Strand compression device

Abstract

Strand Compression Device The invention relates to a device (100) for compressing a strand (102) composed of a plurality of elementary strands, comprising: a tensioning member (109) adapted to tension a strand in its longitudinal direction; a compression means adapted to compress the strand in a compression direction perpendicular to the longitudinal direction of the strand, the compression means comprising a movable anvil (107) in the compression direction and a lower plate (104); characterized in that it further comprises a laser profilometer (101) configured to determine the cross-sectional profile of the strand during its compression. Figure for the abstract: Fig. 1

Description

Title of the invention: Strand compression device technical field

[0001] The invention relates to the field of material characterization, and particularly that of composite materials. Previous technique

[0002] Composite material parts are generally obtained by impregnating a fibrous preform with a matrix. The mechanical properties of composite materials are partly related to those of the fibrous preforms used in their preparation.

[0003] The mechanical properties of fibrous preforms depend on the weave topology, particularly the chosen textile pattern and the spacing between the strands, as well as on the nature and number of fibers they contain. The yarns, also called strands, that make up the fibrous textures of composite materials are generally composed of several strands, themselves composed of fibers. These yarns (or strands) are usually twisted to prevent the strands from separating from one another. Twisting means that the individual strands constituting the strands are not directly aligned with the overall direction of the strand. Such twisting is useful for improving the cohesion of the individual strands and influences the mechanical properties of the strand, particularly the compaction forces required to compress the strand in a direction perpendicular to its principal direction.

[0004] To know precisely the mechanical properties of the part made of composite material, it is therefore necessary to analyze the properties of the fibrous preform and for this, it is necessary to know the elementary mechanical behaviors of the strands which constitute it.

[0005] The behavior of the strands varies with the nature, number, and twist of the elementary strands constituting the strands. And, while the behavior of the strands has been the subject of some numerical simulations, these cannot be used alone and must be validated by comparison with experimental data, which are particularly difficult to obtain.

[0006] Experimental devices exist to characterize the behavior of strands during compression tests. However, none of these devices allows obtaining sufficiently precise geometric information to validate theoretical models and numerical simulations.

[0007] For example, the experimental setup described in the article "An experimental technique to study the transverse mechanical behaviour of polymer monofilaments", July 2005, Experimental Techniques 29(4), p. 26-31, only allows access to the thickness and width of the strand during compression, which is not sufficient to evaluate the evolution of the cross-section of the strand without requiring additional approximations.

[0008] There is therefore an interest in having more precise experimental data in order to validate theoretical models and numerical simulations.

[0009] The invention aims precisely to propose an experimental device allowing the characterization of the mechanical behavior of strands composed of a plurality of elementary strands, and also to have more precise geometric information during a compression of these strands. Description of the invention

[0010] To this end, the invention relates in a first embodiment to a device for compressing a strand composed of a plurality of elementary strands comprising:

[0011] - a tensioning element capable of putting a strand under tension in its direction longitudinal;

[0012] - a compression means capable of compressing the strand in a direction of compression perpendicular to the longitudinal direction of the strand, the compression means comprising a movable anvil in the direction of compression and a lower plate;

[0013] characterized in that it further comprises a laser profilometer configured to determine the cross-sectional profile of the strand during its compression.

[0014] The device according to the invention makes it possible to study the deformation of the strand during compression. The laser profilometer, in particular, allows for the real-time acquisition, and therefore as a function of the applied stress, of the evolution of the cross-sectional profile of the strand. Specifically, the laser profilometer enables this acquisition at several points along the longitudinal direction of the strand. This makes it possible to reconstruct the cross-sectional profile of the strand at each instant of compression and at each point of the compressed strand. This therefore makes it possible to observe the evolution of the cross-section along the strand as a function of the applied stress. This acquisition makes it possible to study the mechanical behavior of the strands reliably, for example, to validate numerical models. Furthermore, the method is simpler to use compared to methods used to achieve the same measurement in the prior art.

[0015] The "cross-sectional profile of the strand" is understood as the shape of the smallest outer envelope comprising all the elementary strands of the strand in the plane perpendicular to the longitudinal direction of the strand. In other words, this profile characterizes the shape of the outer perimeter of the strand in a plane of section of the latter perpendicular to its largest dimension.

[0016] This parameter is essential to be able to deduce from the test other mechanical quantities characteristic of the behavior of the strand, in particular the volumetric fiber ratio.

[0017] Prior art techniques commonly used to characterize the compressive behavior of a strand do not allow access to the cross-sectional profile. For example, existing transverse compaction devices only capture the strand's width and thickness during compression, and the exact profile is chosen by assumption as a known analytical curve (circular, elliptical, etc.). This assumption is unnecessary when the device described above is used, as the profile is then determined experimentally. This results in greater measurement accuracy and, consequently, greater reliability of the constitutive laws that can be deduced from these compression experiments.

