Stiffened panels and method of fabricating stiffened panels

Abstract

Disclosed herein is a method (1500) of fabricating stiffened panels (100). The method (1500) includes placing (1502) a layer of non-stick thermal-resistant material on a surface plate (202). Further, placing (1504) a first layer of a skin material (102) over the layer of the non-stick thermal-resistant material. Further, setting (1506) a core (104) over the first layer of the skin material (102). Further, placing (1508) a second layer of a skin material (106) over the set core (104). Furthermore, performing (1510) a co-curing operation by applying pressure under vacuum on the first layer of the skin material (102), the set core and the second layer of the skin material (106) to bond together.

Description

FIELD OF THE INVENTION[1] The present disclosure relates to sandwich panels and more particularly, to stiffened panels and a method of fabricating stiffened panels for achieving fibre continuity in all plane directions and having improved structural properties of high strength, rigidity, durability, and lightweight.BACKGROUND[2] Stiffened panels are essential structural elements extensively used in aerospace, marine, and civil engineering applications to provide stability to thin-walled structures. Typically, a stiffened panel consists of an outer skin made from a thin and high-strength material that encloses a core layer composed of lightweight structural materials. However, the conventional fabrication techniques for stiffened panels often fail in real-world applications, compromising their structural integrity and performance of the panel.[3] In one conventional technique, stiffened panels are fabricated using the hot-press moulding method, where the skin and core layers are bonded together by applying adhesive to the mating surfaces of the sandwich structure. While this approach is widely used due to its simplicity and cost-effectiveness, it often suffers from debonding at the adhesive interface between the skin and core layers. This debonding can significantly compromise the mechanical integrity of the stiffened panels, especially under dynamic loading conditions, risking structural failure during mid-operation and potentially leading to catastrophic consequences.[4] Furthermore, the conventional stiffened panels often fail to maintain fibre continuity within the core layer, which can lead to stress concentrations, delamination, and premature failure under mechanical loading. The discontinuity disrupts the efficient transfer of loads across the sandwich structure, reducing the overall stiffness and fatigue resistance of the conventional stiffened panels, and making them vulnerable to buckling or fracture during service.[5] In another conventional technique, stiffened panels are fabricated using a metallic core formed by punching two metal sheets together to create a corrugated structure. Multiple corrugated sheets are then spot-welded to form the complete metallic core, which is subsequently spot-welded to the outer skin to assemble the stiffened panel. However, this method is highly time-consuming and labour-intensive. Moreover, the inspection and rework of spot welds are challenging due to limited accessibility and the potential for hidden defects, which can compromise the reliability and structural performance of the final fabricated stiffened panel.[6] Furthermore, conventional stiffened panels often experience high stress concentrations at the interfaces between the sandwiched layers. These localized stresses result in uneven stress distribution across the structure, particularly at the intersections where the skin and core materials meet. Such stress concentrations can act as initiation points for structural failure, leading to cracking, delamination, or buckling under operational loads. Consequently, these panels may fail at loads significantly lower than their rated load-bearing capacity, undermining their reliability in critical applications.[7] Hence, it is desirable to develop a stiffened panel and a method of fabricating a stiffened panel that may prevent one or more limitations of the conventional fabricating techniques.SUMMARY[8] This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention and nor is it intended for determining the scope of the invention.[9] In an embodiment, a method of fabricating stiffened panels is provided. The method includes placing a layer of non-stick thermal-resistant material on a surface plate. The method further includes placing a first layer of a skin material over the layer of the non-stick thermal-resistant material. Further, the method includes setting a core over the first layer of the skin material. Further, the method includes placing a second layer of a skin material over the set core. Furthermore, the method includes performing a co-curing operation by applying pressure under vacuum on the first layer of the skin material, the set core and the second layer of the skin material to bond together.

[10] The stiffened panels fabricated by the method of the present disclosure may achieve fibre continuity in all plane directions. Accordingly, the stiffened panels fabricated by the method of the present disclosure may efficiently transfer loads across the structure, increasing its overall stiffness and fatigue resistance, thereby preventing buckling or fracture during its service life.

[11] Furthermore, the stiffened panels fabricated by the disclosed method by co-curing the first layer of the skin material, the set core and the second layer of the skin material to bond together, may provide improved structural properties of high strength, rigidity, durability, thereby enhancing the load bearing capacity of the stiffened panels while maintaining lightweight, as compared to a conventional stiffened panels for achieving similar load bearing capacity.

