelastic material test support placed in the pressure tank, and a material to be tested arranged in the viscoelastic material test support.

[0009] The material to be tested is a viscoelastic material in the shape of a regular hexahedron.

[0010] The viscoelastic material test support comprises a fixing frame and a plurality of sets of deformation test clamps arranged on the fixing frame.

[0011] The deformation test clamp comprises a fixed elastic sheet, a test elastic sheet, and a clamp block. The fixed elastic sheet has a hollow slot in the middle, the test elastic sheet is arranged through the hollow slot, and the fixed elastic sheet and the test elastic sheet are perpendicular to each other. A strain gauge is attached to the test elastic sheet. Adjacent one end of the fixed elastic sheet and the test elastic sheet is fixedly arranged on the fixing frame, and the adjacent other end is fixedly arranged with the clamp block. The clamp block is provided with an abutting rod perpendicular to the arrangement direction of the test elastic sheet.

[0012] The fixing frame is provided with a mounting station for the material to be tested. The bottom surface of the material to be tested is placed on the mounting station, and the abutting rods of the other viscoelastic material test supports are respectively abutted on the other surfaces of the material to be tested.

[0013] Further, the abutting rod is slidingly arranged on the clamp block.

[0014] One end of the abutting rod is slidingly connected with the fixing frame, and the other end of the abutting rod is provided with an abutting block through the clamp block.

[0015] The abutting rod is provided with a spring, and one end of the spring is abutted with the fixing frame, and the other end of the spring is abutted with the clamp block.

[0016] Further, the abutting rod comprises a sliding rod and a mounting rod which are connected in sequence and can be detached.

[0017] One end of the sliding rod is slidingly connected with the fixing frame, and the other end of the sliding rod is connected with the clamp block.

[0018] The mounting rod is arranged on the side of the sliding rod close to the mounting station.

[0019] The abutting block is arranged on the side of the mounting rod away from the clamp block.

[0020] Further, the fixing frame comprises a bottom plate, a side wall arranged on the periphery of the bottom plate, and a gantry arranged on the side wall.

[0021] The fixing spring, the test spring and the abutting rod of the deformation test clamp abutting the top surface of the material to be tested are arranged on the gantry.

[0022] The fixing spring, the test spring and the abutting rod of the other deformation test clamp are arranged on the side wall.

[0023] Further, the clamp block comprises a right-angle block and a connecting plate connected to one end of the right-angle block, two ends of the right-angle block are respectively used for fixing the fixing spring and the test spring, and the connecting plate is used for fixing the abutting rod.

[0024] Further, the fixing spring and the test spring are fixed on the fixing frame and the clamp block through the clamp block.

[0025] Further, the test spring comprises a rectangular section and widened sections arranged at two ends of the rectangular section, and the widened sections are used for fixing the fixing frame and the clamp block through the clamp block.

[0026] Further, the pressure tank comprises an openable cavity, a pressure charging and discharging port connected with the cavity, an exhaust valve and a pressure sensor.

[0027] The application also provides a method for measuring the bulk modulus of a viscoelastic material based on the electrical measurement method.

[0028] S1, place the bottom surface of the material to be tested in the installation station, install a set of deformation test clamps on each surface of the material to be tested, and obtain the initial value of the strain gauge on each deformation test clamp;

[0029] S2, place the viscoelastic material test support installed with the material to be tested in the pressure tank, and inject liquid medium into the pressure tank until the liquid medium reaches the set pressure;

[0030] S3, obtain the pressure value in the pressure tank and the deformation data of the strain gauge on each deformation test clamp, and calculate the bulk modulus of the material to be tested through the deformation data.

[0031] The beneficial effects of the present application are that the present application precisely isolates the interference in the non-measurement direction through the double elastic sheet structure of the fixed elastic sheet and the test elastic sheet of the deformation test clamp, realizes the full-surface monitoring of the polyhedron of the material to be tested and the reference positioning of the installation station through the fixed frame, realizes the direct, in-situ and high signal-to-noise ratio measurement of the bulk strain of the viscoelastic material under the hydrostatic pressure environment, completely eliminates the indirect theoretical error and system deviation, and provides true value data support for the life prediction of the propellant. BRIEF DESCRIPTION OF DRAWINGS

[0032] The accompanying drawings illustrate the present application by way of example, and together with the detailed description below, serve to provide a further understanding of the present application. Figure 1 The accompanying drawings illustrate the present application by way of example, and together with the detailed description below, serve to provide a further understanding of the present application.

