DEVICE FOR PERFORMING TESTS ON A MATERIAL SAMPLE

Description

[0001] The present invention relates to the field of apparatus for the characterization of material samples.

[0002] It is well known to characterize the compressive or tensile strength of materials by applying forces to samples of these materials and characterizing their responses in terms of stress and / or strain. It has been observed that some compressible materials, such as porous materials, have mechanical properties that vary depending on the hydrostatic pressure of the environment in which the material is located. There is a need to characterize the behavior of materials by taking into account the hydrostatic pressure within the material in order to predict its behavior in a given environment where the material is subjected to specific mechanical and / or hydrostatic stresses. However, characterizing a material as a function of the hydrostatic pressure of its environment is particularly complex and costly to perform.Equipment for carrying out tests is presented, for example, in documents US3975950A and WO2017 / 076343A1. SUBJECT OF THE INVENTION

[0003] One object of the present invention is to provide apparatus for carrying out tests on a sample of material enabling the resolution of at least some of the defects of the aforementioned prior art. SUMMARY OF THE INVENTION

[0004] For this purpose, the invention provides apparatus for carrying out tests on a sample of material, the apparatus comprising: a chamber delimited externally by a chamber wall and in which is arranged a receiving area for said sample of material; at least one movable head relative to said chamber wall, the head being movable between a first position in which the movable head is away from the sample receiving area and a second position in which the movable head is in the sample receiving area to apply forces on the sample.

[0005] The apparatus according to the invention comprises a hydraulic circuit and a hydraulic valve device selectively adopting a chamber isolation configuration in which the chamber is hermetically sealed and a fluid evacuation configuration out of the chamber in which fluid can be evacuated out of the chamber via said hydraulic circuit, the apparatus also comprising at least one force sensor arranged to measure forces applied to the sample located in the sample reception area and at least one pressure sensor arranged to measure a hydraulic pressure inside the chamber.

[0006] The apparatus according to the invention makes it possible to test / characterize the mechanical behavior of a material sample located in a controlled environment, i.e. in the chamber, where it is possible to precisely measure and control: the forces applied to the sample; and the hydrostatic pressure applied to the sample; and any combination, time variation, of forces and hydrostatic pressures applied to the sample.

[0007] The apparatus according to the invention is thus particularly suitable for characterizing the mechanical properties of a material, preferably a porous material or a compressible material, when it is subjected to given / controlled forces and to a given / controlled hydrostatic pressure, before, during or after the application of said forces.

[0008] The effects of hydrostatic pressure variation on the mechanical behavior of the material can thus be precisely characterized in a particularly economical way.

[0009] The movable head within the chamber allows for varying the forces applied to the sample, while the ambient hydrostatic pressure in the chamber is controlled by the hydraulic circuit and the hydraulic valve system. The controlled sequencing of the movable head's movement and the hydrostatic pressure is useful for inducing deformations of the sample in height and / or volume, and for characterizing the response of the sample's constituent material to the forces it transmits and the hydrostatic pressure of its surrounding environment.

[0010] The force sensor allows measurement of forces applied to the sample by the moving head, reaction forces of the sample and the pressure sensor allows measurement of the pressure in the chamber which makes it possible to characterize the influence of these stresses on the deformation of the sample.

[0011] In a preferred embodiment of the invention, the apparatus comprises a stop placed in the chamber, the stop and said at least one movable head being arranged on either side of the sample receiving area to be able to selectively compress said sample between the stop and said at least one movable head, said at least one force sensor being arranged to measure a support force of the sample against the stop.

[0012] In this way the force sensor is precisely positioned relative to the stop which is in the chamber, which improves the reproducibility of force measurements.

[0013] Preferably, this stopper has a flat surface for supporting the sample such that the contact between the sample and the stopper is exclusively located on this flat surface.

[0014] This facilitates the characterization of the sample's behavior at the point of contact with the stop. Ideally, this stop is shaped like a plate.

[0015] According to the invention: said at least one movable head is carried at the end of a sliding rod which slides in a sealed manner, that is to say in a sealed manner, through the wall of the chamber; a sealing surface is carried by the sliding rod; and a fluid outlet is made through the wall of the chamber, the sealing surface being arranged: on the one hand so that on a first part of the stroke of the sliding rod, the sealing surface allows the passage of fluid via the fluid outlet, the hydraulic valve device then being in configuration of evacuating fluid out of the chamber; and on the other hand so that on a second part of the stroke of the sliding rod, said sealing surface prohibits the passage of fluid via the fluid outlet, the hydraulic valve device then being in configuration of isolating the chamber.

[0016] The invention is particularly advantageous and economical to implement since the sliding rod which carries the moving head is used on the one hand to move the moving head and vary the forces applied to the sample (for example by imposing a variation in the height of the sample) and on the other hand used as a valve element to selectively close the fluid outlet of the chamber and thus allow the variation of the hydrostatic pressure (with a variation in the volume of the chamber) as a function of the displacement of the rod and / or the forces applied to this rod.

[0017] This simplicity of design is favorable to the reproducibility of deformations or stresses successively applied to the sample of material tested.

[0018] Thus, the apparatus according to the invention allows perfect reproducibility of the test conditions successively implemented to test a sample or a series of samples.

[0019] Preferably, the chamber wall has several pairs of windows, with the windows of each pair positioned on either side of the sample receiving area. Each window is arranged to allow viewing, from outside the chamber, of a sample located within the sample receiving area. Each of these windows is transparent and resistant to the pressure differential between the inside and outside of the chamber.

