Method for evaluating an electrical property

Abstract

The invention relates to a method for evaluating an electrical property associated with a first part (1), comprising: - bringing first electrically conductive surfaces (1a, 2a) of the first and of a second part (1, 2) into electrical contact; - using first and second clamping members (O1, O2) to apply a predetermined compressive force on the first conductive surfaces (1a, 2a); and - measuring an electrical voltage between first and second electrodes (E1, E2) pressed against second surfaces of the first and second parts (1, 2) while an electrical current (Ix) flows from one of the parts (1, 2) to the other by passing via the first surfaces (1a, 2a); and - evaluating an electrical-resistance value (R) as a function of the measured voltage and of a value of the intensity of said electrical current (Ix).

Description

[0001] METHOD FOR EVALUATING AN ELECTRICAL PROPERTY

[0002] The present invention relates to the field of methods for evaluating at least one electrical property associated with at least one first part.

[0003] BACKGROUND OF THE INVENTION

[0004] It is common to seek to produce / obtain parts with particular / expected electrical properties / characteristics, such as electrical resistance, surface electrical resistance, surface electrical resistivity or other.

[0005] The evaluation of one or more electrical properties associated with a given part makes it possible to know whether this part or the process used for its production or assembly conforms or not to predefined criteria (for example manufacturing tolerances, standards, quality criteria, technical specifications).

[0006] The evaluation of a given electrical property associated with at least one given part is for example useful to know:

[0007] - if the external surface of the part is suitable for its purpose (characterization of the layer or converted surface of the part); and / or

[0008] - whether or not the part is suitable for forming a particular electrical connection; and / or

[0009] - whether or not the part can be integrated into a particular piece of equipment to perform a particular function; and / or

[0010] - if the part has sufficient resistance to corrosion.

[0011] For example, in the field of fuel cell manufacturing, to limit the risk of cell failure, or to characterize a stage of cell manufacturing, it is interesting to evaluate the electrical characteristics / properties of parts or sets of parts. This will allow us to characterize bipolar plate type parts before integrating them as a stack in the cell.

[0012] The evaluation of an electrical characteristic of an external surface of a part can be used to, for example, characterize a surface treatment applied to this part, such as machining and / or chemical and / or electrochemical and / or thermal treatment and / or chemical conversion and / or the formation of deposit(s) / coating(s) / layer(s) of conductive material (electrochemical deposition or by high-speed projection).

[0013] Given the wide variety of possible parts and possible methods for obtaining such parts, it is particularly difficult to obtain tools / methods for evaluating surface electrical conduction characteristics which are precise, allow reproducibility of the evaluation and which are representative of different surface portions of the part evaluated.

[0014] SUBJECT OF THE INVENTION

[0015] An object of the present invention is to provide a method for evaluating at least one electrical property associated with at least one first part which is simple to implement.

[0016] SUMMARY OF THE INVENTION

[0017] To this end, according to a first aspect, the invention relates to a method for evaluating an electrical property associated with at least one first part, comprising:

[0018] - bringing a first electrically conductive surface of the first part into electrical contact with a first electrically conductive surface of a second part; - applying, using first and second clamping members clamping the first part against the second part, a predetermined compressive force of the first conductive surface of the first part against the first conductive surface of the second part; and

[0019] - measuring an electrical voltage between a first electrode pressed against a second electrically conductive surface of the first part and a second electrode pressed against a second electrically conductive surface of the second part while an electric current, applied by a current generator, flows from one of the first or second parts to the other of the first and second parts via each of said first electrically conductive surfaces thus compressed against each other by the application of said predetermined compressive force, the first and second conductive surfaces of the first part being electrically connected to each other, the first and second conductive surfaces of the second part being electrically connected to each other; and

[0020] - the evaluation of an electrical resistance value as a function of the measured voltage and a value of the intensity of said electric current.

[0021] The electrical resistance evaluated with the method of the invention constitutes an electrical property associated at least with the first part, insofar as this resistance depends on internal and surface electrical resistance characteristics specific to the first part.

[0022] However, the method according to the invention could also comprise an additional step of evaluating said electrical property associated with said at least one first part as a function of said evaluated electrical resistance value. In this case, said electrical property associated with said at least one part could be a surface conductivity or another characteristic.

[0023] The application, with the first and second clamping members, of the predetermined compressive force of the first conductive external surface of the first part against the first conductive external surface of the second part makes it possible to fix a particularly influential factor:

[0024] - the passage of electric current between the first and second parts via their respective first external surfaces; and

[0025] - the value of the voltage measured between the electrodes.

[0026] Thus, the application of the predetermined compressive force makes it possible to obtain a tension measurement and a resistance value evaluation which is particularly representative of the electrical resistance associated with the first part when the latter is placed in a given contact condition with the second part.

[0027] The method according to the invention is thus a particularly simple, effective, reliable and reproducible means of characterizing an electrical property associated with the first part when the latter is placed in contact with the second part and a predetermined / known compressive force is applied to these parts (to force contact between their first conductive surfaces).