[0033] The accompanying drawings illustrate the present application by way of example, and together with the detailed description below, serve to provide a further understanding of the present application. Figure 2 The accompanying drawings illustrate the present application by way of example, and together with the detailed description below, serve to provide a further understanding of the present application.

[0034] The accompanying drawings illustrate the present application by way of example, and together with the detailed description below, serve to provide a further understanding of the present application. Figure 3 The accompanying drawings illustrate the present application by way of example, and together with the detailed description below, serve to provide a further understanding of the present application.

[0035] The accompanying drawings illustrate the present application by way of example, and together with the detailed description below, serve to provide a further understanding of the present application. Figure 4 The accompanying drawings illustrate the present application by way of example, and together with the detailed description below, serve to provide a further understanding of the present application.

[0036] The accompanying drawings illustrate the present application by way of example, and together with the detailed description below, serve to provide a further understanding of the present application. Figure 5 The accompanying drawings illustrate the present application by way of example, and together with the detailed description below, serve to provide a further understanding of the present application.

[0037] In the drawings, 1-viscoelastic material test support; 11-fixed frame; 111-bottom plate; 112-side wall; 113-gantry; 114-installation station; 12-deformation test clamp; 121-fixed elastic sheet; 122-test elastic sheet; 1221-rectangular section; 1222-widened section; 123-clamp block; 1231-right-angle block; 1232-connection plate; 124-abutment rod; 1241-sliding rod; 1242-mounting rod; 125-abutment block; 126-spring; 127-clamp block; 2-pressure tank; 21-cavity; 22-pressure charging and pressure releasing port; 23-exhaust valve; 24-pressure sensor; 3-material to be tested. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0039] It should be noted that all directional indications, such as up, down, left, right, front, back, etc., in the embodiments of the present application are only used to explain the relative position relationship, movement condition, etc. between components in a certain posture (as shown in the drawings), and if the certain posture changes, the directional indications also change accordingly.

[0040] In addition, the description such as "first", "second" and the like in the present application is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise explicitly specified.

[0041] In the present application, unless otherwise explicitly specified and limited, the terms "connection", "fixation" and the like should be understood in a broad sense, for example, "fixation" can be fixed connection, or detachable connection, or integral; can be mechanical connection, or electrical connection, or physical connection or wireless communication connection; can be directly connected, or indirectly connected through an intermediate medium, or the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For a person of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0042] In addition, the technical solutions of each embodiment of the present application can be combined with each other, but it must be based on the fact that a person of ordinary skill in the art can realize it, and when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, and is not within the scope of protection claimed by the present application.

[0043] As shown in the accompanying drawings, the present application provides a viscoelastic material bulk modulus measurement device based on electrical measurement method, which comprises a pressure tank 2, a viscoelastic material test support 1 for being placed in the pressure tank 2, and a material to be tested 3 arranged in the viscoelastic material test support 1. Figure 1 - the accompanying drawings Figure 5 As shown in the accompanying drawings, the present application provides a viscoelastic material bulk modulus measurement device based on electrical measurement method, which comprises a pressure tank 2, a viscoelastic material test support 1 for being placed in the pressure tank 2, and a material to be tested 3 arranged in the viscoelastic material test support 1.

[0044] The material to be tested 3 is a viscoelastic material in the shape of a regular hexahedron; the viscoelastic material can be used as a propellant grain, and the mechanical properties thereof are time-dependent, and the material performance will degrade with the extension of storage time.

[0045] The viscoelastic material testing support 1 comprises a fixing frame 11 and a plurality of sets of deformation testing clamps 12 arranged on the fixing frame 11; when the material to be tested 3 is in the shape of a regular hexahedron, the material to be tested 3 has three mutually parallel faces, and the deformation testing clamps 12 are arranged in a total of five, one of which is arranged on the top face of the material to be tested 3, and the other four are arranged on the four side faces of the material to be tested 3.