[0020] In this way the dimensional variations of the sample in the chamber can be measured by making observations of the sample, through the porthole(s), from outside the chamber.

[0021] In another respect, the invention relates to an assembly comprising: a test bench; and apparatus according to any one of the embodiments of the apparatus according to the invention; said apparatus being removably fixed on a base belonging to the test bench and the test bench comprising an actuator for forcing the displacement of said movable head relative to the chamber wall.

[0022] This embodiment of the assembly according to the invention is particularly useful because it allows any mechanical resistance test bench for materials to be equipped with the ability to test materials under variable and controlled hydrostatic pressure.

[0023] The apparatus consists of a tool that can be assembled on the test bench so as to use the test bench actuator to apply forces on the sample and to vary the hydrostatic pressure in the chamber.

[0024] This method of implementation is particularly economical to implement.

[0025] Other features and advantages of the invention will become apparent from the following description of a particular and non-limiting embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Reference will be made to the attached drawings, including: [ Fig. 1 ] there figure 1 presents an assembly 0 according to the invention comprising a test bench equipped with an actuator 102, in this case a cylinder, the apparatus 1 according to the invention being assembled on this test bench to test a sample 2 placed in the chamber 3 of the apparatus 1, in this case in a sample reception zone 5; [ Fig. 2a ] there figure 2a presents apparatus 1 according to the invention illustrated in the figure 1while it is used to exert a uniaxial compressive force on a sample in order to deform it, chamber 3 is open at the fluid outlet 7d so that the fluid present in the chamber can escape freely while the compressive forces applied by the moving head 6 on the sample 2 vary (in this apparatus configuration, the hydrostatic pressure in the chamber remains invariant / constant, for example equal to one atmosphere); [ Fig. 2b ] there figure 2b presents apparatus 1 according to the invention illustrated in the figure 1whereas it is used to compress the sample of porous compressible material 2 solely by varying the hydrostatic pressure in the chamber 3, by moving the sliding rod 60 and without applying uniaxial compressive forces via the moving head 6, here we study the behavior of the sample under the effect of the single variation of hydrostatic pressure which is measured; Fig. 2c ] there figure 2c presents apparatus 1 according to the invention illustrated in the figure 1while it is used to compress the material sample 2 in two successive stages, the first stage consisting of a uniaxial deformation of the sample by compression of the sample between the moving head 6 and the stop 11 under constant hydrostatic pressure in the chamber and the second stage combining the uniaxial deformation of the sample by compression of the sample 2 between the head 6 and the stop 11 and a deformation by variation (increase) of the hydrostatic pressure in the chamber 3 (this second stage allows a mixed stress application on the sample); [ Fig. 3 ] there figure 3illustrates the application on sample 2 of an imposed loading path C1 using apparatus 1 according to the invention, this test with the imposed loading path C1 makes it possible to define theoretical limit curves CL1, CL2 which, for example, characterize respectively the elastic and plastic limit of sample 2 as a function of shear stress values ​​q in the material of the sample and as a function of hydrostatic pressure values ​​p in the material of the sample (several tests following different loading paths make it possible to define precisely the shape of the curves CL1, CL2 to characterize the theoretical behavior of the material of the sample). DETAILED DESCRIPTION OF THE INVENTION

[0027] According to a first aspect, the invention relates to apparatus 1 for carrying out tests on a sample of material 2, this apparatus 1 being illustrated in the Figures 1 , 2a, 2b, 2c .

[0028] According to a second aspect, the invention relates to an assembly 0, illustrated in the figure 1 , this assembly 0 comprising a test bench 100 and an apparatus 1 according to the invention, the apparatus 1 being removably fixed on a base 101 belonging to the test bench 100 and the test bench 100 comprising an actuator 102 for forcing the displacement of a movable head 6 of the apparatus 1 relative to the wall 4 of chamber 3 of the apparatus 1.

[0029] The assembly 0 according to the invention may also include a sample of material 2 disposed in the sample receiving area 5.

[0030] In a particular and preferred embodiment of assembly 0 according to the invention, the sample 2 is surrounded by a protective sheath 2a of the sample, said sheath 2a being deformable and opposing the passage of hydraulic fluid (typically water) into the interior of the sample.

[0031] The deformation of the sheath causes a variation in the volume of the sample which is compressible in nature possibly porous such that the hydrostatic pressure in the sample varies according to the forces applied on the sheath by the moving head and / or by the ambient hydrostatic pressure in the chamber.

[0032] The sheath prevents the fluid present in the chamber from entering the sample, which could alter its mechanical behavior.

[0033] Thus, in the case where the sample is dry matter, such as a clumped dry laundry capsule or a dry medicinal tablet, the sheath prevents the hydraulic fluid present in the chamber from causing dissolution of the sample and a change in the mechanical characteristics of the sample.

[0034] Similarly, if the sample is a block of foam, the sleeve prevents the hydraulic fluid present in the chamber from penetrating the foam cells and altering their mechanical behavior.

[0035] This sheath, for example, is made of latex.

[0036] In summary, the use of such a deformable sheath makes it possible to characterize the mechanical behavior of the sample material under a given hydrostatic pressure without the hydraulic fluid degrading the sample.

