ISSN: 1945-7553
CODEN: JTEVAB
Page Count: 6

Fatigue and Corrosion Fatigue of Beryllium-Copper Spring Materials

Bagheri, R
Lehigh University, Bethlehem, PA

Miller, GA
Lehigh University, Bethlehem, PA

(Received 7 February 1992; accepted 18 September 1992)

Abstract

Fine gage, 0.006-in. (0.15-mm) thick, beryllium-copper (Be-Cu) spring materials with tensile strength in the range of 70 to 145 ksi (482 to 999 MPa) were subjected to cyclic loading in air and salt water environments. Plain and notched (center hole) “hour glass” specimens were subjected to sinusoidal loading with R = (minimum maximum) stress = 0.1 at cyclic frequencies of 50 Hz in air and 1 Hz in salt water. Fatigue life was typically from 10⁴ to 10⁶ cycles with crack initiation as the dominant fatigue process.

The excellence fatigue performance of Be-Cu alloys in salt water is well-known, however, current findings demonstrate 10 to 37% reduction in fatigue strength of unnotched specimens in this environment for a life of 3 × 10⁵ cycles. This strength degradation is attributed to the use of a lower cyclic frequency for present than for previous tests, i.e., 1 versus about 20 Hz. There was no effect of salt water on crack initiation in notched specimens.

The ratios of the fatigue strengths, namely (cold-rolled annealed) and (aged/annealed), for plain and notched specimens tested in air, decreased from 2 to about 1.4 as fatigue life increased from 10⁴ to 10⁶ cycles. This effect is attributed to cyclic hardening of the annealed material. The fatigue stress concentration factor, K_t = (plain notched) fatigue strength, increased by about 30% as fatigue cycles increased from 10⁴ to 10⁶. The ranking of K_f values of the various material conditions from highest to lowest was: cold-rolled, aged, and annealed.

Keywords:
beryllium-copper (Be-Cu) alloys, corrosion fatigue, cyclic loading, environmental effects, fatigue, spring materials

Paper ID: JTE11751J
DOI: 10.1520/JTE11751J
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