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Gas Turbines: Structures and Dynamics

Analytical Correction of Nonlinear Thermal Stresses Under Thermomechanical Cyclic Loadings

[+] Author and Article Information
Sarendra Gehlot, Pradeep Mahadevan, Ragupathy Kannusamy

 Honeywell Technology Solutions Lab, Bangalore, India 560076

J. Eng. Gas Turbines Power 134(10), 102505 (Aug 22, 2012) (7 pages) doi:10.1115/1.4007113 History: Received June 29, 2012; Revised July 09, 2012; Published August 22, 2012; Online August 22, 2012

Automotive turbocharger components frequently experience complex thermomechanical fatigue (TMF) loadings which require estimation of nonlinear plastic stresses for fatigue life calculations. These field duty cycles often contain rapid fluctuations in temperatures and consequently transient effects become important. Although current finite element (FE) software are capable of performing these nonlinear finite element analyses, the turnaround time to compute nonlinear stresses for complex field duty cycles is still quite significant and detailed design optimizations for different duty cycles become very cumbersome. In recent years, a large number of studies have been made to develop analytical methods for estimating nonlinear stress from linear stresses. However, a majority of these consider isothermal cases which cannot be directly applied for thermomechanical loading. In this paper a detailed study is conducted with two different existing analytical approaches (Neuber’s rule and Hoffman-Seeger) to estimate the multiaxial nonlinear stresses from linear elastic stresses. For the Neuber’s approach, the multiaxial version proposed by Chu was used to correct elastic stresses from linear FE analyses. In the second approach, Hoffman and Seeger’s method is used to estimate the multiaxial stress state from plastic equivalent stress estimated using Neuber’s method for uniaxial stress. The novelty in the present work is the estimation of nonlinear stress for bilinear kinematic hardening material model under varying temperature conditions. The material properties including the modulus of elasticity, tangent modulus and the yield stress are assumed to vary with temperature. The application of two analytical approaches were examined for proportional and nonproportional TMF loadings and suggestions have been proposed to incorporate temperature dependent material behavior while correcting the plasticity effect into linear stress. This approach can be effectively used for complex geometries to calculate nonlinear stresses without carrying out a detailed nonlinear finite element analysis.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Neuber’s uniaxial rule for determining nonlinear equivalent stress

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Figure 2

Change of yield surface due to temperature for uniaxial case

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Figure 3

Change of yield surface due to temperature for multiaxial case

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Figure 4

Bilinear kinematic stress versus strain plots under varying temperature condition

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Figure 5

(a) Plate with two holes model chosen for study. Locations A and B are used for nonlinear stress prediction. (b) Thermal duty cycle applied at the two holes.

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Figure 6

Comparison of nonlinear stress in X direction (horizontal in Fig. 5) at location A

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Figure 7

Comparison of nonlinear stress in Y direction (vertical direction in Fig. 5) at location A

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Figure 8

Comparison of nonlinear stress in X direction at location B

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Figure 9

Comparison of nonlinear stress in Y direction at location B

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Figure 10

Turbine housing model and locations chosen for comparison

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Figure 11

(a) Variation of orientation of principal stress for location A. (b) Variation of stress ratio for location A.

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Figure 12

(a) Variation of orientation of principal stress for location B. (b) Variation of stress ratio for location B.

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Figure 13

Comparison of nonlinear stress (first principal stress) for location A under proportional loading

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Figure 14

Comparison of nonlinear stress (second principal stress) for location A under proportional loading

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Figure 15

Comparison of nonlinear stress (first principal stress) for location B under nonproportional loading

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Figure 16

Comparison of nonlinear stress (second principal stress) for location B under nonproportional loading

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