[0037] Apparatus 1 according to the invention comprises: a chamber 3 delimited externally by a metal wall 4 of chamber 3 and in which is provided a receiving area 5 for the sample of material 2; at least one movable head 6 relative to said wall of chamber 4 between a first position in which the movable head 6 is away from the receiving area of ​​sample 5 and a second position in which the movable head 6 is in the receiving area of ​​sample 5 to apply forces on the sample 2.

[0038] The wall 4 of the chamber is rigid to limit wall deformation during the testing of the sample.

[0039] The apparatus 1 comprises a hydraulic circuit 7 and a hydraulic valve device 8 selectively adopting: an isolation configuration of chamber 3 in which the chamber is hermetically sealed (by hermetically sealed we mean that the chamber is closed, that is to say hermetically sealed to retain the fluids); and a fluid evacuation configuration out of chamber 3 in which fluid can be evacuated out of the chamber via said hydraulic circuit 7.

[0040] THE Figures 1 And 2b present the hydraulic valve device 8 while it is in isolation configuration of chamber 3, the chamber being airtight.

[0041] THE figures 2a and 2c present the hydraulic valve device 8 when it is in fluid evacuation configuration so that the fluid contained in chamber 3 can be evacuated via the hydraulic circuit 7 and more particularly via a fluid outlet 7d which is made through the wall 4 of the chamber and which belongs to the hydraulic circuit 7.

[0042] Here, the hydraulic valve device 8 includes an annular seal which is carried by a sliding rod 60 which slides sealingly through the wall 4 of the chamber 3.

[0043] Depending on the sliding position of rod 60 relative to chamber wall 4, the seal is: be placed between chamber 3 and fluid outlet 7d to create a sliding seal preventing fluid from flowing from chamber 3 to fluid outlet 7d (the hydraulic valve device 8 then being in chamber 3 isolation configuration as on the Figures 1 And 2b); or placed in an insertion passage of the rod 60 towards the chamber to create a sliding seal opposing the passage of fluid from the chamber to the insertion passage of the rod and to allow the passage of fluid from chamber 3 to the fluid outlet 7d (the hydraulic valve device 8 then being in the configuration of evacuating fluid out of chamber 3 as illustrated in the figures 2a and 2c ).

[0044] In the embodiment illustrated in figures 1 to 2c , the insertion passage of the stem has an internal annular groove into which the fluid outlet 7d opens, this annular groove being chamfered at its terminal ends to facilitate the sliding of the valve system seal 8 when it is in relation to the annular groove.

[0045] Thus, when the seal of the valve system 8 is opposite the groove and more particularly opposite the fluid outlet 7d, then the seal is less compressed and is therefore less likely to tear when passing opposite the fluid outlet 7d.

[0046] To this end, the fluid outlet 7d opens at the bottom of the annular groove, preferably equidistant from the annular chamfers of this annular groove.

[0047] The apparatus 1 according to the invention also includes at least one force sensor 9 arranged to measure forces applied to the sample 2 located in the sample receiving area 5 and at least one pressure sensor 10 arranged to measure hydraulic / hydrostatic pressure inside the chamber 3.

[0048] Said at least one force sensor 9 could be arranged so that said forces applied to the sample 2 are measured directly at the contact of the moving head 6 and / or directly at the contact of the sample 2.

[0049] However, this would imply that the force sensor 9 would be mechanically exposed in the chamber, risking damage to it.

[0050] To avoid these inconveniences, it is proposed that the force sensor 9 be arranged so that the said forces applied to the sample 2 are measured indirectly by the sensor 9, without this sensor 9 being in contact with the moving head 6 and / or the sample 2.

[0051] To this end, the force sensor 9 is placed between a stop 11 and a fixed part of the chamber, in this case this fixed part is a surface of a base 12 in such a way that the forces applied on the sample 2 by the moving head 6 are retransmitted via the stop 11 to the sensor 9 to be measured while keeping the sensor 9 in a protected area, away from the moving head 6 and away from the sample 2, between the stop 11 and the base 12.

[0052] As will be seen below, this base 12 forms a lower part of the wall 4 of chamber 3.

[0053] The apparatus 1 or the test bench 100 includes a displacement sensor 70 of the moving head 6 relative to the chamber 3.

[0054] This displacement sensor 70 is functionally connected to a recording unit 80 to record representative values ​​of displacements of the moving head measured by said displacement sensor 70.

[0055] This displacement sensor 70 can be arranged to measure the displacement of the rod 60 relative to the chamber wall, for example in the manner of a linear encoder.

[0056] Thanks to the movable head 6, the force sensors 9 and pressure sensors 10 and the valve system 8, it is possible to test in a controlled environment the mechanical behavior of a sample in response to a mechanical stress applied to the sample.

[0057] This mechanical stress applied to sample 2 can be a variation of the hydrostatic pressure of the chamber by displacement of the rod 60 and / or a variation of the forces applied by the movable head 6 on the sample.

[0058] The apparatus according to the invention is thus particularly suitable for characterizing the mechanical properties of a compressible material, such as a porous material, when it is subjected to a given / controlled variation of forces and to a given / controlled constant or variable hydrostatic pressure.

[0059] As illustrated on the figures 1 to 2c , the movable head 6 is a compression head arranged to be able to compress the sample 2 located in the sample reception area 5, between the movable head 6 and the stop 11 placed in the chamber 3.

[0060] In other words, this stop 11 and said at least one movable head 6 are arranged on either side of the sample receiving area 5 in order to be able to selectively compress the sample 2 between the head 6 and the stop 11.