[12] To further clarify the advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[13] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[14] Figure 1 illustrates a perspective view of a fabricated stiffened panel, in accordance with an embodiment of the present disclosure;

[15] Figure 2 illustrates a schematic front view of a setup for fabricating stiffened panels depicting a surface plate, in accordance with an embodiment of the present disclosure;

[16] Figure 3 illustrates a schematic front view of the setup depicting a first layer of a skin material placed on the surface plate, in accordance with an embodiment of the present disclosure;

[17] Figure 4 illustrates a schematic front view of the setup depicting a row of a first support material placed on the first layer of the skin material, in accordance with an embodiment of the present disclosure;

[18] Figure 5 illustrates a schematic front view of the setup depicting a first layer of a core material placed on the row of the first support material, in accordance with an embodiment of the present disclosure;

[19] Figure 6 illustrates a schematic front view of the setup depicting a row of a second support material placed on the first layer of the core material, in accordance with an embodiment of the present disclosure;

[20] Figure 7 illustrates a schematic front view of the setup depicting a roll of fibre reinforced material placed at an intersection of each second support material and the first layer of the core material, in accordance with an embodiment of the present disclosure;

[21] Figure 8 illustrates a schematic front view of the setup depicting a second layer of the core material placed on the row of the second support material, in accordance with an embodiment of the present disclosure;

[22] Figure 9 illustrates a schematic front view of the setup depicting a row of a third support material placed on the second layer of the core material, in accordance with an embodiment of the present disclosure;

[23] Figure 10 illustrates a schematic front view of the setup depicting a second layer of the skin material placed on the row of the third support material, in accordance with an embodiment of the present disclosure;

[24] Figure 11 illustrates a schematic front view of the setup depicting a co-cured fabricated stiffened panel, in accordance with an embodiment of the present disclosure;

[25] Figure 12 illustrates an enlarged part view of the co-cured fabricated stiffened panel depicting curved fillet at each intersection of the co-cured fabricated stiffened panel, in accordance with an embodiment of the present disclosure;

[26] Figure 13 illustrates a schematic front view depicting unidirectional fibre continuity of a core of the co-cured fabricated stiffened panel, in accordance with an embodiment of the present disclosure;

[27] Figure 14 illustrates a schematic front view of one or more shape structure arrangements of the core for the co-cured fabricated stiffened panel, in accordance with an embodiment of the present disclosure; and

[28] Figure 15 illustrates a flowchart depicting an exemplary method of fabricating stiffened panels, in accordance with an embodiment of the present disclosure.

[29] Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. Furthermore, in terms of the construction of the device, a plurality of components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. DETAILED DESCRIPTION OF FIGURES

[30] For the purpose of promoting an understanding of the principles of the present disclosure, reference will now be made to the various embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the present disclosure is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the present disclosure as illustrated therein being contemplated as would normally occur to one skilled in the art to which the present disclosure relates.

[31] It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the present disclosure and are not intended to be restrictive thereof.

[32] Whether or not a certain feature or element was limited to being used only once, it may still be referred to as "one or more features" or "one or more elements" or "at least one feature" or "at least one element." Furthermore, the use of the terms "one or more" or "at least one" feature or element do not preclude there being none of that feature or element, unless otherwise specified by limiting language including, but not limited to, "there needs to be one or more…" or "one or more elements is required."

[33] Reference is made herein to some "embodiments." It should be understood that an embodiment is an example of a possible implementation of any features and / or elements of the present disclosure. Some embodiments have been described for the purpose of explaining one or more of the potential ways in which the specific features and / or elements of the proposed disclosure fulfil the requirements of uniqueness, utility, and non-obviousness.

[34] Use of the phrases and / or terms including, but not limited to, "a first embodiment," "a further embodiment," "an alternate embodiment," "one embodiment," "an embodiment," "multiple embodiments," "some embodiments," "other embodiments," "further embodiment", "furthermore embodiment", "additional embodiment" or other variants thereof do not necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and / or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and / or elements may be described herein in the context of only a single embodiment, or in the context of more than one embodiment, or in the context of all embodiments, the features and / or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and / or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

[35] Any particular and all details set forth herein are used in the context of some embodiments and therefore should not necessarily be taken as limiting factors to the proposed disclosure.

