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Research Papers

Fatigue Life Modeling of Anisotropic Materials Using a Multiaxial Notch Analysis

[+] Author and Article Information
Z. J. Moore

 The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA

R. W. Neu1

 The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332; School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332rick.neu@gatech.edu

1

Corresponding author.

J. Eng. Mater. Technol 133(3), 031001 (Jun 23, 2011) (11 pages) doi:10.1115/1.4004050 History: Received May 11, 2010; Revised April 18, 2011; Published June 23, 2011; Online June 23, 2011

Fatigue life modeling of anisotropic materials such as directionally-solidified (DS) and single-crystal Ni-base superalloys is often complicated by the presence of notches coupled with dwells at elevated temperatures. This paper focuses on an approach for predicting low cycle fatigue that includes notch geometry effects while taking into consideration material orientation. An analytical model based on a generalization of the Neuber notch analysis to both multiaxial loading and anisotropic materials is used to determine the localized stress-inelastic strain response at the notch. The material anisotropy is captured through a multiaxial generalization of the Ramberg–Osgood relation using a Hill’s criterion. The elastic pseudo stress and pseudo strain response in the vicinity of the notch used as input in the Neuber analysis is determined from an anisotropic elastic finite element analysis. The effects of dwells at elevated temperature are captured using an equivalent strain rate. A nonlocal approach is needed to correlate the life of notched specimens to smooth specimens.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

(Color online) Multiaxial anisotropic Ramberg–Osgood fits at 750 °C for longitudinal (L) and transverse (T) orientations

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Figure 2

Cylindrically-notched uniaxial specimens showing kt  = 2 geometry on left and kt  = 3 geometry on right (units in mm)

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Figure 3

(Color online) Finite element mesh of notched specimen

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Figure 4

(Color online) Stress components across the net section of the notch comparing influence of (a) notch severity in the longitudinal orientation and (b) material orientation for the kt  = 2 notch

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Figure 5

(Color online) (a) Anisotropic linear elastic finite element analysis of kt  = 2 specimen in longitudinal orientation showing the Hill’s stress and (b) corresponding crack initiation locations

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Figure 6

(Color online) Plot of orientation function f(ω,750 °C) based on trends reported in Erickson and Harris [22] and Bernhardi and Mücke [24] and fit to CM247LC DS life data at 0° (L-oriented) and 90° (T-oriented)

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Figure 7

(Color online) Definition of ω

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Figure 8

(Color online) Flow chart summarizing algorithm

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Figure 9

(Color online) Model correlations to experimental life data at 750 °C: (a) longitudinal oriented and (b) transverse oriented

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Figure 10

(Color online) Model correlations to experimental life data at 950 °C for longitudinal oriented

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Figure 11

(Color online) Model correlations to experimental life data containing dwells in compression (denoted HC) or in tension (HT) and conducted at a slower strain rate (SSR) at 750 °C: (a) longitudinal oriented and (b) transverse oriented

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Figure 12

(Color online) Model correlations to experimental life data containing dwells in compression (denoted HC) and conducted at a slower strain rate (SSR) at 950 °C for longitudinal oriented

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