Creep testing machine

Abstract

A creep test machine (1, 1') comprising: a frame (2); a lever (3) pivotally mounted on the frame and carrying a mass (7); a first tie rod (4.1) connected to the frame and provided with means for securing a first end of a test specimen (E); a second tie rod (4.2) connected to the lever and provided with means for securing a second end of the specimen; and a specimen loading device (20) comprising a structure (27) defining a chamber (28) of variable volume, and a movable element (22) mounted to move freely between a high position in which the mass is supported by the movable element which supports the lever, and a low position in which the mass is supported by the lever, the position of the movable element being a function of the chamber volume. The chamber is selectively in fluidic communication with a pressurized fluid source (S) and an exhaust flow restrictor (R). FIGURE IN ABBREVIATION: Fig. 2A

Description

Title of the invention: Fining testing machine

[0001] The present invention relates to the characterization of the physical resistance of a material, and more particularly to a finishing test machine allowing a test specimen to be subjected to a tensile force applied in a repeatable manner.

[0002] BACKGROUND OF THE INVENTION

[0003] Creep tests consist of subjecting a test specimen to a constant load over a determined period, which may be longer or shorter, and at a given temperature. They are generally carried out using a machine T which comprises, as illustrated in [Fig. 1]: • a frame B provided with a fixing point for a first bar B1 for fixing a lower end of the test specimen E, • a lever L mounted pivotally on the frame B around a substantially horizontal axis X, transverse to the lever L, and having a first end provided with a second bar B2 for fixing an upper end of the specimen E; and • a hydraulic cylinder V of the "bottle jack" type arranged to exert a vertical pushing force on the lever L intended to support said lever L, the cylinder V being equipped with a discharge screw S allowing to control the start of the retraction of the cylinder V but also to control the speed of retraction of said cylinder V.

[0004] The first bar B1 is connected to the frame by a ball joint and the second bar B2 is connected to the lever L by a clevis mounted rotatably on the lever around an axis substantially parallel to the axis X of rotation of said lever L, said first and second bars B1, B2 extending along a substantially vertical axis of traction Z.

[0005] A second end of the lever L, opposite the first end of said lever L, carries a plate P on which rests a mass M.

[0006] When stopped, the jack V is, as shown in [Fig.1], deployed and supports the lever by compensating for the force resulting from the application of the weight of the mass M on the second end of the lever L, so that said mass M exerts no force on the specimen E. In operation, the jack V is retracted by unscrewing the discharge screw S, so that the second bar B2 is subjected to a tensile force directed substantially upwards, the intensity of which depends on the weight of the mass M, this tensile force being transmitted to the specimen E which then tends to lengthen.

[0007] The loading speed of the test specimen E via the mass M thus depends on the retraction speed of the cylinder V, which is itself a function of the amplitude of the unscrewing of the discharge screw S. Therefore, the loading of the test specimen E is more or less rapid, with the possibility of shocks transmitted to the specimen E in the event of sudden retraction of the cylinder V, which can affect the results of finishing tests.

[0008] Moreover, the unscrewing of the discharge screw S is done manually, so that for a given mass M, the loading speed of the test specimen E is difficult to repeat from one test to another. And even if it were, it would be difficult to prove.

[0009] SUBJECT OF THE INVENTION

[0010] The invention therefore aims to provide a finishing test machine allowing for repeatable and shock-free loading of the test specimen. Summary of the invention

[0011] To this end, the invention proposes a flaking testing machine comprising: • a building; • a lever mounted pivoting on the frame around an axis transverse to the lever, and carrying a mass; • a first tie rod having one end connected to the frame and another end provided with first means of fixing one end of a test specimen; • a second tie rod having one end connected to the lever and the other end provided with second means for securing a second end of the test specimen; and • a test specimen loading device comprising a structure defining a chamber of variable volume, and a movable element mounted freely in translation between a high position in which the mass is supported by the movable element which supports the lever, and a low position in which the mass is supported by the lever, the position of the movable element being a function of the volume of the chamber.

[0012] The chamber is selectively in fluidic communication with a pressurized fluid source and an exhaust flow limiter via a second valve.

[0013] Thus, when the structure is in fluidic communication with the pressurized fluid source, the pressure inside the chamber tends to increase, which leads to an increase in the volume of the chamber and therefore a displacement of the moving element towards the high position in which the mass exerts no tensile force on the specimen via the lever.

[0014] When the chamber of the structure is no longer in fluidic communication with the pressurized fluid source but is in fluidic communication with the flow limiter, the pressure inside the chamber tends to decrease, which leads to a decrease in the volume of the chamber and therefore a displacement of the moving element towards the lower position in which the snare exerts a tensile force on the test specimen via the lever.

