TECHNICAL FIELD

[0001] The present disclosure is related to a method for producing a carbon fibre reinforced plastic (CFRP) part and more particularly to a method for producing a CFRP part by filament winding.

BACKGROUND

[0002] Filament winding carbon fibre reinforced plastic is a method for producing hollow pieces, such as tank or pressure vessel, where a bundle of carbon fibres is embedded in a matrix resin is wound around a mandrel. Once the desired wall thickness is obtained by winding the carbon fibres bundle, the resin embedded carbon fibres is cured at the curing temperature of the resin and then cooled at room temperature.

[0003] However, it is desirable to increase the mechanical performances of the finished CFRP part and to reduce the manufacturing cost of such parts.

[0004] In view of such a problem, US2018044748 and US2018230567 teach modifying the composition of the metallic mandrel to obtain a pressure vessel having better mechanical performances and US2018148533 teaches modifying the composition of the matrix resin to reduce the curing time.

[0005] Currently, it remains desirable to increase the mechanical performances of the finished CFRP part and to reduce the manufacturing cost of such parts.

SUMMARY

[0006] In one aspect, the present disclosure relates to a method for producing a fibre reinforced plastic part.

[0007] Therefore, according to embodiments of the present disclosure, a method for producing a fibre reinforced plastic part is provided. The method includes:

- impregnating a bundle of fibres with a liquid curable resin;

- winding the impregnated fibre bundle on a mandrel with different winding patterns, each winding pattern forming a layer, so as to form an uncured fibre reinforced plastic part; - thermally curing the resin of the uncured fibre reinforced plastic part so as to form the fibre reinforced plastic part; and

- cooling the fibre reinforced plastic part to room temperature from an external surface of the fibre reinforced plastic part, wherein the cooling rate is equal to or greater than -2.0°C/min (degree Celsius per minute), the cooling rate being measured in the layer being closest to the mandrel.

[0008] The mandrel rotates around an axis and the layers are defined as inner and outer in relation to the rotation axis of the mandrel, the inner layer being closer to the mandrel than the outer layer. When referring to layer numbers, the first layer is the layer closest to the mandrel while the outer layer/last layer is the layer having the external surface of the fibre reinforced plastic part.

[0009] By providing such method, especially a faster cooling rate, it has been found that a gradient of temperature is formed within the thickness of the part, i.e., from the outer layer to the inner layer, the inner layer being the layer closer to the mandrel and the layer which cools at the lower cooling rate. The gradient of temperature induces residual compressive stresses in the part.

[0010] Indeed, in known method, cooling rate for fibre reinforced plastic part is smaller than -0.50°C/min, typically equal to 0.15°C/min, so as to minimize the formation of a gradient of temperature within the thickness of the part during cooling. Such slow cooling rate is obtained by controlling the decrease in temperature of the part after curing, for example in an oven.

[0011] Thus, thanks to the method, it is possible to shorten the cooling time and to reduce the costs of production of such a part by avoiding controlled slow cooling in an oven, which requests energy consumption.

[0012] According to some embodiments, the cooling rate is equal to or greater than -4.0°C/min, preferably equal to or greater than -6.0°C/min, more preferably equal to or greater than -8.0°C/min.

[0013] According to some embodiments, the fibres may be carbon fibres.

[0014] As non-limiting examples of carbon fibres, carbon fibres from Toray may be cited, such as T300, T700, T720, T800, etc.

[0015] According to some embodiments, the winding step may include the winding of alternated layers of hoop layers and helical layers.

[0016] Hoop layers may be defined as layer having an angle comprised approximately between 85° and 95°, preferably between 89° and 91°, while helical layers may be defined as layer having an angle comprised between 10° and 60°.

[0017] According to some embodiments, the last layer may be a hoop layer.

[0018] According to some embodiments, an outermost helical layer has a thickness greater than or equal to 0.5 a wall thickness of the fibre reinforced plastic part.

[0019] The outermost helical layer may be the layer before the external hoop layer.

[0020] According to some embodiments, the layers may have each a thickness, the thickness of at least one layer may be different from the thickness of the other layers.

[0021] It is understood that each layer may have a different thickness and/or some layers may have different thickness and some layers may have a same given thickness.

[0022] According to some embodiments, the resin may be an epoxy resin.

[0023] As non-limiting examples, epoxy resin such as Araldite LY1564/ Aradur 3474 form Huntsman or any similar may be cited.

[0024] According to some embodiments, the mandrel may form a liner of the fibre reinforced plastic part.

[0025] According to some embodiments, the mandrel may comprise polyamide.

[0026] As non-limiting example, the polyamide may be a modified PA6.

[0027] According to some embodiments, the cooling may be carried out by immersion of the fibre reinforced plastic part into dry ice.