[36] The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises... a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

[37] Embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings.

[38] Figure 1 illustrates a perspective view of a fabricated stiffened panel 100, in accordance with an embodiment of the present disclosure.

[39] The stiffened panel 100 of the present disclosure may be applied in aerospace, marine, and civil engineering applications to improve the load-bearing capacity and to provide an overall stability of thin-walled structures. The stiffened panel 100 may include a first layer of a skin material 102, a core 104, and a second layer of a skin material 106.

[40] The stiffened panel 100 of the present disclosure may be fabricated using a co-curing operation performed by applying pressure under vacuum on the first layer of the skin material 102, the core 104, and the second layer of the skin material 106 to bond together in a single stage for fabrication.

[41] Accordingly, the stiffened panel 100 fabricated based on the present disclosure using the co-curing operation applied to bond the first layer of the skin material 102, the core 104, and the second layer of the skin material 106 together in the single stage for fabrication may facilitate in achieving fibre continuity in all plane directions, i.e., in the entire length and width direction of stiffened panel 100. This may facilitate efficient transfer of loads across the stiffened panel 100.

[42] Further, the fabricated stiffened panel 100 using the co-curing operation applied together in the single stage for fabrication may prevent the need for applying an adhesive between the interface of mating surfaces. Accordingly, the stiffened panel 100 may prevent failure due to debonding of the layers 102, 106 and the core 104 under dynamic loading conditions, thereby preventing structural failure during mid-operation and preventing potential catastrophic consequences associated with debonding of the stiffened panel 100. Furthermore, the fabricated stiffened panel 100 may have increased overall stiffness and fatigue resistance, facilitating its application in numerous load-bearing applications.

[43] Subsequent paragraphs with respect to Figures 2 to 11 will explain in detail the fabrication of the stiffened panels 100 of the present disclosure.

[44] Figure 2 illustrates a schematic front view of a setup 200 for fabricating stiffened panels 100 depicting a surface plate, in accordance with an embodiment of the present disclosure.

[45] In an embodiment, the setup 200 may include the surface plate 202. In an embodiment, the surface plate 202 may be one of a flat surface plate or a curved surface plate. The surface plate 202 may be thoroughly cleaned to remove any foreign particles. Further, in an embodiment, a layer of non-stick thermal-resistant material (not shown) may be applied on the surface plate 202. The layer of non-stick thermal-resistant material may facilitate extraction of the co-cured stiffened panels 100, once fabricated. In an example, the layer of non-stick thermal-resistant material may be a layer of Teflon-coated release film or release agent.

[46] Figure 3 illustrates a schematic front view of the setup 200 depicting a first layer of a skin material 102 placed on the surface plate 202, in accordance with an embodiment of the present disclosure.

[47] As shown, the first layer of the skin material 102 may be placed over the layer of the non-stick thermal-resistant material. In an embodiment, the first layer of the skin material 102 may be one of a carbon fibre reinforced material, a glass fibre reinforced material, or an aramid fibre reinforced material. Further, the setup 200, at this stage, may be subjected to an intermediate de-bulking through vacuum to remove any air at the mating interfaces between the first layer of the skin material 102 and the layer of the non-stick thermal-resistant material.

[48] Subsequent paragraphs with respect to Figures 4 to 9 will explain in detail about setting of the core 104 over the first layer of the skin material 102. The core 104 may be set to fabricated one of multiple constructional shaped structures, as per the requirement. In one embodiment, the set core 104 may include a hexagonal shaped structure. In another embodiment, the set core 104 may include a square shaped structure. In another embodiment, the set core 104 may include a trapezoid shaped structure. In yet another embodiment, the set core 104 may include any other shaped structure, without departing from the scope of the present disclosure.

[49] Figure 4 illustrates a schematic front view of the setup 200 depicting a row of a first support material 402 placed on the first layer of the skin material 102, in accordance with an embodiment of the present disclosure.

[50] In an embodiment, each first support material 402 may have a first predefined shape. The first predefined shape may be configured based on the structure of the core 104. As shown, the row of the first support material 402 may be placed on the layer of the skin material 102. Further, each first support material 402 may include a layer of a release agent (not shown) applied onto all surfaces of the first support material 402 prior to placing over the layer of the skin material 102. The layer of the release agent may facilitate easy removal of each first support material 402 from the co-cured stiffened panels 100, once fabricated.