[0015] The flow limiter is chosen so that the moving element moves from the high position to the low position at a speed slow enough to ensure shock-free loading of the specimen.

[0016] According to a particular feature, the moving element exerts, in the high position, a pulling force on the lever.

[0017] According to another particular feature, the chamber is connected to the pressurized fluid source via a first valve, and to the exhaust flow limiter via a second valve.

[0018] In particular, the first valve and the second valve are solenoid valves.

[0019] In particular, the first valve is normally closed and the second valve is normally open.

[0020] According to another particular characteristic, the structure is an inflatable structure.

[0021] In particular, the movable element comprises an upper cross member and a lower cross member connected by two rods to form a rectangular frame extending in a substantially vertical plane. The upper and lower cross members extend respectively above and below a substantially horizontal platform fixedly mounted on the frame, the inflatable structure being arranged between the upper cross member and the platform to move the movable element between the upper and lower positions, and the lower cross member being arranged to support the lever.

[0022] In particular, the inflatable structure rests on the platform and the upper cross member rests on said inflatable structure.

[0023] In particular, the movable element comprises two first spacers each mounted to slide on one of the two rods between the platform and the lower cross member so as to guarantee, between said platform and said lower cross member, a minimum gap corresponding to the upper position of said movable element.

[0024] In particular, the movable element also includes two second spacers, each mounted to slide on one of the two rods between the platform and the upper cross member so as to guarantee, between said platform and said upper cross member, a minimum gap corresponding to the lower position of said movable element.

[0025] The invention also relates to a method for performing a fineness test on a specimen using such a testing machine. The method comprises the following steps: • while the chamber is not in fluidic communication with the flow limiter, put the chamber in fluidic communication with the pressurized fluid source so as to bring the moving element to the high position; • when the moving element is in the raised position, stop the fluidic communication between the chamber and the pressurized fluid source; • fix the ends of the test specimen to the first tie rod and the second tie rod; • Connect the chamber to the flow limiter. Brief description of the drawings

[0026] The invention will be better understood in the light of the following description, which is purely illustrative and not limiting, and should be read in conjunction with the accompanying drawings, among which:

[0027] [Fig-1] [Fig.1] is a schematic view of a fineness testing machine according to art previous;

[0028] [Fig.2A] [Fig.2A] is a schematic view of a fineness testing machine according to a particular embodiment of the invention, in which the moving element is in the raised position;

[0029] [Fig.2B] [Fig.2B] is a view identical to that of [Fig.2A], in which the moving element is in the lower position;

[0030] [Fig.3] [Fig.3] is a schematic view of a variant of the test machine land illustrated in [Fig.2A]. DETAILED DESCRIPTION OF THE INVENTION

[0031] With reference to Figures 2A-2B and according to a particular embodiment of the invention, a finishing test machine 1 comprises: • a structure 2 resting on a substantially horizontal ground; • a lever 3 mounted pivoting on the frame 2 around an axis X transverse to the lever 3, the axis X being substantially horizontal; • a first tie rod, here a first tensile bar 4.1, having a lower end connected to the frame 2 and an upper end provided with first means for fixing a first end of a test specimen E; and • a second tie rod, here a second tension bar 4.2, having an upper end connected to the lever 3 and a lower end provided with second means for fixing a second end of the specimen E.

[0032] The test specimen E is here in the form of a rod (cylindrical or flat) having shouldered ends to be engaged in housings of the first and second bars 4.1, 4.2. The first bar 4.1 and the second bar 4.2 extend, with the test specimen E, along a substantially vertical loading axis Z.

[0033] The lower end of the first bar 4.1 is connected to the frame via a load-sensing cell 5 arranged to deliver a signal representative of the tensile force exerted on the first bar 4.1 along the loading axis. The load-sensing cell 5 is known in itself and comprises, for example, a bar equipped with one or more strain gauges connected to an electronic measuring circuit. The upper end of the second bar 4.2 is connected to the lever 3 by a clevis 6 rotatably mounted on the lever 3 about an axis substantially parallel to the X-axis of rotation of said lever 3.

[0034] The lever 3 comprises a first end 3.1 on which the yoke 6 is mounted, and a second end 3.2, opposite the first end 3.1, carrying a mass 7 having here a weight approximately equal to twenty kilograms. The axis X of rotation of the lever 3 is located away from the second end 3.2 of the lever 3 by a distance corresponding here approximately to three-quarters of the length of said lever 3 so as to take advantage of a lever arm 3 which, in a manner known per se, amplifies the weight of the mass 7 to load the test specimen E via a tensile force here approximately equal to three thousand Newtons.