[0061] The stop 11 is arranged to transmit the compressive forces it receives to the force sensor 9, which is itself supported against a surface of the wall 4 of chamber 4, this surface being here a surface of the base 12.

[0062] Thus, said at least one force sensor 9 which is between the stop 11 and the surface of the base 12 is arranged to measure the support force of the sample 2 against the stop 11.

[0063] As we understand it from figures 1 to 2c , the movable head 6 is carried at the end of a sliding rod 60 which slides in a sealed manner through the wall 4 of the chamber 3.

[0064] In this case, the sliding rod 60 slides with a seal through an upper portion 4b of the wall 4 of chamber 3.

[0065] The sliding rod 60 allows a uniaxial compressive force to be transmitted to the material of the sample 2 and, when the hydraulic valve device is in chamber isolation configuration, to control the variation of hydrostatic pressure in the chamber.

[0066] It should be noted that in uniaxial compression ( figure 2a ), it is preferable that chamber 3 not be filled with a liquid. It can optionally be filled with a gas to perform uniaxial compression tests under a controlled atmosphere.

[0067] In some embodiments, the sliding rod 60 may belong to a piston of the apparatus 1 according to the invention.

[0068] However, in the preferred embodiment illustrated in the figure 1 , this sliding rod 60 forms an interface between a rod of a piston 102 which belongs to the test bench 100 on which the apparatus 1 is removably assembled.

[0069] Thus, apparatus 1 is arranged to be assembled on a test bench 100 usually available in materials resistance laboratories to provide, at a lower cost, an option for characterizing samples in a pressure-controlled hydrostatic environment.

[0070] Preferably, the apparatus 1 includes a base 12 fixed in a removable manner, for example via clamping flanges (not shown), on the base 101 which belongs to the test bench 100.

[0071] The force sensors 9 and pressure sensors 10 are fixed on the base 12 and a lower portion of the wall of the chamber 4 is defined by a face of the base 12.

[0072] The hydraulic circuit 7 includes a hydraulic fluid inlet line 7a which opens into the chamber 3, this inlet line 7a passing through the base 12.

[0073] Thus, the base 12 forms a lower portion of the wall 4 of the chamber 3 which carries the force sensors 9 and pressure sensors 10 while allowing the passage of the intake pipe 7a.

[0074] In this way the functional connections necessary for the transmission of measurements from sensors 9, 10 and for the supply of fluid to equipment 1 are grouped on the same base 12 in the lower part of the equipment.

[0075] The connection with peripheral equipment of apparatus 1 and the positioning of apparatus 1 on test bench 100 are thus greatly facilitated because they are located at the base level.

[0076] The hydraulic circuit 7 also includes a non-return valve 7a1 arranged to, on the one hand, allow the passage of hydraulic fluid through the inlet pipe 7a and towards the chamber and, on the other hand, prevent the passage of hydraulic fluid from the chamber 3 towards the inlet pipe 7a.

[0077] In this case, the non-return valve 7a1 consists of a movable ball in the pipe 7a between: a restriction formed in the fluid inlet duct 7a to oppose the passage of the ball into the chamber 3 while allowing the passage of fluid around the ball towards the chamber 3; and a seat formed in the fluid inlet duct 7a against which the ball can come to rest in a sealed manner in order to oppose the passage of fluid from the chamber 3 towards the duct 7a.

[0078] The hydraulic circuit 7 may also include a pump 7b hydraulically coupled to the inlet line 7a in order to force the passage of hydraulic fluid from a fluid reservoir 7c into the chamber 3 via the hydraulic fluid inlet line 7a.

[0079] The actuator 102 which belongs to the test bench 100 is fixed on a structure 103 of the test bench which is mechanically linked to said base 101. This actuator 102 is for example a piston 102 which comes to rest on the sliding rod 60 to control its movement / sliding.

[0080] Structure 103 and base 101 are arranged to define a space in which the base 12 and chamber 3 of apparatus 1 are positioned, the distance between structure 103 and base 101 being invariable at least for the entire duration of the test.

[0081] The sliding rod 60 is preferably assembled in a detachable manner vis-à-vis the piston rod 102 of the test bench 100 and in such a way that the sliding rod 60 and the piston rod 102 are secured to each other in movement.

[0082] In this way, it is the movement of the piston rod 102 of the test bench 100 which allows the movement of the sliding rod 60 of the apparatus 1 to be controlled.

[0083] This embodiment is economical to implement since it is not necessary to equip the device with an actuator.

[0084] The assembly between the piston rod 102 and the sliding rod 60 can be done by multiple means known as a tenon mortise joint blocked by a flange.

[0085] The valve device 8 includes a sealing surface 8a carried by the sliding rod 60.

[0086] In this case, the sealing surface 8a is an external lateral surface of a seal carried by the sliding rod 60.

[0087] A fluid outlet 7d is made through the wall of chamber 3.

[0088] The said sealing surface 8a is arranged so that, on a first part of the stroke of the sliding rod 60, the sealing surface 8a allows the passage of fluid via the fluid outlet 7d, the hydraulic valve device then being in fluid evacuation configuration out of the chamber.

[0089] Said sealing surface 8a is also arranged so that, on a second part of the stroke of the sliding rod 60, said sealing surface prevents the passage of fluid via the fluid outlet 7d, the hydraulic valve device then being in chamber isolation configuration.

[0090] In other words, when the sliding rod 60 is on its first part of stroke which is distinct from said second part of stroke, the sealing surface 8a allows the passage of fluid out of chamber 3 towards the fluid outlet 7d, the hydraulic valve device 8 then being in fluid evacuation configuration out of chamber.