[0028] The invention can be used to characterize the contact resistance specific to the first given part when this first part is placed in a particular mechanical connection context with a second part (the applied compressive force makes it possible to characterize the mechanical connection context between the first and second parts).

[0029] In a preferred embodiment of the method according to the invention:

[0030] - the first surfaces of the first and second parts are flat surfaces;

[0031] - the first part has first and second perforations and the second part has first and second perforations;

[0032] - the first clamping member comprises a centering rod passing through the first perforations of the first and second parts so that the first perforations are coaxial with each other; and

[0033] - the second clamping member comprises a centering rod passing through the second perforations of the first and second parts so that the second perforations are coaxial with each other.

[0034] In this way, the relative positioning between the first surfaces of the first and second parts is particularly precise and the contact surface between the first surfaces is thus well characterized since the clamping members allow the relative positioning between the first and second parts and the clamping of the first surfaces against each other with the predetermined compressive force.

[0035] Preferably, the centering rods are at least partially threaded rods and each first and second clamping member comprises a clamping nut arranged to form, with the centering rod which corresponds to it, a screw-nut clamping system, said predetermined compression force being obtained by applying a predetermined tightening torque to each of said nuts.

[0036] Thus, the compression force is easily adjustable and quantifiable according to the tightening torque applied.

[0037] Preferably, the second surfaces of the first and second parts are planar and parallel to the first surfaces of the first and second parts.

[0038] This shape feature facilitates:

[0039] - the application of the compression force;

[0040] - contact between the device and the electrodes; as well as

[0041] - the application, on the flat surfaces of the parts, of surface treatments or the formation of homogeneous layers favorable to homogeneous electrical contact between the parts.

[0042] Preferably, the voltage measurement between the first and second electrodes is carried out using an ohmmeter comprising said current generator, said ohmmeter comprising voltage measurement terminals +U, -U respectively connected to said first and second electrodes and first and second intensity measurement terminals +1, -I via which said current generated by the current generator passes, the first intensity measurement terminal +1 being connected via a first electrical conductor to the first part and the second intensity measurement terminal -I being connected via a second electrical conductor to the second part.

[0043] In this case:

[0044] - the first conductor is electrically connected to a third leg of the first part by means of a crocodile clip or any other removable electrical connection means; and

[0045] - the second conductor is electrically connected to a third leg of the second part by means of another crocodile clip or any other removable electrical connection means.

[0046] In a preferred embodiment of the method according to the invention, the first electrode is carried by a first support of a measuring device and the second electrode is carried by a second support belonging to the measuring device, said first and second supports being mounted to move relative to each other to move the first and second electrodes relative to each other and exert a clamping force on the first and second parts between said first and second electrodes respectively bearing against said respective second conductive surfaces of the first and second parts.

[0047] While said predetermined compressive force is intended to promote electrical contact between the first surfaces of the parts, the clamping force is primarily intended to improve electrical contacts between the electrodes and the second conductive surfaces of the first and second parts.

[0048] Preferably, the first and second electrodes are made of a conductive and corrosion-resistant material, for example stainless steel, in order to limit the risk of corrosion / oxidation of the electrodes, to maintain a constant level of surface electrical conductivity on the electrodes.

[0049] According to a second aspect, the invention also relates to a measuring apparatus for evaluating at least one electrical property associated with at least a first part of a device comprising first and second parts, a first electrically conductive surface of the first part being in contact against a first electrically conductive surface of the second part, the apparatus comprising:

[0050] - first and second supports;

[0051] - a first electrode carried by the first support;

[0052] - a second electrode carried by the second support;

[0053] - an ohmmeter;

[0054] - said first and second supports being electrically insulated from each other and being mounted to move relative to each other to move the first and second electrodes relative to each other and to be able to exert a clamping force on the first and second parts of the device between said first and second electrodes;

[0055] - said ohmmeter comprising a current generator, first and second voltage measuring terminals +U, -U and first and second current measuring terminals +1, -I, the first voltage measuring terminal +U being electrically connected to the first electrode, the second voltage measuring terminal -U being electrically connected to the second electrode, the first current measuring terminal +1 being arranged to be electrically connected, via a first electrical conductor of the ohmmeter, to the first part, and the second current measuring terminal -I being arranged to be electrically connected, via a second electrical conductor of the ohmmeter, to the second part, said ohmmeter being arranged to measure a voltage between the first and second electrodes while:

[0056] - said clamping force is applied, via said first and second electrodes, against respective second conductive surfaces of the first and second parts; and that

[0057] - an electric current Ix generated by said generator flows, via the first and second electrical conductors, passing from one of the first or second parts to the other of the first and second parts; said ohmmeter being arranged to evaluate an electrical resistance value as a function of the measured voltage and a value of the intensity of said electric current.

[0058] This apparatus according to the invention is particularly advantageous because it makes it possible to measure an electrical resistance value associated at least with the first part while this first part is placed in contact with a second part and these first and second parts are placed between the first and second electrodes while exerting a clamping force on the first and second parts of the device between said first and second electrodes.

