Inorganic Strain Gauges

Abstract

The present invention relates to a device (50) for measuring deformation comprising a deformable body (55) and a strain gauge (5), the strain gauge comprising a support (15) in contact with the deformable body and a metallic resistive element (10) in contact with the support, the resistive element having a resistance that varies with deformation of the deformable body, the support being made from at least one support material that is electrically insulating, porous and comprises at least one heat-resistant, optionally hydrated, ceramic compound.

Description

[Technical field]

[0001] The present invention relates to the measurement of deformation by means of contact strain gauges. [Background technology]

[0002] A contact strain gauge makes it possible to measure the deformation of a body in a given direction and for this purpose it is in contact, generally with an adhesive bond, with the body whose deformation it is desired to measure.

[0003] As shown in Figure 1, a contact strain gauge 5 consists of a metallic resistive element 10 in the form of a wire or track fastened in the usual way to a thin, electrically insulating support 15. The resistive element has a serpentine shape 20. It is formed for the most part from straight sections 25 which run parallel to one another and are connected by connecting sections 30. Both ends of the serpentine shape are extended by connection pads 35 for connecting the gauge to some equipment, for example by welding a connecting cable.

[0004] Deformation ε of a deformable body in direction X xx To measure , the strain gauge is adhesively bonded to the body such that the straight section 25 is arranged parallel to the direction X.

[0005] During deformation of the body, the straight section of length l expands or contracts, which manifests itself as a variation in the resistance R of the wire.

[0006] The variation in resistance ΔR is, in a first approximation, proportional to the extension Δl of each straight section according to equation (1).

[0007]

number

[0008] In equation (1), K is a constant that represents the gauge factor depending on the material of the wire, for example, K is 2 for constantan or nickel-chromium wire, and 3.2 for Elinvar wire.

[0009] Since the deformation of the wire is assumed to correspond to the deformation of the part of the body to which the strain gauge is fastened, the deformation of the body ε xx It is possible to determine

[0010]

number

[0011] It is therefore possible to determine the stress applied to the body along the axis X below the strain gauge when the body has an elastic behavior.

[0012] The deformable body may in particular be part of a mechanical sensor, in which case it is represented as a test body, the measurement of whose deformations therefore makes it possible to indirectly determine mechanical quantities such as forces, accelerations, pressures, vibration amplitudes, etc.

[0013] The support of the strain gauge is made from an electrically insulating material so as not to interfere with the measurement of the variation in the resistance of the wire, and it is thin enough so that deformation of the straight section matches deformation of the portion of the body it covers.

[0014] Generally, the support is made from a polymeric material.

[0015] For example, supports with a thickness of about 20 to 30 μm can be obtained by using epoxy resin. High-precision strain gauges can be produced in this way, but they cannot be used at temperatures above 100 °C. In order to extend the temperature range of the gauges to 350 °C, gauge supports have been developed that are obtained by hot rolling under pressure of a mixture of epoxy resin and phenolic resin reinforced with glass fibers. The gauges obtained in this way can measure deformations of at most 2.0%.

[0016] Gauges with a polyimide support are also known. Such supports are flexible and strong, and polyimide, when reinforced with fillers, has a limit of deformation at break of about 20% up to 400° C. Gauges with a polyimide support are more suitable, especially for deformation measurements where high accuracy is not required.

[0017] Various methods are also known for manufacturing strain gauges that include organic-based supports.

[0018] For example, one of them obtains so-called membrane strain gauges, which are formed using techniques from the fields of printed circuits, photolithography and selective etching from an epoxy resin support having a thickness of between 20 and 30 microns, and from a metal sheet having a thickness of 50 microns.

[0019] It is known to manufacture strain gauges using printing techniques. The deformation of the body on which the gauge is printed is determined, for example, from the change in resistivity of a metal particle filler in a polymer binder. Non-patent document 1 and Non-patent document 2 describe examples of such printed gauges. However, the temperature range of use of printed gauges is limited. Furthermore, they require complex manufacturing equipment with limited capacity and therefore limit the dimensions of the body that can be fitted with the gauge.

[0020] There are few strain gauges that can be placed in contact with a body and measure the deformation of that body at temperatures above 400°C.