[0035] The mass 7 rests here on a platform 8 which is suspended from the lever 3 by a suspension sling 9 having a lower end to which the platform 8 is fixed and an upper end connected to the lever 3 by a clevis 10 mounted rotatably on the lever 3 around an axis substantially parallel to the axis X of rotation of said lever 3 and of the second traction bar 4.2.

[0036] The test machine 1 also includes means for measuring (not shown) the elongation of the specimen E. The measuring means may include LVDT (Linear Variable Differential Transformer) inductive sensors, capacitive sensors, optical or interferometric devices...

[0037] The test machine 1 also includes a heating device arranged to bring and maintain the test specimen E at a predefined test temperature. The heating device comprises a tubular furnace 11 mounted to slide on the frame 2 along an axis substantially parallel to the loading axis of the test specimen E, between a clearance position, illustrated in [Fig. 2A], in which the furnace is clear of the test specimen E, and a heating position, illustrated in [Fig. 2B], in which the furnace 11 surrounds the test specimen E. The temperature of the test specimen E is regulated, for example, by means of a thermocouple in thermal contact with a surface of the test specimen E.

[0038] The test machine 1 further comprises a loading device 20 for the test specimen E. The loading device 20 comprises a substantially horizontal platform 21 fixedly mounted on the frame 2, and a movable assembly 22 slidably mounted on the platform 21 along a lifting axis for the mass 7 approximately vertical, between a high position illustrated in [Fig.2A] and a low position illustrated in [Fig.2B].

[0039] The movable element 22 comprises an upper cross member 23 extending above the platform 21, and a lower cross member 24 extending below said platform 21 and comprising a central hole 24.1 through which the suspension sling 9 extends freely. The upper cross member 23 and the lower cross member 24 are connected to each other by two cylindrical rods 25 and, together with the rods 25, form a rectangular frame extending in a substantially vertical plane. Each of the rods 25 extends freely through a hole 21.1 provided in the platform 21.

[0040] The movable element 22 also includes two first cylindrical spacers 26.1, each mounted to slide on one of the two rods 25 between the platform 21 and the lower cross member 24 so as to guarantee, between said platform 21 and said lower cross member 24, a minimum distance corresponding to the upper position of said movable element 22 (shown in [Fig. 2A]). The first spacers 26.1 are identical and have a diameter greater than that of the holes 21.1 in the platform 21, so that they form first stops to the movement of the movable element 22.

[0041] The movable element 22 also includes two second cylindrical spacers 26.2, each slidably mounted on one of the two rods 25 between the platform 21 and the upper cross member 23 so as to guarantee, between said platform 21 and said upper cross member 23, a minimum gap corresponding to the lowered position of said movable element 22 (shown in [Fig. 2B]). The second spacers 26.2 are identical and have a diameter larger than that of the holes 21.1 in the platform 21, so that they form second stops against the movement of the movable element 22.

[0042] The loading device 20 also includes an inflatable structure 27 disposed between the platform 21 and the upper cross member 23 of the moving element 22. The inflatable structure 27 comprises: • an upper wall 27.1 substantially flat, rigid and on which rests the upper cross member 23 of the movable element 22; • a lower wall 27.2 that is substantially flat, rigid, and rests on the platform 21; and • a closed, elastically deformable side wall 27.3, having a rounded cross-section and connecting an edge of the upper wall 27.1 to an edge of the lower wall 27.2.

[0043] The upper wall 27.1, the lower wall 27.2 and the side wall 27.3 thus define a chamber 28 of variable volume, so that the position of the movable element 22 is a function of the volume of the chamber 28, and therefore of the pressure prevailing inside said chamber 28.

[0044] The upper wall 27.1 includes an inflation and deflation port for the inflatable structure. The port is connected to a pressurized air source S via a first solenoid valve El, and to an exhaust flow restrictor R via a second solenoid valve E2. The air pressure supplied by the source S is between five and six bar. The first solenoid valve El and the second solenoid valve E2 are "on / off" solenoid valves in that they have only two possible states: a fully open state and a fully closed state. The first solenoid valve El, for example, is a normally closed solenoid valve, that is, it is in its fully closed state when no power is supplied and in its fully open state when power is supplied.The second solenoid valve E2 is, for example, a normally open solenoid valve, that is, one which is in its fully open state in the absence of power supply and which is in its fully closed state when it is powered.

[0045] When the first solenoid valve E1 is in its open state and the second solenoid valve E2 is in its closed state, the chamber 28 of the inflatable structure 27 is in fluidic communication with the pressurized air source S. The pressure inside the chamber 28 then tends to increase, which leads to an increase in the volume of the chamber 28 and therefore a displacement of the movable element 22 towards the upper position ([Fig. 2A]).

