Abstract
Transition of composite laminates for a modular blade. The real load distribution per element F.sub.2 is flattener, overlapping with the theoretical load distribution per element F.sub.2theor by a non-homogeneous hybrid laminate across the width of the same, with an area at the ends having a very high modulus of elasticity E.sub.2ext and an area in the centre having a lower modulus of elasticity E.sub.2int. Furthermore, the transition has a variable length with respect to the width of the cap, to the width of the joint and to the angle of optimal design for transferring the lead ?, all according to the formula L.sub.transition=0.5(W.sub.joint?W.sub.cap)tan.sup.?1(?).
Claims
1-5. (canceled)
6. A transition of composite laminates for a modular blade, between a laminate of the cap and a laminate of the joining area, which houses its metallic parts inside, characterized by having a non-homogeneous hybrid laminate along its width, with a distribution of variable rigidity along it, with an area at the ends where the modulus of elasticity E2ext is very high and an area in the center where the modulus of elasticity E2int is very low and because it has a length variable with respect to the cap width, the width of the joint and the most optimal design angle to transfer the load ?.
7. The transition of laminates according to claim 6, wherein the non-homogeneous hybrid laminate where the unidirectional carbon or glass fiber is replaced by biaxial glass fiber or unidirectional glass fiber in the case of carbon fiber laminates, the sides being the area with high density of unidirectional fiber and the center where biaxial glass fiber predominates or unidirectional glass fiber in the case of carbon fiber laminates.
8. The transition of laminates according to claim 6, wherein the non-homogeneous hybrid laminate flattens the load distribution per element F2, overlapping it with the theoretical load distribution per element F2theor through a relationship of elastic modules E2int/E2ext in the range of 60%-80%
9. The transition of laminate widths according to claim 6, further comprising flattening the load distribution per element bringing it closer to the F2limit through a ratio of elastic modules E2int/E2ext in the range of 40%-60%.
10. The transition of laminate widths according to claim 6, wherein the angle ? is in the range of 5 to 10?.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] A brief description will be given below for a series of drawings useful for better understanding the invention and that expressly relate to an embodiment of said invention that is presented as a non-limiting example thereof.
[0020] FIG. 1a shows a blade in plan with the integration of the joint, FIG. 1b is the section of the joint, showing the comparison of widths between the cap area and the joint area, and FIG. 1c the transition of said widths of panel.
[0021] FIGS. 2a, 2b and 2c show a second embodiment with the blade joint in a different place, with a much more relevant panel width transition.
[0022] FIG. 3a shows the joint area with its sectioned laminates, FIG. 3b shows the load distribution in the joint elements and the corresponding force reaction curve.
[0023] FIGS. 4a and 4b show the improved joint zone, its load distribution and its new load distribution curves.
[0024] FIG. 5 represents another alternative.
DETAILED DESCRIPTION
[0025] As shown in FIG. 1a, the area where the connection of a modular blade (1) can be established can be selected closer to the root or closer to the tip. Each selected location requires an integration between the cap (2) of the blade, generally with the same width along the entire length of the blade, and the increase in the width of the cap (joint area), necessary to accommodate the metal elements of the joint, and which can be generated by increasing its lamination, or by using a preform (3).
[0026] FIG. 1b shows the width of the cap (W.sub.cap) with little difference compared to the width of the joint (W.sub.joint 1) for places close to the tip of the blade and is the joint called Joint 1 in the previous figure.
[0027] FIG. 1c shows the width transition between the cap (W.sub.cap) and the joint zone (W.sub.joint 1) is defined by the angle ?, which is defined as a design criterion of the joint, typically in the range of 5 to 10? for this type of transitions. By having a panel width ratio (joint and blade cap) close to 1, the resulting transition is relatively short. The cap (2) is formed by mainly unidirectional UD composite material. The joint area (3) must house the metal elements necessary to withstand the stresses of the joint and therefore has larger dimensions with a transition part (4) and a joining part (5). The transition part (4) has a length called (L.sub.transition).
[0028] FIG. 2a shows that there are sections in which the difference in width between the cap (2) and the joint area is more pronounced (3), when it is established in intermediate places of the blade (1).
[0029] The widths are detailed in FIG. 2b. The width of the cap (W.sub.cap) remains the same and the joint area (W.sub.joint 2) is wider, given the greater number of metal joining elements that it has to accommodate, being in a blade area with higher loads. It is the union called Joint 2 in the previous figure.
