SPECIMEN AND MECHANICAL SHEAR TESTING METHOD
The Tervette, a shear test piece with a 'dumbbell' configuration, addresses the challenge of determining shear cycles to failure for aircraft turbomachine dawn feet, enabling predictive maintenance and ensuring engine safety by simulating shear loads and analyzing crack propagation.
Patent Information
- Application Number
- FR2022008058
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2022-08-03
- Publication Date
- 2025-04-11
- Estimated Expiration
- 2042-08-03
AI Technical Summary
Current methods are unable to effectively determine the number of cycles to failure in shear for the dawn foot of an aircraft turbomachine, which is critical for maintenance and engine operation.
A mechanical test piece in shear, known as the 'Tervette,' is designed with a monobloc body featuring two symmetrical parts that mimic the shape of dawn feet, connected at a plane of symmetry, allowing for a 'dumbbell' configuration to test shear behavior.
The Tervette enables the simulation of shear loads on dawn feet, allowing for the determination of crack propagation laws and stress states, thereby facilitating predictive maintenance and ensuring safe engine operation.
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Abstract
Description
Title of the invention: TEST SPECIMEN AND METHOD FOR MECHANICAL SHEAR TESTING Technical field of the invention
[0001] The present invention relates to a test piece and a method for mechanical shear testing. Technical background
[0002] A rotor disk 10 of an aircraft turbomachine is partially shown in Figures 1 and 2 and comprises at its periphery cells 12 which are intended to receive by male-female fitting roots 14 of rotor blades 16. The roots 14 and the cells 12 therefore have complementary shapes which are for example dovetail-shaped as in the example shown, or fir-shaped.
[0003] It is known to insert a shim, called a shim 18, between the foot 14 and the bottom 12a of the cell 12 of the disc 10. In operation, these shims 18 are subjected to vibrations such that they can move and disengage from the cells 12.
[0004] During a maintenance operation on an aircraft turbomachine, it is not unusual to observe the disengagement or loss of foils 18.
[0005] However, if there is disengagement or even loss of a foil 18, this changes the pressure distribution exerted by the cell 12 of the disk 10 on the bearing surfaces 20 of the root 14 of the blade 16. This modifies the stress state, particularly in shear. This increases sharply until cracks begin to form in the root 14 of the blade 16. In this case, it is necessary to be able to determine whether or not it is possible to wait for the next maintenance and engine removal operation, for example. And therefore, for this, it is necessary to be able to determine the number of propagation cycles. Thus, propagation laws are necessary and are obtained by carrying out tests with CT type specimens, which is the acronym for Compact Tension. These specimens must be adapted to shear loading in order to carry out predictive tests.
[0006] The test pieces of current technology do not allow this objective to be achieved.
[0007] The present invention provides a solution to this problem, which is simple, effective and economic. Summary of the invention
[0008] The invention provides a mechanical shear test specimen, this specimen comprising a single-piece body having a first axis and comprising a first part having a dovetail shape in cross-section comprising a first zone of lesser thickness and a second zone of greater thickness, characterized in that the body comprises a second part which has a cross-section identical to the first part, the first and second parts being connected to each other at a first plane which is a plane of symmetry of the body and which passes between the zones of lesser thickness of the first and second parts.
[0009] The present invention therefore proposes a particular configuration of mechanical test specimen which makes it possible to test the shear behavior of a blade root. For this, the test specimen comprises the equivalent of two blade roots which form a single block and which are arranged symmetrically. To determine the shear behavior of a blade root at its bearing surfaces on a cell of a disc, the two parts of the test specimen are connected to each other at the thinner zones of these parts or these roots. This configuration gives the test specimen a general “dumbbell” shape.
