Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L1/00—Measuring force or stress, in general
  • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
  • G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
  • G01L1/246—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using integrated gratings, e.g. Bragg gratings
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
  • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
  • G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
  • G01M11/3172—Reflectometers detecting the back-scattered light in the frequency-domain, e.g. OFDR, FMCW, heterodyne detection
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
  • G01M5/0016—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings of aircraft wings or blades
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
  • G01M5/0033—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings by determining damage, crack or wear
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
  • G01M5/0041—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings by determining deflection or stress

Definitions

• the present invention relates to the technical domain of monitoring structures in composite material.
• the object of the present invention is a method for monitoring a structure in composite material.
• the present invention also relates to a monitoring device, as well as to an assembly comprising the monitoring device and the structure in composite material to be monitored.
• composite materials are used on a large scale and some known particular applications in the automotive, aerospace, naval industry, as well as in the industry of the production of renewable energies, such as the production of wind turbines, and/or turbo-machines, as well as in the sports sector, for example in the sector of high-performance vehicles (racing), also including racing craft and the like.
• Such composite materials can be provided in panels, shells, domes, plates, slabs, beams, sticks or other elements or structures or bodies which are necessarily subjected, when in operating conditions, to high static and dynamic loads and stresses and strains.
• the operating temperatures to which known structural elements in composite material are subjected can reach levels and excursions which contribute to the premature deterioration of the material.
• the components made of such composite materials are subject to premature deterioration, such as in the case of competition vehicle parts, as well as aerospace vehicle shells.
• structures in composite materials are typically light and thin, albeit sturdy and resistant.
• the composite material is formed by a plurality of material layers, such as a multilayer material which drowns sheets of fabric such as pre-impregnated carbon fibre sheets ("pre-preg") in a matrix
• pre-preg pre-impregnated carbon fibre sheets
• Fibre Bragg Grating fibre-optic (or "FBG”) sensors have also been proposed for monitoring structures because they are adapted to detect local strains without interfering with the static and dynamic behaviour of the structure itself, given the light weight and small footprint thereof.
• the prior art document US-2019-390985 shows a flexion sensor itself composed of a pair of FBG sensors integrated in a single body of elastomeric material and a descriptive numerical model of the dynamic behaviour of the sensor thus constructed.
• EP 1 635 034 also discloses the application of FBG-type sensors to structures to be monitored.
• an apparatus for detecting the radius of curvature of a structural element is more specifically disclosed.
• the device shows various types of structures in which optical sensors can be inserted or glued and which are arranged to be more or less permanently associated with the structure to be monitored.
• a measurement below the surface of the structural element can only be carried out by providing cavities in the structural element itself into which the external structural elements carrying the optical sensors can be inserted, thus causing alterations in the mechanical characteristics of the structure to be monitored, all the greater the more the optical sensors are to be inserted deep into the thickness.
• optical sensors remain in any case integrated in structural elements outside the structure to be monitored. Furthermore, in the cited document the position of the optical sensors with respect to the structure to be monitored is clearly indicated as superficial and it is generally indicated that several optical sensors can be arranged in different, preferably opposite, positions. Since the optical sensors are located on structures outside the one to be monitored, and which are thus inevitably positioned exclusively on the outer surface of the structure to be monitored, the device does not allow to detect the conditions in the thickness of the structure to be monitored and only makes it possible to perform an estimate of overall changes in shape, such as the measurement of the radius of curvature.
• WO 2021/041605 discloses a flexible filament to which one or more fibre-optic sensors for detecting the strain of the flexible filament are stably associated, by means of a buffer material. Also in this case, the fibre-optic sensors are positioned on the surface of the element to be monitored and no specific positions in which they must be arranged with respect to the section of the structural element to be monitored are indicated.
• fibre-optic strain sensors are mutually flanked and arranged, in the body section, opposite with respect to the neutral axis (not necessarily symmetrical);
• the sensors are prevented from being exposed to environmental conditions outside the structure to be monitored, which can also be extreme, during the monitoring operations, with the result of providing an improved measurement accuracy.
• improved protection is provided to the FBG sensors, resulting in improved detection and extended service life.
• a monitoring device 1 comprises at least one pair of fibre-optic strain sensors 11, 12.
