Strain measurement device and installation of such a device in an element

Abstract

A strain measurement method and device are provided. The strain measurement device includes at least one filiform strain sensor and a support of longilinear shape on which the filiform strain sensor is positioned. The strain measurement device also includes a stiffener.

Claims

1. A method for measuring a strain in a given direction within a structural element, comprising: introducing a binder into a hole formed in the structural element; inserting a strain measurement device into the hole filled with the binder, the strain measurement device including at least one filiform strain sensor, a hollow support of longilinear shape on which the filiform strain sensor is positioned and a stiffener; and connecting the filiform strain sensor of the strain measurement device to a measurement device.

2. The method according to claim 1, wherein the stiffener is arranged inside the hollow support and wherein the method further comprises withdrawing the stiffener after the strain measurement device is inserted into the hole.

3. The method according to claim 2, wherein inserting the strain measurement device into the hole filled with binder comprises gripping the stiffener.

4. The method according to claim 1, wherein the filiform strain sensor is an optical fibre Bragg grating.

5. The method of claim 1, wherein the stiffener is at most fixed to the support at one point.

6. The method of claim 1, wherein the support has a longitudinal direction and width, with the support further comprising a wall having a thickness and having an external surface on which the filiform strain sensor is positioned by one or more connecting points, a main strain direction of the filiform strain sensor being arranged parallel to the longitudinal direction of the support.

7. The method of claim 1, wherein the support is blocked by a cap, an end of which extends beyond an end of the support.

8. The method of claim 1, wherein the strain measurement device comprises a thin tube encapsulating at least the filiform strain sensor with a binder.

9. The method of claim 1, further introducing a second strain sensor, free of deformation with respect to the support, and situated in an internal volume defined by the wall of the hollow support.

10. The method according to claim 1, wherein the support of longilinear shape has an external surface on which the filiform strain sensor is positioned.

11. The method according to claim 1, wherein: the structural element has a first surface, and wherein the hole formed in the structural element has a first end that opens onto the first surface; inserting the strain measurement device into the hole filled with the binder comprises inserting the strain measurement device into at least one measurement zone associated with the hole; and the stiffener and a wall of the hollow support are coupled together so as to define a space between the stiffener and the wall of the hollow support so that the hollow support retains a freedom of movement with respect to bending.

12. The method according to claim 11, further comprising withdrawing the stiffener from the hole after inserting the strain measurement device into the hole.

13. The method according to claim 11, wherein the hollow support has an external surface on which the filiform strain sensor is positioned.

14. The method according to claim 1, wherein: the structural element has a first surface, and wherein the hole formed in the structural element has a first end that opens onto the first surface; inserting the strain measurement device into the hole filled with the binder comprises inserting the strain measurement device into at least one measurement zone associated with the hole; the hollow support has an internal wall surrounding an internal volume; and the stiffener and the internal wall of the hollow support are coupled together so as to define a space between the stiffener and the internal wall of the hollow support so that the hollow support retains a freedom of movement with respect to bending.

15. The method according to claim 1, wherein the hollow support has an internal wall defining an internal volume, wherein the internal volume is closed by a cap coupled to the hollow support at a distal end, and wherein the method further comprises coupling the stiffener to the cap, wherein the stiffener is not directly coupled to the internal wall of the hollow support.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The various embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:

(2) FIG. 1 represents a device according to various embodiments of the present disclosure;

(3) FIG. 2 shows in detail one end of the device intended to be inserted to the bottom of a hole;

(4) FIG. 3 represents the device in a fastener; and

(5) FIG. 4 shows in detail the device in the bottom of the hole.

DETAILED DESCRIPTION

(6) The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses of the present disclosure. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

(7) A device according to the various teachings of the present disclosure comprises a support 1 one end 11 of which is closed by a cap 2, a stiffener 3, and an optical fibre Bragg grating as filiform strain sensor 4. The description which follows would however be valid with any type of filiform strain sensor, twisted or not twisted, as mentioned previously, in place of a fibre Bragg grating.

(8) In the exemplary embodiment represented in FIGS. 1 to 4, the support 1 has a hollow cylindrical shape with a circular cross section, i.e. a tubular shape. It comprises a wall 12 having an external surface 13 and an internal surface 14 delimiting an internal volume 15. It also comprises two ends, one end 11 of which is blocked by a cap 2, inserted at least partially into the internal volume 15. The cap 2 serves on the one hand to stop some binder being introduced into the support when the device is inserted into a hole 53, and on the other hand part to hold a stiffener 3.

(9) The support 1 has a width 16 and a length 17. The width 16 corresponds to an external diameter of the support 1 (measured orthogonally to a longitudinal axis D).

