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Thermo-mechanical Fatigue Crack Propagation in Inconel 718

Jacobsson, Lars LU (2007)
Abstract
Thermo-mechanical fatigue crack propagation in Inconel 718 has been studied with different methods. In-situ observations with a scanning electron microscope (SEM) were performed, the crack propagation process was followed cycle by cycle and the influences from load, temperature, and microstructure on the crack growth were analyzed. To measure the displacements an image analysis technique was developed and to measure the contact between the fracture surfaces the electrical potential drop signal was measured over the crack mouth.

The phenomenon of crack closure has been investigated by measuring the displacements between the fracture surfaces close to the crack tip and by measuring the electrical contact between the crack surfaces.... (More)
Thermo-mechanical fatigue crack propagation in Inconel 718 has been studied with different methods. In-situ observations with a scanning electron microscope (SEM) were performed, the crack propagation process was followed cycle by cycle and the influences from load, temperature, and microstructure on the crack growth were analyzed. To measure the displacements an image analysis technique was developed and to measure the contact between the fracture surfaces the electrical potential drop signal was measured over the crack mouth.

The phenomenon of crack closure has been investigated by measuring the displacements between the fracture surfaces close to the crack tip and by measuring the electrical contact between the crack surfaces. A study of cracks under steady state growth conditions and subjected to an overload was also conducted.

Thermo-mechanical fatigue was performed in-situ within the SEM and a heating device was developed to generate thermal cycles. A heating wire was placed on the test specimen and fixed with aluminum oxide paste to heat the test specimen, and the grips on the load cell were cooled with water. Differences between thermo-mechanical cycles in-phase and out-of-phase were compared with iso-thermal cycles in the temperature intervals 300–550°C and 300–630°C. These tests showed significant differences in crack propagation mechanisms and crack propagation rates.

Thermo-mechanical fatigue tests were also performed using cylindrical specimens with a diameter of 6.3 mm. To generate the thermal cycles, a system blowing alternately hot and cold air through a nozzle onto the test specimen was constructed. Thermo-mechanical load cycles were performed in-phase and out-of-phase with different load ratios R in the temperature range 200–550°C. Crack closure level and crack length were measured using the potential drop technique.

A correlation between effective J-integral range and crack propagation rate was found after compensating for crack closure, making the ΔJeff a possible fracture mechanical parameter for prediction of crack propagation rates under given loading conditions. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Johansson, Sten, Linköpings Universitet, Linköping
organization
publishing date
type
Thesis
publication status
published
subject
keywords
crack closure, image analysis, potential drop, in-situ scanning elecron microscopy, crack propagation experiments, Thermo-mechanical fatigue, Inconel 718
pages
120 pages
publisher
Materials Engineering
defense location
Room M:E, M-building, Ole Römers väg 1, Lund University Faculty of Engineering
defense date
2007-12-18 10:15
external identifiers
  • Other:ISRN LUTFD2/TFMT--07/1013--SE(1-120)
project
Life2
language
English
LU publication?
yes
id
28120923-05d4-47b5-abca-3bc8fe4e1865 (old id 618496)
date added to LUP
2007-11-22 13:11:33
date last changed
2016-09-19 08:45:13
@misc{28120923-05d4-47b5-abca-3bc8fe4e1865,
  abstract     = {Thermo-mechanical fatigue crack propagation in Inconel 718 has been studied with different methods. In-situ observations with a scanning electron microscope (SEM) were performed, the crack propagation process was followed cycle by cycle and the influences from load, temperature, and microstructure on the crack growth were analyzed. To measure the displacements an image analysis technique was developed and to measure the contact between the fracture surfaces the electrical potential drop signal was measured over the crack mouth. <br/><br>
The phenomenon of crack closure has been investigated by measuring the displacements between the fracture surfaces close to the crack tip and by measuring the electrical contact between the crack surfaces. A study of cracks under steady state growth conditions and subjected to an overload was also conducted. <br/><br>
Thermo-mechanical fatigue was performed in-situ within the SEM and a heating device was developed to generate thermal cycles. A heating wire was placed on the test specimen and fixed with aluminum oxide paste to heat the test specimen, and the grips on the load cell were cooled with water. Differences between thermo-mechanical cycles in-phase and out-of-phase were compared with iso-thermal cycles in the temperature intervals 300–550°C and 300–630°C. These tests showed significant differences in crack propagation mechanisms and crack propagation rates. <br/><br>
Thermo-mechanical fatigue tests were also performed using cylindrical specimens with a diameter of 6.3 mm. To generate the thermal cycles, a system blowing alternately hot and cold air through a nozzle onto the test specimen was constructed. Thermo-mechanical load cycles were performed in-phase and out-of-phase with different load ratios R in the temperature range 200–550°C. Crack closure level and crack length were measured using the potential drop technique.<br/><br>
A correlation between effective J-integral range and crack propagation rate was found after compensating for crack closure, making the ΔJeff a possible fracture mechanical parameter for prediction of crack propagation rates under given loading conditions.},
  author       = {Jacobsson, Lars},
  keyword      = {crack closure,image analysis,potential drop,in-situ scanning elecron microscopy,crack propagation experiments,Thermo-mechanical fatigue,Inconel 718},
  language     = {eng},
  pages        = {120},
  publisher    = {ARRAY(0x7ac6f28)},
  title        = {Thermo-mechanical Fatigue Crack Propagation in Inconel 718},
  year         = {2007},
}