[0018] In one embodiment, the laser profilometer is movable in a direction parallel to the longitudinal direction of the strand. This embodiment makes it possible to acquire the cross-sectional area of ​​the strand at several points along its length, and thus to increase the number of measurements during a test. For example, the cross-sectional area of ​​the strand can be acquired along the entire length of the portion of the strand that is compressed during the test.

[0019] For example, the mobility of the laser profilometer can be ensured by placing the latter on a micrometric bench whose direction of movement is parallel to the longitudinal direction of the strand.

[0020] In one embodiment, the lower plate of the compression means comprises a transparent portion. It is understood that the transparency of the lower plate refers to the wavelength of the light emitted by the laser profilometer.

[0021] In this embodiment, the laser profilometer and the strand can be arranged on either side of the lower plate of the compression means. This embodiment provides a simplified arrangement of the laser profilometer, which can then be placed directly vertically under the sample.

[0022] In one embodiment, the element enabling the movement of the movable anvil is arranged on an upper plate parallel to the lower plate and the movement of the movable anvil, fixed to the upper plate, is guided by a plurality of columns parallel to the direction of compression.

[0023] This arrangement makes it possible to avoid parasitic bending of the compression member or the strand during compression.

[0024] According to another aspect of the invention, a method for characterizing the compression behavior of a strand comprising at least the following steps:

[0025] - the loading of a strand into the tension element of a device described above;

[0026] - the compression of the strand by means of compression by displacement of the movable anvil in the direction of compression; and

[0027] - the acquisition of the cross-sectional profile of the strand during compression using the laser profilometer.

[0028] As described above, this characterization method allows access to the cross-sectional profile of the strand during compression in a more reliable manner and without requiring any assumptions, unlike prior art characterization methods.

[0029] This method makes it possible to validate compression constitutive laws of strands comprising a plurality of elementary strands with greater precision than currently feasible experiments.

[0030] In one embodiment, the method includes repeating the step of acquiring the cross-section profile of the strand at several points spaced apart in its longitudinal direction.

[0031] This embodiment makes it possible to increase the number of measurements, and therefore the reliability of the results, without increasing the number of tests actually carried out.

[0032] For example, in such an embodiment, the strand is loaded and then compressed to a given compression, the laser profilometer makes several acquisitions at several points spaced in the longitudinal direction of the strand, then the compression is increased, and the laser profilometer then makes the acquisitions at each of the points spaced in the longitudinal direction and so on until the desired maximum compression is reached.

[0033] This particular embodiment makes it possible to obtain the evolution of the cross-section of the strand as a function of the compression applied for several points spaced apart in the longitudinal direction. Brief description of the drawings

[0034] [Fig.1] Fig.1 schematically represents a device in one embodiment of the invention.

[0035] [Fig.2] The [Fig.2] represents the cross-sectional strand profile acquired under the conditions of Example 1. Description of the implementation methods

[0036] The invention is now described by means of figures and an example detailing particular embodiments which are present for the purpose of improving understanding of the invention but which should not be interpreted restrictively.

[0037] Fig. 1 represents a device 100 in one embodiment.

[0038] The device 100 allows the energizing of a strand 102 in its longitudinal direction by means of a rack system 109 connected on the other side of the device to a dynamometer 103 which allows the tension applied to the strand 102 to be determined.

[0039] The "longitudinal direction" of strand 102 is understood as the direction in which strand 102 has the largest dimension.

[0040] In the embodiment, the strand 102 is present between a lower plate 104, comprising a transparent glass pane 105, and the upper plate 106.

[0041] Of course, the glass 105 is sufficiently strong to withstand the compression conditions that will be applied to the strand 102. For example, the glass 105 can be a sapphire glass or a tempered glass.

[0042] The device 100 further includes a laser profilometer 101, for example a linear laser profilometer, arranged to acquire the cross-section of the sample in the compression direction.

[0043] The device 100 further includes an upper plate 106, which can move relative to the lower plate 104.

[0044] For this purpose, the plate 106 is attached to means for moving 108, which allow its movement in the direction of compression.

[0045] For example, the upper platform 106 can be moved, thanks to the means of moving 108, along a perfect unidirectional sliding-type movement, along columns 111a, 111b, 11 le and 11 Id, here of which there are 4. The columns 11 la to 11 Id allow the upper platform 106 to be guided, and prevent any parasitic bending of the latter.