[0046] The deformation testing clamp 12 comprises a fixed spring 121, a testing spring 122 and a clamp block 123; the fixed spring 121 is provided with a hollow slot in the middle, the testing spring 122 is arranged through the hollow slot, and the fixed spring 121 and the testing spring 122 are perpendicular to each other; a strain gauge is attached to the testing spring 122; the adjacent one end of the fixed spring 121 and the testing spring 122 is fixedly arranged on the fixing frame 11, and the adjacent other end is fixedly arranged with the clamp block 123; the clamp block 123 is provided with an abutting rod 124 perpendicular to the arrangement direction of the testing spring 122; wherein the fixed spring 121 mainly bears the main pressure and possible overturning moment transmitted by the clamp block 123 due to the deformation of the material to be tested 3, so as to ensure the stability of the contact between the deformation testing clamp 12 and the material to be tested 3, and the testing spring 122 is mainly caused by the small normal displacement of the material to be tested 3 transmitted through the abutting rod 124. This design greatly isolates the interference of the non-measurement direction force (such as lateral force or torsional load) and the overall posture change of the deformation testing clamp 12 on the testing spring 122, significantly improves the signal-to-noise ratio and accuracy of the strain measurement, and makes the measurement results more truly reflect the volume compression characteristics of the material. In addition, the adjacent one end of the fixed spring 121 and the testing spring 122 is fixedly arranged on the same fixing frame 11, forming a stable reference point, and the other end is jointly connected with the clamp block 123, thereby forming a double support structure, which improves the stability of the deformation testing clamp 12 when transmitting pressure, the ability to resist lateral shaking and the tolerance to installation errors. Reduces measurement errors caused by loosening of the deformation testing clamp 12 or sample installation deviation.

[0047] The abutting rod 124 is aligned with the deformation direction of the material to be tested 3, and the abutting rod 124 is designed to be perpendicular to the arrangement direction of the testing spring 122 (i.e. perpendicular to the stress direction of the testing spring 122), which, combined with the arrangement direction of the fixed spring 121, ensures that the force applied to the surface of the material to be tested 3 is along the normal direction of the sample surface, meeting the basic requirements of volume compression testing.

[0048] The fixing frame 11 is provided with a mounting station 114 of the material to be tested 3, and the bottom surface of the material to be tested 3 is placed on the mounting station 114, and the abutting rods 124 of the other viscoelastic material testing supports 1 are respectively abutted on the other surfaces of the material to be tested 3. Among them, the mounting station 114 provides a stable and accurate positioning plane for the material to be tested 3. The bottom surface of the material to be tested 3 is directly placed thereon, which ensures that the material to be tested 3 has a fixed and reliable spatial position reference. At this time, the top surface of the material to be tested 3 directly feeds back the displacement of the material to be tested 3 in the Z direction through the corresponding deformation test fixture 12. The two groups of deformation test fixtures 12 corresponding to the two parallel side surfaces of the material to be tested 3 can test the displacement of the two parallel side surfaces. At this time, all the sample surfaces (top and side surfaces) not in contact with the mounting station 114 are defined as independent target surfaces for applying pressure and measuring deformation. Taking the material to be tested 3 as a regular hexahedron as an example, at this time, the bottom surface of the material to be tested 3 is supported and fixed by the mounting station 114, the corresponding deformation test fixture 12 tests the Z-direction compression displacement of the material to be tested 3, and the other four deformation test fixtures 12 respectively test the X-direction and Y-direction compression displacement of the side surface of the material to be tested 3. In addition, the bottom surface of the material to be tested 3 is directly placed on the mounting station 114, which can avoid the movement of the material to be tested 3 during compression, thereby avoiding the problem of inaccurate measurement. It can ensure the accurate connection of all deformation test fixtures 12 and the material to be tested 3, and reduce the displacement measurement error caused by unclear connection or uneven contact.

[0049] In one embodiment, the abutting rod 124 is slidingly arranged on the clamp block 123.

[0050] One end of the abutting rod 124 is slidingly matched with the fixing frame 11, and the other end is provided with an abutting block 125 penetrating through the clamp block 123.

[0051] The abutting rod 124 is provided with a spring 126, and one end of the spring 126 is abutted with the fixing frame 11, and the other end is abutted with the clamp block 123.

[0052] In the embodiment, when the abutting rod 124 is fixedly connected with the clamp block 123, the abutting rod 124 and the clamp block 123 are fixedly connected as a rigid whole, so as to ensure that the normal deformation of the material surface is transmitted to the test sheet 122 without loss and hysteresis through the abutting block 125, and the stability and test precision of the whole deformation test fixture 12 are greatly improved. The abutting rod 124 is in sliding fit with the fixed frame 11, so as to limit the movement direction of the abutting rod 124, and enable the abutting rod 124 to move in single degree of freedom along the compression direction of the material to be tested 3, so as to ensure measurement accuracy and realize automatic centering during installation. The overall rigid structure ensures that the abutting surface is always perpendicular to the normal line of the material, so as to avoid interference of shear components caused by deflection of the contact point. The spring 126 is arranged, so as to enable the abutting rod 124 to adapt to the deformation of the material to be tested 3, and enable the abutting rod 124 to be in close contact with the material to be tested 3. Specifically, during the test, the material to be tested 3 slowly shrinks in volume under pressure. The spring 126 enables the abutting rod 124 to freely move in the guide groove of the clamp block 123 and the fixed frame 11, so as to enable the abutting block 125 to be always in close contact with the surface of the material to be tested 3, and avoid contact failure or gap caused by material shrinkage.

