Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Specific casing or vane material
Reexamination Certificate
2002-07-29
2004-06-22
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Specific casing or vane material
C416S24100B, C219S121850, C219S121760
Reexamination Certificate
active
06752593
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to articles manufactured by laser shock peening techniques, and, more particularly, to various article constructions exhibiting enhanced compressive residual stress characteristics induced by laser shock peening, such as selectively configured compressive residual stress distribution profiles having a desired asymmetry appearing within processed workpieces or objects, such as an airfoil.
2. Description of the Related Art
Laser shock processing has found use in applications involving the enhancement of certain structural features such as the leading and trailing edges of turbine engine compressor or other airfoils. Various strategies have focused upon finding adequate laser beam spot patterns to process the airfoil. However, little attention has been given to determining useful techniques that can provide desired shockwave groups and accompanying stress distribution profiles.
In a typical application, when a shockwave from a single laser irradiated spot on the surface of a material propagates into the material from the surface, the peak pressure is highest at the surface and then decreases (i.e., attenuates) with increasing depth into the material. If the peak pressure is high enough, namely, above the dynamic yield strength of the workpiece, the shockwave plastically deforms the material below the surface in an amount generally proportionate to the amount that the peak pressure is above the dynamic yield strength.
The plastic yielding gives rise to plastic strain in the material, which creates the compressive residual stresses desired by the process. As the peak pressure of the shockwave decreases with increasing depth below the surface, the amount of plastic strain also decreases. This factor limits the depth of the compressive residual stress that can be introduced into the workpiece.
SUMMARY OF THE INVENTION
Various articles of manufacture are provided that exhibit deep compressive residual stress characteristics induced by laser shock peening, such as an asymmetrical or other selectively configured compressive residual stress distribution profile. The article may include a gas turbine engine component such as an airfoil that exhibits an asymmetrical stress distribution profile through the thickness dimension of a thin section of the airfoil. The asymmetrical stress distribution profile will be selectively tailored to produce compressive residual stress properties within the airfoil that have desired behaviors and objectives, such as retarding crack propagation, inhibiting the growth of incipient flaws, strengthening the material at high fatigue locations, increasing the high cycle fatigue strength at specific location, providing a desired shape on curvatures, and other such uses as typically understood in the art.
According to one article of manufacture, the article includes a plurality of laser shock peened surfaces including at least one set of adjacent non-overlapping laser shock peened surfaces simultaneously formed with one another. The article also includes a plurality of regions each having deep compressive residual stresses imparted by laser shock peening extending into the article from a respective laser shock peened surface.
The spaced-apart relationship between the simultaneously formed, adjacent non-overlapping laser shock peened surfaces is chosen such that the respective shockwaves induced by laser shock peening will encounter one another as they propagate through the article. The shockwaves will intersect at a location disposed generally between the laser shock peened surfaces.
In one form, the encountering shockwaves will interact in a manner generally exhibiting a constructive interference effect. In this manner, the respective deep compressive residual stress regions that extend from each of the adjacent non-overlapping laser shock peened surfaces will overlap and significantly increase the peak pressure experienced by the material in the vicinity of the shockwave intersection plane. Various laser spot beam patterns may be employed to produce selective arrangements of shockwave interaction locations.
According to another article of manufacture, the article includes a plurality of laser shock peened surfaces including at least one set of opposing laser shock peened surfaces formed at different times and disposed at different ones of opposing sides of the article. The article also includes a plurality of regions each having deep compressive residual stresses imparted by laser shock peening extending into the article from a respective laser shock peened surface.
In this manner of article production, the opposing time-staggered shockwaves induced by laser shock peening will meet at a location apart from a mid-plane of the article, producing an asymmetrical compressive residual stress profile through a thickness dimension of the article. The relative difference between the arrival times of the laser beams used to laser shock peen the opposing sides of the article is chosen to facilitate control of the profile characteristics by selectively determining the interior location where the opposing shockwaves will encounter one another.
According to another article of manufacture, the article includes a plurality of laser shock peened surfaces including at least one set of opposing laser shock peened surfaces simultaneously formed with one another at different ones of opposing sides of the article using laser beams having different pulse lengths. The article also includes a plurality of regions each having deep compressive residual stresses imparted by laser shock peening extending into the article from a respective laser shock peened surface.
The use of such differential laser beam pulse lengths results in the development of opposing shockwaves induced by laser shock peening that attenuate at different rates as they propagate through the article. This disparate attenuation in the shockwaves will produce compressive residual stress regions extending from the respective laser shock peened surfaces having a stress distribution profile that exhibits an asymmetry along a thickness dimension of the article.
According to another article of manufacture, the article includes a plurality of laser shock peened surfaces including at least one set of laterally offset laser shock peened surfaces simultaneously formed with one another at different ones of opposing sides of the article. The article also includes a plurality of regions each having deep compressive residual stresses imparted by laser shock peening extending into the article from a respective laser shock peened surface.
This lateral offset has the effect of creating an imbalance in the forces that are developed within the article as the shockwaves induced by laser shock peening propagate through the article. This force imbalance exerts a moment force on the material, tending to rotate it around an axis perpendicular to the displacement vector connecting the laterally-offset, opposing laser shock peened surfaces, and laying in the nominal mid-thickness phone between the opposing laser-peened surface.
Additionally, the oppositely-directed shockwaves will interact in a generally asymmetrical manner relative to a mid-plane of the article, producing a shockwave interaction zone generally centered about the mid-plane but exhibiting wing-type portions that extend toward opposite ones of the article surfaces in an oblique manner relative to the mid-plane. A corresponding asymmetrical stress distribution profile will accompany this particular form of shockwave interaction associated with the simultaneous formation of laterally offset laser shock peened surfaces disposed at opposing sides of the article.
Various forms of selective contouring and geometrical reshaping can be accomplished using these shockwave interaction effects. For example, various spatial features such as bending, deformation, and controlled curvatures can be established, formed, or otherwise introduced into the article.
The invention, in one form thereof, is direct
Clauer Allan H.
Dulaney Jeff L.
Lahrman David F.
Toller Steve M.
Knuth Randall J.
LSP Technologies Inc.
White Dwayne J.
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