[0021] (2003) describes the formation of strain gauges in contact with the turbine blades of aircraft engines by depositing, by cathodic sputtering, a layer of aluminum Al2O3 surrounded by a resistive layer made of a NiCr / PdCr alloy. Such gauges are therefore suitable for measuring deformations at the operating temperature of the blades of 900°C. However, the method described by Kayser et al. does not allow the use of 1m diameter gauges that can be introduced into the vacuum chamber of the cathodic sputtering device. 3It can only be used for bodies with a volume less than 100 mm. It cannot be attached to structures, for example bridges, or industrial instruments, for example presses that apply weights of several tons using such a method. Moreover, such a method cannot be used for any type of material that constitutes the body, in particular materials that may degas and that may prevent obtaining the vacuum necessary to perform the cathodic sputtering. [Prior art documents] [Non-patent literature]

[0022] [Non-Patent Document 1] "INKtellingent printed strain gauge", M. Maiwald et al., Sensors and Actuators A, 162, pp. 198~201 (2010) [Non-Patent Document 2] "Nanoparticle films as sensitive strain gauges", J.Herrmann et al., Appl.Phys.Lett., 91, 183105 (2007) [Non-Patent Document 3] "High temperature thin-films strain gauges", P. Kayser et al., Sensors and Actuators A, 37~38, pp.328~332 (1993) Summary of the Invention [Problem to be solved by the invention]

[0023] Therefore, there is a need to overcome the above-mentioned deficiencies. [Means for solving the problem]

[0024] The present invention proposes a device for measuring deformations comprising a deformable body and a strain gauge, the strain gauge comprising a support in contact with the deformable body and a metallic resistive element in contact with the support, the resistive element having a resistance that can be varied by the deformation of the deformable body, the support being made from at least one support material that is electrically insulating, porous and comprises at least one heat-resistant, optionally hydrated, ceramic compound.

[0025] The device according to the invention makes it possible to measure the deformation of a deformable body at temperatures above 400°C, or above 700°C, or even above 1000°C.

[0026] Moreover, as will become clearer below, the strain gauge can be easily formed on a body that can have a large size, in particular, it can be formed directly on-site without having to send the body back to a factory to have the gauge deposited thereon.

[0027] The ceramic compound may represent more than 50% by mass of the support material.

[0028] The ceramic compound may be selected from Al2O3, AlN, SiO2, MgO, mica, SiC, ZrO2, ZrSiO2, CaO, Cu2O, CuO, Y2O3, indium tin oxide, TiO2 and mixtures thereof.

[0029] The ceramic compound is preferably an oxide.

[0030] The support material may comprise or consist of a hydrated cement and / or a hardened ceramic adhesive.

[0031] The support material may comprise a binding matrix and a filler formed from particles dispersed within the binding matrix, the binding matrix binding the particles together so as to impart cohesive strength to the support material.

[0032] The weight of the filler may represent at least 50% of the weight of the support material.

[0033] The filler may comprise or consist of at least one particulate fraction formed from particles made from at least one material selected from Al2O3, AlN, SiO2, MgO, mica, SiC, ZrO2, ZrSiO2, CaO, Cu2O, CuO, Y2O3, indium tin oxide, TiO2 and mixtures thereof.

[0034] It may comprise or consist of at least one particulate population formed of particles made from at least one oxide material selected from Al2O3, SiO2, MgO, mica, SiC, ZrO2, ZrSiO2, CaO, Cu2O, CuO, Y2O3, indium tin oxide, TiO2 and mixtures thereof.

[0035] The filler may comprise or consist of a plurality of particulate populations, the particles of each population being made from a material or materials different from the material or materials making up the other particulate populations.

[0036] The bonding matrix preferably comprises more than 90% by weight, or more than 95% by weight, or more than 99% by weight of inorganic binder.

[0037] The inorganic binder may be a hydrated hydraulic binder.

[0038] The inorganic binder can include at least one compound selected from sodium silicate, lime, alumina silicate, calcium silicate, calcium aluminate, clay, particularly silicon clay, fly ash, particularly capable of being activated by an alkaline material, and mixtures thereof.