[0053] In the embodiment, the deformation test fixture 12 has high anti-interference and stability, can accurately obtain the normal displacement of the material to be tested 3, and greatly improves the measurement accuracy.

[0054] In one of the embodiments, the abutting rod 124 comprises a sliding rod 1241 and a mounting rod 1242 which are detachably connected in sequence. Preferably, the sliding rod 1241 and the mounting rod 1242 are threadedly connected, so as to greatly simplify the connection difficulty.

[0055] One end of the sliding rod 1241 is in sliding connection with the fixed frame 11, and the other end is connected with the clamp block 123, that is, the sliding rod 1241 and the clamp block 123 can be fixedly connected or in sliding connection.

[0056] The mounting rod 1242 is arranged on the side of the sliding rod 1241 close to the mounting station 114.

[0057] The abutting block 125 is arranged on the side of the mounting rod 1242 away from the clamp block 123. Preferably, the abutting block 125 adopts a disc structure, so as to increase the contact area.

[0058] In the embodiment, the abutting rod 124 can be conveniently installed and debugged.

[0059] In one of the embodiments, the fixed frame 11 comprises a bottom plate 111, a side wall 112 arranged on one side of the bottom plate 111, and a portal frame 113 arranged on the side wall 112.

[0060] The fixed spring 121, the test spring 122 and the abutting rod 124 of the deformation test clamp 12 abutting the top surface of the material to be tested 3 are all arranged on the gantry 113;

[0061] The fixed spring 121, the test spring 122 and the abutting rod 124 of the deformation test clamp 12 are all arranged on the side wall 112.

[0062] In this embodiment, the gantry 113 is used to fix the deformation test clamp 12 on the top and can be used to facilitate the transfer of the entire viscoelastic material test support 1 by the staff or the mechanical arm. The side wall 112 can be used to install the remaining deformation test clamp 12 and physically protect the deformation test clamp 12, thereby improving the stability of the viscoelastic material test support 1 during the transfer process.

[0063] In one embodiment, the clamp block 123 includes a right-angle block 1231 and a connecting plate 1232 connected to one end of the right-angle block 1231. The two ends of the right-angle block 1231 are respectively used to fix the fixed spring 121 and the test spring 122. The connecting plate 1232 is used to fix the abutting rod 124.

[0064] In this embodiment, the right-angle block 1231 has the fixed spring 121 (used for main force bearing) and the test spring 122 (used for pure strain sensing) fixed on both sides, respectively, to physically isolate the deformation fields of the two. The connecting plate 1232 serves as a mounting base for the abutting rod 124, which transmits the deformation of the material to be tested 3 to the sensing unit boundary without damage. The Z-shaped structure composed of the right-angle block 1231 and the connecting plate 1232 can greatly reduce the deformation interference of the clamp block 123 itself relative to the support plate structure.

[0065] In one embodiment, the fixed spring 121 and the test spring 122 are fixed on the fixed frame 11 and the clamp block 123 by the clamp block 127. That is, the two ends of the fixed spring 121 are fixed on the fixed frame 11 and the clamp block 123 by the clamp block 127, and the two ends of the test spring 122 are fixed on the fixed frame 11 and the clamp block 123 by the clamp block 127. This simplifies the installation difficulty of the fixed spring 121 and the test spring 122.

[0066] In one embodiment, the test spring 122 includes a rectangular section 1221 and widened sections 1222 arranged at both ends of the rectangular section 1221. The widened sections 1222 fix the fixed frame 11 and the clamp block 123 by the clamp block 127.

[0067] In this embodiment, the rectangular section 1221 is designed to maintain equal cross-section and equal strength to ensure that the strain gradient of the strain gauge pasting area is small enough. The widened sections 1222 have increased width to form a flexible transition zone, reduce stress concentration at the clamping position, and improve clamping stability.