[0059] By exerting such a clamping force during the voltage measurement, the apparatus according to the invention makes it possible to limit measurement errors linked to unstable contact between the electrodes and the first and second parts of the device.

[0060] Thus, the apparatus according to the invention offers a particularly simple means to implement for evaluating an electrical property associated with at least a first part while a particular mechanical contact is applied between the first and second parts.

[0061] The electrical property associated with said at least one first part is here an electrical resistance value but it could be another electrical property calculated by an ohmmeter calculator as a function of said electrical resistance value evaluated by the ohmmeter.

[0062] The apparatus according to the invention facilitates the reproducibility of the conditions for evaluating the electrical characteristics of parts, which thus limits the uncertainties in evaluating the electrical characteristics.

[0063] It should be noted that the clamping force applied via the electrodes could also be used for the generation of all or part of said predetermined compressive force of the first conductive surface of the first part against the first conductive surface of the second part.

[0064] In any of the embodiments of the apparatus according to the invention, the latter is preferentially adapted for implementing the method of the invention according to any of its embodiments.

[0065] According to a third aspect, the invention relates to a device comprising first and second parts, the first part having a first electrically conductive surface in contact against a first electrically conductive surface of the second part, the first part comprising a second electrically conductive surface and the second part comprising a second electrically conductive surface, said second electrically conductive surfaces being arranged on either side of said device in such a way that an electric current Ix can pass from one of said second surfaces to the other of said second surfaces by passing via each of said first surfaces of the first and second parts.

[0066] The device according to the invention is essentially characterized in that it comprises first and second clamping members clamping the first part against the second part by applying a predetermined compressive force of the first conductive surface of the first part against the first conductive surface of the second part.

[0067] The main advantage of the device according to the invention is that it integrates the clamping members which generate the predetermined compression force, which makes it possible to manipulate / move the device to subject it to different environments while maintaining the compression force between these parts.

[0068] Thus, the device of the invention may be placed in a corrosive environment, such as a salt spray, to assess the effects of the environment on the first and second parts as they are compressed against each other by the clamping members integrated into the device.

[0069] Maintaining the compressive force throughout the handling of the device and throughout its exposure in the given environment thus makes it possible to reproduce more faithfully the conditions to which electrical elements are normally exposed under mechanical stress.

[0070] The device according to the invention described in the present application is particularly suitable for:

[0071] - the implementation of the method according to the invention; and

[0072] - the evaluation of at least one electrical characteristic of at least one part of the device by the measuring device according to the invention.

[0073] It should be noted that the predetermined compression force is a force intrinsic to the device (because it is generated by the device's own clamping members) whereas the clamping force is a force extrinsic to the device which is applied to the device, via the electrodes of the measuring device.

[0074] In the case where the device according to the invention is used with the measuring apparatus according to the invention, then the first and second parts are compressed against each other:

[0075] - on the one hand thanks to the predetermined compression force (intrinsic to the device) which is applied by the clamping members of the device alone; and

[0076] - on the other hand thanks to the clamping force (extrinsic to the device) which is applied via the electrodes of the measuring device.

[0077] BRIEF DESCRIPTION OF THE DRAWINGS Other characteristics and advantages of the invention will emerge clearly from the description given below, for information purposes and in no way limiting, with reference to the appended drawings, in which: [Fig. 1a] Figure 1a is a schematic view of the measuring apparatus S0 according to the invention, without its ohmmeter, while it is used to position a device D according to the invention comprising first and second parts 1, 2 and clamping members 01, 02 for exerting a compressive force on these parts 1 and 2 against each other; [Fig. 1b] Figure 1b is a schematic view of the measuring apparatus SO of Figure 1a with its ohmmeter UC connected to the first and second electrodes E1, E2 for evaluating at least one electrical property associated with the first and second parts 1, 2 of the device D according to the invention;

[0078] [Fig. 2] Figure 2 is a schematic top view of the device D according to the invention with its first and second parts 1, 2 not yet assembled to each other by the clamping members 01, 02 of the device D;

[0079] [Fig. 3] Figure 3 is a schematic top view of the device D according to the invention while the first and second parts 1, 2 are connected to each other by the clamping members 01, 02 of the device which exerts the predetermined compressive force of the first conductive surface 1a of the first part 1 against the first conductive surface 2a of the second part 2. DETAILED DESCRIPTION OF THE INVENTION

[0080] With reference to figures 1a and 1b, the invention relates to a measuring apparatus S0 for evaluating at least one electrical property associated with at least a first part 1 of a device D comprising first and second parts 1, 2.

[0081] In this case, the measuring device S0 is arranged to measure an electrical property, here a resistance R associated with the first and second parts 1, 2, this resistance being estimated / measured between second surfaces 1b, 2b of the first and second parts 1, 2, which are arranged on either side of the device D, while a first electrically conductive surface 1a of the first part 1 is in contact against a first electrically conductive surface 2a of the second part 2.

[0082] The S0 device includes:

[0083] - first and second supports SI, S2;

[0084] - a first electrode El carried by the first support

[0085] 51;

[0086] - a second electrode E2 carried by the second support

[0087] 52;

[0088] - a UC ohmmeter.

