Method and system for in-service detection of deformations in a structural element of a vehicle

Abstract

A method for the in-service detection of changes to the material of a structural element of a vehicle comprises the steps of applying a plurality of electrodes (10) onto the surface of said structural component; electrically connecting these electrodes (10) to a detection system, with which one or more values of electrical resistance and / or voltage difference between at least one pair of said electrodes (10) are detected; comparing these detected values with one or more predetermined values; and, if at least one of the detected values is equal to or greater than a corresponding predetermined value, generating information indicative of a change to the state of the structural component that has occurred between said pair of electrodes (10).

Description

[0001] Method and system for in-service detection of deformations in a structural element of a vehicle

[0002] Technical field

[0003] The present invention generally falls within the automotive field; particularly, the invention relates to a system and method for designing and manufacturing a structural component made of composite material, integrating a self-damage detection system for monitoring the health of the component during use.

[0004] Summary of the invention

[0005] Lightweight composite structures for automotive use are known, such as suspension arms made of composite material, uprights, or crossbeams, manufactured through various production processes, such as for example injection moulding, compression moulding (applied for example to Sheet Moulding Compound), thermoforming, etc.

[0006] Said processes allow the production of components the structures of which, primarily made of composite materials, are locally reinforced using glass, carbon, or bio-based fibres.

[0007] However, such components cannot always ensure equivalent mechanical performance compared to structurally similar elements traditionally made of metal.

[0008] In this regard, the object of the invention is to facilitate the integration and use of composite materials in suspension structural elements.

[0009] In particular, integrating a monitoring system within the component enables health analysis by evaluating potential damage occurred during use, promoting the adoption of "exotic" materials in structural applications.

[0010] The invention is characterised by the use of materials incorporating discontinuous conductive fibres, combined with monitoring systems capable of assessing the material response in terms of structural mechanical characteristics, eliminating the need for traditional sensors.

[0011] Said detection relies on a monitoring procedure of the structural condition of the component, evaluating its integrity and reducing the risk of unexpected failures, enhancing vehicle safety.

[0012] Moreover, based on the structural response, the load applied to the wheel hub can be estimated and transmitted to a processing and control system to improve control strategies during vehicle operations.

[0013] Said monitoring system for the component condition provides advantages in reliability and performance, as it also enables a continuous integrity monitoring by identifying potential damages or degradations before they become critical to component functionality. This improves vehicle performance and integrity, ultimately being advantageous when reducing costs is envisaged.

[0014] Vehicle safety is also enhanced since the system can detect potential failures (e.g., cracks in the component) and communicate them in real-time to the maintenance centre for intervention before failure occurs.

[0015] Additionally, the system, by conveniently providing data on the structure's response to various loads and working conditions, can aid in optimising component sizing and performance in future development.

[0016] According to one embodiment, a system according to the invention comprises three elements: a polymer composite material modified with discontinuous electrically conductive fibres (e.g., short carbon-based fibres) as the detection mechanism's basis. The reinforcement type and the quantity added to the polymer are conveniently defined to activate a selfdetection phenomenon induced by forming conductive networks within the material.

[0017] Adding conductive fibres to the polymer material does not require modifications to the component production processes, making the technology cost-effective. The system combines the structural performance of composite materials with self-detection characteristics activated by microscopic phenomena.

[0018] Components made with such materials can interface with a real-time acquisition system and without any traditional sensor using electrodes, obtained for example by depositing a layer of conductive adhesive onto the component surface. The electrodes allow measurements via an interface designed to acquire signals from the structural component and communicate with the processing unit.

[0019] The measurement system can be a voltage divider, designed to adapt the measurement circuit to the monitored points (electrodes or electrode pairs) and the electromechanical properties of the material being used. The acquisition system is preferably configured to be compatible with automobile power supplies and not require additional power sources.

[0020] The anomaly detection system can identify the presence of structural damage and estimate its severity using models implementable on the control unit of the vehicle. Combining the electrical signal with the positions of the measurement points, the system can estimate the damage location with accuracy proportional to the density of the measurement points all around the detected damage. Electrical signal anomalies are detected when the current path encounters structural anomalies (e.g., a crack, high local deformation), inducing a local increase in electrical resistance. The increase correlates with damage magnitude relative to the initial resistance of the conductive path, which in turn depends on the distance between the measurement points. Therefore, the system sensitivity depends on the distance of the measurement points, increasing as the measurement point distance decreases.

[0021] The structural component (e.g., a suspension arm for an automotive vehicle) can be manufactured via injection moulding or other known processes such as for example SMC (sheet moulding compound) compression moulding.

[0022] The "self-detection" technology can be conveniently based on composite materials produced with polymers enhanced or reinforced with discontinuous fibres, making the material conductive through the percolation mechanism. Including for example short carbon fibres in the polymer composite creates a conductive network within the polymer matrix, that can be used for the detection of resistivity changes in the material due to applied mechanical loads.

