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November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Aditya A. Walvekar Ph.D. Research Assistant An Experimental Study and Fatigue Damage.

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Presentation on theme: "November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Aditya A. Walvekar Ph.D. Research Assistant An Experimental Study and Fatigue Damage."— Presentation transcript:

1 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Aditya A. Walvekar Ph.D. Research Assistant An Experimental Study and Fatigue Damage Model for Fretting Fatigue

2 2 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Outline Motivation Objective Fretting Fatigue Test Rig Experimental results Fatigue Damage Model Fretting Fatigue Life Predictions Summary Future work

3 3 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Motivation Fretting is associated with the small amplitude relative oscillatory motion between two solid surfaces in contact Fretting fatigue is a damage mechanism observed in a machine components subjected to fretting in tandem with fluctuating bulk stresses If the material is concurrently subjected to partial slip fretting and fluctuating bulk loading, stress concentration at the contact region results in premature nucleation and acceleration of crack growth when compared to fatigue situations without fretting * ASTM E : Standard Guide for Fretting Fatigue Testing Fretting Fatigue Test configuration *

4 4 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Objective Experimental investigation of the fretting fatigue behavior of AISI 4140 vs. Ti-6-4 in a cylinder-on-flat contact configuration –Analyze the effect of bulk stress on the fretting fatigue life at a fixed normal load –Analyze the crack propagation i.e. crack length vs. number of cycles Develop a model based on damage mechanics to analytically investigate fretting fatigue –Incorporate Voronoi tessellation to account for the randomness of the material microstructure and conduct life variability studies

5 5 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Fretting Fatigue Test Rig A fretting test fixture was designed and developed which was coupled with an MTS machine to impose the fretting fatigue damage Schematic of fretting fatigue test rig Fretting fatigue fixture mounted on MTS machine

6 6 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Experimental Results Fretting and bulk stress vs. life Picture of contact pads and specimen assembled in the test rig

7 7 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Determination of estimated crack initiation (Bulk Stress = 348 MPa) Pictures of the crack growth taken as the test is running (Bulk Stress = 348 MPa) Estimated crack initiation life – cycles First visible crack observed at cycles with a length of 765 microns Crack length vs. life cycles (Bulk Stress = 348 MPa)

8 8 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Disp. Amp. (micron) Normal force (N) Contact stress (MPa) Average tangential load at gross slip (N) COF Coefficient of Friction Measurement Fretting wear test at gross slip (displacement amplitude = 150 μm) A fretting test was performed in the gross slip regime to determine the coefficient of friction The specimen was only held with the bottom grip while the top end of specimen was free Completely-reversed sinusoidal displacement at a frequency of 1 Hz was applied to the specimen

9 9 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Finite Element Model The geometry and the applied loading conditions (a = 365 μm) Finite element mesh using Voronoi Tessellation Randomness of material microstructure topology is simulated using Voronoi tessellation to account for the variability in fretting fatigue life The sinusoidal reaction stress with amplitude “σ reaction ” is applied on the left edge of the lower body in phase with the bulk stress to model F T F T /F N obtained from experiments and FE model

10 10 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Model Validation To validate the stress distribution obtained from the FE model, shear and tangential stress distribution on the contact surface were compared with the analytical solution Comparison of shear stress and normalized tangential stress distribution on the contact surface at the positive peak of the fretting cycle obtained using FE model and analytical solution. (Bulk Stress = 400 MPa)

11 11 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Fatigue Damage Model Stresses resolved along the Voronoi grain boundaries

12 12 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Iteration No.E (1-D) (GPa)D Variation of Elasticity Modulus Stress vs. strain plot at various cycles for the variation of elasticity modulus test

13 13 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Evaluation of Damage Parameters

14 14 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Fretting Fatigue Life Predictions Fatigue Damage model was used for predicting fretting fatigue life of 30 randomly generated microstructure domains for four different loading conditions Degree of scatter is quantified using two-parameter Weibull probability distribution Loading conditions applied and predicted Weibull slope and strength parameters Material properties used in the analysis Weibull probability plot for fretting fatigue lives Comparison between the fretting fatigue lives from model and experiments

15 15 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Summary A fretting fixture was designed, built and used with an MTS 810 machine simulating the fretting fatigue in a cylinder-on-flat configuration For a fixed contact pressure, the fretting fatigue life decreased with increasing bulk stress A fatigue damage finite element model was proposed to replicate the fretting fatigue experiments and numerically estimate the fretting fatigue life The fretting fatigue lives predicted by the fatigue damage model are in good agreement with the experimental results The predicted fatigue life data displayed a larger degree of scatter for the lower bulk stress when the contact pressure is fixed

16 16 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Future Work Modify the fatigue damage model to include crack propagation Evaluate the effects of shot-peening, residual stress on Fretting Fatigue behavior Analyze the effects of inclusions and voids on the fretting fatigue life Incorporate plasticity in the fatigue damage model


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