[0039] Furthermore, the bonding matrix may contain less than 5% or less than 1% of its mass of organic binders. In particular, the bonding matrix may be free of organic compounds, which are understood to be any compound whose chemical formula contains at least carbon and hydrogen atoms.

[0040] The support material may be sintered.

[0041] The support material is electrically insulating, i.e. 14 It has a volume resistivity of greater than Ω.cm and a breakdown voltage, measured with alternating current, of greater than 6000V.

[0042] The support has a porosity preferably between 10% and 40% in order to give the support good mechanical strength.

[0043] The porosity of the support can be determined in the following way: First, the support is infiltrated with resin. A piece of the support thus infiltrated is cut and then polished to obtain a good surface condition. Polishing is carried out with at least 1200 grade paper, preferably with diamond paste. Images are generated with a scanning electron microscope (SEM), preferably in a mode with backscattered electrons, which gives a high contrast between the support material and the resin. Each image has at least 1024 x 768 pixels. The magnification used is such that the width of the image is between 50 and 100 times the average size of the pores, in particular taking into account pores with a size between 10 nm and 10 μm. The first image can be generated by visual estimation of the average size of the pores. The area occupied by the pores is determined by image analysis by the erosion / dilation method implemented in an image analysis software such as ImageJ (https: / / imagej.nih.gov / ij / ). The porosity is determined by the sum of the area occupied by all the pores in the image relative to the sum of all the areas of each image.

[0044] The support may be a single layer or a multilayer support.

[0045] The support can include more than one support material, for example, the support is a multi-layer support, where each layer of the support is a different support material.

[0046] The support preferably has a thickness at least 40 times smaller than the thickness of the deformable body. A good mechanical connection between the strain gauge and the deformable body is thus ensured. The thickness of the deformable body is measured below the support in a direction perpendicular to the support.

[0047] The thickness of the support is between 0.05 mm and 5.00 mm. It can be chosen according to the characteristics of the resistive element to ensure optimal electrical insulation between the deformable body and the resistive element.

[0048] Preferably, the support has a thin profile, for example the ratio of length to thickness of the plate is at least 10, preferably at least 100.

[0049] The support may be planar or curved.

[0050] The resistance member may comprise a plurality of straight sections connected in pairs by connectors so as to have a serpentine shape. The connectors may be straight or curved.

[0051] It may have between 1 and 500 straight sections.

[0052] The straight portions may each have a length between 0.3 mm and 150 mm.

[0053] In one variant, the resistive members may be tracks formed on a support, which may be formed by depositing a resistive paste or by blasting a powder of metal particles.

[0054] The resistive member may be a hardened ceramic adhesive, which may be a hydrated cement, preferably filled with a metal selected from Ni, Ag and mixtures thereof.

[0055] The thickness of the track may be between 0.025 mm and 1 mm. The width of the track may be between 0.025 mm and 15 mm. The distance between two adjacent straight sections may be between 0.025 mm and 15 mm. It is measured in the plane of the support along an axis perpendicular to the axis of extension of one of the straight sections.

[0056] The resistive element may be a wire. The wire may have a diameter between 0.025 mm and 1.0 mm. The wire may be deposited before curing of the support material. Preferably, the wire is coated in the support material, preferably over its entire side.

[0057] The resistance members can have various cross sections, for example circular, rectangular or square cross sections. The cross-sectional area can range from 0.0005 to 15 mm 2 It can be between.

[0058] The resistance of the resistive element may be between 50 Ω and 2000 Ω, preferably 120 Ω or 350 Ω. A high resistance resistive element may improve the accuracy of the deformation measurement according to equation (1).

[0059] The resistive member may comprise more than 40% by mass of at least one metal selected from copper, aluminum, gold, silver, titanium, palladium, nickel, iron, platinum, titanium, tin, and alloys thereof. Specifically, the resistive member may comprise more than 40% by mass of at least one metal selected from silver, nickel, and mixtures thereof.