[0023] A method using a similar principle is known from EP 3 128 202 Al, which concerns an automotive leaf spring with specific electrodes at the ends thereof connected to a detector that records internal damage when current flows through the component. However, this solution differs by using a composite material with continuous fibres adapted for creating a continuous lattice for the entire length of the component. In particular, the solution proposed in the aforementioned document provides that the component is manufactured by overlapping layers of fibrous fabric (thus made of continuous fibres), exposed to a resin supplemented with conductive nanoparticles.

[0024] However, such a configuration is poorly suited for use with injection or compression moulding techniques, which are preferably envisaged for the present invention and are characterised by the discontinuity between the fibre and the matrix, and more importantly requires the electrodes to be applied at the ends of the component, wherein instead it may be preferable to monitor the material locally, even at multiple points. Thanks to the present invention, it becomes instead possible to assess the state of the component in one or more of its portions, rather than necessarily over its entire extent, thereby enabling more capillary and reliable monitoring.

[0025] The fibre dispersion technology can then be integrated into a conventional composite parts production process, therefore involving no increased production costs.

[0026] Conductive fibres can be the same carbon fibres constituting the initial polymer composite material or possibly additives or conductive elements dispersed within the mixture.

[0027] If conductive elements are not present in the starting mixture, in the case of injection moulding process they can be added in the hopper during the injection moulding process.

[0028] Also in case of SMC compression moulding, the starting material can be reinforced with particles / fibres / strands - or, more generally, carbon fibre reinforcements - making the material conductive due to the percolation mechanism.

[0029] Carbon fibres possess notable mechanical properties, and their addition to the polymer composite totally improves also the stiffness and strength of the material.

[0030] The nanoscale percolation mechanism (or microscale) can functionalise the reinforced polymer, enhancing its conductivity and allowing current to flow within the component. The load applied to the structural part induces a deformation state, which in turn modifies the carbon network governing overall conductivity, resulting in signal variation proportional to the applied load.

[0031] In the event of incipient damage, typically starting with a crack within the material, the current flow will be interrupted, causing a sharp signal variation that can be analysed and processed to evaluate the presence of damage in the component and predict its occurrence or ultimate failure.

[0032] One advantage of this detection technology according to the invention, compared to known systems using traditional sensors is based on the scalability of the sensor network, which minimally affects the cost and complexity of the system.

[0033] Indeed, higher sensor density improves the system precision, which in conventional sensorisation methods would mean increasing the number of sensors and, consequently, the cost of the system. In a method and system according to the invention, as the material serves as the detection vehicle, increasing measurement points alone enhances precision of the system with negligible impact on system cost.

[0034] Acquiring and processing multiple signals coming from the monitored part allows detecting anomalies in the structural response of the part induced by damage and estimating its location within the component.

[0035] Damage detection and localisation capability are influenced by the density of the measurement points in the damaged area.

[0036] The above and other objects and advantages are achieved, according to one aspect of the invention, by a system and method having the characteristics defined in the appended claims.

[0037] Brief description of the drawings

[0038] The functional and structural features of some preferred embodiments of a system and method according to the invention will now be described. Reference is made to the accompanying drawings, wherein:

[0039] - figure 1 is a schematic perspective view of a structural component whereon electrodes have been applied for detecting electrical parameters based on the material's state, an exemplary microscopic structure detail is shown, according to one embodiment of the invention;

[0040] - figure 2 is a schematic side view of a structural component showing a perimeter distribution of detection electrodes;

[0041] - figures 3A to 3C are schematic exemplary views illustrating the micro structure of the material in an unperturbed state, one wherein the material undergoes mechanical tension, and one wherein a crack is present, respectively; and

[0042] - figure 4 is an illustrative diagram showing the variation in electrical conductivity (measured in S / cm on the ordinate) in a polymer matrix (PA6) composite added with carbon black, when the carbon black weight percentage changes (on the abscissa).

[0043] Detailed description

[0044] Before detailing various embodiments of the invention, it is clarified that the invention is not limited in its application to the construction details and component configurations presented in the following description or illustrated in the drawings. The invention may adopt other embodiments and be practiced or implemented in various ways. Furthermore, it is understood that the phraseology and terminology are for descriptive purposes and should not be construed as limiting. With reference to the figures by way of example, a method for the in-service detection of deformations and / or fissures and / or cracks and / or irreversible microstructural changes to a structural element of a vehicle comprises the steps of providing a structural component of a vehicle made at least partially from a polymer matrix composite material reinforced with electrically conductive discontinuous fibres dispersed within the matrix, preferably in a random and / or homogeneous manner. Such fibres are preferably of millimetric or micrometric scale, significantly smaller than the dimensions of the structural component.