[51] In an embodiment, a roll of a fibre reinforced material 404 may be placed at an intersection of each of the row of the first support material 402 and the first layer of the skin material 102. Further, a length of the roll of the fibre reinforced material 404 may run along a width of the first layer of the skin material 102, thereby ensuring that a fibre continuity of the roll of the fibre reinforced material 404 is maintained. In an embodiment, the first support material 402 may include a curved profile at the intersection, forming voids at the intersection. Further, the roll of the fibre reinforced material 404 may be placed at the intersection to fill the voids formed due to the curved profile of the first support material 402 at the intersection. In an embodiment, the roll of the fibre reinforced material 404 may be formed in one of a unidirectional (UD) arrangement or a bi-directional (BD) arrangement.

[52] Figure 5 illustrates a schematic front view of the setup 200 depicting a first layer of a core material 502 placed on the row of the first support material 402, in accordance with an embodiment of the present disclosure.

[53] In an embodiment, the core 104 may include a plurality of layers. In an embodiment, the core 104 may be of a material comprising one of a carbon fibre reinforced material, a glass fibre reinforced material, or an aramid fibre reinforced material. In an embodiment, the plurality of layers of the core 104 may include the first layer of the core material 502. The first layer of the core material 502 may be placed over the row of the first support material 402, covering the voids at the intersection filled by the roll of fibre reinforced material 404. Further, the setup 200, at this stage, may again be subjected to an intermediate de-bulking through vacuum to remove any air at the mating interfaces between the first layer of a core material 502 and the row of the first support material 402.

[54] Figure 6 illustrates a schematic front view of the setup 200 depicting a row of a second support material 602 placed on the first layer of the core material 502, in accordance with an embodiment of the present disclosure.

[55] In an embodiment, each second support material 602 may have a second predefined shape. The second predefined shape may also be configured based on the structure of the core 104. In an embodiment, the second predefined shape may be different from the first predefined shape. As shown, the row of the second support material 602 may be placed on the first layer of the core material 502. Further, each second support material 602 may include a layer of the release agent (not shown) applied onto all surfaces of the second support material 602 prior to placing on the first layer of the core material 502. The layer of the release agent may facilitate easy removal of each second support material 602 from the co-cured stiffened panels 100, once fabricated.

[56] Figure 7 illustrates a schematic front view of the setup 200 depicting the roll of fibre reinforced material 404 placed at an intersection of each second support material 602 and the first layer of the core material 502, in accordance with an embodiment of the present disclosure.

[57] As shown, the roll of fibre reinforced material 404 may be placed at the intersection of each second support material 602 and the first layer of the core material 502. In an embodiment, the roll of the fibre reinforced material 404 may run along a width of the first layer of the core material 502, thereby ensuring that the fibre continuity of the roll of the fibre reinforced material 404 is maintained. In an embodiment, the second support material 602 may include a curved profile at the intersection, forming voids at the intersection. Further, the roll of the fibre reinforced material 404 may be placed at the intersection to fill the voids formed due to the curved profile of the second support material 602 at the intersection.

[58] Figure 8 illustrates a schematic front view of the setup 200 depicting a second layer of the core material 802 placed on the row of the second support material 602, in accordance with an embodiment of the present disclosure.

[59] In an embodiment, the plurality of layers of the core 104 may include the second layer of the core material 802. In an embodiment, the second layer of a core material 802 may be placed over the row of the second support material 602, covering the voids at the intersection filled by the roll of fibre reinforced material 404. Further, the setup 200, at this stage, may again be subjected to an intermediate de-bulking through vacuum to remove any air at the mating interfaces between the second layer of the core material 802 and the row of the second support material 602.

[60] Figure 9 illustrates a schematic front view of the setup 200 depicting a row of a third support material 902 placed on the second layer of the core material 802, in accordance with an embodiment of the present disclosure.

[61] In an embodiment, each third support material 902 may have a third predefined shape. The third predefined shape may be configured based on the structure of the core 104. In an embodiment, the third predefined shape may be different from the second predefined shape. In an embodiment, the first predefined shape of the first support material 402 and the third predefined shape of the third support material 902 may be the same. Further, the third predefined shape of the third support material 902 may be the inverse of the first predefined shape of the first support material 402.