[0046] The compression means of the device further includes an anvil 107. The anvil 107 may be made of treated steel and must allow uniform compression over the entire width of the strand 102. In [Fig.1], the direction of compression is the vertical direction.

[0047] For example, the anvil 107 can be a smooth, treated steel cylindrical plate with a diameter between 3 and 10 cm.

[0048] The anvil 107 can be moved in the direction perpendicular to the lower 104 and upper 106 plates, so as to cause compression of the strand 102, between the anvil 107 and the glass 105.

[0049] The anvil can be moved by suitable means 108 known as such, and here arranged on the upper plate 106. As described above, the movement of the upper plate 106 can be a perfect unidirectional sliding type movement, the entire upper plate 106, the movement means 108 and the anvil 107 moving along the columns 11a to 11Id which ensure a unidirectional movement.

[0050] During the compression of the strand 102 between the anvil 107 and the window 105, the laser profilometer 101, arranged below the window 105, can acquire the cross-section of the strand 102.

[0051] The compression force applied to the strand 102 depends on the displacement command applied by the means for moving the anvil 108.

[0052] The device 100 thus allows the acquisition of the cross-section of the strand 102 by the laser profilometer 101 as a function of a chosen compression applied to the strand 102.

[0053] The laser profilometer 101 can also be mobile, for example by means of a micrometric bench 110 on which it is placed.

[0054] The micrometer bench 110 allows the movement of the laser profilometer 101 in the longitudinal direction of the strand 102, for example over the entire length of the window 105.

[0055] This allows the cross-section of the strand to be acquired at several points along the strand 102 during strand compression. This results in a greater quantity of data being acquired during a single compression step of the strand 102, which makes it possible to verify the homogeneity of the compression, for example, or to obtain data with greater statistical precision.

[0056] In one embodiment, the device 100 may further include post-processing means 112 for the signal acquired by the laser profilometer 101 during the compression of the strand 102.

[0057] These post-processing means can be integrated directly into the device 100, or the device 100 can include a means of transmitting the signal acquired by the laser profilometer 101 to a computer located remotely from the device. Examples

[0058] A strand comprising 4 twisted strands each comprising 12000 carbon fibers is placed in the device of [Fig.1] described above.

[0059] The device is equipped with an LJ-V7060 laser profilometer positioned below the sample, with a 10 mm thick glass plate separating it from the sample.

[0060] The laser profilometer is arranged on a micrometer bench that can move in the longitudinal direction of the strand.

[0061] The strand is put under compression, and the cross-section is acquired by the laser profilometer for a plurality of points that are little spaced apart in the longitudinal direction, so that the result corresponds to a continuous profile of the cross-section over a short distance of the sample in the longitudinal direction.

[0062] Figure 2 illustrates the experimental result obtained by the laser profilometer. It can be seen that the cross-section profile is acquired very precisely, and that it does not correspond to a simple curve (circle, ellipse) as is generally assumed in prior art models.

[0063] The device of the invention therefore allows for a better characterization of compression tests than prior art installations.

Claims

Demands

1. Device (100) for compressing a strand (102) composed of a plurality of elementary strands comprising: - a tensioning member (109) capable of putting a strand under tension in its longitudinal direction; - a compression means capable of compressing the strand uniformly over its entire width in a compression direction perpendicular to the longitudinal direction of the strand, the compression means comprising a movable anvil (107) in the compression direction and a lower plate (104); characterized in that it further comprises a laser profilometer (101) configured to determine the cross-sectional profile of the strand during its compression.

2. Device according to claim 1, wherein the laser profilometer (101) is movable in a direction parallel to the longitudinal direction of the strand (102).

3. Device according to claim 1 or 2, wherein the lower plate (104) of the compression means comprises a transparent part.

4. Device according to claim 3, wherein the laser profilometer (101) and the strand (102) are arranged on either side of the lower plate (104) of the compression means.

5. Device according to any one of claims 1 to 4, wherein the member (108) enabling the movement of the movable anvil (107) is disposed on an upper plate parallel to the lower plate (104) and the movement of the movable anvil, integral with the upper plate (106), is guided by a plurality of columns (1 lia, 111b, 11 le, 11 Id) parallel to the direction of compression.

6. A method for characterizing the compression behavior of a strand (102) comprising at least the following steps: - loading a strand into the tensioning member (109) of a device according to any one of claims 1 to 5; - compressing the strand by means of compression by displacement of the movable anvil (107) in the direction of compression; and - acquiring the cross-sectional profile of the strand during compression by means of the laser profilometer (101).

7. A characterization method according to claim 6, comprising repeating the step of acquiring the profile of the cross-section of the strand (102) at several points spaced in its longitudinal direction.

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