[0045] According to one embodiment, the discontinuous fibres are short carbon fibres (optionally in combination with glass fibres), and more preferably short carbon fibres with lengths less than 6 mm and / or lengths equal to or less than 1 mm (preferably between 250 pm and 900 pm) once incorporated into the material. Alternatively or in combination, the discontinuous fibres may be long carbon fibres (optionally in combination with glass fibres), and even more preferably long carbon fibres with lengths less than 13 mm and / or lengths equal to or less than 1 mm (preferably between 250 pm and 900 pm) once incorporated into the material. This embodiment is particularly suitable when the method according to the present invention includes for example the step of manufacturing the structural component through injection moulding.

[0046] According to one embodiment, the discontinuous fibres are cut or chopped carbon fibres (optionally in combination with glass fibres), and more preferably carbon fibres having a length between 25 mm and 50 mm. This embodiment is particularly suitable when the method according to the present invention includes, for example, the step of manufacturing the structural component through SMC compression moulding.

[0047] The method also includes the steps of applying a plurality of electrodes 10 onto the surface of the structural component; electrically connecting these electrodes 10 to a detection system (not illustrated), capable of detecting an electrical resistance value and / or a voltage difference between at least one pair of these electrodes 10; detecting one or more values of electrical resistance and / or voltage difference between at least one pair of these electrodes 10; providing an electronic processing system (not illustrated), configured to receive signals from the detection system indicative of the value or values detected in the previous step; comparing these detected values with one or more predetermined values; and comparing, by means of the electronic processing system, said detected value or values with the predetermined value or values. Preferably, the electrically conductive fibres are dispersed discontinuously within the matrix, such that electrical conduction between two electrodes 10 through the composite material is enabled by the dispersion of the fibres within the material, rather than by fibres having a length sufficient to extend continuously between the two electrodes 10.

[0048] If at least one of the said detected values is equal to or greater than a corresponding predetermined value, the method further involves the step of generating, by means of the electronic processing system, information indicative of a change in the state of the structural component that has occurred between at least one pair of electrodes 10.

[0049] As in fact exemplified in Figures 3 to 3C, in a resting state (Figure 3A), the material presents an initial distribution of fibres F incorporated into a polymer matrix M, associated with specific electrical behaviour of the material being influenced by such a distribution.

[0050] When the material is subjected to mechanical stress (Figure 3B), the distribution of fibres F is modified, thereby changing the conductivity and / or electrical resistance characteristics of the material. When a crack forms in the material (Figure 3C), it could locally break the conductive network, causing further changes to the conductivity and / or electrical resistance characteristics of the material. Therefore, by detecting an electrical resistance value and / or voltage difference between two electrodes placed at the ends of the illustrated region, it is possible to determine whether and to what extent a change in the material’s state has occurred, based on its altered electrical behaviour.

[0051] According to an embodiment, said predetermined comparison value is a threshold value indicative of fracture and / or damage and / or the presence of fissures and / or cracks and / or microstructural changes of the material from which the structural component is made. In this case, the generation of information indicative of a change in the state of the structural component occurs when the value detected between the at least one pair of electrodes 10 equals the predetermined threshold comparison value. According to an embodiment, said predetermined value is indicative of electrical resistance and / or a voltage difference between the same pair or pairs of electrodes 10 considered in the detection step, but detected prior to said step. This makes it possible, for example, to maintain a history of detections, starting from an initial detection that is compared with subsequent one or ones. In this case, the generation of information indicative of a change in the state of the structural component will occur when the value detected between at least one pair of electrodes 10 differs (preferably is higher) from the predetermined comparison value.

[0052] According to an embodiment, the detection system comprises a voltage divider.

[0053] According to an embodiment, at least one of the electrodes 10 is applied at a surface point of the structural component other than an end of the same, and / or there are at least three electrodes 10.

[0054] According to an embodiment some of the electrodes 10 may be formed by depositing a layer of electrically conductive adhesive onto a portion of the surface of the structural element.

[0055] According to an embodiment, the material of the structural component is preferably a polymer matrix composite material to which electrically conductive fibres have been added in a proportion between 0.1% and 65% by volume.

[0056] According to an embodiment, the material of the component may include electrically conductive fibres in a proportion equal to or greater than 10% by weight.

[0057] According to an embodiment, the material of the structural element can be reinforced with carbon fibres.

[0058] According to an embodiment, the structural element may be a suspension arm for a vehicle.

[0059] According to another aspect of the invention, a system for the in-service detection of deformations and / or fissures and / or cracks and / or irreversible microstructural changes in a structural element of a vehicle comprises a structural component of a vehicle made at least partially of a polymer matrix composite material reinforced with electrically conductive fibres dispersed discontinuously within the matrix; a plurality of electrodes 10 applied onto the surface of the structural component; a detection system electrically connected to these electrodes 10 and configured to detect an electrical resistance value and / or a voltage difference between at least one pair of said electrodes 10; and an electronic processing system configured to receive from the detection system signals indicative of electrical resistance values and / or voltage differences between at least one pair of said electrodes 10, process system processes these signals to obtain indicative values of electrical resistance and / or voltage difference between at least one pair of electrodes 10 and compare the detected values with one or more predetermined values indicative of a change in the structural component state occurring between two or more electrodes 10.

