Assessment of Residual Stress and Determination of Stress Directionality by Instrumented Indentation Technique

2007 ◽  
Author(s):  
Dongil Kwon ◽  
Min-Jae Choi ◽  
Kug-Hwan Kim ◽  
Kyung-Woo Lee ◽  
Kwang-Ho Kim
Keyword(s):  
Residual Stress ◽  
Stress Measurement ◽  
Quantitative Relation ◽  
Instrumented Indentation ◽  
Promising Alternative ◽  
Target Region ◽  
Indentation Technique ◽  
Conventional Tests ◽  
Depth Curve ◽  
Knoop Indenter

The instrumented indentation technique has taken the limelight as a promising alternative to conventional residual stress measurement methods for welds with rapid microstructural gradients because of its easy and nondestructive testing procedure. The technique is based on the key concept that the deviatoric-stress part of residual stress affects the indentation load-depth curve. By analyzing the difference between the residual stress-induced curve and residual stress-free curve, the quantitative residual stress of the target region can be evaluated. To determine the stress-free curve of the target region, we take into consideration microstructural changes that accommodate strength differences. In addition, we determine the ratio of the non-equibiaxial residual stress by using an asymmetric Knoop indenter, which has an elongated four-sided pyramidal geometry. We find that the load-depth curve is changed on penetration direction of the long diagonal for Knoop indenter, and derive a quantitative relation between the stress ratio and the load difference through both theoretical analysis and experiments. Finally, indentation tests and conventional tests were performed on the welded zone to verify the applicability of the technique. The estimated residual stress values obtained from instrumented indentation technique agreed well with those from conventional tests.

Application of Instrumented Indentation Technique to Evaluate Residual Stress and Stress Directionality

2008 ◽  
Vol 385-387 ◽  
pp. 889-892
Author(s):  
Min Jae Choi ◽  
In Geun Kang ◽  
Kwang Ho Kim ◽  
Dong Il Kwon
Keyword(s):  
Residual Stress ◽  
Stress Measurement ◽  
Indentation Load ◽  
Hole Drilling ◽  
Specimen Preparation ◽  
Instrumented Indentation ◽  
Promising Alternative ◽  
Indentation Technique ◽  
Ultrasonic Methods ◽  
Process Characterization

The instrumented indentation technique (IIT) is a powerful method for evaluating mechanical properties of materials such as elastic modulus, tensile strength, fracture toughness and residual stress. Especially, IIT is a promising alternative to conventional methods of residual stress measurement such as hole drilling, saw cutting, X-ray/neutron diffraction, and ultrasonic methods because of its various advantages of nondestructive specimen preparation, easy process, characterization of material properties on local scales and measurement of in-service structures. Evaluation of residual stress using IIT is based on the key concepts that the deviatoric-stress part of the residual stress affects the indentation load-depth curve and that the quantitative residual stress in a target region can be evaluated by analyzing the difference between the residual stress-induced indentation curve and residual stress-free curve. To verify the applicability of the suggested technique, indentation tests were performed on the welded zone.

Instrumented-Indentation-Technique-Based Residual Stress Characterization for Weldment of Structural Components

2006 ◽  
Author(s):  
Dongil Kwon ◽  
Jung-Suk Lee ◽  
Kwang-Ho Kim ◽  
Afshin Motarjemi ◽  
Julian Speck
Keyword(s):  
Residual Stress ◽  
Welding Process ◽  
Indentation Load ◽  
Welding Residual Stress ◽  
Hole Drilling ◽  
Structural Components ◽  
Instrumented Indentation ◽  
Indentation Technique ◽  
Safety And Reliability ◽  
Depth Curve

The weld joints in structural components have long been considered important sites for safety and reliability assessment. In particular, the residual stress in piping weldments induced by the welding process must be evaluated accurately before and during service. This study reports an indentation technique for evaluating welding residual stress nondestructively. Indentation load-depth curves were found to shift with the magnitude and direction of the residual stress. Nevertheless, contact depths in the stress-free and stressed states were constant at a specific indentation load. This means that residual stress induces additional load to keep contact depth constant at the same load. By taking these phenomena into account, welding residual stress was obtained directly from the indentation load-depth curve. In addition, the results were compared with values from the conventional hole-drilling and saw-cutting method.