[0028] In another aspect, the present disclosure relates to a tank including a fibre reinforced plastic part.

[0029] Therefore, according to embodiments of the present disclosure, a tank including a fibre reinforced plastic part is provided. The fibre reinforced plastic part is obtained by the above-described method.

[0030] According to some embodiments, the tank may include the mandrel.

[0031] It is intended that combinations of the above-described elements and those within the specification may be made, except where otherwise contradictory.

[0032] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure, as claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description, serve to explain the principles thereof.

[0034] Fig. 1 shows a flow chart of a method according to embodiments of the present disclosure;

Fig. 2 shows a step of winding an impregnated fibre bundle on a mandrel;

Fig. 3 shows a fibre reinforced plastic part;

Fig. 4 shows strain and temperature sensors;

Fig. 5 shows a step of winding an impregnated fibre bundle on a mandrel with the sensors of Fig. 4;

Fig. 6 shows a sectional view of a fibre reinforced plastic part for testing;

Fig. 7 shows the temperature measurements in different layers of the fibre reinforced plastic part of Fig. 6;

Fig. 8 shows rupture test measurements for different fibre reinforced plastic part obtained with different cooling rates.

DETAILED DESCRIPTION

[0035] Reference will now be made in detail to exemplary embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

[0036] Fig. 1 shows a flow chart of a method 100 for producing a fibre reinforced plastic part 10 according to embodiments of the present disclosure.

[0037] The method 100 may include a step of impregnating 102 a bundle of fibres with a liquid curable resin and a step of winding 104 the impregnated fibre bundle 12 on a mandrel 14 with different winding patterns (see Fig. 2), each winding pattern forming a layer, so as to form an uncured fibre reinforced plastic part.

[0038] The method 100 may include, after the winding step 104, a step of thermally curing 106 the resin of the uncured fibre reinforced plastic part so as to form the fibre reinforced plastic part 10. [0039] The method 100 may include, after the thermally curing step 106, a step of cooling 108 the fibre reinforced plastic part 10 to room temperature from an external surface 16 of the fibre reinforced plastic part 10, wherein the cooling rate is equal to or greater than -2.0°C/min, the cooling rate being measured in the layer being closest to the mandrel 14.

[0040] In the exemplary embodiment of Fig. 2, the mandrel 14 may form a liner of the fibre reinforced plastic part 10. Thus, there is no additional step for removing the mandrel 14 from the fibre reinforced plastic part 10. After cooling, the mandrel 14 and the fibre reinforced plastic part 10 may form a tank 20.

[0041] However, it may be possible that the mandrel 14 may be removed from the fibre reinforced plastic part 10 in an additional step.

[0042] In the exemplary embodiment of Fig. 2, the mandrel 14 may be made of polyamide, the fibres of the bundle of fibres may be carbon fibres and the liquid curable resin may be an epoxy resin.

[0043] As non-limiting example of polyamide, PA6 may be chosen.

[0044] As non-limiting example of carbon fibres, T700 carbon bundles from Toray may be chosen.

[0045] As non-limiting example of epoxy resin, araldite LY1564 may be chosen.

[0046] As shown at Fig. 2, the mandrel 14 has a cylindrical shape having an axis A.

[0047] As a non-limiting example, the mandrel 14 may have cylindrical body 14A having an external diameter equal to 375 mm (millimetre) and a length L equal to 400 mm, with two caps 14B at each end of the cylindrical body 14A. The tank obtained with such a mandrel 14 may have a volume equal to 50 L (litre).

[0048] As a non-limiting example, the mandrel 14 may have cylindrical body 14A having an external diameter equal to 120 mm (millimetre) and a length L equal to 655 mm, with two caps 14B at each end of the cylindrical body 14A. The tank obtained with such a mandrel 14 may have a volume equal to 10 L (litre).

[0049] As shown at Figs. 2 and 6, the winding step 104 may include the winding of alternated layers of hoop layers H and helical layers HE.

[0050] In the exemplary embodiment shown at Fig. 6, the winding step 104 includes alternated layers of five hoop layers H1-H5 and four helical layers HE1- HE4. In the exemplary embodiment shown at Fig. 6, the first and last layers may be hoop layers Hl, H5. The first hoop layers Hl, inner layer, is defined as the layer being closer to the mandrel 14 than the outer layer, last hoop layer H5. When referring to layer numbers, the first layer is the layer closest to the mandrel 14 while the outer layer/last layer is the layer having the external surface 16 of the fibre reinforced plastic part 10.

[0051] In the exemplary embodiment of Fig. 3, the curing step 106 is carried out with an increase in temperature from 30°C to the curing temperature, e.g., 110°C in 6.5 hours and with a plateau of 12 hours at 110°C.

