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Research Papers

Microstructure-Sensitive Fatigue Modeling of AISI 4140 Steel

[+] Author and Article Information
J. B. Jordon

Department of Mechanical Engineering,
The University of Alabama,
Tuscaloosa, AL 35401

M. F. Horstemeyer

Department of Mechanical Engineering,
Mississippi State University,
Mississippi State, MS 39762;
Center for Advanced Vehicular Systems,
Mississippi State University,
Mississippi State, MS 39762

Contributed by the Materials Division of ASME for publication in the Journal of Engineering Materials and Technology. Manuscript received May 9, 2013; final manuscript received September 9, 2013; published online February 5, 2014. Assoc. Editor: Irene Beyerlein.

J. Eng. Mater. Technol 136(2), 021004 (Feb 05, 2014) (9 pages) Paper No: MATS-13-1081; doi: 10.1115/1.4025424 History: Received May 09, 2013; Revised September 09, 2013

A microstructure-based fatigue model is employed to predict fatigue damage in 4140 steel. Fully reversed, strain control fatigue tests were conducted at various strain amplitudes and scanning electron microscopy was employed to establish structure-property relations between the microstructure and cyclic damage. Fatigue cracks were found to initiate from particles near the free surface of the specimens. In addition, fatigue striations were found to originate from these particles and grew radially outward. The fatigue model used in this study captured the microstructural effects and mechanics of nucleation and growth observed in this ferrous metal. Good correlation of the number of cycles to failure between the experimental results and the model were achieved. Based on analysis of the mechanical testing, fractography and modeling, the fatigue life of the 4140 steel is estimated to comprise mainly of small crack growth in the low cycle regime and crack incubation in the high cycle fatigue regime.

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Figures

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Fig. 1

(a) Unetched micrograph of a representative AISI 4140 showing inclusions, carbides, etc. (b) Typical etched appearance of the AISI 4140 revealing course pearlite and proeutectoid phases.

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Fig. 2

Effective stress–strain comparison of tension, compression, and torsion of AISI 4140 steel at 300 K and at a strain rate of 0.01/s

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Fig. 3

Strain-life results of AISI 4140 steel tested under fully reversed conditions

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Fig. 4

Stress amplitude versus number of cycles for AISI 4140 steel for the strain amplitude ranging from 1.0% to 0.185%

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Fig. 5

Cyclic stress amplitude versus plastic strain amplitude for AISI 4140 steel

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Fig. 6

Representative hysteresis loops of the AISI 4140 steel for first and half-life cycle of the 0.4% strain amplitude. Specimen F10 failed at 9075 cycles.

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Fig. 7

(a) SEM micrograph of an overview of specimen F13 and (b) a magnified view of the fractured particle that initiated the fatigue crack. Specimen F13 was tested at strain amplitude of 0.002 and failed at 343,075 cycles.

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Fig. 8

(a) SEM micrograph of an overview of specimen F1, and a magnified view of the fractured particle (highlighted) that initiated the fatigue crack. (b) Specimen F1 was tested at strain amplitude of 0.01 and failed at 588 cycles.

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Fig. 9

A magnified view of the particle that initiated the fatigue crack shown in Fig. 7. Striations are clearly seen near the top of the particle as highlighted in this image. Specimen F13 was tested at a strain amplitude of 0.002 and failed at 343,075 cycles.

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Fig. 10

A magnified view of striations observed on microcliffs of specimen F10 at a distance of 300 μm from the initiation site. Specimen F10 was tested at a strain amplitude of 0.004 and failed at 9075 cycles.

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Fig. 11

A magnified view specimen F13 showing a region of striations at 600 μm from the initiation site. Specimen F13 was tested at a strain amplitude of 0.002 and failed at 343,075 cycles.

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Fig 12

Striation spacing versus crack length for specimens tested at amplitudes of 0.002, 0.003, and 0.004 strain amplitudes

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Fig. 13

Experimental AISI 4140 steel strain-life results (R = −1) versus the MSF model correlations. Also shown is the incubation and small crack growth predictions of the model.

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Fig. 14

MSF model comparison to notched fatigue specimens tested under constant displacement. The MSF model predictions were based on finite element internal state variable plasticity results of the notched specimen. An isometric view of the notched cylindrical specimen is shown. Local stress/strain state was used as input for the MSF model.

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