[0060] Specifically, the resistance member may be an alloy selected from the following: - Constantan containing, by weight, 55% nickel and 34% copper; - Karma, which contains, by weight, 74% nickel, 20% chromium, 3% aluminium and 3% iron; - an isoelastic composition containing, by weight, 36% nickel, 8% chromium, 0.5% molybdenum and 55.5% iron; - Nichrome V, containing 80% nickel and 20% chromium by mass - an alloy containing, by weight, 92% platinum and 8% tungsten, - Armour, containing, by mass, 70% iron, 20% chromium and 10% aluminium.

[0061] Further, the strain gauge may include connection pads in contact with the support and the resistive member for contacting the strain gauge to a measuring device that measures the variation in resistance during deformation of the body. The connection pads may be tin plated. The connection pads may be formed from the same material as the resistive member. A cable connecting the measuring device to the strain gauge may be welded to one of the connection pads.

[0062] The deformable body may be made of metal, or a cementitious material, or a ceramic, or a glass, or a plastic, particularly a thermoplastic, or a composite, particularly an epoxy-fiberglass composite.

[0063] The volume of the deformable body is 1m 3 Over or 5m 3 It could be beyond.

[0064] The deformable body may be a structure or part of a structure, for example a civil engineering structure, for which measurement of deformation is desired.

[0065] The part of the deformable body in contact with the support may be planar or curved, for example it has the shape of a cylinder of revolution or a sphere.

[0066] The device according to the invention may be, for example, a sensor for measuring a mechanical quantity, being a pressure or a deformation, comprising a test body comprising a deformable body, the sensor being such that by measuring the deformation of the test body it is possible to deduce the value of the mechanical quantity.

[0067] The deformable body is, for example, a thermoforming mould. Measurement of the deformation of the deformable body can enable the determination of the pressure in the thermoforming mould, in particular at the moulding surface.

[0068] According to another example, the deformable body is a filling channel of a plastic injection mould. Measurement of the deformation of the deformable body can allow the determination of the oscillation amplitude of the channel and therefore the monitoring of the propagation of the polymerization front of the plastic material injected into the mould.

[0069] According to yet another example, the deformable body is a casting, for example a pump body. Measurement of the deformation of the deformable body may allow the determination of the vibration amplitude of the deformable body, for example in order to perform preventive maintenance of the deformable body when the amplitude exceeds a nominal value.

[0070] According to yet another example, the deformable body is a prosthesis, for example made from titanium. Measurement of the deformation allows the determination of the strength of the force applied to the prosthesis.

[0071] The present invention further provides a method for measuring deformation, comprising the steps of: - providing a device according to the invention, - heating the deformable body to a temperature greater than 400°C, or greater than 500°C, or greater than 700°C, or greater than 1000°C; - measuring deformation of the body using a strain gauge; The present invention relates to a method comprising the steps of:

[0072] Finally, the present invention relates to a method for manufacturing a device for measuring deformations, comprising the steps of: a) forming at least one layer by depositing a composition on a deformable body; b) curing the layer to form a support; c) depositing a resistive material in contact with the support such that the device is in accordance with the present invention; The present invention relates to a method comprising the steps of:

[0073] The composition may be a cement paste or a ceramic adhesive. The cement paste comprises a hydraulic binder, such as silica and / or lime, and water. The ceramic paste comprises particles of at least one refractory ceramic in a binder. The refractory ceramic particles may be dispersed in a solvent.

[0074] The binder is - inorganic compounds, in particular chosen from clay, lime, sodium silicate and mixtures thereof, and / or - organic compounds selected from the group consisting of tar, bitumen, pitch, in particular modified starch, lignosulfonates, molasses, cellulose, cellulose derivatives, polyvinyl alcohol, polybutadiene, and mixtures thereof; may include.

[0075] The composition can comprise at least 50% by mass of at least one material selected from Al2O3, AlN, SiO2, MgO, mica, SiC, ZrO2, ZrSiO2, CaO, Cu2O, CuO, Y2O3, indium tin oxide, TiO2, and mixtures thereof.

[0076] In particular, it may contain, for at least 50% by mass, aluminum or zircon or zirconia, and therefore the composition may be considered to be heat resistant.

[0077] For example, the composition may be selected from the alumina-based adhesive ALUCEM-HT2, the alumina-based adhesive JYALUCEM20, the zircon-based adhesive ZIRCOCEM1 or ZIRCO CEM5 / 5F, or the zirconia-based adhesive ZIRCOCEM9, all available from Anderman.

