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Research Papers

# Experimental and Numerical Characterization of the Cyclic Thermomechanical Behavior of a High Temperature Forming Tool Alloy

[+] Author and Article Information
Sean B. Leen

Mechanical and Biomedical Engineering, College of Engineering and Informatics, NUI Galway, Galway, Irelandsean.leen@nuigalway.ie

Department of Mechanical, Materials and Manufacturing Engineering, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UKepxaad@nottingham.ac.uk

Thomas H. Hyde

Department of Mechanical, Materials and Manufacturing Engineering, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UKthomas.hyde@nottingham.ac.uk

J. Manuf. Sci. Eng 132(5), 051013 (Oct 05, 2010) (12 pages) doi:10.1115/1.4002534 History: Received June 19, 2009; Revised September 06, 2010; Published October 05, 2010; Online October 05, 2010

## Abstract

This paper describes high temperature cyclic and creep relaxation testing and modeling of a high nickel-chromium material (XN40F) for application to the life prediction of superplastic forming (SPF) tools. An experimental test program to characterize the high temperature cyclic elastic-plastic-creep behavior of the material over a range of temperatures between $20°C$ and $900°C$ is described. The objective of the material testing is the development of a high temperature material model for cyclic analyses and life prediction of SPF dies for SPF of titanium aerospace components. A two-layer viscoplasticity model, which combines both creep and combined isotropic-kinematic plasticity, is chosen to represent the material behavior. The process of material constant identification for this model is presented, and the predicted results are compared with the rate-dependent (isothermal) experimental results. The temperature-dependent material model is furthermore applied to simulative thermomechanical fatigue tests, designed to represent the temperature and stress-strain cycling associated with the most damaging phase of the die cycle. The model is shown to give good correlation with the test data, thus vindicating future application of the material model in thermomechanical analyses of SPF dies for distortion and life prediction.

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## Figures

Figure 5

One dimensional rheological representation of the two-layer viscoplasticity model (5)

Figure 6

Identification of coefficients C and γ for strain rate 5×10−4 s−1

Figure 3

Stress-strain loops representing cyclic hardening behavior of XN40F alloy for 0.6% strain range and strain rate of 5×10−4 s−1 at 20°C, 500°C, 700°C, and 900°C

Figure 4

Stress histories from stress relaxation tests carried out at 700°C and 900°C on XN40F alloy

Figure 1

(a) Geometry of thermomechanical fatigue test specimen and (b) photograph of in situ specimen with induction coil with extensometer

Figure 2

Measured stabilized stress-strain loops for XN40F for different temperatures and strain ranges for a strain rate of 5×10−4 s−1

Figure 11

Validation of power law creep constants A and n and two-layer viscoplasticity constant f at 700°C and 900°C

Figure 12

Validation of identified NLKH and creep two-layer model constants for different strain ranges at 700°C for a strain rate of 5×10−4 s−1

Figure 7

Comparison of predicted NLKH model responses using identified NLKH constants for different strain ranges at 20°C and 500°C

Figure 8

Comparison of predicted NLKH model responses using identified NLKH constants for different strain ranges at 700°C and 900°C

Figure 9

Identification of isotropic hardening parameter b for XN40F alloy for 5×10−4 s−1 strain rate and 0.6% strain range at (a) 20°C, (b) 500°C, and (c) 700°C

Figure 10

Comparison of combined kinematic-isotropic hardening model with tests at 20°C, 500°C, and 700°C

Figure 13

Validation of identified NLKH and creep two-layer model constants for different strain ranges at 900°C for a strain rate of 5×10−3 s−1

Figure 14

Validation of identified NLKH and creep two-layer model constants for different strain ranges at 900°C for a strain rate of 5×10−4 s−1

Figure 15

Measured and predicted (two-layer model) strain-rate effect on cyclic stress-strain curve at 900°C

Figure 16

Typical imposed strain-temperature cycle for simulative TMF test

Figure 17

Comparison of FE-predicted and measured stabilized cyclic stress-strain response for simulative TMF test (Δε=1%)

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