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During the war the General Electric Co. was forced to make fatigue tests on gas-turbine buckets, because a correlation between standard test specimens and actual bucket performance was very difficult to obtain. While our experience in this work has been largely with gas-turbine buckets, it would seem that this difficulty applies to a wide variety of parts that are subjected to reversed bending stresses. The buckets have, roughly speaking, a crescent-like cross-section. In precision cast buckets, the metal usually has a finer grain structure at the points of the crescent than in the heavier mid-section. Grain structure has a pronounced effect on the fatigue strength and grain structure is determined by the shape of the cast part; consequently, fatigue tests on actual buckets became a necessity. Under operating conditions, the buckets are subjected to periodic disturbing forces as they pass through regions of alternately high and low gas pressures. In view of this, it was logical to vibrate these buckets with an interrupted air stream.
Quinlan, F. B.
General Electric Co., Schenectady, N. Y.