[0091] When the sliding rod 60 is on its second part of the stroke, its sealing surface 8a is then between the fluid outlet 7d and the chamber 3 to prevent the passage of fluid from the chamber 3 to the fluid outlet 7d, the hydraulic valve device 8 being then in isolation configuration to oppose any transfer of fluid between the chamber and the outside of the chamber.

[0092] Thus, the sliding rod 60 is used for: apply forces on the sample (via the movable head carried by the sliding rod 60); and to selectively close the fluid outlet of the chamber and thus vary the hydrostatic pressure in the chamber according to the force applied on the rod 60.

[0093] This is advantageous because it allows, with the help of a single actuator 102 coupled to the sliding rod 60, to vary the forces applied to the sample (at least on the first part of the stroke of the rod 60), and on the second part of the stroke of the rod 60, to vary the hydrostatic pressure in the chamber 3 and consequently to deform the sample 2 under the effect of the variation in hydrostatic pressure.

[0094] According to a first approach, the measurement of the variation in volume of the sample as a function of the applied hydrostatic pressure can be estimated as a function of a measurement of the displacement of the sliding rod 60 relative to the wall 4 of chamber 3.

[0095] Indeed, the variation in the sample volume corresponds to the volume of the rod 60 introduced into the chamber when the valve device 8 is in its isolation configuration. The volume of the rod introduced into the chamber when the valve device 8 is in its isolation configuration is equal to the cross-sectional area of ​​the rod 60 multiplied by the insertion depth of the rod 60 into the chamber from the moment the isolation configuration is adopted.

[0096] Another approach to calculating the variation in sample volume will be presented later in conjunction with the use of one or more cameras.

[0097] Following this alternative approach, the longitudinal deformation of the sample is obtained from the displacement of the rod 60 measured by the displacement sensor 70 and the diametrical deformation of the sample is obtained by analyzing images recorded during the test through the windows 40.

[0098] This apparatus 1 allows for the following: simple stress tests by applying forces to the sample via the moving head 6, without variation of hydrostatic pressure; or simple stress tests by applying a variation of hydrostatic pressure without applying forces by the moving head; or mixed stress tests combining / phasing chronologically: a stress by applying forces to the sample via the moving head as a function of the displacement of the rod 60 (typically a uniaxial compression type stress); and a hydrostatic compression stress of the sample, the latter stress being also controlled by displacement of the rod 60 which is also controlled by the displacement of the piston 102.

[0099] The simplicity of operation of apparatus 1 allows a test condition to be faithfully reproduced over several consecutive tests to measure the behavior of one or more samples.

[0100] As can be seen on the figures 1 to 2c , the fluid outlet 7d opens inside chamber 3, at the top of this chamber.

[0101] This allows for better gas evacuation through the top of the chamber, making it easy to fill the chamber with hydraulic fluid, which is liquid and incompressible by nature. This allows the behavior of the sample to be measured while it is completely immersed in the hydraulic fluid, avoiding the disturbances / approximations induced by the presence of a compressible gas (other than that possibly contained within the sample).

[0102] As illustrated on the figures 1 to 2c , the apparatus 1 also includes a programming spacer 61 assembled between said at least one movable head 6 and said end of the sliding rod 60.

[0103] The movable head 6 has a position relative to the end of the sliding rod 60 which is fixed / determined by a proper dimension, in this case the length, of said programming spacer 61.

[0104] This programming spacer 61 is selectively removable to vary the position of the movable head 6 relative to the end of the sliding rod 60.

[0105] In simple hydrostatic compression ( figure 2b ), the cell is filled with an assumed incompressible liquid and the programming spacer 61 is either removed or replaced by a spacer 61 dimensioned so that the sample 2 fixed on the upper jaw 6a does not touch the stop 11 during the entire duration of the simple hydrostatic test.

[0106] During the simple hydrostatic test, the displacement of the rod 60 causes a change in the internal volume of the chamber. This volume change is directly imposed on the sample 2. The pressure (induced by the sample's reaction) in the cell is measured by the pressure sensor 10. As previously mentioned, the volumetric deformation of the sample can be obtained from the displacement measurement of the rod 60 taken by the sensor 70 and / or from the analysis of the images of the sample generated by the camera(s) 20 and recorded during the test.

[0107] In mixed compression (uniaxial and hydrostatic, figure 2c), the chamber is filled with a liquid. The length of the programming spacer 61 is chosen so that on a first part of the stroke of the rod, the sample is in contact with the stop 11 and undergoes uniaxial compression while the valve device 8 is in fluid evacuation configuration via the outlet 7d and that on a second part of the stroke of the rod the valve device is in chamber isolation configuration (the rod 60 acts as a distributor), the sample being both axially compressed between the head 6 and the stop 11 and hydrostatically compressed by the ambient hydrostatic pressure of the liquid (hydraulic fluid) in the chamber 3 under the effect of the sole movement of the rod 60.

[0108] In this mixed axial and hydrostatic compression configuration, the axial force is measured by the force sensor 9, the pressure by the sensor 10, the axial deformation of the sample by the measurement of the displacement of the rod 60 carried out by the sensor 70 and the variation in volume of the sample is calculated by analysis of the images delivered by the camera(s) 20.

[0109] It should be noted that in cross-sectional planes perpendicular to a longitudinal direction of the sliding rod 60, the sliding rod 60 has a cross-section greater than the cross-section of the programming spacer 61.

