초록

An elastomeric spherical bearing includes a multiple of elastomeric layers with an essentially equivalent fatigue life.

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1. A method of providing a thickness of a spherical elastomeric bearing comprising: adjusting each layer thickness of an elastomeric bearing having uniform pitch strain to satisfy: γs=0.576⁢C[(0.8⁢C)[[[1Life-(Cγθ)-α]1α]⁢(0.8⁢C)-γβ]-1]11.6to produce a uniform fatigue life of each bearing layer where:

1. A method of providing a thickness of a spherical elastomeric bearing comprising: adjusting each layer thickness of an elastomeric bearing having uniform pitch strain to satisfy: γs=0.576⁢C[(0.8⁢C)[[[1Life-(Cγθ)-α]1α]⁢(0.8⁢C)-γβ]-1]11.6to produce a uniform fatigue life of each bearing layer where:C and α are constants derived from curve fitting methods to approximate the particular S-N curve;Life is the desired fatigue life;γθis the pitch strain;γβis the flap strain; andproviding a first layer thickness and changing the first layer thickness to a different, second layer thickness in response to the adjusting. 2. A method as recited in claim 1, wherein the thickness of each layer is varied until the Pitch Strain, the Pitch Strain (γθ) is approximately 35% for all layers. 3. A method as recited in claim 1, wherein C is between 4000 and 6000. 4. A method as recited in claim 1, wherein C is ˜5000. 5. A method as recited in claim 1, wherein uniform pitch strain is calculated to satisfy: Gi=Gi-1⁢Ri-13⁢ϕi-1⁢sin⁢⁢BiRi3⁢ϕi⁢sin⁢⁢Bi-1where: Gi is the elastomer layer shear modulus;Gi−1 is the previous elastomer layer shear modulus (starting at the layer closest to the focal point);Ri is the mean radius of the layer,Ri−is the mean radius of the previous layer (starting at the layer closest to the focal point), and φi=cos Ai·(sin Ai)2+2·cos Ai−cos Bi·(sin Bi)2−2·cos Bi where: Ai is the Inner Angle and Bi is the outer angle, to produce a uniform fatigue life of each bearing layer. 6. A method as recited in claim 3, wherein the thickness of each layer is varied until the Pitch Strain (γθ) is approximately 35% for all layers. 7. An elastomeric spherical bearing comprising: a multiple of elastomeric layers produced by the method of claim 1; anda shim mounted between at least two of said multiple of elastomeric layers, each of said multiple of elastomeric layers having an essentially equivalent fatigue life. 8. The elastomeric spherical bearing as recited in claim 7, wherein an inner layer of said multiple of elastomeric layers is mounted to a central bearing element having a spherical bearing surface. 9. The elastomeric spherical bearing as recited in claim 8, wherein an inner layer of said multiple of elastomeric layers is mounted to a rotor assembly component. 10. The elastomeric spherical bearing as recited in claim 8, wherein an outer layer of said multiple of elastomeric layers is mounted to a cuff structures of a rotor assembly. 11. A method of providing a thickness of for a spherical elastomeric bearing comprising the steps of: 1.) Determining Loads and Motions;2.) Determining Fatigue Life Desired;3.) Entering Bearing Dimensions;4.) Entering Bearing Elastomer Material Properties;5.) Calculating Geometries;6.) Calculating Shape Factors Per Layer;7.) Calculating Effective Compression Modulus (Ec) Per Layer;8.) Calculating Radial And Axial Strains To Get Compression Shear Strain Per Layer;)9.) Calculating Stiffnesses (Radial, Axial, Flapping, And Torsional Stiffnesses);10.) Calculating Torsional Strain and add layers to achieve allowable torsional strain;11.) Calculating the Shear Modulus to Achieve A Uniform Torsional Strain;12.) Calculating a Flapping Strain;13.) Calculating Shear Strain Allowable;14.) Calculating Life;15.) Varying the Thicknesses Of Each Layer To Meet Shear Strain Allowable to Achieve Uniform Life; and16.) providing a first layer thickness and changing the first layer thickness to a different, second layer thickness during the varying. 12. A method as recited in claim 11, wherein said Determining Loads and Motions further comprise: a. Determine the axial load;b. Determine the radial load;c. Determine the vibratory pitch motion (theta) angle;d. Determine the flapping (cocking) motion angle. 13. A method as recited in claim 11, wherein said Entering Bearing Dimensions further comprise: a. Inner radius (Ri), Inner Angle (Bi), Inner Angle (Ai), Side Angle (Alpha); and Side Angle (Blpha);b. Enter Shim thickness. 14. A method as recited in claim 11, wherein said Entering Bearing Elastomer Material Properties further comprise: a. Entering Bulk modulus of elastomer, (Kb, psi); andb. Entering the fist layer shear modulus (G, psi). 15. A method as recited in claim 11, wherein said calculating radial and axial strains to obtain compression shear strain further comprises: a. changing a layer thickness to achieve allowable compression strain.