[0089] The first and second supports SI, S2 are electrically insulated from each other and are mounted to move relative to each other to move the first and second electrodes E1, E2 relative to each other and to exert a clamping force on the first and second parts 1, 2 of the device D between said first and second electrodes E1, E2 while:

[0090] - the first electrode El is supported against a second electrically conductive surface of the first part 1; and that

[0091] - the second electrode E2 is supported against a second electrically conductive surface of the second part 2. As illustrated in figure 1b, said ohmmeter UC comprises a current generator (in this case a direct current generator), first and second voltage measurement terminals +U, -U and first and second intensity measurement terminals +1, -I.

[0092] The first voltage measuring terminal +U is electrically connected to the first electrode El, the second voltage measuring terminal -U is electrically connected to the second electrode E2.

[0093] The first current measuring terminal +1 is arranged to be electrically connected, via a first electrical conductor 31 of the ohmmeter UC, to the first part 1.

[0094] The second current measuring terminal -I is arranged to be electrically connected, via a second electrical conductor 32 of the ohmmeter UC, to the second part 2.

[0095] Said ohmmeter UC is arranged to measure a voltage between the first and second electrodes E1, E2 while:

[0096] - said clamping force is applied, via said first and second electrodes E1, E2, against respective second conductive surfaces of the first and second parts 1, 2; and that

[0097] - an electric current Ix generated by said generator flows, via the first and second electrical conductors 31, 32, passing from one of the first or second parts 1 to the other of the first and second parts 2 passing via each of said first electrically conductive surfaces of said first and second parts 1, 2.

[0098] Furthermore, the ohmmeter UC is arranged to evaluate an electrical resistance value R as a function of the measured voltage and a value of the intensity of said electrical current Ix, more particularly as a function of a value of direct electrical current Ix delivered by the current generator during said voltage measurement.

[0099] As indicated previously, the electrical resistance value R evaluated as a function of the measured voltage and the value of the intensity of the electric current Ix applied by the generator (which is a direct current generator) is an electrical property associated at least with the first part 1 of the device D comprising the first and second parts 1, 2.

[0100] The estimated value of electrical resistance R associated with the first part 1 is for example estimated using the formula: R = U / I; where

[0101] R is an electrical resistance in ohms;

[0102] U is the voltage in volts measured between the electrodes E1, E2; and

[0103] I is the intensity in amperes of the direct current Ix applied by the current generator and which circulates from one part 1 to the other, passing through their first surfaces 1a, 2a which are in contact with each other.

[0104] This resistance value R can also be used to estimate another electrical characteristic associated at least with the first part 1 such as its surface resistivity or its volume resistivity.

[0105] For an object of resistance R, cross-sectional area A, and length l, the volume resistivity, p, is given by the equation p = RA / l.

[0106] It should be noted that the intensity of the current Ix is chosen to be sufficiently high to ensure a stable measurement (over the same test campaign, and from one campaign to another), but not too high to avoid any significant heating by the Joule effect, and therefore a fluctuation in the electrical contact resistance.

[0107] Thus, the current intensity Ix is preferably between 0.004 and 0.13 amperes per mm2, preferably 0.01 A / mm2.

[0108] The intensity of the applied current can be defined to guarantee a temperature variation during the measurement which is lower than a predetermined maximum temperature threshold, in order not to cause significant heating of the material, due to the passage of current, which could lead to a variation in resistance.

[0109] For this purpose, the measuring device may include:

[0110] - a temperature probe to assess a temperature variation;

[0111] - means for storing temperature values ​​measured by the temperature probe during voltage measurement; the generator possibly being arranged to vary the intensity delivered as a function of temperatures measured by the probe.

[0112] The application of the clamping force via the first and second electrodes E1, E2 of the S0 device allows stability and reproducibility of the contact conditions between the electrodes and the parts, which makes the measurement conditions reproducible.

[0113] The results of a series of measurements carried out on one or more D devices are thus comparable with each other.

[0114] It should be noted that the evaluated electrical resistance value R may depend on:

[0115] - the electrical contact resistance between the first electrode El and the second conductive surface lb of the first part 1;

[0116] - the resistance of the electrical connection between the second conductive surface lb of the first part 1 and the first conductive surface la of the first part

[0117] 1 ;

[0118] - the electrical contact resistance between the first surfaces 1a, 2a of the first and second parts 1, 2 (this electrical contact resistance is particularly dependent on the geometry of the contact zones between the first surfaces and the compressive force compressing the first surfaces 1a, 2a against each other);

[0119] - the resistance of the electrical connection between the first conductive surface 2a of the second part 2 and the second conductive surface 2b of the second part 2; and

[0120] - the electrical contact resistance between the second electrode E2 and the second conductive surface 2b of the second part 2.

[0121] The measuring apparatus S0, the device according to the invention D and the evaluation method according to the invention each contribute to the improvement of the measurement conditions and to the reproducibility of the measurement conditions, which is favorable to making the evaluation of the electrical property associated at least with said first part more reliable.