[0068] In one of the embodiments, the pressure tank 2 comprises an openable cavity 21, a pressurizing and depressurizing port 22 connected to the cavity 21, an exhaust valve 23 and a pressure sensor 24. The cavity 21 is used to accommodate the material to be tested 3, the viscoelastic material testing support 1 and the liquid medium. The pressurizing and depressurizing port 22 is used to inject or discharge the liquid medium into the cavity 21. The exhaust valve 23 is used to remove air when injecting into the cavity 21, and the pressure sensor 24 is used to monitor the pressure of the liquid medium in the cavity 21.

[0069] The present application also provides a method for measuring the bulk modulus of viscoelastic material based on the electrical measurement method, which uses the method for measuring the bulk modulus of viscoelastic material based on the electrical measurement method, and comprises the following steps:

[0070] S1, placing the bottom surface of the material to be tested 3 in the installation station 114, and installing a set of deformation testing clamps 12 on each surface of the material to be tested 3, and obtaining the initial value of the strain gauge on each deformation testing clamp 12;

[0071] S2, placing the viscoelastic material testing support 1 with the material to be tested 3 in the pressure tank 2, and injecting the liquid medium into the pressure tank 2 until the liquid medium reaches the set pressure;

[0072] S3, obtaining the pressure value in the pressure tank 2 and the deformation data of the strain gauge on each deformation testing clamp 12, and calculating the bulk modulus of the material to be tested 3 through the deformation data.

[0073] In this embodiment, the normal micro-strain of the material to be tested 3 is directly captured through multiple sets of deformation testing clamps 12, and after the model of "surface strain-bulk strain" is constructed, the measurement result can truly reflect the bulk modulus of the viscoelastic material under the hydrostatic pressure state, so that the measurement error is minimal. The true value of the bulk modulus of the viscoelastic material is directly collected, replacing the existing indirect calculation method, and the systematic theoretical deviation caused by the anisotropy, tensile-compressive difference and time dependence of the material is completely avoided.

[0074] The problems of inaccurate calculation of traditional indirect calculation theory, low applicability of one-way compression test and large system error of three-way confining pressure test are solved. Specifically, for the systematic error of the oil pressure device, the volumetric modulus measuring device measures the displacement of the test piece in XYZ three directions under compression, and directly obtains the volume change of the test piece, instead of using the overall volume change in the high-pressure container to represent the volume change of the test piece. This direct measurement method effectively eliminates the systematic errors of the oil pressure device such as poor sealing, deformation of the metal container itself, and compression of the medium liquid, thereby improving the system accuracy of the test. At the same time, the traditional method to eliminate the systematic error of the oil pressure device is to do calibration experiments, and each group of pressure needs to do corresponding loaded experiments and unloaded experiments. Since the volume deformation of the test piece is directly measured, repeated calibration experiments are not needed to eliminate the influence of medium liquid compression and container deformation, thereby simplifying the test process.

[0075] In addition, the measurement method can accurately measure the multi-directional displacement change of the test material 3 under hydrostatic pressure, and can compare whether the multi-directional displacement is consistent to observe whether the material is an isotropic material. That is, the measurement device and method have good applicability for the volumetric modulus measurement of non-isotropic materials, and can also observe and analyze the isotropic performance of the material.

[0076] In one embodiment, the calculation model includes a volumetric calculation model.

[0077] The volumetric modulus calculation model is:

[0078] ;

[0079] wherein, P is the measured pressure in the pressure tank 3; is the initial side length of the test material 3; x is the displacement data measured by the pressure test fixture in each direction.

[0080] Specifically, the volumetric modulus definition formula is: ;

[0081] wherein, P is the measured pressure in the pressure tank 3, ΔV is the volume change of the test material 3, V 0 is the initial volume of the test material 3.

[0082] P which can be directly obtained by the pressure sensor, V 0 can be measured and determined in advance. ΔV which needs to be obtained from the displacement in each direction, taking the test material 3 as a regular hexahedron:

[0083] ;

[0084] wherein is the original edge length of the cubic specimen, is the displacement in three directions.

[0085] For small deformation (ε ), the high order small terms are ignored, and the expansion is:

[0086]

[0087] The bulk modulus is:

[0088] If it is an isotropic material, i.e. only the displacement in any direction is measured , then the bulk modulus K is calculated as: .

[0089] The above is only the embodiment of the present application, and does not limit the present application. Any skilled person in the art can make many possible changes, modifications or modifications to the technical solution of the present application without departing from the scope of the technical solution of the present application, and the equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present application shall fall within the scope of protection of the technical solution of the present application.