[0010] The test piece according to the invention may comprise one or more of the following characteristics, taken in isolation from one another, or in combination with one another:
[0011] — said thicknesses are measured in directions parallel to each other and in a plane perpendicular to said first axis;
[0012] — said thicknesses are measured in directions parallel to each other and to said foreground;
[0013] - each of the first and second parts further comprises a parallel block piped, the second zone of each part being located between the block and the first zone of this part;
[0014] - each block comprises free lateral faces which are perpendicular to said plane, and a free end face which is parallel to this plane;
[0015] - the first and second zones of each part comprise front faces extending in the same second plane perpendicular to the foreground, and rear faces extending in the same third plane perpendicular to the foreground;
[0016] - one of the free lateral faces of each block is parallel to the second plane and in set back from this second plane, and one of the free lateral faces of each block is parallel to the third plane and set back forward from this third plane;
[0017] - the test piece comprises rectilinear grooves formed in the body at the level of the foreground;
[0018] - the test piece comprises a first groove between the front faces of the first part and the front faces of the second part, and a second groove between the rear faces of the first part and the rear faces of the second part; and
[0019] - the grooves extend over the entire thickness of the first zones.
[0020] The present invention also relates to a method of mechanical shear testing using a test piece as described above, in which it comprises a shear stress stage of this test piece.
[0021] The test piece according to the invention may comprise one or more of the following characteristics, taken in isolation from one another, or in combination with one another:
[0022] - the method further comprises a step of determining the Paris law in fis ration according to mode I;
[0023] - the method further comprises a step of determining the Paris law in fis ration according to mode II;
[0024] - the stressing step is carried out by means of an Arcan type test system. Brief description of the figures
[0025] Other characteristics and advantages will emerge from the following description of a non-limiting embodiment of the invention with reference to the appended drawings in which:
[0026] [Fig-1] [Fig.l] is a partial schematic view of a rotor disc of a tur- aircraft engine,
[0027] [Fig.2] [Fig.2] is a partial schematic perspective view of a rotor disc, a shim being inserted between the blade root and the bottom of the disc cell,
[0028] [Fig.3] [Fig.3] is a schematic perspective view of a mechanical shear test specimen according to one embodiment of the invention,
[0029] [Fig.4] [Fig.4] is a very schematic view of an Arcan type test system for implementing a method according to the invention,
[0030] [Fig.5] [Fig.5] is a schematic perspective view of a mechanical shear test specimen according to an alternative embodiment of the invention, and
[0031] [Fig.6] [Fig.6] is an enlarged view of part of [Fig.5]. Detailed description of the invention
[0032] Figures 1 and 2 have been described above and show a rotor disk 10 equipped at its periphery with rotor blades 16 of which only one is shown.
[0033] A blade 16 comprises a blade 22 which is connected to a foot 14 by a platform 24. The foot 14 is fitted into the cell 12 of the disc 10 and has a shape complementary to this cell 12, here in a dovetail.
[0034] A dovetail foot 14 essentially comprises two portions, namely a first bulb-shaped portion 14a and a second portion 14b which forms a connecting stilt between the platform 24 and the first portion 14a. The first portion 14a has a thickness E1 greater than the thickness E2 of the second portion 14b.
[0035] The first portion 14a comprises a surface 26 opposite the platform 24, which faces the bottom 12a of the cell 12, and two inclined lateral flanks 28. These flanks 28 form the bearing surfaces 20 intended to cooperate by bearing with corresponding walls of the cell 12 to retain the blade 16 in the cell 12 when the disc 10 rotates around its axis of rotation and the blade 16 is subjected to centrifugal forces in operation.
[0036] The aforementioned thicknesses E1 and E2 are measured in directions parallel to each other and to the surface 26.
[0037] The present invention proposes a mechanical test specimen which makes it possible in particular to obtain crack propagation laws for blade roots subjected to shear loading.
[0038] [Fig.3] illustrates a first embodiment of a test piece 100 according to the invention.
[0039] This test piece 100 comprises a single-piece body 102 which is for example made of a metal alloy, based on titanium for example (as is the case with TiAl).