[0030] FIG. 2c shows the transition of cap widths (W.sub.cap) to the joint area (W.sub.joint 2) in this case, maintaining the same ? by design criterion. The transition length (L.sub.transition) is greater than in the previous embodiment, since the increase in width of the joint is significantly greater.
[0031] The formula that governs the transition between the cap (W.sub.cap) and the joint zone (W.sub.joint 1, W.sub.joint 2) is the following:
[00001]
Wherein:
[0032] L.sub.transition is the length of the laminate width transition (4), [0033] W.sub.joint is the width of the joints (W.sub.joint 1, W.sub.joint 2), [0034] W.sub.cap is the width of the cap, and [0035] ? is the width reduction angle that the laminate has at the transition.
[0036] Thus, the transition length is equal to one-half the width of the joint minus the width of the cap, divided by the tangent of ?.
[0037] FIG. 3a shows a plan view with the cap (2) sectioned according to AA and the joint area (3) sectioned according to BB. The cap has a material with an elastic modulus E1 and the laminate in the joining area (3) is made with a material with an elastic modulus E2.
[0038] FIG. 3b shows how the width of the joint (W.sub.joint) (5) means that the load (F.sub.1) received from the cap laminate tends to go predominantly through the central elements that are aligned with it (2), instead of by the lateral elements. The load is transferred by shear from the center of the laminate to the end elements, so that if it does not have sufficient transition length, it reaches the corners in a more diminished manner than through the center (F2).
[0039] This makes the real load reaction curve of F.sub.2 (7) different from the theoretical curve F.sub.2theor (6), which would be defined by the geometry of the blade in this area and the hypothesis of deformation of the beam with a flat cross section (Navier hypothesis). The central elements have an overload with respect to the theoretical load, while those in the corners receive less load. This limits the load transfer capacity of the joint, since it will be limited by the maximum allowable load per element, which limits the capacity of the central elements. Furthermore, this situation represents a loss of efficiency of the lateral elements, which means that their full potential cannot be used and their number must be increased to maintain the load-carrying capacity of the section.
[0040] FIG. 4a shows the behaviour of the sectioned cap AA and the joining area when its lamination is carried out with a non-homogeneous lamination sequence along its width, providing it with variable rigidity along the width, adding in the center a lower modulus material than on the sides so that the load transfer is more uniform. In the end area, a laminate with a higher modulus of elasticity E.sub.2ext is maintained (typically unidirectional carbon or glass fiber) while in the center the number of high modulus layers is lowered and those of low modulus are gradually increased (typically biaxial glass fiber or unidirectional glass fiber in the case of carbon fiber laminates) to decrease the elastic modulus E.sub.2int. In the area between the two, a laminate transition is defined, giving a module transition area between both ends E.sub.2transition. The solid line shows the elastic modulus E.sub.2 of the previous embodiment, with uniform lamination, and the current elastic modulus is shown in the dashed line, varying along the width of the piece.
[0041] FIG. 4b shows the new load distribution according to the hybrid laminate where its rigidity has been adjusted in width. By adjusting the rigidity of the laminate, the theoretical load curve (6) of F.sub.2theor and the real curve (7) of F.sub.2 are superimposed, improving the capacity of the joint. This is achieved with a ratio of elastic moduli E.sub.2int/E.sub.2ext in the range of 40%-60%. Furthermore, taking this laminate stiffness adjustment to greater differences (ratio of elastic moduli E.sub.2int/E.sub.2ext in the range of 60%-80%), the total flattening of the curve (8), called F.sub.2limit, would be achieved. This would significantly improve the behaviour of the joint, being able to extract the maximum of the individual load passing capacity of each joint element, with the consequent optimization in their number and in the size and cost of the joint. In this case, the section of the joint would no longer deform with a flat section (Navier's law), not due to an unintended three-dimensional effect caused by the width transition, but rather due to the design effect of the laminate's stiffness which was the objective of the blade designer.
[0042] FIG. 5 shows a natural alternative to achieve a correct transfer of load from the cap to the joint area, making a very long transition. To ensure that the load is correctly transferred by shear to the lateral elements with laminate of uniform rigidity, the angle of the joint, ?, must be greatly reduced (of the order of 2? to 3?), and therefore the length of the transition must be lengthened.
[0043] This solution results in very long lamination transitions, and is therefore very inefficient in weight and cost. On the contrary, the solution proposed with the non-homogeneous laminate allows the reduction of the piece length (larger a angles), together with the increase in the efficiency of the lateral elements, which represents a significant reduction in the weight and cost of the union.