[62] As shown, the row of the third support material 902 may be placed on the second layer of the core material 802. Further, each third support material 902 may include a layer of the release agent applied onto all surfaces of the third support material 902 prior to placing over the second layer of the core material 802. The layer of the release agent may facilitate easy removal of each third support material 902 from the co-cured stiffened panels 100, once fabricated.

[63] In an embodiment, a roll of the fibre reinforced material 404 may be placed at an intersection of each third support material 902 and the second layer of the core material 802. Further, a length of the roll of the fibre reinforced material 404 may run along a width of the second layer of the core material 802, thereby ensuring that the fibre continuity of the roll of the fibre reinforced material 404 is maintained. In an embodiment, the third support material 902 may include a curved profile at the intersection, forming voids at the intersection. Further, the roll of the fibre reinforced material 404 may be placed at the intersection to fill the voids formed due to the curved profile of the third support material 902 at the intersection.

[64] In an embodiment, the row of the first support material 402, the first layer of the core material 502, the row of the second support material 602, the second layer of the core material 802, and the row of the third support material 902 may set the core 104 of the stiffened panel 100 for fabrication.

[65] Figure 10 illustrates a schematic front view of the setup 200 depicting the second layer of the skin material 106 placed on the set core 104, in accordance with an embodiment of the present disclosure.

[66] As shown, the second layer of the skin material 106 may be placed over the set core 104. In an embodiment, the second layer of the skin material 106 may be one of a carbon fibre reinforced material, a glass fibre reinforced material, or an aramid fibre reinforced material. Further, the setup 200, at this stage, may again be subjected to an intermediate de-bulking through vacuum to remove any air at the mating interfaces between the second layer of the skin material 106 and the set core 104.

[67] Further, the setup 200, at this stage, may be bagged for performing the co-curing operation to the first layer of the skin material 102, the set core 104 and the second layer of the skin material 106. Further, the operation of co-curing may be performed by applying pressure under vacuum to the first layer of the skin material 102, the set core 104 and the second layer of the skin material 106 to bond together in a single stage for fabrication. In a non-limiting example, the operation of co-curing may be performed by applying a pressure of about 4 bar under vacuum. In another non-limiting example, any other amount of pressure may be applied under vacuum based on the type of material of the first layer of the skin material 102, the set core 104, and the second layer of the skin material 106, without departing from the scope of the present disclosure. Further, the setup 200 may be unbagged upon successful performance of the co-curing operation.

[68] Figure 11 illustrates a schematic front view of the setup 200 depicting the co-cured fabricated stiffened panel 100, in accordance with an embodiment of the present disclosure. Figure 12 illustrates an enlarged part view of the co-cured fabricated stiffened panel 100 depicting a curved fillet 1102 at each intersection of the co-cured fabricated stiffened panel 100, in accordance with an embodiment of the present disclosure. Figures 11 and 12 are described in conjunction hereinafter for ease of explanation.

[69] In an embodiment, each support material 402, 602, 902 may be removed from the first row, second row, and the third row post performing the co-curing operation.

[70] As shown in Figure 11, the co-cured fabricated stiffened panel 100 may include an inbuilt curved fillet 1102 at each intersection where the roll of the fibre reinforced material 404 had been placed. Further, the placing of the roll of the fibre reinforced material 404 at the intersection forms the inbuilt curved fillet 1102 of uniform width. In an embodiment, the inbuilt curved fillet 1102 at each intersection may be a result of the conformity of the fibre reinforced material 404 to the curved profile of each support material 402, 602, 902. An enhanced view of a section 1102 of Figure 11 is shown in Figure 12, depicting the continuity of the fabricated stiffened panel 100, running in a continuous manner, between the co-cured first and second layer of the core material 502, 802, and the roll of the fibre reinforced material 404 placed at the intersection. Accordingly, the formation of the inbuilt corner fillets 1102 at the intersection may enhance the strength of the fabricated stiffened panel 100 and prevent stress concentrations. Further, the formation of the inbuilt corner fillets 1102 may facilitate efficient transfer of loads across the structure, enhancing the overall stiffness and fatigue resistance, and making the fabricated stiffened panel 100 resistant to local buckling or fracture during service.

[71] Figure 13 illustrates a schematic front view depicting unidirectional fibre continuity of the core 104 of the co-cured fabricated stiffened panel 100, in accordance with an embodiment of the present disclosure.