[0052] In the exemplary embodiment of Fig. 3, the cooling step 108 is carried out by immersion of the fibre reinforced plastic part 10 into dry ice. Dry ice has a temperature of -78.8°C.

[0053] Example 1

[0054] For measuring the strain and the temperature in the layers of the fibre reinforced plastic part 10, sensors 18 are laminated on the impregnated fibre bundle 12 of each hoop layer H1-H5 during the winding step 104 as shown at Fig. 5. The impregnated fibre bundle 12 was winded on the abovedescribed mandrel 14. The fibre bundles 12 are made of T700 carbon bundles from Toray and the epoxy resin is Araldite LY1564/Aradur 3474.

[0055] The mandrel 14 is a cylindrical body 14A having an external diameter equal to 375 mm (millimetre) and a length L equal to 400 mm, with two caps 14B at each end of the cylindrical body 14A. The tank 20 obtained with such a mandrel 14 may have a volume equal to 50 L

[0056] Two different types of sensors 18 have been used, sensors 18A made of optic fibre including strain sensors 18B and a temperature sensor 18C and sensors 18D made of optic fibre including strain sensors 18B. Both types of sensors 18A, 18D included a connector 18E.

[0057] For the sensors 18A including a temperature sensor 18C, the temperature sensor 18C and the connector 18E are located respectively at one end of the sensor 18A.

[0058] For hoop layers Hl, H3 and H5, sensors 18A have been used, while for hoop layers H2 and H4, sensors 18D have been used. Thus, strain is measured in each loop layers H1-H5, while temperature is measured in loop layers Hl, H3 and H5.

[0059] As a non-limiting exemplary embodiment, sensors 18A, 18B may include strain sensors 18B spaced from one another by a distance equal to 213 mm. [0060] At the end of the winding step 104, in view in section, the Example presents a structure as shown at Fig. 6 with the strain sensors 18B laminated with each loop layers H1-H5.

[0061] As non-limiting example, in the fibre reinforced plastic part 10 of Fig. 7, the hoop layer Hl may have a thickness of 1.63 mm, the helical layer HE1 may have a thickness of 7.41 mm, the hoop layer H2 may have a thickness of 4.9 mm, the helical layer HE2 may have a thickness of 13.09 mm, the hoop layer H3 may have a thickness of 4.91 mm, the helical layer HE3 may have a thickness of 5.59 mm, the hoop layer H4 may have a thickness of 4.91 mm, the helical layer HE4 may have a thickness of 7.25 mm, the hoop layer H5 may have a thickness of 1.91 mm. As shown at Fig. 7, although having different thicknesses, the helical layers HE1-HE4 all present a thickness larger than the thickness of the hoop layers H1-H5. It is understood that each hoop layer Hl- H5 may have a different thickness and that the helical layers HE1-HE4 may have the same thickness, the thickness of some helical layers may also be equal to or smaller than the thickness of some hoop layers.

[0062] The curing step 106 is carried out with an increase in temperature from 30°C to the curing temperature, e.g., 110°C in 6.5 hours and with a plateau of 12 hours at 110°C.

[0063] During the cooling step 108, temperatures are measured in hoop layers Hl, H3 and H5, as reported at Fig. 7, in which X axis represents the measure temperature (in °C) and the X axis represents the time (in seconds).

[0064] As shown at Fig. 8, the cooling rate measured at the first hoop layer Hl is approximately equal to -2.24°C/min, i.e., the temperature of the first hoop layer Hl varies from 110°C to 25°C in 38 min (minutes). As shown at Fig. 8, the temperature drop of the external surface 16 of the fibre reinforced plastic part 10, i.e., the temperature measured in the fifth hoop layer H5, is larger than the temperature drop in the first hoop layer Hl.

[0065] Comparative example 1

[0066] A Comparative example 1 was produced with the same method as for the Example 1, the only difference being the cooling step. The Comparative example 1 was made with the same materials and the same layer thickness as the Example. For the Comparative example, the cooling from 110°C to 25°C was carried out in an oven at a cooling rate of -0.15°C/min, i.e., a cooling time of more than 9.5 hours.

[0067] Rupture test [0068] Three ring specimens have been cut out of the Example 1 F1-F3 and the Comparative example 1 S1-S3.

[0069] The rupture test was carried out according to standard EN-1228 on Instron SATEC 1200 kN test machine with a 1200 kN load cell - class 0.5. It is a compression test with an initial contact force of 500 N and loading speed of 5.0 mm/min (millimetre per minute). The internal diameter of the ring specimens was equal to 314 mm and the external diameter of the ring specimens was equal to 374 mm. The rings have each a width of 40 mm, as measured along the direction of the axis A of the fibre reinforced plastic part 10.