[0040] XYZ is defined as an orthonormal reference frame. The body 102 has a first axis A which extends parallel to the X axis. The body 102 may have an elongated shape along the axis A.
[0041] The body 102 comprises two parts 104, 106 which are identical and symmetrical with respect to a first plane PI which is both a plane of symmetry and a connecting plane. The plane PI is here parallel to the plane XY.
[0042] The parts 104, 106 form or represent roots 14 of blades 16. Thus, each part 104, 106 has a dovetail shape in cross section and comprises a first portion or zone 104b, 106b of smaller thickness E2 and a second portion or zone 104a, 106a of greater thickness EL
[0043] The part 104, which is referred to for example as the lower part, has its zone 104a of greater thickness E1 which is located below the zone 104b of smaller thickness E2.
[0044] The part 106, which is referred to for example as the upper part, has its zone 106a of greater thickness E1 which is located above the zone 106b of smaller thickness E2.
[0045] The parts 104, 106 are connected to each other at the level of the plane PI which passes through the middle of the body 102 and between the zones 104b, 106b.
[0046] P2 can also be defined as another plane of symmetry perpendicular to PI and passing through the axis A and in the middle of the body 102. P3 can also be defined as another plane of symmetry perpendicular to PI and P2 and passing in the middle of the body 102.
[0047] As is the case with a blade root, the zones 104a, 106a of each part 104, 106 comprise two inclined lateral flanks 110 which are intended to reproduce the bearing surfaces 20 of a blade 16.
[0048] In the example shown, each of the parts 104, 106 further comprises a block 112 parallelepiped, the second zone 104a, 106a of each part 104, 106 being located between the block 112 and the first zone 104b, 106b of this part.
[0049] Each block 112 comprises free lateral faces 112a, 112b which are perpendicular to the plane P1. The two faces 112a are parallel to the plane P3 and arranged on either side of this plane P3. The two faces 112b are parallel to the plane P2 and arranged on either side of this plane P2.
[0050] Each block 112 comprises a free end face 112c which is parallel to the plane PL
[0051] The zones 104a, 104b, 106a, 106b of each part 104, 106 comprise front faces 114 extending in the same second plane P4 perpendicular to the first plane PI, and rear faces 116 extending in the same third plane P5 perpendicular to the first plane PL. The planes P4 and P5 are parallel to the plane P3 and extend on either side of this plane P3.
[0052] One of the faces 112a of each block 112, called the front face, is parallel to the second plane P4 and set back towards the rear relative to this second plane P4.
[0053] The other of the free faces 112a of each block 112, called the rear face, is parallel to the third plane P5 and set back towards the front relative to this third plane P5.
[0054] [Fig.4] illustrates an example of a mechanical testing system 200, here of the Arcan type, which can be used to carry out mechanical stresses on the test piece 100.
[0055] [Fig.4] shows that the portion 104 of the test piece 100 is held clamped in a first jaw 202 and that the portion 106 is held clamped in a second jaw 204.
[0056] The jaw 202 is connected to a first arm 206 capable of producing a tensile force in a first direction (arrow F). The jaw 204 is connected to a second arm 208 capable of producing a tensile force in a second direction (arrow F'), which is parallel and opposite to the first direction.
[0057] The jaws 202, 204 are spaced from each other in the plane PI and are capable of being moved respectively in the opposite directions (arrows F and F') so that shear forces are applied in the test piece 100 in the plane PL.
[0058] The present invention thus proposes a method of mechanical shear testing using a test piece 100, such as that illustrated in [Fig. 3], in which it comprises a step of shear stressing this test piece 100, for example using the system 200 of [Fig. 4].
[0059] The method may comprise a step of determining the Paris law in cracking according to mode I.
[0060] The method may comprise a step of determining the Paris law in cracking according to the IL mode. For this, the test piece 100 is advantageously of the type of that shown in figures 5 and 6. These figures represent an alternative embodiment of the test piece 100 in which grooves 118 are formed in the body 102 at the level of the first plane PI.