[72] As shown, the core 104 of the co-cured fabricated stiffened panel 100 of the present disclosure may achieve the unidirectional fibre continuity in all plane directions. In particular, the unidirectional fibre continuity in all plane directions may be achieved due to the core 104 being set up in layers 502, 802 between the first layer of the skin material 102, and the second layer of the skin material 106, followed by the co-curing operation to bond together in a single stage for fabrication, thereby preventing any discontinuity there between.

[73] Accordingly, a continuous load path may be achieved throughout the co-cured fabricated stiffened panel 100, thereby enhancing inter-laminar strength of the co-cured fabricated stiffened panel 100, when compared to the conventional stiffened panels held together merely by the tensile strength of the adhesion between the sandwiched core joined using adhesives. Further, performing of the co-curing operation of applying pressure under vacuum to bond together the first layer of the skin material 102 and the second layer of the skin material 106 with the core 104, integrates each of the first layer of the skin material 102, the core 104, and the second layer of the skin material 106 at the mating interface. Therefore, the co-cured fabricated stiffened panel 100 of the present disclosure enhances the overall load-bearing capacity when compared to the conventional stiffened panels, and prevents debonding of the fabricated stiffened panel 100 during mid-operation, especially under dynamic loading conditions. Accordingly, premature failure of the fabricated stiffened panel 100 under mechanical loading may also be prevented.

[74] In one example, the minimum inter-laminar shear strength of the co-cured fabricated stiffened panel 100 of the present disclosure may be about 31.3 MPa, as compared to the tensile strength of the adhesion of the conventional stiffened panels of about 4MPa-7MPa.

[75] Further, the fibre reinforced material 404 placed at the respective intersection may run along a width of the stiffened panel 100, thereby ensuring that the fibre continuity of the roll of the fibre reinforced material 404 may be maintained when the co-curing operation is performed on the stiffened panel 100 for fabrication. Accordingly, a continuous load path may be achieved throughout the co-cured fabricated stiffened panel 100, enhancing the strength and preventing the stress concentrations of the co-cured fabricated stiffened panel 100.

[76] Figure 14 illustrates a schematic front view of one or more shape structure arrangements of the core 104 for the co-cured fabricated stiffened panel 100, in accordance with an embodiment of the present disclosure.

[77] In an embodiment, the core 104 of the co-cured fabricated stiffened panel 100 may include one or more arrangements, within the scope of the present disclosure. Referring to (A), the core 104 may be fabricated to have an arc shaped structure. Accordingly, each support material 402, 602, 902 may be designed to have a respective predefined shape to facilitate the fabrication of the stiffened panel 100 having the core 104 of the arc shaped structure.

[78] Referring to (B), the core 104 may be fabricated to have a sinusoidal shaped structure. Accordingly, each support material 402, 602, 902 may be designed to have a respective predefined shape to facilitate the fabrication of the stiffened panel 100 having the core 104 of the sinusoidal shaped structure.

[79] Referring to (C), the core 104 may be fabricated to have a rectangular shaped structure. Accordingly, each support material 402, 602, 902 may be designed to have a respective predefined shape to facilitate the fabrication of the stiffened panel 100 having the core 104 of the rectangular shaped structure.

[80] Referring to (D), the core 104 may be fabricated to have a trapezoidal shaped structure. Accordingly, each support material 402, 602, 902 may be designed to have a respective predefined shape to facilitate the fabrication of the stiffened panel 100 having the core 104 of the trapezoidal shaped structure.

[81] Referring to (E), the core 104 may be fabricated to have a triangular shaped structure. Accordingly, each support material 402, 602, 902 may be designed to have a respective predefined shape to facilitate the fabrication of the stiffened panel 100 having the core 104 of the triangular shaped structure.

[82] In an alternative embodiment, the core 104 of the fabricated stiffened panel 100 may be any other shaped structure without departing from the scope of the present disclosure.

[83] Figure 15 illustrates a flowchart depicting an exemplary method 1500 of fabricating stiffened panels 100, in accordance with an embodiment of the present disclosure. The method 1500 may be performed over the setup 200, the details of which have been explained in conjunction with Figures 2 to 11, and the same are not repeated here for the sake of brevity.