[0046] When the first solenoid valve El is in its closed state and the second solenoid valve E2 is in its open state, the chamber 28 of the inflatable structure 27 is in fluidic communication with the flow limiter R. The pressure inside the chamber 28 then tends to decrease, which leads to a decrease in the volume of the chamber 28 and therefore a displacement of the moving element 22 towards the lower position ([Fig.2B]).

[0047] When the first solenoid valve E1 and the second solenoid valve E2 are in their closed state, the pressure inside the inflatable structure 27 is stable and therefore the volume of the chamber 28 is constant. The moving element 22 is then static.

[0048] The loading device 20 further comprises a third cylindrical stop 29 which is axially fixed to the suspension sling 9 and which has a diameter greater than that of the hole 24.1 provided in the lower cross member 24 of the movable element 22. The third stop 29 is located a predetermined distance from the upper end of the suspension sling 9, such that: • when the position of the movable element 22 is between the upper position and an intermediate position between said upper position and the lower position, the lower cross member 24 of the movable element 22 is supported against the third stop 29, so that the movable element 22 supports the second end 3.2 of the lever 3 by exerting, via the third stop 29, a substantially vertical tensile force on the suspension sling 9 carrying the mass 7, and therefore on the lever 3; • when the position of the moving element 22 is between the intermediate position and the lower position, the lower cross member 24 of the moving element is moved away from the third stop 29, so that the lever 3 is not supported by the moving element 22; and • when the movable element 22 is in the high position, the distance separating the first tension bar 4.1 from the second tension bar 4.2 is such that the first end and the second end of the specimen E can be fixed respectively to the upper end of the first tension bar 4.1 and to the lower end of the second tension bar 4.2, the lever 3 then exerting no tensile force on the specimen E.

[0049] The operation of the test machine 1 will now be detailed.

[0050] While the second solenoid valve E2 is in the closed state and the furnace 11 is in the release position, the first solenoid valve E1 is moved from the closed state to the open state so as to increase the pressure inside the chamber 28 of the inflatable structure 27 and thus increase the volume of said chamber 28 until the movable element 22 is in the raised position ([Fig. 2A]). The second end 3.2 of the lever 3 is then supported by the movable element 22, which then exerts a tensile force on said second end 3.2 via the third stop 29 fitted to the suspension sling 9. The mass 7 is then supported by the movable element 22.

[0051] Once the moving element 22 is in the raised position, the first solenoid valve El is brought from the open state to the closed state, and then the first end and the second end of the specimen E are fixed respectively to the upper end of the first tensile bar 4.1 and to the lower end of the second tensile bar 4.2. The specimen E is then not subjected to any tensile force.

[0052] The furnace 11 is then brought from the release position to the heating position so as to bring and maintain the test specimen E at the test temperature.

[0053] When the test specimen E has reached the stabilized test temperature, the second solenoid valve E2 is brought from the closed state to the open state, so that the pressurized air contained in the chamber 28 of the inflatable structure 27 tends to escape through the flow limiter R. The pressure inside the chamber 28, and therefore the volume of said chamber 28, then decreases at a rate dependent on the leakage rate of the flow limiter R, so that the moving element 22 moves from the high position to the low position via the intermediate position.

[0054] Between the high position and the intermediate position, the movable element 22 supports the second end 3.2 of the lever 3 via the third stop 29 and supports the mass 7 resting on the platform 8. The test specimen E is then subjected to no tensile force.

[0055] Between the intermediate position and the lower position, the lower cross member 24 of the movable element 22 is moved away from the third stop 29. The specimen E is then subjected, via the second tensile bar 4.2, to a tensile force proportional to the mass 7 resting on the platform 8.

[0056] The rate at which the test specimen E is loaded thus depends on the rate at which the moving element 22 moves from the upper to the lower position, and therefore on the rate at which the inflatable structure 27 deflates, which is itself a function of the leakage rate of the flow restrictor R. The flow restrictor R is chosen so as to generate a leakage rate that allows the descent rate of the moving element 22 to be sufficiently slow and / or gradual to ensure that the test specimen E is loaded without shock. The tensile force to which the test specimen E is subjected here increases from zero to three thousand Newtons in approximately one minute.

[0057] It will be noted that for a given mass 7, the deflation speed of the inflatable structure 27 is repeatable, the high position of the moving element 22 and the leakage rate of the flow limiter R remaining unchanged between two tests.

[0058] Fig. 3 illustrates a test machine 1' which is none other than a variant of the test machine 1 illustrated in Figures 2A-2B.