[0061] In the example shown, these grooves 118 are rectilinear. A first groove 118 is formed between the front faces 114 of the first part 104 and the front faces of the second part 106. A second groove 118 is formed between the rear faces 116 of the first part 104 and the rear faces of the second part 106.
[0062] As seen in [Fig.6], the grooves 118 can extend over the entire thickness E2 of the first zones 104b, 106b.
[0063] The grooves 118 have, for example, a general V or U shape in cross section.
[0064] In a particular embodiment of the test piece 100, each groove 118 has a V-shape whose walls form an angle of between 50° and 70°, and preferably 60°. Each groove 118 has a depth of between 50 and 200qm, preferably between 80 and 120qm, and for example 100qm. At the bottom of each groove, the walls of the groove are connected by a rounded portion having a radius of between 5 and 50qm, and preferably between 10 and 30qm.
Claims
Claims
1. A mechanical shear test specimen (100), this specimen comprising a single-piece body (102) having a first axis (A) and comprising a first part (104) having in cross-section a dovetail shape comparable to the root of a first rotor blade of an aircraft turbomachine, this dovetail comprising a first zone (104b) of smaller thickness (E2) forming a blade root stilt, and a second zone of greater thickness (El) forming a blade root bulb, characterized in that the body (102) comprises a second part (106) which has a cross-section identical to the first part (104) and which is therefore comparable to the root of a second rotor blade of an aircraft turbomachine, the first and second parts (104, 106) being connected to each other at a first plane (PI) which is a plane of symmetry of the body (102) and which passes between the zones (104b,106b) of lower thickness of the first and second parts (104, 106).,
2. A test tube (100) according to claim 1, wherein each of the first and second portions (104, 106) further comprises a parallelepiped block (112), the second zone (104a, 106a) of each portion (104, 106) being located between the block (112) and the first zone (104b, 106b) of that portion.
3. Test tube (100) according to claim 2, in which each block (12) comprises free lateral faces (112a, 112b) which are perpendicular to said plane (PI), and a free end face (112c) which is parallel to this plane (PI).
4. Test piece (100) according to one of claims 1 to 3, in which the first and second zones (104a, 104b, 106a, 106b) of each part (104, 106) comprise front faces (114) extending in the same second plane (P4) perpendicular to the first plane (PI), and rear faces (116) extending in the same third plane (P5) perpendicular to the first plane (PI).
5. Test tube (100) according to claim 4, dependent on claim 3, in which one of the free lateral faces (112a) of each block (112) is parallel to the second plane (P4) and set back towards the rear relative to this second plane (P4), and one of the free lateral faces (112a) of each block (112) is parallel to the third plane (P5) and set back towards the front relative to this third plane (P5).
6. Test tube (100) according to one of claims 1 to 5, in which it comprises rectilinear grooves (118) formed in the body (112) at the level of the first plane (PI).
7. A test piece (100) according to claim 6, dependent on claim 4 or 5, wherein it comprises a first groove (118) between the front faces (114) of the first part (104) and the front faces (114) of the second part (106), and a second groove (118) between the rear faces (116) of the first part (104) and the rear faces (116) of the second part (106).
8. Test piece (100) according to claim 7, wherein the grooves (118) extend over the entire thickness of the first zones (104b, 106b).
9. Method of mechanical shear testing using a test piece (100) according to one of the preceding claims, in which it comprises a step of shearing this test piece (100).
10. Method according to claim 9, the test piece (100) being as defined in one of claims 1 to 5, in which it further comprises a step of determining the Paris law in cracking according to mode I.
11. Method according to claim 9, the test piece (100) being as defined in claim 6 or 7, in which it further comprises a step of determining the Paris law in cracking according to the TT mode.
12. 11. Method according to one of claims 9 to 11, in which the stressing step is carried out by means of an Arcan type test system (200).