Composite structure and forming method thereof

Abstract

The present application discloses a composite structure and a method for forming the same. A composite structure includes a multilayer laminate having a plurality of material layers and at least one crack barrier layer extending within the plurality of material layers. The multilayer laminate is folded to define a first web region and a second web region in a face-to-face relationship, and a folded tip region defined between the first web region and the second web region. The at least one crack barrier layer is configured to limit crack propagation through the plurality of material layers in the folded tip region.

Description

Technical Field

[0001] The field relates generally to composite structures and, more particularly, to stamped and formed blade stringer composite structures having improved impact and crack propagation resistance. Background Art

[0002] The manufacture of multilayer laminated structures generally includes combining layers of metallic (e.g., aluminum, titanium, or corrosion resistant steel (CRES)) and / or non-metallic (e.g., carbon fiber, boron, or glass fiber) reinforcement materials with a matrix material to form a rigid structure. The reinforcement materials strengthen and reinforce the laminated structure, and the matrix material supports the reinforcement materials after the curing process. The multilayer laminated structures generally have a high strength-to-weight ratio and can be formed into a variety of shapes and sizes. At least some known aircraft components are manufactured from multilayer laminated structures of non-metallic composite materials, such as carbon fiber reinforced polymers (CFRP). Composite materials are used in combination with metallic materials, such as aluminum, titanium, and / or steel, to reduce the overall weight of the aircraft. Reducing the overall weight generally helps to increase the fuel efficiency of the aircraft. However, conventional multilayer laminated structures manufactured from CFRP may be susceptible to damage, such as the formation of microcracks and delamination of the structure during its service and / or manufacturing. Known damage to these structures may be small and difficult to detect during regular maintenance.

[0003] This section is intended to introduce the reader to various aspects of the art that may be relevant to the various aspects of the disclosure described and / or claimed below. This discussion is considered helpful in providing the reader with background information to better understand the various aspects of the disclosure. Thus, it should be understood that these statements should be read from this perspective, rather than as an admission of the prior art. Summary of the invention

[0004] In one aspect, a composite structure includes a multilayer laminate having a plurality of material layers and at least one crack barrier layer extending within the plurality of material layers. The multilayer laminate is folded to define a first web region and a second web region in a face-to-face relationship, and a fold tip region defined between the first web region and the second web region. The at least one crack barrier layer is configured to limit crack propagation through the plurality of material layers in the fold tip region.

[0005] In another aspect, a stringer includes a first web region, a second web region in face-to-face relationship with the first web region, and a fold tip region defined between the first web region and the second web region. A base extends from the web. The base includes a first base region extending from the first web region and a second base region extending from the second web region. The web and the base are formed from a multilayer laminate including a plurality of material layers and at least one crack barrier layer extending within the plurality of material layers. The at least one crack barrier layer is configured to limit crack propagation through the plurality of material layers in the fold tip region.

[0006] In yet another aspect, a method of forming a composite structure includes forming a multilayer laminate including a plurality of material layers and at least one crack barrier layer extending within the plurality of material layers, and folding the multilayer laminate to define a first web region and a second web region in a face-to-face relationship, and a folded tip region defined between the first web region and the second web region. The method also includes curing the multilayer laminate, wherein the at least one crack barrier layer is configured to limit crack propagation through the plurality of material layers in the folded tip region.

[0007] Various improvements exist with respect to the features noted in the above aspects of the present disclosure. Further features may also be incorporated into the above aspects of the present disclosure. These improvements and additional features may exist alone or in any combination. For example, the various features discussed below with respect to any exemplary embodiment of the present disclosure may be incorporated into any of the above aspects of the present disclosure alone or in any combination. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a schematic diagram of an exemplary composite structure.

[0009] Figure 2 yes Figure 1 An enlarged view of the folded top region of the composite structure is shown in FIG.

[0010] Figure 3 Shown is the Figure 1 A series of process steps for forming a composite structure are shown in FIG.

[0011] Corresponding reference characters indicate corresponding parts throughout the drawings. DETAILED DESCRIPTION

[0012] Embodiments described herein relate to a stamped blade stringer composite structure with increased impact and crack propagation resistance. The composite structure can be used as a stringer in an aircraft structure. The composite structure is formed by a multilayer laminated structure that has been folded to define a base, a web, and a folded tip region in the web. At least some known composite material manufacturers cut off the folded tip region from the web to reduce the risk of cracks or delamination initiated in the folded tip region extending to the rest of the composite structure. In this exemplary embodiment, the multilayer laminated structure is formed by a plurality of material layers and a crack barrier layer extending within the plurality of material layers. The crack barrier layer is positioned to help limit crack propagation through the plurality of layers in the folded tip region. In addition, in some embodiments, the detection layer extends across the folded tip region to help provide impact damage detection. The resulting composite structure has increased strength, more robust lateral impact tip resistance, and barely visible impact damage detection capabilities.

[0013] Figure 1 1 is a schematic diagram of an exemplary composite structure 100. In the exemplary embodiment, the composite structure 100 includes a web 102 and a base 104 extending perpendicularly relative to the web 102. Alternatively, the web 102 is oriented obliquely relative to the base 104. The web 102 includes a first web region 106, a second web region 108 in face-to-face relationship with the first web region 106, and a folded tip region 110 defined between the first web region 106 and the second web region 108. The base 104 includes a first base region 112 extending from the first web region 106 and a second base region 114 extending from the second web region 108. The first base region 112 includes a first tapered end 116, and the second base region 114 includes a second tapered end 118. For example, in some embodiments, the composite structure 100 is coupled to a skin panel 120 or a separate base charge (not shown) of an aircraft (not shown). The composite structure 100 helps support the skin panel 120 and increases the stiffness of the skin panel.

[0014] Figure 2 1 is an enlarged schematic diagram of folded tip region 110. In the exemplary embodiment, composite structure 100 includes a multilayer laminate 122 having a plurality of material layers 124 and at least one crack barrier layer 126 extending within the plurality of material layers 124. For example, multilayer laminate 122 has a first surface 128 and an opposing second surface 130. As will be described in more detail below, multilayer laminate 122 is folded upon itself to form composite structure 100. When folded, first surface 128 is exposed to the outside environment, and second surfaces 130 in first web region 106 and second web region 108 are in face-to-face contact to define a central core 132.

[0015] At least one crack barrier layer 126 is positioned between the outer surface 128 and the central core 132. For example, the plurality of layers 124 and the crack barrier layer 126 are aligned contiguously in at least one dimension of the composite structure 100. More specifically, in one embodiment, the layers 124 and the crack barrier layer 126 extend from the first tapered end 116 to the second tapered end 118 such that the at least one crack barrier layer 126 extends throughout the fold tip region 110. Alternatively, the crack barrier layer 126 has a shorter length and is limited to extending within certain areas of the composite structure 100, such as extending only across the fold tip region 110. Cracks and / or delaminations may initiate within the central core 132 and propagate through the multilayer laminate 122. Thus, the at least one crack barrier layer 126 is positioned to help limit crack propagation through the plurality of layers 124 in the fold tip region 110.

[0016] In the exemplary embodiment, at least one crack barrier layer 126 includes a first crack barrier layer 134 and a second crack barrier layer 136 spaced apart from each other within the multi-layer laminate 122, the first crack barrier layer 134 being positioned closer to the central core 132 than the second crack barrier layer 136, and the second crack barrier layer 136 being positioned closer to the outer surface 128 than the first crack barrier layer 134. In addition, the first crack barrier layer 134 is positioned closer to the central core 132 than the outer surface 128. Thus, the first crack barrier layer 134 is positioned at a predetermined distance D from the central core 132. The first crack barrier layer 134 limits the propagation of a crack that may have been initiated at the central core 132 beyond the predetermined distance D. In one embodiment, the laying position of the first crack barrier layer 134 within the multi-layer laminate 122 is determined according to a threshold thickness of the fold tip region 110. Thus, a crack (not shown) in the multi-layer laminate 122 is limited from propagating to a length greater than the threshold thickness. The threshold thickness may be about 50%, about 40%, or about 25% of the total thickness T of the fold tip region 110. In addition, the second crack barrier layer 136 is positioned at a distance from the first crack barrier layer 124 to provide redundant crack propagation protection in the event that crack propagation extends beyond the first crack barrier layer 134.

[0017] Material layer 124 and crack barrier layer 126 may be made of any material that enables the composite structure to function as described herein. In the exemplary embodiment, layer 124 has a first structural configuration and crack barrier layer 126 has a second structural configuration that is different from the first structural configuration. Therefore, positioning crack barrier layer 126 made of a different material than the rest of layer 124 in multi-layer laminate 122 facilitates forming a discontinuity in multi-layer laminate 122, which facilitates reducing the propagation of crack growth therein.

[0018] In addition, the layers 124 and crack barriers 126 for inclusion in the multilayer laminate are selected based on resin compatibility and thermal expansion considerations. For example, the layers 124 and crack barriers 126 may be pre-impregnated with a resin selected to achieve sufficient compatibility to form the multilayer laminate 122. The layers 124 and crack barriers 126 may be impregnated with the same resin or different resins. In addition, the layers 124 and crack barriers 126 are selected so that the materials of the layers 124 and crack barriers 126 have a difference in thermal expansion coefficient that is less than a predetermined threshold. The predetermined threshold may be 25%, 20%, or 10% based on the overall difference in thermal expansion coefficient values ​​of the materials of the layers 124 and crack barriers 126. Thus, the layers 124 and crack barriers 126 are selected to facilitate the formation of a structurally sound multilayer laminate 122 having a reduced likelihood of delamination occurring therein. In one embodiment, the layers 124 are made of a pre-impregnated unidirectional carbon fiber material, and the crack barriers 126 are made of a pre-impregnated bidirectional carbon fiber material. The bi-directional carbon fiber material may be a woven sheet of carbon fiber having fibers oriented in any direction that enables the crack barrier layer 126 to function as described herein. For example, the woven sheet may have a 0 / 90 or 45 / 45 degree fiber orientation.

[0019] In the exemplary embodiment, the multilayer laminate 122 also includes a detection layer 138 that extends across the folded tip region 110 and across at least a portion of the first web region 106 and the second web region 108. The detection layer 138 can be made of any material that enables the composite structure 100 to function as described herein. In one embodiment, the detection layer 138 is made of a fiberglass reinforced plastic material, also commonly referred to as fiberglass. The composition of the detection layer 138 is selected to help visualize impact damage caused to the composite structure 100. For example, fiberglass is generally more brittle than CFRP materials, such that the same force applied to the fiberglass or CFRP materials will be more easily seen on the fiberglass and more easily detected.

[0020] The detection layer 138 also helps protect the folded top region 110 from impact damage. Figure 1, the folded tip region 110 may be susceptible to different types of impacts, such as a first impact 140, a second impact 142, and a third impact 144. The first impact 140 is generally axially aligned with the web 102, the second impact 142 is oriented at approximately 45 degrees relative to the web 102, and the third impact 144 is oriented approximately 10 degrees relative to the web 102 and generally transverse to the web 102. Without the detection layer 138, the composite structure 100 with the folded tip region 110 is generally capable of withstanding non-critical impact damage from the third impact 144 having a force less than a predetermined threshold. The addition of the detection layer 138 enables the composite structure 138 to withstand non-critical impact damage from the first impact 140 and the second impact 142 having a force less than a predetermined threshold. Thus, the folded tip region 110 provides a robust shear resistance to help resist lateral impact damage caused by the third impact 144, and the detection layer 138 increases the robustness of the folded tip region 110 to help resist damage caused by the first impact 140 or the second impact 142. The folded tip region 110 also resists interlaminar buckling.

[0021] Figure 3 A method for making the composite structure 100 ( Figure 1 14 and 15. The exemplary embodiment of the present invention is a series of process steps for forming the composite structure 100 by stamping and forming the composite structure 100. In the exemplary embodiment, a stamping and forming device 146 is used to form the composite structure 100. The stamping and forming device 146 includes a stamping tool 148 and a die 150. The die 150 includes a pair of punching modules 152 spaced apart from each other at a certain distance to define a cavity 154 therebetween. The stamping tool 148 can be translated relative to the die 150, and the punching modules 152 can be translated relative to each other to adjust the size of the cavity 154.

[0022] In this exemplary embodiment, the punch tool 148 is initially positioned at a distance from the die 150. The first process step 156 includes forming the multilayer laminate 122 and positioning the multilayer laminate 122 on the die 150. The multilayer laminate 122 is positioned to extend across the cavity 154. The second process step 158 includes translating the punch tool 148 toward the die 150 to help force the multilayer laminate 122 into the cavity 154 and begin folding the multilayer laminate 122 to define the folded tip region 110. Once the punch tool 148 is fully inserted into the cavity 154, the punch tool 148 is removed therefrom in a third process step 160 so that only the multilayer laminate 122 remains within the cavity 154. The fourth process step 162 includes translating the die blocks 152 toward each other to help further fold the multilayer laminate 122 so that the first web region 106 and the second web region 108 are in a face-to-face relationship. The multilayer laminate 122 may then be removed from the die 150 and cured to form the composite structure 100 , or cured in place within the die 150 .

[0023] Exemplary embodiments of composite structures that are folded to define a fold tip region having a crack barrier extending therein are described in detail above. Aspects of the composite structures are not limited to the specific embodiments described herein, but rather, components of the composite structures may be used independently and separately from other components described herein. For example, aspects of the composite structures may include any composite structure in which it is desired to inhibit the propagation of crack extensions therein.

[0024] When introducing elements of the present disclosure or embodiments thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," "consisting of," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of terms referring to specific orientations (e.g., "top," "bottom," "side," etc.) is for convenience of description and does not require any specific orientation of the items described.

