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: Finage testing machine

[0001] The present invention relates to the characterization of the physical resistance of a material, and more particularly to a finishing testing machine making it possible to subject a test specimen 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 given period, which may be more or less long, and at a given temperature. They are generally carried out using a machine T which comprises, as illustrated in [Fig.l]: • a frame B provided with a point for fixing a first bar B1 for fixing a lower end of the test piece E, • a lever L pivotally mounted 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 test piece E; and • a hydraulic cylinder V of the “bottle jack” type arranged to exert on the lever L a vertical thrust force intended to support said lever L, the cylinder V being equipped with a discharge screw S making it possible 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 yoke mounted to rotate 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 traction axis 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 stationary, the jack V is, as shown in [Fig.l], 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 does not exert any force on the test piece E. In service, the jack V is retracted by unscrewing the relief 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 test piece E which then tends to lengthen.

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

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

[0009] SUBJECT OF THE INVENTION

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

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

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

[0013] Thus, when the structure is in fluid communication with the source of pressurized fluid, the pressure inside the chamber then tends to increase, which causes an increase in the volume of the chamber and therefore a movement of the mobile element towards the high position in which the mass does not exert any tensile force on the test piece via the lever.

[0014] When the chamber of the structure is no longer in fluid communication with the source of pressurized fluid but is in fluid communication with the flow limiter, the pressure inside the chamber then tends to decrease, which results in a reduction in the volume of the chamber and therefore a movement of the movable element towards the low position in which the mass exerts a tensile force on the test piece via the lever.

[0015] The flow limiter is chosen so that the moving element passes from the high position to the low position at a speed slow enough to guarantee loading of the test piece without shock.

[0016] According to a particular characteristic, the movable element exerts, in the high position, a traction force on the lever.

[0017] According to another particular characteristic, the chamber is connected to the source of pressurized fluid 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 together by two rods to form a rectangular frame extending in a substantially vertical plane. The upper cross member and the lower cross member 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 high position and the low position, 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 mobile element comprises two first spacers each slidably mounted on one of the two rods between the platform and the lower crosspiece so as to guarantee, between said platform and said lower crosspiece, a minimum spacing corresponding to the high position of said mobile element.

[0024] In particular, the mobile element also comprises two second spacers each slidably mounted on one of the two rods between the platform and the upper crosspiece so as to guarantee, between said platform and said upper crosspiece, a minimum spacing corresponding to the low position of said mobile element.

[0025] The invention also relates to a method for carrying out a finishing test on a test piece using such a testing machine. The method comprises the following steps: • while the chamber is not in fluid communication with the limiter flow rate, put the chamber in fluid communication with the source of pressurized fluid so as to bring the movable element into the high position; • when the moving element is in the high position, stop the fluid communication between the chamber and the source of pressurized fluid; • fix the ends of the test piece 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 light of the following description, which is purely illustrative and non-limiting, and must be read in conjunction with the appended drawings, among which:

[0027] [Fig-1] [Fig.l] is a schematic view of a finishing testing machine according to the art anterior;

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

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

[0030] [Fig.3] [Fig.3] is a schematic view of a variant of the testing machine of finishing 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 testing machine 1 comprises: • a frame 2 resting on a substantially horizontal ground; • a lever 3 pivotally mounted 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 traction 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 traction 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 test piece E.

[0032] The test piece E is here in the form of a rod (cylindrical or flat) having here 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 piece 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 detection cell 5 arranged to deliver a signal representative of the force of traction exerted on the first bar 4.1 along the loading axis. The load detection cell 5 is known per se 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 yoke 6 rotatably mounted on the lever 3 around an axis substantially parallel to the axis X 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 substantially equal to twenty kilograms. The axis X of rotation of the lever 3 is distant from the second end 3.2 of the lever 3 by a distance corresponding here substantially to three-quarters of the length of said lever 3 so as to take advantage of a lever arm 3 making it possible, in a manner known per se, to amplify the weight of the mass 7 to load the test piece E via a tensile force here substantially equal to three thousand Newtons.