Nondestructive Evaluation of Welding Residual Stress in Power Plant Facilities Using Instrumented Indentation Technique

2005 ◽  
Vol 297-300 ◽  
pp. 2122-2127 ◽  
Author(s):  
Yeol Choi ◽  
Yun Hee Lee ◽  
Jae Il Jang ◽  
Sang Ki Park ◽  
Kwang Ho Kim ◽  
...  
Keyword(s):  
Residual Stress ◽  
Power Plant ◽  
Welding Process ◽  
Indentation Load ◽  
Welding Residual Stress ◽  
Hole Drilling ◽  
Instrumented Indentation ◽  
Indentation Technique ◽  
Safety And Reliability ◽  
Depth Curve

The weld joints in power-plant pipelines have long been considered important sites for safety and reliability assessment. In particular, the residual stress in pipeline weldments induced by the welding process must be evaluated accurately before and during service. This study reports an indentation technique for evaluating welding residual stress nondestructively. Indentation load-depth curves were found to shift with the magnitude and direction of the residual stress. Nevertheless, contact depths in the stress-free and stressed states were constant at a specific indentation load. This means that residual stress induces additional load to keep contact depth constant at the same load. By taking these phenomena into account, welding residual stress was obtained directly from the indentation load-depth curve. In addition, the results were compared with values from the conventional hole-drilling and saw-cutting methods.

Nondestructive Measurement of Non-Equibiaxial Welding Residual Stresses Using Instrumented Indentation Technique With Knoop Indenter

2010 ◽  
Author(s):  
Min-Jae Choi ◽  
Young-Cheon Kim ◽  
Won-Seok Song ◽  
Dongil Kwon
Keyword(s):  
Experimental Data ◽  
Residual Stress ◽  
Residual Stresses ◽  
Diffraction Method ◽  
Biaxial Stress ◽  
Instrumented Indentation ◽  
Welded Structures ◽  
Indentation Technique ◽  
Knoop Indenter ◽  
Depth Curves

Welding residual stresses which are generated in almost all welded structures unavoidably can come to be serious cause of fracture and failure of in-service welded structures. Various techniques have been developed to measure and estimate welding residual stresses such as hole-drilling method, saw-cutting method, X-ray/neutron diffraction method and so on. The instrumented indentation technique (IIT) is being attracted to significant alternative as a measurement method of residual stresses because of it’s nondestructive characteristic and usefulness of measurement on local scales. Basic concept of IIT to evaluate residual stresses is to compare two indentation load-depth curves that are measured experimentally between under stress-free state and under stressed state. In case of using Vickers indenter, average surface residual stress can be measured quantitatively from analyzing measured load diffrerence. Each x, y directional residual stresses can be evaluate by using Knoop indenter. Indenting each directions with Knoop indenter, difference load-depth curves are measured under non-equibiaxial stress state. Residual stress directionality can be expressed as the function of the load-difference ratio calculated from the load-depth curves and the conversion factor ratio that is constant regardless of indentation depth. This function was verified with the experimental data and the results of finite element analyses on various biaxial stress states, Knoop indentation model showed good agreement between the experimental data and the simulation results.

A New Method for Nondestructive Evaluation of Mechanical Properties Using Instrumented Indentation Technique

2007 ◽  
Vol 26-28 ◽  
pp. 1239-1242
Author(s):  
Kyung Woo Lee ◽  
Kug Hwan Kim ◽  
Kwang Ho Kim ◽  
Dong Il Kwon
Keyword(s):  
Residual Stress ◽  
Tensile Properties ◽  
Indentation Test ◽  
Indentation Load ◽  
Instrumented Indentation ◽  
Target Region ◽  
The Difference ◽  
Stress States ◽  
Analytic Models ◽  
Depth Curve

The development of the instrumented indentation test (IIT), which gives accurate measurements of the continuous variation in indentation load as a function of depth, has paved the way to assessing tensile properties and residual stress in addition to hardness by analyzing the indentation load-depth curve. In this study, analytic models and procedures are presented for evaluating tensile flow properties and residual stress states using IIT. Tensile properties were obtained by defining representative stress and strain beneath the spherical indenter. The evaluation of residual stress is based on the concepts that the deviatoric stress part of the residual stress affects the indentation load-depth curve, and that analyzing the difference between the residual stressinduced indentation curve and the residual stress-free curve permits evaluation of the quantitative residual stress in a target region.

