The Effects of Contact Stress and Slip Distance on Fretting Fatigue Damage in Ti-6Al-4V/17-4PH Contacts PDF Download

Author: MJ. Lutian
Publisher:
ISBN:
Category : Coefficient of friction
Languages : en
Pages : 22

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Book Description
A comprehensive evaluation of fretting fatigue variables was conducted on shot-peened Ti-6A1-4V forging material in the ?-STOA condition in contact with 17-4PH pins, a material couple representative of helicopter dynamic component interfaces. Utilizing test equipment incorporating independent fatigue stress and fretting slip displacement control (as described elsewhere in this symposium), a test matrix spanning slip distances, ?, of 25 ? ? ? 75 ?m and contact stresses, ?f, of 70 ? ?f ? 200 MPa. Fatigue stresses were used which resulted in cycle lives ranging from run out, >107 to 103. A flat against flat contact geometry was used with the contact area covering ~10 mm2. Representative fretting scars through out the test matrix were examined via serial section analysis and the crack number, density, location, length and flank angle noted through the scar volume. A fretting fatigue endurance map of contact stress vs. slip distance shows that slip amplitude dominates mean fretting fatigue strength at 107 cycles under the tested conditions with contact stress playing only a moderate role. The fretting surface could be characterized as moderately pitted with dense third body debris. The debris was determined to be TiO2. Critical cracks formed through a linking of smaller cracks across the fretting scar as evidenced by a number of nucleation sites on the fracture surface. The coefficient of friction, COF, was observed to increase from its initial value of 0.15 to a stable 0.75 through the first 103-104 cycles.