[0110] This makes it easier to assemble the equipment 1 since the programming spacer 61 (with a cross-section smaller than that of the rod 60) can be inserted into the chamber 3 through the bore where the rod 60 slides.

[0111] Preferably, the apparatus 1 according to the invention comprises a set of programming spacers 61 of different dimensions, each given programming spacer 61 of the set of spacers being adapted to be assembled between said at least one movable head 6 and said end of the sliding rod 60.

[0112] In this way, the operator can select a programming spacer 61 or a combination of several programming spacers 61 to define the fixed distance between said at least one movable head 6 and said end of the sliding rod 60 and thus define the phasing between the uniaxial compression stage and the hydrostatic compression stage, depending on the sliding position of the sliding rod 60.

[0113] For a given sample size 2, defining the distance between the movable head 6 and the end of the sliding rod allows us to determine: the distance of movement of the rod 60 required to start the application of force by the movable head 6 on the sample 2; and the distance of movement of the sliding rod 60 required for the hydraulic valve device 8 to change from its fluid discharge configuration to its isolation configuration.

[0114] The programming spacer 61 is here in the form of a straight cylinder, the movable head 6 being connected to the sliding rod 60 by means of a connecting piece 62 which passes through the programming spacer 61.

[0115] This connecting piece 62 has an end part screwed into a complementary thread formed in the sliding rod 60 so as to keep the programming spacer 61 tight between the movable head 6 and the sliding rod 60.

[0116] As illustrated on the figures 1 to 2c, the wall 4 of chamber 3 has a removable upper portion forming an upper cover 4b for sealing an upper opening of chamber 3.

[0117] The sliding rod 60 slides in a sealed manner through a passage through this upper cover 4b.

[0118] The movable head 6 and the programming spacer 61 are respectively sized to be able to pass through the upper opening of the chamber.

[0119] In other words, the chamber wall includes an intermediate portion 4c having said upper opening of the intermediate portion 4c.

[0120] The cover 4b is assembled in a removable and airtight manner against the intermediate wall 4c to close the upper opening of the chamber while guiding the movement of the sliding rod 60 through the passage through the upper cover 4b.

[0121] With this design, it is possible to introduce a large sample through this top opening.

[0122] Preferably, the movable head 6 has an upper jaw 6a for fixing a portion of the material sample 2 by tightening the upper jaw 6a around a part of the sample 2.

[0123] In this way, the sample is simply positioned in the chamber since it is only supported by the jaw 6a of the movable head 6.

[0124] The wall 4 of chamber 3 has at least one window 40 to view, from outside chamber 3, the sample located in the sample reception area 5.

[0125] In this case, equipment 1 includes two pairs of portholes.

[0126] The portholes of a given pair of portholes 40 are aligned along an alignment direction specific to that given pair of portholes.

[0127] The alignment directions of the pairs of portholes are perpendicular to each other.

[0128] In this way, the sample in the chamber can be observed from several observation points arranged all around the sample.

[0129] To facilitate observation of the sample, apparatus 1 includes at least one camera 20 to generate images of the sample located in the sample reception area 5.

[0130] Ideally, each camera should be at least 20 placed facing a porthole 40 that corresponds to it.

[0131] The apparatus shown has a single camera, but it could have one camera per window, each camera being oriented to observe the sample reception area.

[0132] Apparatus 1 includes a recording unit 80 which is functionally connected to each at least one camera 20 in order to record dimensional characteristics of the sample observable on images generated by each of said at least one camera.

[0133] Preferably, the recording unit 80 is also functionally connected to at least one force sensor 9 and to at least one pressure sensor 10 in order to record signals delivered by said at least one force sensor 9 and by said at least one pressure sensor 10.

[0134] The recording unit 80 includes a recording medium 81 where the recorded data is stored.

[0135] Furthermore, the test bench 100 or possibly the apparatus 1 according to the invention may also include a control unit 90 which is functionally connected to the actuator 102 of the test bench 100 to control the movement of the sliding rod 60.

[0136] This control unit 90 can also be functionally linked to the recording unit 80 in order to control the recording of the signals delivered by said at least one force sensor 9, by said at least one pressure sensor 10 and to control the recording of the representative values ​​of displacements of the moving head 6 measured by said displacement sensor 70.

[0137] This control unit 90 can also be functionally connected to said pump 7b of the hydraulic circuit 7 in order to control the filling of the chamber with hydraulic fluid.

[0138] Equipment 1 can also be equipped with a fluid level detector arranged to signal a state of filling of the chamber with hydraulic fluid, this fluid level detector being preferably located at the outlet 7d and being preferably connected to said control unit 90.

[0139] In this embodiment, the control unit 90 is arranged to control the actuator 102 responsible for the movement of the rod 60 according to a fluid level measurement signal in the chamber delivered by the level detector.

[0140] Furthermore, the recording unit 80 can deliver to the control unit 90, parametric values ​​of the test to be carried out, such as a particular instruction for the movement of the rod 60 (speed and / or position instruction), a particular instruction for the forces to be applied to the rod 60.

[0141] Recording the signals from the various sensors 9, 10, 70, and cameras 20, during the course of the test allows us to record a chronology of the forces applied by the moving head 6, the hydraulic pressures applied by the hydraulic fluid, as well as the mechanical behavior of the sample 2 in response to these stresses.