[0078] The paste may have a viscosity, as measured by a vortex or Couette viscometer, between 1000 cps and 100,000 cps.

[0079] In step a), the composition may be coated on a support.

[0080] The coating of the composition may be carried out using a brush, a syringe, or preferably using a printing device, preferably a 3D printing device.

[0081] The 3D printing device can include a robot with a base and an articulating arm that can move relative to the base. The base can be fastened to a frame or mounted on a transport vehicle. The printing device can include a printing nozzle supported by the articulating arm through which a bead of the composition can be extruded and deposited in the form of a layer on a support.

[0082] The beads can be deposited on the substrate in multiple passes through the printing nozzle to form a layer, the deposition of several such layers allowing for optimized drying and easy removal of the binder.

[0083] The method can include smoothing the layer so that the layer has a predetermined thickness. The smoothing can include moving a smoothing tool over one side of the layer. The smoothing tool can be, for example, a squeegee or a brush.

[0084] In step b), hardening may result from the setting of the hydraulic binder contained in the cement paste.

[0085] Hardening may result from evaporation of a solvent contained in the adhesive. The constituents of the binder may additionally react with the materials that make up the refractory ceramic particles so as to bond the particles together.

[0086] Hardening may also be achieved by sintering the composition.

[0087] The method may include heating the layer formed in step a) to accelerate the hardening of the layer. Heating may be carried out until the temperature of the layer is at least 50° C.

[0088] Heating may be performed by blowing hot air onto the layer, and / or by irradiating the layer with infrared radiation, and / or by forced convection of an air current at ambient temperature.

[0089] At the end of step b), the layer is considered to be cured as soon as the Young's modulus of the support material is at least 80% of the value of the Young's modulus of the support material measured 24 hours after curing.

[0090] In step c) the method preferably comprises printing a resistive element onto the support. The printing of the resistive element may be carried out by a technique selected from screen printing or extrusion of a metallic ink or a metallic paste, and inkjet printing of a metallic ink.

[0091] In one variant, the resistive element may be printed by an additive manufacturing technique, in particular a technique that involves spraying metal particles onto a support, the velocity of the particles being supersonic. Such a technique is called "cold spray".

[0092] The invention will be better understood on reading the following detailed description of non-limiting exemplary embodiments thereof and on examining the accompanying drawings, in which: [Brief description of the drawings]

[0093] [Figure 1]FIG. 1 is a schematic front view of a prior art strain gauge. [Diagram 2] 1 is a schematic perspective view of an exemplary embodiment of a device according to the invention; [Diagram 3] 1 is a diagram of an example of carrying out a manufacturing method according to the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0094] The relative proportions of elements shown in the accompanying drawings have not always been kept to scale for the sake of drawing clarity.

[0095] Figure 2 shows an example of a device 50 according to the invention. The device comprises a deformable body 55 and a strain gauge 5 in contact with the deformable body.

[0096] The strain gauge comprises a support 15 in contact with the deformable body and a resistance member 10 .

[0097] The resistance member 10 is in contact with a face 60 of the support opposite the deformable body 55 .

[0098] The resistance element is a track having a serpentine shape. It has straight sections 25 of length l, for example equal to 10 mm. In the example shown, it comprises six straight sections, this number being non-limiting.

[0099] The straight portions have a thickness W1 that may be equal to 0.5 mm. Adjacent portions are separated by a distance W2, for example equal to 0.1 mm.

[0100] The straight sections are connected to each other in pairs by connecting sections 30 .

[0101] The strain gauge comprises connection pads 35 arranged on a surface 60 of the support which bears the resistive element. The connection pads 35 are in electrical contact with the resistive element 10.

[0102] The support is thin, for example having a thickness e of 50 μm. It has a porosity of more than 10%. For example, it is made from a hardened ceramic adhesive or a hydrated ceramic cement.

[0103] FIG. 3 shows an example of implementing the method for manufacturing a device according to the invention.

[0104] The deformable body 55 having the hemispherical portion 80 is mounted on a clamping member 85 which is threadedly attached to a clamping table 95 .