[0122] The evaluated resistance value is an electrical property associated at least with the first part insofar as it is at least a function of the resistance between the first and second surfaces 1a, 1b of the first part 1 and the respective contact resistances against the first and second surfaces 1a, 1b of the first part 1.

[0123] In order not to influence the electrical conduction between the first and second parts and thus to have an evaluation of the electrical property as representative as possible of the electrical resistance to the passage of current via only the first surfaces 1a, 2a of the device D, the members 01, 02 may be electrically non-conductive (the members 01, 02 being arranged so that the passage of current between the parts 1, 2 takes place exclusively via the contact zones between the first surfaces 1a, 2a).

[0124] The measuring device SO may comprise controlled means for applying, using the electrodes, a clamping force to the device D and means for adjusting said clamping force and storing current values ​​of clamping force applied during the voltage measurement.

[0125] To this end, the controlled means of the device may be a traction or compression bench applying forces to at least one of the supports carrying the electrodes, the controlled means being controlled as a function of a measurement of the applied clamping force and a predetermined setpoint of the clamping force to be applied.

[0126] Alternatively, to simplify the application of the clamping force to the device D via the electrodes, the measuring device SO may comprise a pair of elastic means 41, 42, in this case a pair of compression springs 41, 42.

[0127] These elastic means 41, 42, arranged to elastically oppose the separation of the first and second electrodes E1, E2 relative to each other and to together generate said clamping force of the first and second parts 1, 2 between said first and second electrodes E1, E2.

[0128] As illustrated in Figs 1a, 1b, at least one of said first and second supports S1, S2 is slidably mounted along guide columns 43, 44 which are parallel to each other. Each of these guide columns 43, 44 is connected by a connection of the embedding type on a base S4 of the device S0.

[0129] The elastic means 41, 42 are here helical compression springs each extending around one of the columns 43, 44 which corresponds to it.

[0130] In this particular case, each elastic means 41, 42 bears on one side against the base S4 and on the other against the second support S2 which is in the form of a plate sliding along the guide columns 43, 44.

[0131] The first support SI is here connected to the guide columns 43, 44 via a fitting-type connection in such a way that the base S2, the columns 41, 42 and the first support SI form a mechanically rigid assembly, the second support S2 being guided in linear translation along the columns 43, 44 of this rigid assembly.

[0132] The clamping force applied by the electrodes E1, E2 under the effect of the springs 41, 42 is here proportional to the spacing distance between the second conductive surfaces.

[0133] Typically, the stiffness of the springs 41, 42 can be chosen so that when the electrodes are spaced apart from each other by 5 mm (to clamp a device D with a thickness of 5 mm), the clamping force applied would then be at least 10 newtons, preferably at least 100 newtons, preferably at least 1000 newtons.

[0134] The apparatus according to the invention is used here to evaluate at least one characteristic of at least one part 1 which belongs to a device D according to the invention.

[0135] The device D is illustrated, in side view, in figures 1a and 1b, this device D being clamped between the two electrodes E1, E2. As indicated previously, the device D comprises first and second parts 1, 2, the first part 1 having a first electrically conductive surface 1a in contact against a first electrically conductive surface 2a of the second part 2.

[0136] The first part 1 comprises a second electrically conductive surface 1b.

[0137] Likewise, the second part 2 comprises a second electrically conductive surface 2b.

[0138] The second surfaces 1b, 2b are arranged on either side of said device D in such a way that an electric current Ix can pass from one of the second surfaces 1b, 2b to the other of the second surfaces 1b, 2b by passing via each of said first surfaces 1a, 2a.

[0139] As illustrated in Figures 1a and 3, the device D also comprises first and second clamping members 01, 02 clamping the first part 1 against the second part 2 by applying a predetermined compressive force of the first surface 1a of the first part 1 against the first conductive surface 2a of the second part 2.

[0140] Typically, the first and second clamping members 01, 02 are arranged so that the predetermined compressive force forcing the first surfaces 1a, 2a against each other is at least 0.5 newtons per mm. 2 of contact between the first surfaces.

[0141] This surface density of compressive force is chosen because it is representative of the majority of compressive forces generally applied in electrically conductive assemblies intended to transmit forces between parts.

[0142] Preferably, the first surfaces 1a, 2a are flat. The first part 1 has first and second perforations 1c, 1d.

[0143] The second part 2 also has first and second perforations 2c, 2d.

[0144] The first clamping member 01 comprises a centering rod Tl passing through the first perforations 1c, 2c of the first and second parts 1, 2 so that the first perforations 1c, 1d are coaxial with each other.

[0145] The second clamping member 02 comprises a centering rod T2 passing through the second perforations Id, 2d of the first and second parts 1, 2 so that the second perforations Id, 2d are coaxial with each other.

[0146] Thus, the clamping means 01, 02 allow precise positioning of the parts 1, 2 relative to each other to obtain a contact surface between parts 1, 2 of perfectly known and reproducible dimensions and geometry, including in the event of replacement of a part of the device D by another of identical shape.