[0142] Preferably, apparatus 1 also includes a unit for calculating the variation in sample volume, generating a value representative of a variation in sample volume: based on a measured displacement value of said sliding rod 60 relative to the wall 4 of chamber 3; and / or based on said dimensional characteristics of sample 2 observable on images generated by each of said at least one camera 20 and / or; based on the measured displacement value of said at least one sliding rod 60 and said dimensional characteristics of sample 2 observable on images generated by each of said at least one camera 20.

[0143] Since the hydraulic fluid contained in the chamber is incompressible, the change in volume of the sample subjected to a given change in hydrostatic pressure corresponds to the change in the internal volume of the chamber induced by the movement of the sliding rod 60, i.e. by the movement of the piston rod 102.

[0144] Thus, apparatus 1 according to the invention makes it possible to calculate a variation in the volume of the sample as a function of a measured value of displacement of the sliding rod 60, possibly taking into account the compressibility of the hydraulic fluid and / or the deformation capacity of the wall of the chamber as a function of a given hydrostatic pressure measured by the pressure sensor 10.

[0145] The behavior of the sample is characterized as follows: depending on the variation in pressure, the variation in the volume of the sample); and / or depending on the forces applied to the sample by the moving head and / or depending on images of the sample obtained by the camera(s) 20.

[0146] There figure 3 illustrative: a test carried out on a sample of porous material using apparatus 1 according to the invention; and limit curves of material behavior CL1, CL2 which can be deduced using the results of several tests.

[0147] Curve C1 of the figure 3 represents a C1 loading path imposed / applied to a sample of porous material to characterize the theoretical behavior of the material if it were subjected to other theoretical loading paths.

[0148] The abscissa of the stress plane corresponds to an internal stress on the sample by hydrostatic compression p.

[0149] Since sample 2 is enclosed in a hermetically sealed sheath 2a, the variation in volume of the sample combined with the measurement of hydrostatic pressure in the chamber allows us to deduce the current hydrostatic pressure p in the sample.

[0150] In this example, the first loading path C1 is imposed by the equipment 1 by moving the rod 60 which carries the movable head 6 relative to the chamber 3 filled with hydraulic fluid.

[0151] This loading path C1 first includes a uniaxial loading (part C1a of the curve) carried out by moving the movable head 6 to compress the sample 2 against the stop 11 while the valve system 8 is in fluid evacuation configuration.

[0152] Thus, on this part C1a, despite the introduction of the rod 60 into the chamber 3, the hydrostatic pressure in the chamber remains constant since the fluid escapes freely via the fluid outlet.

[0153] The straight curve C1a shows a growth in hydrostatic pressure in the sample because the sample is compressed while it is closed in the airtight sheath.

[0154] This loading path C1 then includes a mixed loading (part C1b of the curve) combining the compression of the sample between the moving head 6 and the stop 11 with hydrostatic compression because, at point Cx, the valve system 8 switches to an isolation configuration to increase the hydrostatic pressure in the chamber and in the sample as the compressive force applied to the rod 60 is increased. By carrying out several successive tests following different loading paths, limit curves CL1 and CL2 specific to the sample can be deduced and which allow the theoretical behavior of the sample material to be predicted for other loading paths.

[0155] Each limit curve CL1 and CL2 expresses a limit of material behavior in shear q as a function of hydrostatic pressure p in the material.

[0156] The CL1 curve is, for example, an elastic deformation limit and the CL2 curve is, for example, a plastic deformation limit.

[0157] From experience, it appears that each limit curve CL1, CL2 is in the shape of a semi-ellipse.

[0158] The x-axis is the limiting axis of each of these semi-ellipses and it also forms the axis of symmetry of each of the complete ellipses to which these semi-ellipses CL1, CL2 belong.

[0159] By performing a uniaxial compression test, a straight line C1x is determined through which the semi-ellipse passes, the point of intersection C10 between the semi-ellipse and the straight line C1x corresponding to a notable change in elastic or plastic behavior of the sample.

[0160] By carrying out a mixed loading test along the C1 curve, a second point C11 of the semi-ellipse is determined which also corresponds to a notable change in the behavior of the sample, such as the transition from the exclusively elastic deformation domain to the plastic deformation domain.

[0161] By repeating the test with other mixed loading paths, we can define at least a third point of the semi-ellipse CL1.

[0162] Using these three or more points of the semi-ellipse, we can extrapolate the general curve of the semi-ellipse CL1, which allows us to know a limit of the sample's behavior valid for a plurality of theoretical loading paths.

[0163] The same method is applied to determine the CL2 curve.

[0164] Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0165] Thus, the movable head 6 could be pivoted to apply a controlled torque to the material sample in order to characterize its torsional behavior and / or its bending behavior under controlled hydrostatic pressure.

