Computational-experimental approaches for fatigue reliability assessment of turbine bladed disks

: A series of constant strain range tests was made for a wide variety of materials producing fatigue lives varying from a few cycles to about one million cycles. The specimens were subjected to axial, compression-tension, low-frequency fatigue about a zero mean strain. Load range was measured periodically throughout each test, enabling an analysis of fatigue results in terms of elastic, plastic, and total strains. Materials tested were AISI 4130 (soft and hard)., AISI 4340 (annealed and hard), AISI 52100, AISI 304 ELC (annealed and hard), AISI 310 (annealed), AM 350 (annealed and hard), Inconel X, Titanium (6Al-4V), 2014-T6, 5456-H311, and 1100 aluminum, and beryllium.

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Fatigue behavior of materials under strain cycling in low and intermediate life range

Recent concern over abnormal stresses imposed on the shafts of large turbine-generators, due to high speed switching of network faults, has led to intensive investigation of this phenomenon. Elaborate computer programs were developed for simulated model studies which revealed that hitherto unexpectedly high shaft stresses can occur merely by tripping a three-phase short circuit near the power station at an unfavorable instant. The effects of circuit breaker reclosing, both successful and unsuccessful, were also investigated together with those due to faulty synchronizing. Test data on a 780 MVA unit gained by telemetric means verified the calculated torques and established the damping coefficients in a running unit. The adverse influence of numerous repetitive instances of such over-stressing on life expenditure of rotor materials is being evaluated.

Effect of clearing short circuits and automatic reclosing on torsional stress and life expenditure of turbine-generator shafts

Stochastic fatigue, fracture and damage analysis

Assessment of austenitic stainless steels

Methods are described for constructing a fatigue curve based on strain- fatigue data for use in pressure vessel design. When this curve is used, the same fatigue strengthreduction factor should be used for low-cycle as for highcycle conditions. When evaluating the effects of combined mean and alternating stress, the fatigue strength-reduction factor should be applied to both the mean and the alternating component, but then account must be taken of the reduction in mean stress which can be produced by yielding. The complete fatigue evaluation of a pressure vessel can be a major task for the designer, but it can be omitted, or at least drastically reduced, if certain requirements can be met regarding design details, inspection, and magnitude of transients. Although the emphasis is on pressure vessel design, the same principles could be applied to any structure made of ductile metal and subjected to limited numbers of load cycles.

B. F. Langer

Papers

Design of Pressure Vessels for Low-Cycle Fatigue

Closure to “Discussions of ‘Design of Pressure Vessels for Low-Cycle Fatigue’” (1962, ASME J. Basic Eng., 84, pp. 399–402)