[0035] The mass 7 rests here on a plate 8 which is suspended from the lever 3 by a suspension sling 9 having a lower end to which the plate 8 is fixed and an upper end connected to the lever 3 by a yoke 10 rotatably mounted 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 testing machine 1 also comprises means (not shown) for measuring the elongation of the test piece E. The measuring means may comprise inductive LVDT (Linear Variable Differential Transformer) sensors, capacitive sensors, optical or interferometric devices, etc.

[0037] The testing machine 1 also comprises a heating device arranged to bring and maintain the test piece E at a predefined test temperature. The heating device here comprises a tubular furnace 11 slidably mounted on the frame 2 along an axis substantially parallel to the loading axis of the test piece E, between a release position, illustrated in [Fig. 2A], in which the furnace is released from the test piece E, and a heating position, illustrated in [Fig. 2B], in which the furnace 11 surrounds the test piece E. The regulation of the temperature of the test piece E is for example carried out by means of a thermocouple in thermal contact with a surface of the test piece E.

[0038] The testing machine 1 further comprises a device 20 for loading the test piece E. The loading device 20 comprises a platform 21 which is substantially horizontal and fixedly mounted on the frame 2, and a mobile assembly 22 which is slidably mounted on the platform 21 along a lifting axis of the mass 7 which is substantially 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 form, with the rods 25, 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 comprises two first cylindrical spacers 26.1 each slidably mounted on one of the two rods 25 between the platform 21 and the lower crosspiece 24 so as to guarantee, between said platform 21 and said lower crosspiece 24, a minimum spacing corresponding to the high 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 of the platform 21 so that they form first stops for the movement of the movable element 22.

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

[0042] The loading device 20 also comprises an inflatable structure 27 arranged between the platform 21 and the upper cross member 23 of the mobile element 22. The inflatable structure 27 comprises: • an upper wall 27.1 which is substantially flat, rigid and on which rests the upper crosspiece 23 of the mobile element 22; • a lower wall 27.2 which is substantially flat, rigid and rests on the platform 21; and • a closed, elastically deformable side wall 27.3, having a rounded 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 comprises an orifice for inflating and deflating the inflatable structure. The orifice is connected to a source S of pressurized air via a first solenoid valve El, and to an exhaust flow limiter R via a second solenoid valve E2. The pressure of the air delivered by the source S is here between five and six bars. The first solenoid valve E1 and the second solenoid valve E2 are so-called "on-off" solenoid valves in that they only have two possible states: a fully open state and a fully closed state. The first solenoid valve E1 is, for example, a normally closed solenoid valve, i.e., it is in its fully closed state in the absence of a power supply and is in its fully open state when it is electrically powered. The second solenoid valve E2 is, for example, a normally open solenoid valve, i.e., it is in its fully open state in the absence of a power supply and is in its fully closed state when it is electrically 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 fluid communication with the source S of pressurized air. The pressure inside the chamber 28 then tends to increase, which causes an increase in the volume of the chamber 28 and therefore a movement of the movable element 22 towards the high position ([Fig.2A]).

[0046] When the first solenoid valve E1 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 fluid communication with the flow limiter R. The pressure inside the chamber 28 then tends to decrease, which causes a reduction in the volume of the chamber 28 and therefore a movement of the movable element 22 towards the low 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 movable element 22 is then static.

[0048] The loading device 20 further comprises a third stop 29 of cylindrical shape which is fixed axially on the suspension sling 9 and which has a diameter greater than that of the hole 24.1 formed in the lower crosspiece 24 of the movable element 22. The third stop 29 is distant from the upper end of the suspension sling 9 by a predefined distance, so that: • when the position of the movable element 22 is between the high position and an intermediate position between said high position and the low position, the lower crosspiece 24 of the movable element 22 bears 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 movable element 22 is between the inter position intermediate and the low position, the lower crosspiece 24 of the movable element is distant from the third stop 29, so that the lever 3 is not supported by the movable element 22; and • when the movable element 22 is in the high position, the distance separating the first traction bar 4.1 from the second traction bar 4.2 is such that the first end and the second end of the test piece E can be fixed respectively to the upper end of the first traction bar 4.1 and to the lower end of the second traction bar 4.2, the lever 3 then not exerting any traction force on the test piece 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 disengaged position, the first solenoid valve E1 is brought from the closed state to the open state so as to increase the pressure prevailing 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 high 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 movable element 22 is in the high position, the first solenoid valve E1 is brought from the open state to the closed state, then the first end and the second end of the test piece E are fixed respectively to the upper end of the first traction bar 4.1 and to the lower end of the second traction bar 4.2. The test piece E is then not subjected to any tensile force.