Claims

1. Equipment (1) for carrying out tests on a sample of material (2), the equipment comprising: - a chamber (3) bounded externally by a wall (4) of the chamber (3) and into which is arranged an area (5) for receiving said sample of material (2); - at least one mobile head (6) with respect to said chamber wall (4) between a first position in which the mobile head (6) is away from the sample receiving area (5) and a second position in which the mobile head (6) is located in the sample receiving area (5) to apply forces to the sample (2), the equipment (1) comprising a hydraulic circuit (7) and a hydraulic valve device (8) selectively adopting a configuration for isolating the chamber (3) in which the chamber is hermetic and a configuration for evacuating fluid from the chamber (3) in which fluid can be evacuated from the chamber via said hydraulic circuit (7), the equipment (1) also comprising at least one force sensor (9) arranged to measure forces applied to the sample located in the sample receiving area (5) and at least one pressure sensor (10) arranged to measure a hydraulic pressure inside of the chamber (3), said at least one movable head (6) being carried at the end of a sliding rod (60) which slides in a sealed manner through the wall (4) of the chamber (3), characterised in that the valve device comprises a sealing surface (8a) carried by the sliding rod (60) and a fluid outlet (7d) made through the wall of the chamber, the sealing surface being arranged: - on the one hand, so that during a first stroke part of the sliding rod (60), the sealing surface (8a) allows the passage of fluid via the fluid outlet (7d), the hydraulic valve device then being in the configuration for evacuating fluid away from the chamber; and - on the other hand, so that during a second stroke part of the sliding rod (60), said sealing surface (8a) prevents the passage of fluid via the fluid outlet (7d), the hydraulic valve device then being in the configuration for insulating the chamber.

2. Equipment (1) according to claim 1, comprising a stopper (11) placed in the chamber (3), the stopper (11) and said at least one mobile head (6) being arranged on either side of the sample receiving area (5) to be able to selectively compress said sample (2) between the stopper (11) and said at least one mobile head (6), said at least one force sensor (9) being arranged to measure a bearing force of the sample (3) against the stopper (11).

3. Equipment (1) according to any one of claims 1 or 2, comprising a base (12), said at least one force sensor (9) and said at least one pressure sensor (10) being fixed to said base (12), a lower portion of the wall of the chamber (4) being defined by a face of the base (12).

4. Equipment according to claim 3, wherein the hydraulic circuit (7) comprises a hydraulic fluid intake pipe (7a) opening into the chamber (3).

5. Equipment (1) according to claim 4, wherein the intake pipe (7a) passes through the base (12).

6. Equipment according to any one of claims 4 or 5, wherein the hydraulic circuit comprises a non-return valve (7a1) arranged on the one hand to allow the passage of hydraulic fluid through the intake pipe and towards the chamber and on the other hand to oppose the passage of hydraulic fluid from the chamber towards the intake pipe.

7. Equipment according to any one of claims 1 to 6, wherein the fluid outlet (7d) opens into the chamber (3) at the top of that chamber.

8. Equipment according to any one of claims 1 to 7, comprising at least one programming spacer assembled between said at least one movable head and said end of the sliding rod (60), the movable head (6) having a position relative to the end of the sliding rod that is fixed by at least one proper dimension of said at least one programming spacer (61), said programming spacer (61) being selectively removable to vary said position of the movable head (6) relative to the end of the sliding rod (60).

9. Equipment according to any one of Claims 1 to 8, wherein the wall (4) of the chamber (3) comprises a removable upper portion forming an upper cover (4b) for closing an upper opening of the chamber (3), said sliding rod (60) sliding in a sealed manner through a passage passing through the upper cover (4b), the movable head (6) being sized so as to be able to pass through the upper opening of the chamber.

10. Equipment (1) according to any one of claims 1 to 9, wherein the movable head (6) has a top jaw (6a) for securing a portion of the material sample (2) thereto by clamping the top jaw (6a) around a sample portion (2).

11. Equipment according to any one of claims 1 to 10, wherein the wall (4) of the chamber (3) has at least one window (40) for viewing, from outside the chamber (3), a sample located in the sample receiving area.

12. Equipment according to any one of claims 1 to 11, wherein the wall of the chamber comprises a plurality of pairs of windows, the windows of a pair of windows being located on either side of the sample receiving area and each window being arranged for viewing, from outside the chamber, a sample located in the sample receiving area.

13. Equipment according to any one of claims 1 to 12, comprising a recording unit (80) operatively connected to said at least one force sensor (9) and to said at least one pressure sensor (10) in order to record signals delivered by said at least one force sensor and by said at least one pressure sensor.

14. Equipment according to claim 13, comprising a displacement sensor (70) of the movable head relative to the chamber (3), the displacement sensor (70) being operatively connected to said recording unit (80) for recording representative values of movable head displacements measured by said displacement sensor (70).

15. Equipment according to any one of claims 13 or 14, comprising at least one camera (20) for generating sample images located in the sample receiving area (5).

16. Equipment according to claim 15, wherein the recording unit (80) is operatively connected to each of the at least one camera (20) to record observable dimensional characteristics of the sample on images generated by each of the at least one camera.

17. Equipment according to Claim 16, comprising a unit for calculating the variation in volume of the sample generating a value representative of a variation in volume of the sample as a function of a measured displacement value of said sliding rod (60) relative to the wall (4) of the chamber (3) or as a function of said dimensional characteristics of the sample (2) observable in images generated by each of said at least one camera (20) or as a function of the measured displacement value of said at least one sliding rod (60) and of said dimensional characteristics of the sample (2) observable in images generated by each of said at least one camera (20).

18. Assembly (0) comprising a test bench (100) and an equipment (1) according to any one of claims 1 to 17, said equipment (1) being fixed in a removable manner on a base (101) belonging to the test bench (100) and the test bench (100) comprising an actuator (102) for forcing the displacement of said mobile head (6) with respect to the chamber wall (4).

19. Assembly (0) according to claim 18, further comprising a material sample (2) arranged in the sample receiving area (5).

20. Assembly (0) according to claim 19 wherein the sample (2) is surrounded by a protective sheath for the sample, said sheath being deformable and opposing the passage of hydraulic fluid to the inside of the sample.