Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:—
FIG. 1 is a highly diagrammatic perspective view of a blade according to the present invention;
FIG. 2 is a diagrammatic cross-sectional view of a root portion of the blade of FIG. 1 along its release plane;
FIG. 3 is a diagrammatic illustration of the root portion of FIG. 2 impacting a fan casing of a gas turbine engine; and
FIG. 4 is a schematic illustration of a plurality of panels which are utilised to form a blade according to the present invention.
FIG. 1 shows a blade 10 for a gas turbine engine which includes an aerofoil portion 12 defining leading and trailing edges 12a, 12b and a root portion 14 defining a blade release plane 15. Referring also to FIG. 2 which shows a sectional view through the root portion 14 along the blade release plane 15, it can be seen that the root portion 14 is defined by concave and convex walls 16, 18.
A reinforcing member 20 in the form of a reinforcing membrane extends throughout the aerofoil portion 12 and the root portion 14 between the concave and convex walls 16, 18. The reinforcing member 20 is bonded to the inner surfaces 16a, 18a of the concave and convex walls 16, 18 in predetermined bonding regions 22 (shown diagrammatically in FIG. 2 as solid lines). The root portion 14 also includes a plurality of first and second unbonded regions 24a, 24b (shown diagrammatically as broken lines in FIGS. 1 and 2) in which the reinforcing member 20 contacts the inner surfaces 16a, 18a of the adjacent concave and convex walls 16, 18 but is not bonded to the inner surfaces 16a, 18a. As will be explained in more detail later in the specification, the first and second unbonded regions 24a, 24b facilitate deformation of the root portion 14 upon impact with a fan containment region of a gas turbine engine fan casing.
As can be seen in FIGS. 1 and 2, the root portion 14 generally defines first and second ends 14a, 14b which are located respectively adjacent to the leading and trailing edges 12a, 12b of the aerofoil portion 12. In order to maximise the deformability of the root portion 14 upon impact with a fan casing, the plurality of first and second unbonded regions 24a, 24b are distributed throughout the root portion 14, between the first and second ends 14a, 14b. In embodiments of the invention, the plurality of first and second unbonded regions 24a, 24b are spaced equally between the first and second ends 14a, 14b.
In the embodiment of FIG. 2, the plurality of first and second unbonded regions 24a, 24b are provided at substantially the same location on each side of the reinforcing member 20 between the reinforcing member 20 and the inner surface 16a, 18a of the adjacent concave or convex wall 16, 18.
Although four generally rectangular first and second unbonded regions 24a, 24b are shown in FIGS. 1 and 2, it should be appreciated that any number of first and second unbonded regions 24a, 24b may be provided to achieve the desired deformability of the root portion 14. Moreover the dimensions and/or shape and/or position of the first and second unbonded regions 24a, 24b can be selected to provide the required deformability.
The first and second unbonded regions 24a, 24b extend in a radially inwards direction below the blade release plane 15 and in a radially outwards direction from the root portion 14 towards the aerofoil portion 12 of the blade 10 towards a cavity 26 defined between the concave and convex walls 16, 18. In embodiments of the invention, the unbonded regions 24 can extend into open passage association with the cavity 26 although it is preferred that the unbonded regions 14 stop short of the cavity 26 so that the cavity 26 remains sealed.
FIG. 3 illustrates the impact regime of the root portion 14 with the fan containment region of a gas turbine engine fan casing 28 after fracture of the blade 10. As can be seen in FIG. 3, due to the curved shape of the concave and convex walls 16, 18, it is the first and second ends 14a, 14b of the root portion 14 that initially impact the fan casing 28. By providing one or more first and/or second unbonded regions 24a, 24b, bending and hinging of the root portion 14 about the central region 30, as shown by arrows 31, is facilitated. This allows the root portion 14 to more readily flex and deform, thereby dissipating energy and reducing the impact forces. In particular, the bending causes flexing of the root portion 14 towards the fan casing 28. This causes the central region 30 of the root portion 14, between the first and second ends 14a, 14b, to move in the direction of arrow 32 towards the fan casing 28. The impact surface area between the root portion 14 and the fan casing 28 is thereby increased, providing said dissipation of energy and reduction of the impact forces.