[0060] Various aspects and embodiments of a method and system according to the invention have been described. It is intended that each embodiment can be combined with any other embodiment. Furthermore, the invention is not limited to the described embodiments but may be varied within the scope defined by the appended claims.

Claims

CLAIMS1. A method for the in-service detection of deformations and / or fissures and / or cracks and / or irreversible microstructural changes to a structural element of a vehicle, comprising the steps of: a) providing a structural component of a vehicle, made at least partially of a polymer matrix composite material reinforced with electrically conductive fibres dispersed discontinuously within the matrix; b) applying a plurality of electrodes (10) to the surface of said structural component; c) electrically connecting said electrodes (10) to a detection system, adapted to detect an electrical resistance value and / or a voltage difference between at least one pair of said electrodes (10); d) detecting one or more values of electrical resistance and / or voltage difference between at least one pair of said electrodes (10); e) providing an electronic processing system configured to receive signals from the detection system indicative of the value or values detected in step d), and compare these detected values with one or more predetermined values; f) comparing, by means of the electronic processing system, said detected value or values with said predetermined value or values; g) if at least one of the detected value or values is equal to or greater than a corresponding predetermined value, generating, by means of the electronic processing system, information indicative of a change to the state of the structural component that has occurred between said at least one pair of electrodes (10).

2. The method according to claim 1, wherein the material of the structural component is a polymer matrix composite reinforced with short carbon fibres.

3. The method according to claim 2, wherein the material of the structural component is a polymer matrix composite reinforced with fibres having a length less than 6 mm, and / or a length, at least when incorporated into the material, equal to or less than 1 mm, or preferably a length between 250 pm and 900 pm.

4. The method according to claim 1 or 2, wherein the material of the structural component is a polymer matrix composite reinforced with long carbon fibres.

5. The method according to claim 4, wherein the material of the structural component is a polymer matrix composite reinforced with fibres having a length less than 13 mm, and / or a length, at least when incorporated into the material, equal to or less than 1 mm, or preferably a length between 250 pm and 900 pm.

6. The method according to claim 1, wherein the material of the structural component is a polymer matrix composite reinforced with cut or chopped carbon fibres.

7. The method according to claim 6, wherein the material of the structural component is a polymer matrix composite reinforced with carbon fibres having a length between 25 mm and 50 mm.

8. The method according to any of the preceding claims, wherein said predetermined value is a threshold value indicative of fracture and / or damage and / or the presence of fissures and / or cracks and / or microstructural changes to the material from which the structural component is made.

9. The method according to any of the preceding claims, wherein said predetermined value is indicative of an electrical resistance and / or a voltage difference between the same pair or pairs of electrodes (10) considered in step d), but detected prior to said step d).

10. The method according to any of the preceding claims, wherein at least one of the electrodes (10) is applied at a surface point of the structural component different from an end thereof, and / or at least three electrodes (10) are present.

11. The method according to any of the preceding claims, wherein the detection system comprises a voltage divider.

12. The method according to any of the preceding claims, wherein at least some of theelectrodes (10) are formed by depositing a layer of electrically conductive adhesive on a portion of the surface of the structural element.

13. The method according to any of the preceding claims, wherein the material of the structural component is a polymer matrix composite to which electrically conductive fibres have been added in a proportion between 0.1% and 65% by volume.

14. The method according to any of the preceding claims, wherein the material of the structural component is a polymer matrix composite to which electrically conductive fibres have been added in a proportion equal to or greater than 10% by weight.

15. The method according to any of the preceding claims, wherein the structural element is a suspension arm for a vehicle.

16. A system for the in-service detection of deformations and / or fissures and / or cracks and / or irreversible microstructural changes to a structural element of a vehicle, comprising:- a structural component of a vehicle, made at least partially from a polymer matrix composite material reinforced with electrically conductive fibres dispersed discontinuously within the matrix;- a plurality of electrodes (10), applied to the surface of said structural component;- a detection system electrically connected to said electrodes (10) and capable of detecting an electrical resistance value and / or a voltage difference between at least one pair of said electrodes (10); and- an electronic processing system configured to receive from the detection system signals indicative of electrical resistance values and / or voltage differences between at least one pair of said electrodes (10), process said signals to obtain values indicative of electrical resistance and / or voltage difference between said at least one pair of electrodes (10), and compare said detected values with one or more predetermined values indicative of a change to the state of the structural component occurring between said two or more electrodes (10).

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