[0147] The centering rods T1, T2 are at least partially threaded and each first and second clamping member 01, 02 comprises a clamping nut arranged to form with the centering rod T1, T2 which corresponds to it a screw-nut clamping system.

[0148] The predetermined compressive force is thus obtained by applying a predetermined tightening torque to each of said nuts.

[0149] The second surfaces 1b, 2b of the first and second parts 1, 2 are also flat and parallel to the first surfaces 1a, 2a.

[0150] The first part 1 observed in a direction perpendicular to the second surface lb of the first part 1 comprises a central discoidal zone Zl. The first conductive surface la of the first part 1 comprises a first flat face of the central discoidal zone Zl.

[0151] The second conductive surface 1b of the first part 1 comprises a second flat face of the discoidal central zone Zl of the first part 1.

[0152] These first and second flat faces of the central zone Zl are located on either side of the central zone Zl.

[0153] Similarly, the second part 2 observed in a direction perpendicular to the second surface 2b of the second part 2 comprises a central discoidal zone Z2.

[0154] The first conductive surface 2a of the second part 2 comprises a first flat face of the discoidal central zone Z2 of the second part 2 and the second conductive surface 2b of the second part 2 comprises a second flat face of the discoidal central zone Z2 of the second part 2.

[0155] These first and second flat faces of the central zone Z2 are located on either side of the central zone Z2.

[0156] The discoidal central zones Z1, Z2 of the first and second parts 1, 2 are of the same diameter.

[0157] Each electrode E1, E2 of the device S0 has a flat, circular contact face intended to be placed in contact against one of the central zones Z1, Z2 which corresponds to it.

[0158] Preferably, the diameter of the circular contact face of each electrode E1, E2 is between 90 and 100% of the diameter of the corresponding central zone Z1, Z2.

[0159] Preferably, the central discoidal zone Z1 of the first part 1 has a diameter equal, to plus or minus 5%, to the diameter of the central discoidal zone Z2 of the second part 2. The diameter of the central discoidal zone Z2 of the second part 2 being for example between 20 mm and 100 mm.

[0160] With such diameters of discoidal central zones Zl, Z2, it is considered that the contact surfaces between the parts 1, 2 and between the parts and the electrodes El, E2 are sufficient to allow representative measurements of the surface electrical characteristics of the parts tested.

[0161] As illustrated in Figures 2 and 3, the first part 1 comprises first and second lateral tabs 11, 11' formed on either side of the discoidal central zone Zl.

[0162] These lateral legs 11, 11' extend longitudinally along a longitudinal axis passing through a center of the discoidal central zone Zl of the first part 1.

[0163] Likewise, the second part 2 comprises first and second lateral tabs 21, 21' formed on either side of the central discoidal zone Z2 of the second part 2.

[0164] These legs 21, 21' extend longitudinally along another longitudinal axis passing through a center of the central discoidal zone Z2 of the second part 2.

[0165] The first clamping member 01 clamps the first legs 11, 21 of the first and second parts 1, 2 against each other and the second clamping member 02 clamps the second legs 11', 21' of the first and second parts 1, 2 against each other to generate said predetermined compressive force.

[0166] The first part 1 also comprises a third lateral tab A extending radially relative to the central discoidal zone Z1 of the first part 1. Similarly, the second part 2 comprises a third lateral tab B extending radially relative to the central discoidal zone Z2 of the second part 2.

[0167] These third legs A, B are adapted to allow the passage of a current Ix generated by a current generator of an ohmmeter UC and circulating, from one of said third lateral legs A to the other of said third lateral legs B, passing through said first surfaces 1a, 2a of the first and second parts 1, 2.

[0168] These third lateral legs A, B of the device D extend on either side of the device D which facilitates access to legs A, B to electrically connect them to the terminals of the ohmmeter UC.

[0169] Thanks to these legs A, B, the current generator can be electrically connected to the device D without affecting the quality of the electrical contact between the parts 1, 2 (the third legs A, B are at a distance from the legs 11, 21, 11', 21', via which the compression force is applied).

[0170] Moreover, as these legs A, B are diametrically opposed with respect to the central discoidal zones Zl, Z2, an electrical path is formed between these legs A, B which is perfectly defined and easily reproducible.

[0171] These third legs A, B which are not perforated ensure good distribution of the current between the parts at the level of their respective discoidal zones.

[0172] Preferably, the first and second parts

[0173] I, 2 are of identical shapes to each other.

[0174] Every first, second or third leg given

[0175] II, 11', 21, 21', A, B of any one of the first or second parts is rectangular in shape, a base of the rectangular shape being radially continuous with the discoidal zone Zl, Z2 of the corresponding part. Typically, each rectangular-shaped leg of a given part 1, 2 has a base with a width of between 25% and 50% of the diameter of the discoidal zone of the given part, preferably equal to 30% of this same diameter.

[0176] Thus, for a given part having a discoidal zone of diameter 35 mm, the legs of this part have a base of width between 8.75 mm and 17.5 mm, preferably equal to 11.6 mm.