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

[0053] When the test piece 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 prevailing inside the chamber 28, and therefore the volume of said chamber 28, then decreases at a speed dependent on the leakage rate of the flow limiter R, so that the movable 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 plate 8. The test piece E is then subjected to no tensile force.

[0055] Between the intermediate position and the low position, the lower crosspiece 24 of the movable element 22 is moved away from the third stop 29. The test piece E is then subjected, via the second traction bar 4.2, to a traction force proportional to the mass 7 resting on the plate 8.

[0056] The loading speed of the test piece E thus depends on the speed at which the mobile element 22 passes from the high position to the low position, and therefore on the speed at which the inflatable structure 27 deflates, which is itself a function of the leakage rate of the flow limiter R. The flow limiter R is chosen so as to generate a leakage rate making it possible to obtain a sufficiently slow and / or progressive descent speed of the mobile element 22 to guarantee loading of the test piece E without shock. The tensile force to which the test piece E is subjected here goes 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 mobile element 22 and the leakage flow 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] The testing machine 1' differs from the testing machine in that: • the lever 3 is pivotally mounted 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 traction bar 4.1 is provided with first means for fixing a first end of the test piece E; • the lower end of the second traction bar 4.2 is connected to the lever 3 by means of a yoke mounted to rotate on the lever 3 around an axis substantially parallel to the axis X' of rotation of said lever 3; and • the upper end of the second traction bar 4.2 is provided with the second means for fixing the second end of the test piece E.

[0060] The loading device 20 of the testing machine 1', like its operation, is identical to that of the testing 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 test piece E can be of any type: clamping jaws, pins inserted into holes made at the ends of the test piece E, etc.

[0063] The solenoid valves E1, E2 can be replaced by manual valves.

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

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

[0066] The oven may 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 may 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, etc.).

Claims

Claims

1. A finishing testing machine (1, 1') comprising: • a frame (2); • a lever (3) pivotally mounted on the frame about 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 fixing a second end of the test piece; and • a device (20) for loading the test piece comprising a structure (27) defining a chamber (28) of variable volume, and a movable element (22) mounted free 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 fluid communication with a source (S) of pressurized fluid and an exhaust flow limiter (R).

2. Testing machine (1, 1') according to claim 1, in which the movable element (22) exerts, in the high position, a tensile force on the lever (3).

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

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

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

6. Testing machine (1, 1') according to any one of the preceding claims- preceding, in which the structure (27) is an inflatable structure.

7. Testing machine (1, 1') according to claim 6, wherein the movable element (22) comprises an upper cross member (23) and a lower cross member (24) connected together 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 inflatable structure being arranged between the upper cross member and the platform to move the movable element (22) between the high position and the low position, and the lower cross member being arranged to support the lever.

8. Testing machine (1, 1') according to claim 7, wherein the inflatable structure (27) rests on the platform and the upper cross member (23) rests on said inflatable structure.

9. Testing machine (1, 1') according to claim 7 or 8, wherein the movable element (22) comprises two first spacers (26.1) each slidably mounted on one of the two rods (25) between the platform (21) and the lower crosspiece (24) so ​​as to guarantee, between said platform and said lower crosspiece, a minimum spacing corresponding to the high position of said movable element.

10. Testing machine (1, 1') according to any one of claims 7 to 9, in which the movable element (22) also comprises two second spacers (26.2) each slidably mounted on one of the two rods (25) between the platform (21) and the upper crosspiece (23) so as to guarantee, between said platform and said upper crosspiece, a minimum spacing corresponding to the low position of said movable element.

11. Method for carrying out a creep test on a test piece (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 fluid communication with the flow limiter (R), putting the chamber (28) in fluid communication with the source (S) of pressurized fluid so as to bring the movable element (22) into the high position; • when the movable element is in the high position, stopping the fluid communication between the chamber and the source of fluid under pressure; fix the ends of the test piece 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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