[84] At step 1502, the method 1500 may include placing the layer of non-stick thermal-resistant material on the surface plate 202. At step 1504, the method 1500 may include placing the first layer of the skin material 102 over the layer of the non-stick thermal-resistant material. At step 1506, the method 1500 may include setting the core 104 over the first layer of the skin material 102. At step 1508, the method 1500 may include placing the second layer of the skin material 106 over the set core 104. At step 1510, the method 1500 may include performing the co-curing operation by applying pressure under vacuum on the first layer of the skin material 102, the set core 104 and the second layer of the skin material 106 to bond together.

[85] In an aspect of the present disclosure, the method 1500 for setting the core over the first layer of the skin material 102 at step 1506 may further include placing the row of the first support material 402 having a first predefined shape on the first layer of the skin material 102. The method 1500 may further include placing the roll of the fibre reinforced material 404 at the intersection of each first support material 402 and the first layer of the skin material 102. The method 1500 may further include placing the first layer of the core material 502 over the row of the first support material 402. The method 1500 may further include placing the row of the second support material 602 having the second predefined shape on the first layer of the core material 502. The method 1500 may further include placing the roll of the fibre reinforced material 404 at the intersection of each second support material 602 and the first layer of the core material 502. The method 1500 may further include placing the second layer of the core material 802 over the row of the second support material 602. The method 1500 may further include placing the row of the third support material 902 having the third predefined shape on the second layer of the core material 802. The method 1500 may further include placing the roll of the fibre reinforced material 404 at the intersection of each third support material 902 and the second layer of the core material 802.

[86] In an aspect of the present disclosure, the method 1500 may further include removing, post performing co-curing operation, each support material 402, 602, 902 from the first row, second row, and the third row.

[87] In an embodiment, one or more tests may be performed on the fabricated stiffened panels 100, such as a compression test, an edge compression test, and a cantilever bend test, to evaluate one or more properties of the fabricated stiffened panels 100.

[88] In an example, the fabricated stiffened panels 100 of the present disclosure may be tested for failure by performing the compression test for the core 104 having square, trapezoid and hexagonal shaped structures, respectively. The compression test may be performed in an actual apparatus and may also be predicted through Finite Element (FE) Analysis. The load may be applied in kilo-Newtons (kN). The compression test results are provided in Table 1 below.Table 1

[89] In an example, the fabricated stiffened panels 100 of the present disclosure may be tested for failure by performing the edge compression test for the core 104 having square, trapezoid and hexagonal shaped structures, respectively. The edge compression test may be performed in an actual apparatus and may also be predicted through Finite Element (FE) Analysis. Further, strain experienced at an edge of the core 104 and at an edge of the first and the second layer of the skin 102, 106 may individually be evaluated. The load may be applied in kilo-Newtons (kN). The edge compression test results for the core 104, having the square shaped structure, are provided in Table 2 below.Table 2

[90] The edge compression test results for the core 104, having the trapezoid shaped structure, are provided in Table 3 below.Table 3

[91] The edge compression test results for the core 104, having the hexagonal shaped structure, are provided in Table 4 below.Table 4

[92] The present disclosure may further include several advantages over the existing techniques. For example, the method 1500 of fabricating the stiffened panel 100 using the co-curing operation to bond the first layer of the skin material 102, the core 104, and the second layer of the skin material 106 together in the single stage for fabrication may facilitate achieving fibre continuity in all plane directions, i.e., in the entire length and width direction of stiffened panel 100. This may facilitate in efficient transfer of loads across the stiffened panel 100.

[93] Further, the method 1500 of fabricating the stiffened panel 100 using the co-curing operation applied together in the single stage for fabrication may prevent need for application of adhesive between the interface of mating surfaces. Accordingly, the fabricated stiffened panel 100 may effectively prevent failure due to debonding of the layers 102, 106 and the core 104 under dynamic loading conditions, thereby preventing structural failure during mid-operation and preventing potential catastrophic consequences associated with debonding of the stiffened panel 100. Furthermore, the fabricated stiffened panel 100 may have increased overall stiffness and fatigue resistance, facilitating its application in numerous load bearing applications.

