Ceramic ball bearing fracture test method
AssigneeThe Aerospace Corporation
InventorsMichael James O'Brien, Benjamin Allen Nelson
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Abstract
A mechanical test method prescribes compressing brittle balls in spherical conforming opposing platens producing equatorial bulging, tensile stresses, and resulting indentation crack growth that is imaged for providing direct measurement of the fracture toughness of brittle balls, such as, silicon-nitride balls used in hybrid bearings as well as conventional steel ball bearings, with measurement errors being immune to characterizing the dimensions and positioning of the precrack indentations, so that, the test method is accurate, repeatable, and robust.
Claims16
A method for determining the fracture toughness of a ball having an indentation defining an equator of the ball, the equator defining north and south poles of the ball, the indentation having precracks and a precrack length, the method comprising the steps of,
- applying an applied load in compression through opposing hemispherical surfaces having an arc length angle of less than ninety degrees, the opposing hemispherical surfaces conforming to the surfaces of the ball respectively at the north and south poles so that the ball bulges outwardly at the equator producing tensile stresses,
- load determining a critical applied load when the precrack begins to grow under the tensile stresses at the equator, and
- toughness determining the fractured toughness of the ball from the precrack length and the critical applied load.
Dependencies are inferred from the claim text.