(10) The external surface 13 and the internal surface 14 define between them a thickness 18 of the wall 12, which is at least ten times smaller than the width 16.

(11) The cap 2 has a first end defined by an outer surface 21 and a second end defined by an inner surface 22 directed towards the internal volume 15 of the support 1. The cap 2 has a cylindrical shape complementary to the internal surface 14 of the support 1 in order to provide sealing at the end 11 of the support 1.

(12) The outer surface 21 of the cap 2 and the end 11 of the support 1 are in this case coplanar. Furthermore, the end 11 of the support 1 as well as the surface 21 of the cap 2 shown here have a straight cross section, i.e. orthogonal to the longitudinal axis D of the support 1. According to another exemplary embodiment which is not shown, it could be chamfered so as to facilitate the insertion of the device into the hole, or the surface 21 of the cap 2 could extend beyond the end 11 so as to form a damper when the device abuts the bottom of a hole.

(13) The second end of the cap defined by the surface 22 is parallel to the surface 21. It receives one end 31 of the stiffener 3, which is for example supported by but is generally bonded to a middle of the surface 22.

(14) The stiffener 3 also has a cylindrical shape with a circular cross section, so as to form a rod.

(15) Thus, the support 1, the cap 2 and the stiffener 3 are aligned with respect to the axis D which therefore forms an axis of symmetry of this assembly.

(16) The stiffener 3 and the internal surface 14 define between them a space 19 in the internal volume 15 allowing the support 1 to retain a flexibility despite the presence of the stiffener 3. It is for example possible to position an additional deformation sensor (not shown) in this space in order to compensate for thermal variations for example, as mentioned previously.

(17) Moreover, the stiffener 3 extends beyond the support 1 at its other end 32 which allows a gripping area to be constituted for handling the device.

(18) The filiform strain sensor 4 is in this case a fibre Bragg grating positioned on the external surface 13 of the support 1.

(19) The filiform strain sensor 4 has an axis d parallel to the axis D of the support 1 along which deformation can take place. The axis d therefore constitutes a main strain direction of a measurement zone 43 of the filiform strain sensor 4, in this case at least one fibre Bragg grating. The filiform strain sensor 4 is connected to the support 1 by two spots of binder situated at the ends of the filiform strain sensor 4. In the present exemplary embodiment, the filiform strain sensor 4 extends beyond the support 1 on the side of its end which the stiffener 3 extends beyond. The connecting points are then generally situated at an end 41 of the filiform strain sensor 4 and at a point 42 situated at a distance from the measurement zone 43. The measurement zone is for example situated in the middle of the two points 41, 42.

(20) The device as described previously is intended to be inserted into a hole 53 of an element 5.

(21) According to the present exemplary embodiment, the element 5 has a head 51 and a body 52 such that an axis 57 of the element 5 constitutes an axis of symmetry.

(22) The hole 53 has a surface 55, a first end 54 opening onto a surface 58 of the head 51, and a second end 56 forming a bottom. The hole 53, produced for example in this case by boring, is closed and is not a through hole. When the device is inserted into the hole 53, the end 21 of the cap 2 then abuts the bottom 56 of the hole 53, which guarantees the positioning of the filiform strain sensor 4, and in particular of its measurement zone 43, along the axis 57. The surface 58 can moreover have at least one marker facilitating the orientation of the device in the hole (such a marker is not shown here).

(23) The support 1 or the stiffener 3 can moreover have at least one marker located on the exterior of the element 5 facilitating control of the position of the device.

(24) The hole 53 has moreover a depth along the axis 57 such that, when the device is inserted into the hole 53, the hole 53 comprises at least the measurement zone 43 of the filiform strain sensor 4, i.e., in this case, the fibre Bragg grating. Advantageously, the device extends beyond the end 54 of the hole 53 so as to facilitate its handling.

(25) Before insertion of the device, the hole 53 is partially or completely filled with binder (not shown). The surface 55 of the hole and the device between them define a clearance 59, i.e. a small space, so that the binder then forms a film around the device inserted into the hole 53. Moreover the binder at least covers the measurement zone 43.

(26) Furthermore, the hole 53 is positioned so that the axis 57 of the element 5 is at least approximately merged with the axis D of the support 1 of the device, i.e. the hole 53 is generally formed starting from the centre of the surface 58, so that the device measures the strains as close as possible to the core of the element 5.

(27) In order to take the measurements, the filiform strain sensor 4 is then connected to a measurement device, which is not shown here.

(28) While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the present disclosure as set forth in the appended claims and their legal equivalents.