[0177] In some cases, the third legs allowing the passage of current may have specific widths different from the widths of the first and second legs. Thus, the width of the third leg A, B can be between 1 and 35 mm.

[0178] Ideally, to ensure good reproducibility / representativeness of the measurements, parts 1, 2 are preferably shaped to have a contact surface between their first surfaces which is at least 900 mm2.

[0179] Preferably, each rectangular-shaped leg of a given part 1, 2 has a length of between 50% and 100% of the diameter of the discoidal zone of the given part, this length being preferably equal to 2 / 3 of this same diameter.

[0180] So, for a central discoidal area of ​​35 mm in diameter, the legs will ideally have a length of 23.3 mm.

[0181] The thickness of each of the legs is identical to the thickness of the corresponding part measured at its discoidal area.

[0182] In this way, each leg of a given part 1, 2 has excellent mechanical and electrical continuity with this corresponding central area.

[0183] As parts 1, 2 have identical shapes and have the same thickness across the entire part, it is easy to mass-produce these parts, the geometry of the parts being easily reproducible (for example by cutting a sheet metal under pressure).

[0184] Furthermore, thanks to this common shape of the parts, the parts of the same series can be easily assembled together to form a device D according to the invention (this limits the risk of having several shapes of parts likely to have incompatible geometries).

[0185] Due to the common shape of the parts, it is easy to apply identical or different surface finishes between the parts (e.g. by machining, layer deposition or surface treatment).

[0186] Preferably, these first and second parts form test pieces undergoing one or more surface treatments in order to evaluate the contact resistance between two parts as a function of their respective external surfaces.

[0187] By measuring the resistivity associated with a device D comprising two parts of identical shapes and having, on their respective surfaces, different or identical surface treatments, it is easy to characterize the effect of these surface treatments / pairs of surface treatments on the surface electrical characteristics of the device D.

[0188] In summary, the electrical resistance evaluated with the method of the invention / the measuring apparatus according to the invention constitutes an electrical property associated at least with the first part 1, insofar as this resistance depends at least on internal and surface electrical resistance characteristics specific to the first part.

[0189] The application, with the first and second clamping members 01, 02, of a predetermined compressive force makes it possible to fix a particularly influential factor:

[0190] - the passage of electric current between the first and second parts via their respective first external surfaces; and

[0191] - the value of the voltage measured between the electrodes El, E2.

[0192] The method according to the invention is thus a particularly simple, effective, reliable and reproducible means of characterizing an electrical property associated at least with the first part and with a device D composed of two parts compressed against each other.

[0193] Thanks to the invention, it is possible to know whether a surface treatment, a surface roughness, a layer deposition, a chemical or electrochemical conversion applied to one or more parts of the device D comply or not with predefined expected values ​​in terms of resistance / resistivity.

[0194] Thus, the invention can be used to qualify a method of producing a batch of parts and / or a surface treatment method applied to a batch of parts.

Claims

CLAIMS 1. Method for evaluating an electrical property associated with at least one first part (1), comprising: - bringing a first electrically conductive surface (la) of the first part (1) into electrical contact with a first electrically conductive surface (2a) of a second part (2); - applying, using first and second clamping members (01, 02) clamping the first part (1) against the second part (2), a predetermined compressive force of the first conductive surface (1a) of the first part (1) against the first conductive surface (2a) of the second part (2); and - measuring an electrical voltage between a first electrode (El) pressed against a second electrically conductive surface (1b) of the first part (1) and a second electrode (E2) pressed against a second electrically conductive surface (2b) of the second part (2) while an electric current (Ix), applied by a current generator, flows from one of the first or second parts (1, 2) to the other of the first and second parts (1, 2) passing via each of said first electrically conductive surfaces (la, 2a) thus compressed against each other by the application of said predetermined compressive force, the first and second conductive surfaces (la, 1b) of the first part (1) being electrically connected to each other, the first and second conductive surfaces (2a, 2b) of the second part (2) being electrically connected to each other; and - the evaluation of an electrical resistance value (R) as a function of the measured voltage and a value of the intensity of said electric current (Ix).

2. Method according to claim 1, in which: - the first surfaces of the first and second parts are planar surfaces - the first part has first and second perforations and the second part has first and second perforations; - the first clamping member (01) comprises a centering rod (Tl) passing through the first perforations of the first and second parts (1, 2) so that the first perforations are coaxial with each other; and - the second clamping member (02) comprises a centering rod (T2) passing through the second perforations of the first and second parts (1, 2) so that the second perforations are coaxial with each other.

3. Method according to claim 2 in which the centering rods are at least partially threaded rods and each first and second clamping member comprises a clamping nut arranged to form with the centering rod which corresponds to it a screw-nut clamping system, said predetermined compression force being obtained by applying a predetermined tightening torque to each of said nuts.

4. The method of claim 3, wherein the second surfaces of the first and second parts are planar and parallel to the first surfaces of the first and second parts.