[94] Furthermore, the method 1500 of fabricating the stiffened panels 100 of the present disclosure by placing the roll of the fibre reinforced material 404 at the intersection may result in the formation of the inbuilt corner fillets 1102 at the intersection post co-curing operation. The formation of the inbuilt corner fillets 1102 may enhance the strength of the fabricated stiffened panel 100 and prevent stress concentrations. Further, the formation of the inbuilt corner fillets 1102 may facilitate efficient transfer of loads across the structure, enhancing the overall stiffness and fatigue resistance, and making the fabricated stiffened panel 100 resistant to buckling or fracture during service.

[95] Further, the method 1500 of fabricating the stiffened panels 100 of the present disclosure may facilitate weight saving of about 50% with respect to the conventional stiffened panels fabricated using a metallic core, while not compromising the load bearing strength.

[96] Further, the method 1500 of fabricating the stiffened panels 100 of the present disclosure may be used in the application areas where the fabrication of stiffened panels with a low coefficient of thermal expansion is required. Further, the stiffened panels 100 may be utilised in applications requiring concealed cable routing due to Aerodynamic or any other functional requirements.

[97] Furthermore, the method 1500 of fabricating the stiffened panels 100 of the present disclosure may effectively reduce the lead time in comparison to the conventional techniques used for fabricating metallic stiffened panels.

[98] While specific language has been used to describe the present disclosure, any limitations arising on account thereto, are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein. The drawings and the foregoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment.

Claims

1. A method (1500) of fabricating stiffened panels (100), the method (1500) comprising: placing (1502) a layer of non-stick thermal-resistant material on a surface plate (202); placing (1504) a first layer of a skin material (102) over the layer of the non-stick thermal-resistant material; setting (1506) a core (104) over the first layer of the skin material (102); placing (1508) a second layer of a skin material (106) over the set core (104); and performing (1510) a co-curing operation by applying pressure under vacuum on the first layer of the skin material (102), the set core and the second layer of the skin material (106) to bond together.

2. The method (1500) as claimed in claim 1, wherein for setting (1506) the core (104) over the first layer of the skin material (102), the method (1500) comprises: placing a row of a first support material (402), having a first predefined shape, on the first layer of the skin material (102); placing a roll of a fibre reinforced material (404) at an intersection of each first support material (402) and the first layer of the skin material (102); placing a first layer of a core material (502) over the row of the first support material (402); placing a row of a second support material (602), having a second predefined shape, on the first layer of the core material (502); placing the roll of the fibre reinforced material (404) at an intersection of each second support material (602) and the first layer of the core material (502); placing a second layer of the core material (802) over the row of the second support material (602); placing a row of a third support material (902), having a third predefined shape, on the second layer of the core material (802); and placing the roll of the fibre reinforced material (404) at an intersection of each third support material (902) and the second layer of the core material (802).

3. The method (1500) as claimed in claim 2, wherein the first predefined shape of the first support material (402) and the third predefined shape of the third support material (902) are the same, and the third predefined shape of the third support material (902) is the inverse of the first predefined shape of the first support material (402).

4. The method (1500) as claimed in claim 2, wherein the second predefined shape, is different from the first and third predefined shapes.

5. The method (1500) as claimed in claim 2, wherein placing the roll of fibre reinforced material (404) at the intersection comprises filling voids formed due to a curved profile of the first support material (402), the second support material (602) and the third support material (902) at the respective intersection.

6. The method (1500) as claimed in claim 5, wherein the curved profile of the first support material (402), the second support material (602) and the third support material (902) forms inbuilt corner fillets (1102) at the respective intersection of the fabricated stiffened panels (100).

7. The method (1500) as claimed in claim 2, wherein the roll of fibre reinforced material (404) is formed in one of a unidirectional arrangement or a bi-directional arrangement.

8. The method (1500) as claimed in claim 1, wherein the first layer of the skin material (102) and the second layer of the skin material (106) is one of a carbon fibre reinforced material, a glass fibre reinforced material, or an aramid fibre reinforced material.

9. The method (1500) as claimed in claim 1, wherein the set core (104) includes a unidirectional fibre continuity in all plane directions.

10. The method (1500) as claimed in claim 1, wherein the set core (104) is of a material comprising one of a carbon fibre reinforced material, a glass fibre reinforced material, or an aramid fibre reinforced material.

11. The method (1500) as claimed in claim 1, comprising removing, post performing the co-curing operation, each support material (402, 602, 902) from the first row, second row, and the third row.

12. The method (1500) as claimed in claim 1, wherein the surface plate (202) is one of a flat surface plate and a curved surface plate.