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.

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.

Determination of Residual Stress Directionality by Instrumented Indentation Testing Using Anisotropic Indenter

2018 ◽  
Author(s):  
Sungki Choi ◽  
Jong Hyoung Kim ◽  
Jun Sang Lee ◽  
Kyungyul Lee ◽  
Min-Jae Choi ◽  
...  
Keyword(s):  
Residual Stress ◽  
Indentation Test ◽  
Surface Preparation ◽  
Field Testing ◽  
Indentation Load ◽  
Indentation Testing ◽  
Instrumented Indentation ◽  
Element Analysis ◽  
Knoop Indenter ◽  
Depth Curves

Residual stress is a major factor in failure and fracture in structures or electronic components. Various testing methods are used to measure residual stress: there are saw-cutting, holedrilling, X-ray diffraction and layer-removing methods. In particular, instrumented indentation testing (IIT) has many advantages: it is a simple and non-destructive procedure that can be used for in-field testing. In previous research, we proposed an algorithm for evaluating the magnitude and directionality of residual stress using an asymmetric Knoop indenter with long and short axes in the ratio 7.11:1. Indenting in different directions with a Knoop indenter creates different indentation load-depth curves depending on the residual stress state. In addition, the directionality of the residual stress can be expressed as a function of the load difference ratio calculated from these load-depth curves. However, When the Knoop indentation test is performed at small indentation depths, experimental issues such as surface preparation or indentation normality can become significant as the load difference decreases. In order to solve these issues, we introduce a wedge indenter, that makes it possible to select the edge length independent of indentation depth. We can thus decrease indent size when working in a small testing area. The load difference between the stress-free and stressed state is related to the sensitivity of residual stresses, and a wedge indenter can maximize the sensitivity to residual stress. In this study, we suggest a way to use the wedge indenter and verify the model using cruciform bending specimens and finite element analysis.

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.

Analysis of circumferentially welded thin-walled cylinders to study the effects of tack weld orientations and joint root opening on residual stress fields

2009 ◽  
Vol 223 (5) ◽  
pp. 1037-1049 ◽  
Author(s):  
N U Dar ◽  
E M Qureshi ◽  
A M Malik ◽  
M M I Hammouda ◽  
R A Azeem
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Arc Welding ◽  
Operating Conditions ◽  
Stress Fields ◽  
Welded Structures ◽  
Prime Concern ◽  
Thin Walled ◽  
Tack Weld ◽  
Welding Processes

In recent years, the demand for resilient welded structures with excellent in-service load-bearing capacity has been growing rapidly. The operating conditions (thermal and/or structural loads) are becoming more stringent, putting immense pressure on welding engineers to secure excellent quality welded structures. The local, non-uniform heating and subsequent cooling during the welding processes cause complex thermal stress—strain fields to develop, which finally leads to residual stresses, distortions, and their adverse consequences. Residual stresses are of prime concern to industries producing weld-integrated structures around the globe because of their obvious potential to cause dimensional instability in welded structures, and contribute to premature fracture/failure along with significant reduction in fatigue strength and in-service performance of welded structures. Arc welding with single or multiple weld runs is an appropriate and cost-effective joining method to produce high-strength structures in these industries. Multi-field interaction in arc welding makes it a complex manufacturing process. A number of geometric and process parameters contribute significant stress levels in arc-welded structures. In the present analysis, parametric studies have been conducted for the effects of a critical geometric parameter (i.e. tack weld) on the corresponding residual stress fields in circumferentially welded thin-walled cylinders. Tack weld offers considerable resistance to the shrinkage, and the orientation and size of tacks can altogether alter stress patterns within the weldments. Hence, a critical analysis for the effects of tack weld orientation is desirable.