Claims

1. A device for measuring the bulk modulus of viscoelastic materials based on an electrical measurement method, characterized in that, Includes a pressure vessel (2), a viscoelastic material test holder (1) for placing inside the pressure vessel (2), and a test material (3) placed inside the viscoelastic material test holder (1); The material to be tested (3) is a regular hexahedral viscoelastic material; The viscoelastic material test bracket (1) includes a fixed frame (11) and several sets of deformation test fixtures (12) set on the fixed frame (11). The deformation test fixture (12) includes a fixing spring (121), a test spring (122), and a fixture block (123). The fixing spring (121) has a slot in the middle. The test spring (122) passes through the slot and is perpendicular to each other. A strain gauge is attached to the test spring (122). One adjacent end of the fixing spring (121) and the test spring (122) is fixed on the fixing frame (11), and the other adjacent end is fixed to the fixture block (123). The fixture block (123) is provided with an abutment rod (124) perpendicular to the arrangement direction of the test spring (122). The mounting frame (11) is provided with an installation station (114) for the material to be tested (3). The bottom surface of the material to be tested (3) is placed on the installation station (114), and the abutment rods (124) of the other viscoelastic material test brackets (1) abut against other surfaces of the material to be tested (3). The abutment rod (124) is slidably mounted on the clamp block (123); One end of the abutment rod (124) is slidably engaged with the fixing frame (11), and the other end passes through the clamp block (123) and is provided with an abutment block (125). The abutment rod (124) is fitted with a spring (126), and one end of the spring (126) abuts against the fixing frame (11), and the other end abuts against the clamp block (123); The fixed frame (11) includes a base plate (111), a side wall (112) arranged around the base plate (111), and a gantry frame (113) arranged on the side wall (112). The fixing spring (121), the test spring (122), and the abutment rod (124) of the deformation test fixture (12) that abuts the top surface of the test material (3) are all set on the gantry (113); The fixing spring (121), the test spring (122), and the abutment rod (124) of the other deformation test fixture (12) are all provided on the side wall (112).

2. The device for measuring the bulk modulus of viscoelastic materials based on the electrical measurement method as described in claim 1, characterized in that, The abutment rod (124) includes a sliding rod (1241) and a mounting rod (1242) that are detachably connected in sequence. One end of the sliding rod (1241) is slidably connected to the fixed frame (11), and the other end is connected to the clamp block (123); The mounting rod (1242) is located on the side of the sliding rod (1241) near the mounting position (114); The abutment block (125) is located on the side of the mounting rod (1242) away from the clamp block (123).

3. The device for measuring the bulk modulus of viscoelastic materials based on the electrical measurement method as described in claim 1, characterized in that, The clamp block (123) includes a right-angle block (1231) and a connecting plate (1232) connected to one end of the right-angle block (1231). The two ends of the right-angle block (1231) are used to fix the fixing spring (121) and the test spring (122) respectively. The connecting plate (1232) is used to fix the abutment rod (124).

4. The device for measuring the bulk modulus of viscoelastic materials based on the electrical measurement method as described in claim 1, characterized in that, The fixed spring (121) and the test spring (122) are fixed to the fixed frame (11) and the clamp block (123) by the clamp block (127).

5. The device for measuring the bulk modulus of viscoelastic materials based on the electrical measurement method as described in claim 4, characterized in that, The test spring (122) includes a rectangular section (1221) and widened sections (1222) at both ends of the rectangular section (1221). The widened sections (1222) fix the fixing frame (11) and the clamp block (123) by clamping blocks (127).

6. The device for measuring the bulk modulus of viscoelastic materials based on the electrical measurement method as described in any one of claims 1-5, characterized in that, The pressure tank (2) includes an openable cavity (21), an inlet / outlet (22) connected to the cavity (21), an exhaust valve (23), and a pressure sensor (24).

7. A method for measuring the bulk modulus of viscoelastic materials based on electrical measurement, characterized in that, The method for measuring the bulk modulus of viscoelastic materials based on the electrical measurement method as described in any one of claims 1-6 includes the following steps: S1, place the bottom surface of the material to be tested (3) on the installation station (114), install a set of deformation test fixtures (12) on each surface of the material to be tested (3), and obtain the initial value of the strain gauge on each deformation test fixture (12); S2, place the viscoelastic material test bracket (1) with the material to be tested (3) installed in the pressure tank (2), and inject liquid medium into the pressure tank (2) until the liquid medium reaches the set pressure; S3, obtain the pressure value inside the pressure tank (2) and the deformation data of the strain gauge on each deformation test fixture (12), and calculate the bulk modulus of the material to be tested (3) through the deformation data.

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