The provision of first and/or second unbonded regions 24a, 24b may also promote further fragmentation of the root portion 14 through cracking about the unbonded regions 24a, 24b.
A method for fabricating the blade 10 shown in FIGS. 1 to 3 will now be described with reference to FIG. 4 in which there is shown an arrangement of panels 40 used to fabricate the blade 10. The arrangement 40 comprises a first wall panel 42, or pressure panel, which provides the concave wall 16 of the formed blade 10, and a second wall panel 44, or suction panel, which provides the convex wall 18 of the formed blade 10. The arrangement 40 also includes a reinforcing membrane 46 and two screen members 48a, 48b.
In order to fabricate the blade 10, the first and second wall panels 42, 44 are arranged to sandwich the reinforcing membrane 46 between them. The screen member 48a is also located between the first wall panel 42 and one side of the reinforcing membrane 46 and the screen member 48b is located between the second wall panel 44 and an opposite side of the reinforcing membrane 46.
As can be seen in FIG. 4, each of the screen members 48a, 48b includes a plurality of openings 50 which may be in the form of slots. Where these are provided, bonding can occur between the first and second wall panels 42, 44 and the adjacent surface of the reinforcing membrane 46. However, where the openings 50 are not provided, the screen member 48a, 48b, which is conventionally a silk-screen, prevents bonding between the first and second wall panels 42, 44 and the adjacent surface of the reinforcing membrane 46. Thus, in the screen members 48a, 48b shown in FIG. 4, it is the four downwardly depending leg portions 52a, 52b that result in the formation of the four first and second unbonded regions 24a, 24b in the root portion 14 of the blade 10.
The blade 10 is formed by diffusion bonding and super plastic forming processes which are themselves known in the art.
In the diffusion bonding process, the peripheral edges of the first and second wall panels 42, 44 are secured together by diffusion bonding. Each of the first and second wall panels 42, 44 are also secured to the reinforcing membrane 46 by diffusion bonding in regions where there are openings 50 in the screen members 48a, 48b. In regions where openings 50 in the screen members 50 are not present, diffusion bonding of the first and second wall panels 42, 44 to the reinforcing membrane 46 is prevented.
In the super plastic forming process, the first and second wall panels 42, 44 are deformed to provide the concave and convex walls 16, 18 of the blade 10. The super plastic forming process also provides the cavity 26 as a result of outward expansion of the first and second wall panels 42, 44. Due to the fact that the reinforcing membrane 46 is bonded to the first and second wall members 42, 44 in predetermined bonding regions, which are determined by the location of the openings 50, the super plastic forming process also deforms the reinforcing membrane 46 so that it extends across the cavity 26 to provide a so called line core reinforcement structure.
To complete the diffusion bonding and super plastic forming process, a suitable chemical is introduced into the blade 10 to remove the screen members 48a, 48b by dissolving them.
Although embodiments of the invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that various modifications to the examples given may be made without departing from the scope of the present invention, as claimed.
For example, one or more of the first unbonded regions 24a may be provided between the reinforcing member 20 and the inner surface 16a of the concave wall 16 without any of the second unbonded regions 24b being provided such that the reinforcing member 20 is bonded to the inner surface 18a of the convex wall 18 over its entire inner surface 18a. Alternatively, one or more of the second unbonded regions 24b may be provided between the reinforcing member 20 and the inner surface 18a of the convex wall 18 without any of the first unbonded regions 24a being provided such that the reinforcing member 20 is bonded to the inner surface 16a of the concave wall 16 over its entire inner surface 16a.
The plurality of first and second unbonded regions 24a, 24b may be provided at different positions on each side of the reinforcing member 20 between the reinforcing member 20 and the inner surface 16a, 18a of the adjacent concave or convex wall 16, 18.
Patent Application
20080019838