[0070] Fig. 8 shows the results of the compressive rupture test. The results are represented as the force (in N - Y axis) as a function of the displacement (in mm - X axis).

[0071] As shown at Fig. 8, the ring specimens F1-F3 cut out the Example 1 show a higher force at rupture than the ring specimens S1-S3 cut out the Comparative example 1. From the measurements, the mean value for the force at rupture of the Example 1 is approximately equal to 20000 N and the mean value for the force at rupture of the Comparative example is approximately equal to 13800 N.

[0072] It is also to be noted that ring specimens F1-F3 cut out the Example 1 shows a greater deformation before rupture than the ring specimens S1-S3 cut out the Comparative example 1.

[0073] Example 2

[0074] The fibre bundles 12 are made of T720 carbon bundles from Toray and the epoxy resin is Araldite LY1564/Aradur3474 hot curing epoxy resin.

[0075] The mandrel 14 is a cylindrical body 14A having an external diameter equal to 120 mm and a length L equal to 655 mm, with two caps 14B at each end of the cylindrical body 14A. The tank 20 obtained with such a mandrel 14 may have a volume equal to 10 L.

[0076] As non-limiting example, in the fibre reinforced plastic part 10, the helical layer HE1 may have a thickness of 0.6 mm, the hoop layer Hl may have a thickness between 2.2 mm-2.6 mm, the helical layer HE2 may have a thickness between 4.9 mm-5.8 mm and the hoop layer H2 may have a thickness of 0.6 mm. The outermost helical layer HE2 may have a thickness greater than or equal to 0.5 a wall thickness of the fibre reinforced plastic part 10. [0077] The curing step 106 is carried out with an increase in temperature from 30°C to the curing temperature, e.g., 120°C in 6.5 hours and with a plateau of 12 hours at 120°C. The internal temperature was 107°C inside the mandrel.

[0078] The cooling step 108 is carried out by immersion of the fibre reinforced plastic part 10 into dry ice. Dry ice has a temperature of -78.8°C. After immersion time of 12.5 min, the internal temperature measured in contact with the mandrel was 3°C, i.e., a cooling rate that is equal to or greater than -8.0°C/min.

[0079] Three tanks were made.

[0080] Comparative example 2

[0081] A Comparative example 2 was produced with the same method as for the Example 2, the only difference being the cooling step. The Comparative example 2 was made with the same materials and the same layer thickness as the Example 2. For the Comparative example 2, the cooling from 120°C to 25°C was carried out in an oven at a cooling rate of -0.15°C/min, i.e., a cooling time of more than 9.5 hours.

[0082] Three tanks were made.

[0083] Burst pressure test

[0084] Burst pressure test was performed on Example 2 and Comparative Example 2 according to the Commission Regulation (EU) N°406/2010 of April 26, 2010 (which implements Regulation (EC) N°79/2009 of the European Parliament) - Annex IV/Part 2/4.2.1

[0085] Test setup: Air driven liquid pump by Maximator G150 - 2LVE

[0086] Pressure gauge: HBM - P3IC 2000 bar (sn: 180310082)

[0087] Data acquisition unit: HMB QuantumX MX840 (sn: 0009E50076FA)

[0088] The tests were run on the three tanks of Example 2 and the three tanks of Comparative Example 2. The mean value of the burst pressure for Example 2 was equal to 2011 bar with a standard deviation of 13 bar, whereas the mean value of the burst pressure for Comparative Example 2 was equal to 1791 bar with a standard deviation of 46 bar.

[0089] There is a meaningful difference (around 12%) between the fast cooling (Example 2) in dry ice and the slow cooling (Comparative Example 2) following a natural convection.

[0090] The fast cooling generates a higher compressive stress on the outer layer, which helps in maintaining the structural stability at higher temperature. [0091] Furthermore, the helical layer HE2 concentrated in the outer side of the tank 20 prevents the generation of microcracks that would decrease the compressive stress.

[0092] Throughout the description, including the claims, the term "comprising a" should be understood as being synonymous with "comprising at least one" unless otherwise stated. In addition, any range set forth in the description, including the claims should be understood as including its end value(s) unless otherwise stated. Specific values for described elements should be understood to be within accepted manufacturing or industry tolerances known to one of skill in the art, and any use of the terms "substantially" and/or "approximately" and/or "generally" should be understood to mean falling within such accepted tolerances.

[0093] Where any standards of national, international, or other standards body are referenced (e.g., ISO, etc.), such references are intended to refer to the standard as defined by the national or international standards body as of the priority date of the present specification. Any subsequent substantive changes to such standards are not intended to modify the scope and/or definitions of the present disclosure and/or claims.

[0094] Although the present disclosure herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure.

[0095] It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims.