A process for making a dismountable and/or fixed traction-compression joint to be applied to composite materials

Abstract: A process for making a dismountable and/or fixed traction-compression coupling to be applied to composite materials, in which a basic laminate (1) of composite material is folded at least once to obtain at least one skirt (2) forming an angle close to 90° with the rest of the laminate; by using a transition radius between the skirt and the rest of the laminate, a set of distribution plates (5, 6) is applied over the basic laminate to stabilize the skirt and produce a uniform load distribution, making holes in each set of distribution skirt-plates and introducing traction bolts (4) with an initial pretension in said holes, hence obtaining the connection between the components to be joined. The invention is applicable to the aerodynamic structures of aircraft.

Description: FIELD OF THE INVENTION The object of the present invention is to develop the necessary theoretical concepts and their corresponding manufacturing processes to obtain a traction-compression type of joint between two structural components of which at least one is manufactured with composite materials. The joint is achieved by means of the application of a certain number of bolts under traction, initially mounting said bolts with a pretension by means of applying a tightening torque and having the double object of (1) transmitting the existing loads between the two structural components mentioned, and (2) being possible to assemble and dismantle these two components. BACKGROUND OF THE INVENTION Joints with bolts of the traction-compression type applied on metals have a broad application, both in the machine field as well as within a wide range of vehicles, clearly indicating their usefulness. In high performance composite materials, in which their degree of application and development is currently reduced due to their recent appearance in the art, this type of joints has never been treated directly and in depth. Nevertheless, examples of joints involving composite materials can be found in patent numbers US-A-5 496 002, US-A-4 228 976 and EP-A-0 732 262. Also, a reinforced composite structure and a method for manufacturing same are disclosed in US-A-4,219,980, wherein barbed quill fasteners are used for reinforcing and assembling the structure comprised of a composite panel and a composite web. The use of quill fasteners allows the structure to be formed while in a staged condition, whereby a co-curing and bonding of the components of the structure is obtained in a joined condition. Furthermore, due to the use of the quill fasteners and the location thereof in the structure, it is possible to minimize peel forces in the joint formed between the assembled components of the structure. Moreover, a joint of wooden components having a little thickness is disclosed in FR-A-863.511, wherein the components to be joined are assembled by using screws located transversally to the joint to be formed and wooden angle pieces interposed between said components and bonded to same. The screws pass through the angle pieces and engage nuts or tapped holes drilled in a bar mounted on the end of one of the components to be joined, thereby being obtained the desired joint. In recent years, the applicant has been working and developing structures in composite materials, whose joining has been made under shear. However, it has been considered necessary to have the possibility of applying the dismountable traction-compression type of joint and to fill this gap, the applicant has implemented a technological plan called L.S.S (Large Supporting Surfaces), in which one of its objectives is to develop the type of joint referred to in the present invention. FIELD OF APPLICATION OF THE INVENTION The present invention is applicable to one or both components of any type of structure which, having been manufactured with composite materials, has to be joined under load conditions of considerable traction, whilst, in turn, it is recommendable that they may be assembled and dismantled. These components may be one of the parts of the complex structures belonging to: Aircraft structures and controls (such as lining joints or fittings). Spacecraft joints. Sea and land vehicles. Industrial machinery and equipment. The manufacturing processes involving them include: Tape or tissue pre-impregnated laminates. RTM (Resin-Transfer-Molding). S/RFI (Stitched/Resin Film Infusion). Filament winding. Fiber siting. The materials used may be integrated by different resins and types of fiber, such as: Glass fiber. Carbon fiber. Kevlar. Boron fiber. SUMARY OF THE INVENTION The object of the invention is a process for making a dismountable and/or fixed traction-compression joint between structural components, which is intended to be applied to composite materials used in aircraft structures and controls (such as joints for linings or fittings), joints for spacecraft, sea and land vehicles and industrial machinery and equipment, said composite materials consisting of different resins and different types of fiber such as glass fiber, carbon fiber, boron fiber or Kevlar, the process comprising the steps of folding a basic laminate of composite material, forming at least one of said components, at least once to obtain at least one skirt forming an angle close to 90° with the rest of the laminate, with a transition radius between the skirt and the rest of the laminate; applying a set of distribution plates on the skirt of the basic laminate to stabilize said skirt and produce a uniform load distribution; making holes in both the skirt and distribution plates so that the holes of said skirt register with those of said distribution plates; and introducing traction bolts with a pretension in said holes and in corresponding holes of another component to be joined with said at least one component, thereby obtaining a joint between both components. The skirt or skirts obtained as indicated above can be applied against flat or curved surfaces of the component to be joined to the basic laminate. The load distribution plates can be metallic. Alternatively, the load distribution plates can be of composite material. According to the present invention, in the case of a single flat or curved basic laminate the skirt is folded towards one or other side of the laminate surface, or else the laminate is locally split into two parts which are then folded towards opposite sides of the laminate surface, thereby forming a kind of T. Conversely, in the case of a multiple basic laminate the skirt of each one of the laminates is folded towards one or other side of the surface thereof, or else at least one of said laminates is locally split into two parts which are folded towards opposite sides of the at least one laminate, thereby forming a kind of T, and then the skirts formed are superimposed to obtain a skirt which interactively groups all the laminates of the multiple basic laminate. Likewise, according to the invention, in the case of a multiple laminate ending in a single surface their skirts are folded together towards one or other side of the surface thereof, or else, upon splitting said multiple laminate locally into two parts, such parts are bent towards opposite sides of said surface forming a kind of T. The invention is particularly applicable to the case in which the components to be joined together are comprised of an aerodynamical surface lining-stringer assembly for aircraft structures wherein the laminates are folded to form the skirts. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be understood better by referring to the attached drawings where the essential characteristics of the process of the invention are illustrated, as well as the joint obtained by applying said process. The drawings show: Figure 1: a basic laminate approximately curved in a right angle, Figure 2: the curved laminate of Figure 1 provided with complementary load distribution devices, Figure 3: a basic laminate with a skirt folded towards both sides in a T-shape and with complementary load distribution devices, Figure 4: several laminates to be joined with multiple folded skirts, Figure 5: several laminates to be joined with multiple folded skirts, including a cut laminate, Figure 6: a laminate with multiple skirts folded in T, and Figures 7A, 7B and 7C: seen in front elevation, in side elevation and in plan showing the basic geometrical data of a laminate prepared according to the invention. DETAILED DESCRIPTION OF THE INVENTION The new joint system developed by the invention directed to composite materials is related to an interactive set of complementary theoretical concepts permitting the final object to be reached. The basic theoretical concepts in two specific areas are described below. A) Basic Laminate, Object of the Joint The basic laminate 1 of composite material which is the object of this joint, should be bent when reaching the joint zone or section, such that it remains beyond its plane or own surface with an angle close to 90° by means of a certain folding radius R, to create a skirt 2, folded from the laminate material, as may be seen in Figure 1. Said skirt 2, suitably folded, compacted and then cured, will form the basic core over which the traction-compression joint will be centered and later on provided with a series of holes 3, in which the corresponding bolts 4 will be introduced (see Figure 2). For skirt 2 to be effective, it should be suitably configured using the specific criteria mentioned in the following point and also forming part of the present invention. B) Complementary Devices The traction bolts 4, over which the own load of the joint is concentrated have a specific nature distinguishing them for their high level of concentration, in an opposite position to the load of laminate 1 of composite materials, which is uniform and distributed. Therefore, an intermediate element will be necessary which, like a bridge, satisfies the mission of making the bolts 4 compatible with laminate 1. For this purpose, some devices called distribution plates 5, 6 (See Figures 2 and 3) are applied on each side of the skirt 2. These distribution plates 5, 6 have a double basic purpose: To distribute the concentrated load of the bolts 4 as uniformly as possible over all the skirt 2, and To make a perfect adjustment and stabilization of skirt 2, especially in its critical area of the folding radius R. The distribution plates 5, 6 may be made of metal or the same composite material of the basic laminate 1. The adjustment tolerance between the distribution plates 5, 6 and the folded skirt 2, as well as the nature and characteristics of the traction bolts 4 has been taken into account in the development of the present invention. The forces acting over the basic laminate 1 are represented by the arrows appearing in Figures 1 to 3. Using the aforementioned basic theoretical concepts, different types of joints have been developed, which are shown below and are grouped in two generic areas according to their nature: Type A - With a single basic laminate situated on a simple surface. In this case, the skirt 2 may be folded to one or other side of the reference surface of the basic laminate 1, or partially to both sides, the basic laminate 1 being branched off in two partial skirts 2', 2'' forming a kind of T, as may be seen in Figure 3. Type B - With multiple basic laminates situated in different planes. In this type, two different technologies have been developed: Type B.1 Each one of the laminates 1, 1' is individually treated as was specified for type A and, then, their corresponding folded skirts 2, 2', 2", 2a, 2b are superimposed in a more or less complex manner, hence obtaining a skirt grouping, in an interactive manner, all the laminates 1, 1' which are the object of the joint, as may be seen in Figure 4. Type B.2 In this type, all or part of the laminates 1, 1' that may have a secondary nature, are cut in a suitable transition process until obtaining a single skirt capable of concentrating in itself the load of the rest. Once this situation has been reached, the single laminate obtained may have its skirt folded, by applying either of the Type A possibilities, as illustrated in Figures 5 and 6. Under the point of view of the theoretical definition, the previously studied basic concepts may be summarized by applying the following three phases: Phase 1: Fixing the basic conditioners configuring the object of the joint: Loads that should be transmitted. Geometric configuration. Technical characteristics that should be met. Phase 2: The object of this second phase is to determine some dimensionless parameters whose values define a geometric configuration of the joint, being necessary in this process to guarantee a reasonable level of compatibility and uniformity between values. In the development of the present invention, the applicant has worked intensely with a large number of tests which have allowed six dimensionless parameters to be defined, and by using them, to determine both the degree of influence of each one individually and the overall effect of all of them, always taking into account their compatibility and homogeneity. Referring to Figures 7A, 7B and 7C, the definition of these six dimensionless parameters is given below: (n/t) Relative distance from the bolt 4 to the basic laminate 1 (degree of eccentricity). (e/t) Relative thickness of the distribution plate 6 (degree of uniformity and rigidity). (R/t) Relative internal folding radius (maximum degree of possible micro-deformation). P = (W/D) Relative distance between bolts 4 (degree of uniformity). L (% 90°) Percentage of laminate 1 to zero degrees (degree of laminate effectiveness). (D/t) Relative diameter of the bolts 4 (degree of effectiveness of the own bolt effect). With these six parameters, some analytical expressions or individual charts have been determined which define their corresponding influence factor. The product of the six factors defines the overall factor, determining the specific capacity of the joint obtained. Phase 3 This phase comprises the calculation, the verification of resistance and the optimization of the configuration of phase 2 to determine the reliability of the joint obtained. In all the above, the essential characteristics of the invention have been described, although, as may be understood, it would be possible to make modifications of certain details of the joining process developed by the applicant. For this reason, it is intended that the scope of the invention is only limited by the contents of the following claims.

Claims: A process for making a dismountable and/or fixed traction-compression joint between structural components, which is intended to be applied to composite materials used in aircraft structures and controls (such as joints for linings or fittings), joints for spacecraft, sea and land vehicles and industrial machinery and equipment, said composite materials consisting of different resins and different types of fiber such as glass fiber, carbon fiber, boron fiber or Kevlar, characterized in that it comprises the steps of folding a basic laminate (1) of composite material, forming at least one of said components, at least once to obtain at least one skirt (2) forming an angle close to 90° with the rest of the laminate, with a transition radius (R) between the skirt and the rest of the laminate; applying a set of distribution plates (5, 6) on the skirt (2) of the basic laminate (1) to stabilize said skirt (2) and produce a uniform load distribution; making holes (3) in both the skirt (2) and distribution plates (5, 6) so that the holes of said skirt register with those of said distribution plates; and introducing traction bolts (4) with a pretension in said holes (3) and in corresponding holes of another component to be joined with said at least one component, thereby obtaining a joint between both components. A process according to claim 1, characterized in that the skirt or skirts (2) are applied against flat or curved surfaces of the component to be joined to the laminate (1). A process according to any one of claims 1 and 2, characterized in that the distribution plates (5, 6) are metallic. A process according to claims 1 or 2, characterized in that the distribution plates (5, 6) are of composite material. A process according to any one of claims 1 to 4, characterized in that in the case of a single flat or curved basic laminate (1) the skirt (2) is folded towards one or other side of the laminate surface, or else the laminate (1) is locally split into two parts (2', 2") which are then folded towards opposite sides of the laminate surface, thereby forming a kind of T. A process according to any one of claims 1 to 4, characterized in that in the case of a multiple basic laminate (1, 1') the skirt (2, 2', 2", 2a, 2b) of each one of the laminates is folded towards one or other side of the surface thereof, or else at least one (1') of said laminates is locally split into two parts (2', 2") which are folded towards opposite sides of the at least one laminate, thereby forming a kind of T, and then the skirts formed are superimposed to obtain a skirt which interactively groups the skirts of all the laminates (1, 1') of the multiple basic laminate. A process according to any one of claims 1 to 4, characterized in that in the case of a multiple laminate (1, 1') ending in a single surface their skirts (2, 2', 2") are folded together towards one or other side of the surface thereof, or else, upon splitting said multiple laminate locally into two parts, such parts are folded towards opposite sides of said surface thereby forming a kind of T. A process according to any one of the preceding claims, characterized in that the components to be joined together are comprised of an aerodynamical surface lining-stringer assembly for aircraft structures wherein the laminates (1) are folded to form the skirts (2).

Inventors: CEREZO PANCORBO CARLOS, DE CASTRO NODAL MANUEL, DOMINGUEZ CASADO RAFAEL, GRUESO DIEZ CESAR, HUERTAS GARCIA MANUEL, PEREZ PEREZ ANTONIO, REDONDO VARA ENRIQUE, ROBLEDO SACRISTAN BONIFACIO, CEREZO PANCORBO, CARLOS, DE CASTRO NODAL, MANUEL, DOMINGUEZ CASADO, RAFAEL, GRUESO DIEZ, CESAR, HUERTAS GARCIA, MANUEL, PEREZ PEREZ, ANTONIO, REDONDO VARA, ENRIQUE, ROBLEDO SACRISTAN, BONIFACIO, Grueso Diez, César
Applicants: AIRBUS ESPANA SL, AIRBUS ESPANA, S.L.
Application year: 1999
Main classification: B64C1
IPC codes: B64C1