Residual Stress Estimation with Identification of Stress Directionality Using Instrumented Indentation Technique

2007 ◽  
Vol 345-346 ◽  
pp. 1125-1128 ◽  
Author(s):  
Jae Hwan Han ◽  
Jung Suk Lee ◽  
Yun Hee Lee ◽  
Min Jae Choi ◽  
Gyu Jei Lee ◽  
...  
Keyword(s):  
Residual Stress ◽  
Indentation Load ◽  
Instrumented Indentation ◽  
Indentation Technique ◽  
Residual Stress State ◽  
Significant Research ◽  
Knoop Indentation ◽  
Stress Estimation ◽  
Depth Curve ◽  
Depth Curves

The instrumented indentation technique (IIT) has recently attracted significant research interest because it is nondestructive and easy to perform, and can characterize materials on local scales. Residual stress can be determined by analyzing the indentation load-depth curve from IIT. However, this technique using a symmetric indenter is limited to an equibiaxial residual stress state. In this study, we determine the directionality of the non-equibiaxial residual stress by using the Knoop indentation technique. Different indentation load-depth curves are obtained at nonequibiaxial residual stresses depending on the Knoop indentation direction. A model for Knoop indentation was developed through experiments and theoretical analysis.

Effects of strain hardening and residual stress in impression on the instrumented indentation technique

2006 ◽  
Vol 21 (7) ◽  
pp. 1680-1686
Author(s):  
L.Z. Liu ◽  
Y.W. Bao ◽  
Y.C. Zhou
Keyword(s):  
Residual Stress ◽  
Strain Hardening ◽  
Energy Analysis ◽  
Maximum Load ◽  
Contact Theory ◽  
Elastic Contact ◽  
Instrumented Indentation ◽  
Indentation Technique ◽  
Indentation Tests ◽  
Elastic Loading

Finite element analyses were carried out to simulate the loading, unloading, and reloading processes of indentation tests. It was found that the validity of applying the elastic contact theory to the indentation unloading process is strongly related to the strain hardening and residual stress in impression. It is the combination of strain hardening and residual stress that causes the unloading or reloading curves to show elastic loading in the range from zero to the maximum load whereas the reloading curve on the impression without strain hardening and residual stress shows elastic–plastic loading in the same range. These computations indicate that applying the elastic contact theory to the unloading or reloading processes, the fundamental prerequisite of the instrumented indentation technique, is valid because of the existence of strain hardening and residual stress. The mechanism of this hardening effect is discussed through energy analysis.

Evaluation of Welding Residual Stresses in Power Plant Facilities by Using a Newly Developed Indentation Technique

2002 ◽  
Author(s):  
Jae-il Jang ◽  
Dongil Son ◽  
Yeol Choi ◽  
Yun-Hee Lee ◽  
Won-Jae Ji ◽  
...  
Keyword(s):  
Residual Stress ◽  
Power Plant ◽  
Residual Stresses ◽  
Stress Measurement ◽  
Welding Residual Stress ◽  
Large Scatter ◽  
Indentation Technique ◽  
Cutting Test ◽  
Non Destructive ◽  
Non Destructive Techniques

It is well known that residual stress is one of the important problems in welding design/fabrications and sound maintenance of welded structures. Thus, the demand for quantitative evaluation of welding residual stress has been increased. However, conventional non-destructive techniques for welding residual stress measurement have many difficulties in in-field applications according to poor repeatability, large scatter of obtained data, complex procedures, inaccurate results, and etc. To overcome these difficulties, a newly developed indentation technique was proposed in this study, and applied to evaluate the welding residual stress in electric power plant facilities. By comparing with the stress values obtained from the destructive saw-cutting test, it could be concluded that the new indentation technique is very useful for quantitative/non-destructive evaluation of welding residual stresses in industrial fields such as power plant facilities.

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