Measurement of Weld Mechanical Properties Using an Instrumented Indentation Technique

2017 ◽  
Vol 754 ◽  
pp. 383-386
Author(s):  
Kee Nam Song
Keyword(s):  
Mechanical Properties ◽  
Heat Affected Zone ◽  
Weld Zone ◽  
Base Material ◽  
Metal Structure ◽  
Instrumented Indentation ◽  
Welded Structures ◽  
Indentation Technique ◽  
Lower Confidence ◽  
Welded Structure

Different microstructures in the weld zone of a metal structure including a fusion zone and a heat affected zone, are formed as compared to the base material. Consequently, the mechanical properties in the weld zone are different from those in the base material to a certain degree owing to different microstructures and residual welding stresses. When a welded structure is loaded, the mechanical behavior of the welded structure might be different from the case of a structure with homogeneous mechanical properties. It is known that obtaining the mechanical properties in the weld is generally difficult owing to the narrow regions of the weld and interfaces. As an alternative way to obtain the weld mechanical properties, the weld mechanical properties of Alloy800HT, SUS316L, and Alloy617, were recently measured using an instrumented indentation technique, and the representative weld mechanical properties of these materials were estimated with a 95% lower confidence level for later structural analyses of the welded structures.

Residual Stresses in Steel and Zirconium Weldments

1997 ◽  
Vol 119 (2) ◽  
pp. 137-141 ◽  
Author(s):  
J. H. Root ◽  
C. E. Coleman ◽  
J. W. Bowden ◽  
M. Hayashi
Keyword(s):  
Residual Stress ◽  
Electron Beam ◽  
Neutron Diffraction ◽  
Residual Stresses ◽  
Prolonged Exposure ◽  
Electron Beam Welding ◽  
Three Dimensional ◽  
Diffraction Method ◽  
Outer Diameter ◽  
Stress Relieving

Three-dimensional scans of residual stress within intact weldments provide insight into the consequences of various welding techniques and stress-relieving procedures. The neutron diffraction method for nondestructive evaluation of residual stresses has been applied to a circumferential weld in a ferritic steel pipe of outer diameter 114 mm and thickness 8.6 mm. The maximum tensile stresses, 250 MPa in the hoop direction, are found at mid-thickness of the fusion zone. The residual stresses approach zero within 20 mm from the weld center. The residual stresses caused by welding zirconium alloy components are partially to blame for failures due to delayed hydride cracking. Neutron diffraction measurements in a GTA-welded Zr-2.5Nb plate have shown that heat treatment at 530°C for 1 h reduces the longitudinal residual strain by 60 percent. Neutron diffraction has also been used to scan the residual stresses near circumferential electron beam welds in irradiated and unirradiated Zr-2.5Nb pressure tubes. The residual stresses due to electron beam welding appear to be lower than 130 MPa, even in the as-welded state. No significant changes occur in the residual stress pattern of the electron-beam welded tube, during a prolonged exposure to thermal neutrons and the temperatures typical of an operating nuclear reactor.

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.

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.

scholarly journals Residual Stresses Induced by Surface Working and Their Improvement by Emery Paper Polishing

2020 ◽  
Vol 4 (2) ◽  
pp. 21
Author(s):  
Makoto Hayashi
Keyword(s):  
Residual Stress ◽  
Stainless Steel ◽  
Fatigue Strength ◽  
Residual Stresses ◽  
Diffraction Method ◽  
304 Stainless Steel ◽  
Heat Treated ◽  
Emery Paper ◽  
Type 304 ◽  
Type 304 Stainless Steel

In many of machine parts and structural components, materials surface would be worked. In this study, residual stresses on the surfaces were measured by X-ray diffraction method, and effects of surface working on the residual stresses were examined. In case of lathe machining of type 304 stainless steel bar, the residual stresses in circumferential directions are tensile, and those in axial directions are almost compressive. Highly tensile residual stresses in the circumferential directions were improved by emery paper polishing. 10 to 20 times of polishing changes high tensile residual stresses to compressive residual stresses. In the case of shot peening on a type 304 stainless steel plate, the compressive residual stress inside is several hundred MPa lower than that on the surface. By applying the emery paper polishing to the shot peened surface 10 or 20 times, the residual stress on the surface is improved to −700 MPa. While fatigue strength at 288 °C in the air of the shot peened material is 30 MPa higher than solution heat treated and electro-polished material, the fatigue strength of the shot peened and followed by emery paper polished material is 60 MPa higher. Thus, the emery paper polishing is simple and a very effective process for improvement of the residual stresses.

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.

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