[0105] The robot 100 comprises a base 105 and an articulated arm 110 mounted on the base and fastened to a clamp table. It further comprises an injector 115 with an application nozzle 120 for depositing a composition on the deformable body. The application nozzle is fed via a supply tube 123 by a dispenser 125 containing the composition.

[0106] The robot is controlled by a control unit 130. The control unit 130 comprises a computer 135 having a memory into which a program 140 containing instructions for controlling the robot is loaded, and a processor for executing the instructions.

[0107] A 3D model is defined that includes the geometry of the deformable body and the geometry of the strain gauges that are interpreted by a program to determine various paths for the robot's articulating arm and the opening and closing movements of the delivery nozzle. The 3D model is loaded into the computer's memory.

[0108] In a first step, the dispenser is loaded with at least one heat-resistant ceramic-based composition, the articulated arm is moved along one of the paths along the hemispherical surface 145 of the deformable body, and the composition is deposited to form a layer. The layer is then cured to form the support 15.

[0109] In a second step, a metal paste is introduced into the dispenser instead of the ceramic composition. The articulated arm is then moved along another path along the support and the metal paste is deposited through a coating nozzle onto the support 15 to form the resistor member 10.

[0110] However, the present invention is not limited to the above-described examples, embodiments and modes of implementation. [Explanation of symbols]

[0111] 5 Strain Gauges 10 Resistance members 15 Support 25 Straight section 30 Connecting part 35 Connection Pad 50 Devices 55 Transformable Body 60 sides 80 Hemisphere 85 Clamping member 95 Clamp Table 100 Robots 105 Base 110 Articulated Arm 115 Syringe 120 Application nozzle 123 Supply pipe 125 Dispenser 130 Control Unit 135 Computer 140 Programs 145 Hemisphere e Thickness l Length W1 Thickness W2 Distance

Claims

1. A device (50) for measuring deformation comprising a deformable body (55) and a strain gauge (5), the strain gauge comprising a support (15) in contact with the deformable body and a metallic resistive member (10) in contact with the support, the resistive member having a resistance that can be changed by deformation of the deformable body, the support being made from at least one support material that is electrically insulating, porous and comprises at least one heat-resistant ceramic compound, the support material comprising a hydrated cement and / or a hardened ceramic adhesive.

2. The device of claim 1 , wherein the porosity of the support is between 10% and 40%.

3. The device of claim 1 , wherein the support material is a hydrated cement and / or a hardened ceramic adhesive.

4. The device of claim 1 , wherein the ceramic compound represents more than 50% by mass of the support material.

5. The ceramic compound is Al ２ O ３ , AlN, SiO ２ , MgO, Mica, SiC, ZrO ２ , ZrSiO ２ , CaO, Cu ２ O, CuO, Y ２ O ３ , indium tin oxide, TiO ２ 5. The device of claim 4, wherein the polymer is selected from the group consisting of:

6. The device of claim 1 , wherein the ceramic compound is an oxide.

7. The device of claim 1 , wherein the support has a thickness between 0.025 mm and 5.00 mm.

8. The device of claim 1 , wherein the resistive member is a metal-filled hydrated cement.

9. The device of claim 1 , wherein the support is a single layer support.

10. A method for manufacturing said device (50) for measuring deformation, comprising the steps of: a) forming at least one layer by depositing a composition on said deformable body (55); b) curing said layer to form said support (15); c) depositing a metallic resistive member (10) in contact with said support (15) to obtain the device (50) of claim 1; A method comprising:

11. The method of claim 10, wherein the composition is a cement paste or a ceramic adhesive.

12. The method of claim 10 , wherein the composition in step a) is coated onto the support.

13. The method of claim 10 comprising printing the resistive member onto the support.

14. 14. The method of claim 13, wherein the printing step is performed by a technique selected from screen printing or extrusion of a metal ink or metal paste, and inkjet printing of a metal ink.

15. The method of claim 13 , wherein the resistive member is printed by an additive manufacturing technique.

16. 1. A method for measuring deformation, comprising: Providing a device according to claim 1; heating the deformable body to a temperature greater than 400°C; measuring deformation of the body using a strain gauge; A method comprising:

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