• the structure in composite material 10 can be or can belong to a stick, a beam, a plate, a sheet, a shell, a dome, a bottleneck, a cavity, and/or the like.
• the structure to be monitored can comprise a plurality of changes in concavity.
• the structure to be monitored can have an irregular shape.
• the shape and/or composition of the body or structure in composite material 10 can be chosen to meet various functional operating requirements.
• each of the fibre-optic strain sensors 11, 12 of the pair have an elongated body extending within the body of the structure in composite material to be monitored, and their elongated bodies are mutually separated and disjointed within the body of the structure to be monitored.
• the fibre-optic sensors 11 , 12 extend substantially mutually parallel within the body of the element to be monitored along a longitudinal direction of the element 10.
• the detection points 18 of one sensor 11 or 12 of the pair can be arranged side flanked with the detection points 18 of the other sensor 12 or 11 of the pair, in a same cross section of the structure in composite material 10. In other words, when in operating conditions, the detection points 18 of one sensor 11 are aligned along a transverse direction X which defines a cross-section of the structure to be monitored with the detection points 18 of the other sensor 12.
• each fibre-optic strain sensor 11, 12 comprises a fibre-optic sensor distributed along the longitudinal extension thereof which is interrogated with optical frequency domain reflectometry (OFDR) technique.
• OFDR optical frequency domain reflectometry
• the detection points 18 of one sensor 11 or 12 of the pair are arranged offset with respect to the detection points 18 of the other sensor 12 or 11 of the pair, along the longitudinal extension of the structure to be monitored.
• a display can be provided which is operatively connected with the data processing unit 15, which can be used to display information on the processed strained configuration of the element to be monitored and/or to display instructions and/or signals, for example alarm signals.
• Alarm signals can be made by providing an acoustic signal, as an alternative or in addition to providing the display.
• a memory 16 can be provided which is operatively connected with the data processing unit 15, which can be used to store the acquired and/or detected information and/or information on the time sequence of the acquisitions.
• the operative connection between the fibre-optic strain sensors 11 , 12 of the pair and the data processing unit 15 can comprise at least one cabled connection extending outside the body of the element in composite material 10 by means of at least one access plug 13 provided through the body of the element in composite material to be monitored.
• the access plug 13 can be provided on the outer surface 19 of the structure to be monitored.
• a memory 16 which is operatively connected with the data processing unit 15 and which comprises information on: the load applied to the element in composite material to induce the stress state and/or on the mechanical constraints of the element in composite material and/or on the mechanical properties of the composite material of which the element is formed and/or on a set of allowable values of the computed strained configuration.
• the data processing unit 15 can compare the detected and/or processed information with the information stored in the memory 16, as explained in more detail in this disclosure below.
• the assembly 2 can be made during the fabrication of the structure in composite material 10, by means of embedding the detection device 1 within the body of the structure in composite material, as it is being made.
• the step of embedding can comprise drowning the fibre-optic sensors 11 , 12 of the pair in a matrix of liquid and/or viscous material.
• the embedding step allows the fibre-optic sensors 11 , 12 of the pair to be arranged at a certain distance or depth hi , h2 with respect to the outer surface 14 of the structure to be monitored 10.
• the method comprises the further step of transmitting at least one alarm signal and/or intervening to secure the structure in composite material.
• the method can envisage a processing step of the data on: the load applied F to the structure in composite material 10 to induce a state of stress, and/or on the mechanical constraints of the body in composite material, and/or on the mechanical properties of the composite material of which the body itself is formed. It is thereby possible to determine, based on processed and/or stored data, the number and/or location of the detection points 18 to be provided and/or the foreseen strained configuration of the structure in composite material to be monitored.
• the step of computing a strained configuration can be performed substantially in real time, and for example it is performed substantially simultaneously with the step of obtaining strain measurements.
• such a solution can be integrated, for example, in the carbon and/or fibreglass structures of boats, in the shafts of sail boats as well as in high- performance cars, both to improve the safety thereof and to improve the performance thereof;
• the present invention can be applied in the field of infrastructure and construction.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Aviation & Aerospace Engineering (AREA)
• Optics & Photonics (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Length Measuring Devices By Optical Means (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (4)

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Family Cites Families (4)

• 2022
  • 2022-10-07 IT IT102022000020679A patent/IT202200020679A1/it unknown
• 2023
  • 2023-10-06 AU AU2023358088A patent/AU2023358088A1/en active Pending
  • 2023-10-06 EP EP23798511.4A patent/EP4599221A1/de active Pending
  • 2023-10-06 WO PCT/IB2023/060057 patent/WO2024075077A1/en not_active Ceased

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