72

April 1, 2019Mechanical Engineering Tribology Laboratory (METL)

Motivation & Background• Fretting wear is surface damage which

occurs between contacting bodies experiencing small amplitude oscillatory displacement

• Fretting wear is also known as vibrational wear, wear oxidation, false brinelling, etc.

– Because all machines vibrate, fretting occurs in splines, couplings, bearings, seals, universal joints etc.

• Fretting problems are addressed using one of two opposing methods [2]

– Decreasing the relative motion between the surfaces by increasing the frictional force

– Decreasing the frictional forces to allow greater motion to occur

• Fretting regimes:– Partial slip regime: a portion of the

contact sticks while the remainder slips– Gross slip regime: all the points in the

contact experience relative slip

[1] ASTM E2789-10 : Standard Guide for Fretting Fatigue Testing

[2] Waterhouse, R. B., “Fretting Corrosion”, Published by Franklin Book Co, 1972, ISBN 10:

008-169023

Fretting maps1

Picture & 3D Photomicrograph of a fretting scar

in partial slip

73

April 1, 2019Mechanical Engineering Tribology Laboratory (METL)

Objectives

• Develop a mechanistic understanding of accelerated fretting wear and bonding between Alloy 800H and Inconel 617

– Tribological experiments under controlled environment

o Fretting wear rig that can operate up to 1000 °C

o Using fretting fatigue test rig on an MTS load frame

o Using an MTS torsion fatigue test rig to investigate the effect of torsional stresses

– Microstructure characterization

– Validated macroscopic models informed by properties/mechanisms at the atomistic level.

o Incorporating damage mechanics constitutive relations in a finite element model to analytically investigate the fretting wear

o Using Voronoi tessellation to account for the randomness of the material microstructure and its effects on the fatigue behavior

74

April 1, 2019Mechanical Engineering Tribology Laboratory (METL)

High Temperature

Fretting Tests

• Comparison of COF of Inconel 617 at room and high temperature

• Comparison of in-situ wear measurement of Inconel 617 at room and high temperature

In-situ measurement of wear depth at room and elevated temperatures and air/He

Steady state COF as a function of temperature in air

COF as a function of temperature in

air and helium

75

April 1, 2019Mechanical Engineering Tribology Laboratory (METL)

High Temperature Torsional Fatigue

Tests

• Helical fracture plane as final failure surface

• Crack initiation, crack growth, and final failure region

• 0.1% of the total life was associated with the propagation life

Detailed image of high cycle torsional fatigue of Inconel 617 specimen

at 850°C: a) Broken specimen in a test, b) fracture surface of the

specimen

Comparison of fracture surfaces in torsional fatigue tests of Inconel

617 at 850°C: a) failed at N= 39.5k cycles b) failed at N=9.4m cycles

(a) (b)

(a)

(b)