5. Method according to claim 4, in which: - the first part (1) observed in a direction perpendicular to the second surface of the first part comprises a discoidal central zone, the first conductive surface of the first part comprising a first flat face of the discoidal central zone and the second conductive surface of the first part comprising a second planar face of the discoidal central area; and - the second part observed in a direction perpendicular to the second surface of the second part comprises a discoidal central zone, the first conductive surface of the second part comprising a first flat face of the discoidal central zone of the second part and the second conductive surface of the second part comprising a second flat face of the discoidal central zone of the second part; and - the discoidal central areas of the first and second parts being of the same diameter.

6. Method according to claim 5, in which: - the first part (1) comprises first and second lateral legs (11, 11') formed on either side of the central discoidal zone (Zl) of the first part (1) extending longitudinally along a longitudinal axis passing through a center of the central discoidal zone (Zl) of the first part (1); - the second part (2) comprises first and second lateral legs (21, 21') formed on either side of the discoidal central zone (Z2) of the second part (2) extending longitudinally along another longitudinal axis passing through a center of the discoidal central zone (Z2) of the second part (2), the first clamping member (01) clamping the first legs (11, 21) of the first and second parts against each other and the second clamping member (02) clamping the second legs (11', 21') of the first and second parts (1, 2) against each other to generate said predetermined compressive force.

7. Method according to any one of claims 1 to 6 in which the measurement of voltage between the first and second electrodes (El, E2) is produced using an ohmmeter (UC) comprising said current generator, said ohmmeter (UC) comprising voltage measuring terminals (+U; -U) respectively connected to said first and second electrodes (El, E2) and first and second current measuring terminals (+1; -I) via which said current generated by the current generator passes, the first current measuring terminal (+1) being connected via a first electrical conductor to the first part (1) and the second current measuring terminal (-1) being connected via a second electrical conductor to the second part (2).

8. Method according to any one of claims 6 or 7, wherein the first part (1) comprises a third lateral leg (A) extending radially relative to the discoidal central zone (Zl) of the first part (1) and the second part (2) comprises a third lateral leg (B) extending radially relative to the discoidal central zone (Z2) of the second part (2), said current (Ix) applied by said current generator flowing from one of said third lateral legs (A) to the other of said third lateral legs (B).

9. Method according to any one of claims 1 to 5. 8, wherein the first electrode (El) is carried by a first support (SI) of a measuring device (S0) and the second electrode (E2) is carried by a second support (S2) belonging to the measuring device (S0), said first and second supports (SI, S2) being mounted to move relative to each other to move the first and second electrodes (El, E2) relative to each other and exert a clamping force on the first and second parts between said first and second electrodes (El, E2) respectively bearing against said respective second conductive surfaces of the first and second parts (1, 2).

10. Method according to claim 9, in which at least one of said first and second supports (S1, S2) is mounted to slide along guide columns, said measuring device (S0) comprising a pair of elastic means arranged to exert together said clamping force of the first and second parts between said first and second electrodes (E1, E2).

11. Measuring apparatus (S0) for evaluating at least one electrical property associated with at least a first part (1) of a device (D) comprising first and second parts (1, 2), a first electrically conductive surface of the first part (1) being in contact against a first electrically conductive surface of the second part (2), the apparatus (S0) comprising: - first and second supports (SI, S2); - a first electrode (El) carried by the first support (SI); - a second electrode (E2) carried by the second support (S2); - an ohmmeter (UC); - said first and second supports (SI, S2) being electrically insulated from one another and being mounted to move relative to one another to move the first and second electrodes (El, E2) relative to one another and to be able to exert a clamping force on the first and second parts (1, 2) of the device (D) between said first and second electrodes (El, E2); - said ohmmeter (UC) comprising a current generator, first and second voltage measuring terminals (+U; -U) and first and second voltage measuring terminals current measurement (+1; -I), the first voltage measurement terminal (+U) being electrically connected to the first electrode (El), the second voltage measurement terminal (- U) being electrically connected to the second electrode (E2), the first current measurement terminal (+1) being arranged to be electrically connected, via a first electrical conductor (31) of the ohmmeter (UC), to the first part (1), and the second current measurement terminal (-1) being arranged to be electrically connected, via a second electrical conductor (32) of the ohmmeter (UC), to the second part (2), said ohmmeter (UC) being arranged to measure a voltage between the first and second electrodes (El, E2) while: - said clamping force is applied, via said first and second electrodes (El, E2), against respective second conductive surfaces of the first and second parts (1, 2); and that - an electric current (Ix) generated by said generator flows, via the first and second electrical conductors (31, 32), passing from one of the first or second parts (1) to the other of the first and second parts (2); said ohmmeter (UC) being arranged to evaluate a value (R) of electrical resistance as a function of the measured voltage and a value of the intensity of said electric current (Ix).

12. Measuring apparatus (S0) according to claim 11, comprising a pair of elastic means (41, 42) arranged to elastically oppose the separation of the first and second electrodes (El, E2) relative to each other and to together generate said clamping force of the first and second parts (1, 2) between said first and second electrodes (El, E2).

13. Measuring apparatus (SO) according to any one of claims 11 or 12, wherein at least one of said first and second supports (SI, S2) is slidably mounted along guide columns (43, 44).

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