[0059] Test machine 1' differs from test machine in that: • the lever 3 is mounted pivoting on the frame 2 around an axis X' of rotation carried by the first end 3.1 of the lever 3; • the upper end of the first traction bar 4.1 is connected to the frame 2 via the load detection cell 5; • the lower end of the first tensile bar 4.1 is provided with the first means for fixing a first end of the specimen E; • the lower end of the second traction bar 4.2 is connected to the lever 3 via a clevis mounted rotatably on the lever 3 around an axis substantially parallel to the X' axis of rotation of said lever 3; and • the upper end of the second tensile bar 4.2 is provided with the second means for fixing the second end of the specimen E.

[0060] The charging device 20 of the test machine 1', as well as its operation, is identical to that of the test machine 1.

[0061] 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.

[0062] The means for fixing the ends of the specimen E can be of any type: clamping jaws, pins inserted into holes made at the ends of the specimen E...

[0063] The solenoid valves El, E2 can be replaced by manual valves.

[0064] The leakage rate of the flow limiter R can be fixed or adjustable.

[0065] The lever can be a first or second type lever, but also a third type lever kind.

[0066] The oven can be of any type and is not limited to a sliding oven as described in the embodiments illustrated in figures 2A-2B and 3. The oven can, for example, be fixed and opening.

[0067] Although the inflatable structure 27 is here connected to a source S of pressurized air, it can be connected to any source of pressurized fluid (gas, liquid...).

Claims

1. Demands Testing machine (1, 1') for milling comprising: • a building (2); • a lever (3) mounted pivoting on the frame around an axis (X, X') transverse to the lever, and carrying a mass (7); • a first tie rod (4.1) having one end connected to the frame and an opposite end provided with first means for fixing a first end of a test specimen (E); • a second tie rod (4.2) having one end connected to the lever and another end provided with second means for attaching a second end of the test specimen; and • a test specimen loading device (20) comprising a structure (27) defining a chamber (28) of variable volume, and a movable element (22) mounted freely in translation between a high position in which the mass is supported by the movable element which supports the lever, and a low position in which the mass is supported by the lever, the position of the movable element being a function of the volume of the chamber; the chamber (28) being selectively in fluidic communication with a source (S) of pressurized fluid and an exhaust flow limiter (R), the movable element (22) comprises an upper cross member (23) and a lower cross member (24) connected to each other by two rods to form a rectangular frame extending in a substantially vertical plane, the upper cross member and the lower cross member extending respectively above and below a substantially horizontal platform (21) fixedly mounted on the frame (2), the structure (27) being an inflatable structure disposed between the upper cross member and the platform to move the movable element (22) between the upper position and the lower position, and the lower cross member being arranged to support the lever.

2. Test machine (1, 1') according to claim 1, wherein the moving element (22) exerts, in the raised position, a pulling force on the lever (3).

3. Test machine (1, 1') according to any one of the preceding claims, wherein the chamber (28) is connected to the source (S) of pressurized fluid via a first valve (E1), and to the exhaust flow limiter (R) via a second valve (E2).

4. Test machine (1, 1') according to claim 3, wherein the first valve (E1) and the second valve (E2) are solenoid valves.

5. Test machine (1, 1') according to claim 4, wherein the first valve (E1) is normally closed and the second valve (E2) is normally open.

6. Test machine (1, 1') according to any one of the preceding claims, wherein the inflatable structure (27) rests on the platform and the upper cross member (23) rests on said inflatable structure.

7. Test machine (1, 1') according to any one of the preceding claims, wherein the moving element (22) comprises two first spacers (26.1) each mounted to slide on one of the two rods (25) between the platform (21) and the lower cross member (24) so ​​as to guarantee, between said platform and said lower cross member, a minimum gap corresponding to the upper position of said moving element.

8. Test machine (1, 1') according to any one of the preceding claims, wherein the moving element (22) also comprises two second spacers (26.2) each mounted to slide on one of the two rods (25) between the platform (21) and the upper cross member (23) so as to guarantee, between said platform and said upper cross member, a minimum gap corresponding to the lower position of said moving element.

9. A method for carrying out a fineness test on a specimen (E) using a testing machine (1, 1') according to any one of the preceding claims, comprising the following steps: • while the chamber (28) is not in fluidic communication with the flow limiter (R), put the chamber (28) in fluidic communication with the source (S) of pressurized fluid so as to bring the moving element (22) into the high position; • when the moving element is in the raised position, stop the fluidic communication between the chamber and the pressurized fluid source; • fix the ends of the test specimen to the first tie rod (4.1) and to the second tie rod (4.2); • Connect the chamber to the flow limiter.

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