[0025] As various changes could be made in the above constructions and methods without departing from the scope of the present disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

1. A composite structure (100), comprising: A multi-layer laminate (122), the multi-layer laminate comprising: a plurality of material layers (124); and at least one crack barrier layer (126) extending within the plurality of material layers (124), wherein the multilayer laminate (122) is folded to define a first web region (106) and a second web region (108) in a face-to-face relationship, and a folded tip region (110) defined between the first web region (106) and the second web region (108), wherein the at least one crack barrier layer (126) is configured to extend across the folded tip region to limit crack propagation between the plurality of material layers (124) in the folded tip region (110), wherein the plurality of material layers (124) have a first structural configuration, and the at least one crack barrier layer (126) has a second structural configuration different from the first structural configuration, and Wherein, the at least one crack barrier layer (126) is made of bidirectional carbon fiber material.

2. The composite structure (100) according to claim 1, wherein: The multilayer laminate (122) is folded to further define a first base area (112), the first web area (106), the folded top area (110), the second web area (108) and the second base area (114) in sequence, and the multilayer laminate (122) is folded so that the first web area (106) and the second web area (108) are oriented vertically or obliquely relative to the first base area (112) and the second base area (114).

3. The composite structure (100) according to claim 1, wherein: The plurality of material layers (124) are made of unidirectional carbon fiber material.

4. The composite structure (100) according to claim 1, wherein: The multi-layer laminate (122) further includes a detection layer (138) extending across the folded top region (110).

5. The composite structure (100) according to claim 1, wherein: The at least one crack barrier layer (126) includes a first crack barrier layer (134) and a second crack barrier layer (136) spaced apart from each other within the multi-layer laminate (122).

6. The composite structure (100) according to claim 1, wherein: The plurality of material layers (124) and the at least one crack barrier layer (126) are contiguously aligned in at least one dimension.

7. A beam, comprising: A web (102), the web comprising: first web region (106); a second web region (108) in face-to-face relationship with said first web region (106); and a folded top region (110) defined between the first web region (106) and the second web region (108); and A base (104) extending from the web (102), and the base (104) includes: a first base region (112) extending from the first web region (106); and a second base region (114) extending from the second web region (108), wherein the web (102) and the base (104) are formed of a multilayer laminate (122) including a plurality of material layers (124) and at least one crack barrier layer (126) extending within the plurality of material layers (124), the at least one crack barrier layer (126) being configured to extend across the fold tip region to limit crack propagation between the plurality of material layers (124) in the fold tip region (110), wherein the plurality of material layers (124) have a first structural configuration, and the at least one crack barrier layer (126) has a second structural configuration different from the first structural configuration, and Wherein, the at least one crack barrier layer (126) is made of bidirectional carbon fiber material.

8. The beam according to claim 7, wherein: The plurality of material layers (124) are made of unidirectional carbon fiber material.

9. The beam according to claim 7, wherein: The multi-layer laminate (122) further includes a detection layer (138) extending across the folded top region (110).

10. The beam according to claim 7, wherein: The at least one crack barrier layer (126) includes a first crack barrier layer (134) and a second crack barrier layer (136) spaced apart from each other within the multi-layer laminate (122).

11. The beam according to claim 7, wherein: The plurality of material layers (124) and the at least one crack barrier layer (126) are contiguously aligned in at least one dimension.

12. A method of forming a composite structure (100), the method comprising: forming a multilayer laminate (122) comprising a plurality of material layers (124) and at least one crack barrier layer (126) extending within the plurality of material layers (124); folding the multilayer laminate (122) to define a first web region (106) and a second web region (108) in a face-to-face relationship, and a folded tip region (110) defined between the first web region (106) and the second web region (108); and curing the multilayer laminate (122), wherein the at least one crack barrier layer (126) is configured to extend across the fold tip region to limit crack propagation between the plurality of material layers (124) in the fold tip region (110), wherein forming the multilayer laminate (122) comprises forming the multilayer laminate (122) from the plurality of material layers (124) having a first structural configuration and the at least one crack barrier layer (126) having a second structural configuration different from the first structural configuration, and Wherein, molding the multi-layer laminate (122) includes forming the multi-layer laminate (122) by the plurality of material layers (124) made of unidirectional carbon fiber material and the at least one crack barrier layer (126) made of bidirectional carbon fiber material.

13. The method according to claim 12, wherein: Folding the multilayer laminate (122) includes folding the multilayer laminate (122) to further define a first base area (112), the first web area (106), the folded top area (110), the second web area (108) and the second base area (114) in sequence, and the multilayer laminate (122) is folded so that the first web area (106) and the second web area (108) are vertically oriented relative to the first base area (112) and the second base area (114).

14. The method according to claim 12, wherein: Forming the multi-layer laminate (122) includes positioning a detection layer (138) on the multi-layer laminate (122) to extend across the fold tip region (110) when the multi-layer laminate (122) is folded.

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