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.

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.

Structure Assessment Using Instrumented Indentation: Strength, Toughness and Residual Stress

2018 ◽  
Author(s):  
Dongil Kwon ◽  
Jong Hyoung Kim ◽  
Ohmin Kwon ◽  
Woojoo Kim ◽  
Sungki Choi ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Residual Stress ◽  
Tensile Properties ◽  
Hole Drilling ◽  
Uniaxial Tensile ◽  
Small Scale ◽  
Specimen Preparation ◽  
Instrumented Indentation ◽  
Uniaxial Tensile Testing

The instrumented indentation technique (IIT) is a novel method for evaluating mechanical properties such as tensile properties, toughness and residual stress by analyzing the indentation load-depth curve measured during indentation. It can be applied directly on small-scale and localized sections in industrial structures and structural components since specimen preparation is very easy and the experimental procedure is nondestructive. We introduce the principles for measuring mechanical properties with IIT: tensile properties by using a representative stress and strain approach, residual stress by analyzing the stress-free and stressed-state indentation curves, and fracture toughness of metals based on a ductile or brittle model according to the fracture behavior of the material. The experimental results from IIT were verified by comparing results from conventional methods such as uniaxial tensile testing for tensile properties, mechanical saw-cutting and hole-drilling methods for residual stress, and CTOD test for fracture toughness.

Application of Nondestructive Instrumented Indentation Technique in Small-Scale Testing of Pressure Vessel and Piping Systems

2008 ◽  
Author(s):  
Kyung-Woo Lee ◽  
Kug-Hwan Kim ◽  
Kwang-Ho Kim ◽  
Young-Hwan Choi ◽  
Hae-Dong Chung ◽  
...  
Keyword(s):  
Residual Stress ◽  
Nondestructive Method ◽  
Small Scale ◽  
Specimen Preparation ◽  
Instrumented Indentation ◽  
Destructive Testing ◽  
Indentation Technique ◽  
Piping Systems ◽  
Testing Techniques ◽  
Hardness Model

Most small-scale testing techniques are essentially scaled-down versions of conventional testing techniques: they use specimens of similar geometry applied in a similar manner to estimate properties equivalent to those obtained for larger specimens. However, using these techniques for safety assessment of structures and piping systems requires general agreement about the techniques and validation of their results. In addition, these techniques all require destructive testing. In this study we adopt a new nondestructive method to measure the mechanical properties using the instrumented indentation technique. This technique can be applied directly in small-scale and localized sections because of its high spatial resolution. It also has the significant advantage of simplicity of specimen preparation and experimental procedure. During instrumented indentation testing, the load and penetration depth of an indenter tip driven into the sample are monitored, and material properties such as strength, fracture toughness and residual stress are evaluated from this information: the tensile properties by defining a representative stress and strain underneath a spherical indenter; the residual stress values near weldments by using the stress-insensitive contact hardness model.

Application of Instrumented Indentation Technique to Small-Scale Testing of Pressure Vessels and Piping Systems

2009 ◽  
Author(s):  
Kug-Hwan Kim ◽  
Seung-Kyun Kang ◽  
Min-Jae Choi ◽  
Kwang-Ho Kim ◽  
Dongil Kwon
Keyword(s):  
Residual Stress ◽  
Pressure Vessels ◽  
Small Samples ◽  
Uniaxial Tensile ◽  
Small Scale ◽  
Specimen Preparation ◽  
Instrumented Indentation ◽  
Flow Properties ◽  
Indentation Technique ◽  
Piping Systems

The instrumented indentation technique (IIT) is a powerful tool for measuring mechanical properties by analyzing the load-penetration depth curve. It differs from conventional test methods such as tensile testing, CTOD, etc., in being applicable to small samples and to localized sections where material properties change rapidly. It also has the significant advantage of simplicity in specimen preparation and experimental procedure. Analytic models and procedures are presented here for evaluating flow properties and stress state using IIT; the flow properties are treated by defining the representative stress and strain underneath a spherical indenter and the residual stress by using a stress-insensitive contact hardness model. Flow properties of 5 steel materials were measured by IIT and compared with those from uniaxial tensile tests. The residual stress states of a welded joint were evaluated and compared with those measured by mechanical saw cutting. Examples of the application of IIT to small-scale materials and localized sections of pressure vessel and piping systems in situ are also presented.

Weld Residual Stress Measurement on Ship Structures

2020 ◽  
Vol 36 (01) ◽  
pp. 41-51
Author(s):  
Yu-Ping Yang ◽  
T. D. Huang ◽  
Steve Scholler ◽  
Randy Dull ◽  
Charles R. Fisher ◽  
...  
Keyword(s):  
Residual Stress ◽  
Stress Measurement ◽  
Small Samples ◽  
Magnetic Method ◽  
Hole Drilling ◽  
Mechanical Grinding ◽  
Ship Structures ◽  
X Ray ◽  
Ultrasonic Methods ◽  
Time Required

Weld residual stresses on ship structures were significantly investigated by using a three-step approach. Step 1 is to measure residual stress on small samples in laboratories to validate measurement methods, step 2 is to measure residual stress on three test panels made of DH36, HSLA-65, and HSLA-80 in a shipyard, and step 3 is to measure residual stress on a large mock-up unit and on a tie-down. Step-1 and step-2 study, presented in the Society of Naval Architects and Marine Engineers-2017 conference, concluded that portable X-ray equipment can be used in a shipyard environment to provide reliable measurements. Residual stress was successfully measured on small welded joints, the DH36 panel, and the HSLA-65 panel, but not on the HSLA-80 panel. The reason for poor measurements on the HSLA-80 panel was that the primer on HSLA-80 surfaces blocked the diffracted X-ray. To achieve a good measurement, mechanical grinding and electropolishing were investigated to remove the primer before measurement. The minimum electropolishing time required to remove the compressive stress induced by mechanical grinding was established by experimental trials. With the electropolishing process, reasonable measurements were achieved on the HSLA-80 panel, a tie-down, and the knuckle joints of the large mock-up unit. This study reports the measured stresses on the HSLA-80 panel, the tie-down, and the knuckle joints. Welding, as one of the most important manufacturing processes in shipbuilding, inevitably induces residual stress and distortion on ship structures. Multiple methods have been developed to measure residual stress with nondestructive and destructive techniques. The common nondestructive techniques include X-ray diffraction (XRD) (Gou et al. 2015; Bandyopadhyay et al. 2018; Monine et al. 2018), neutron diffraction (Palkowski et al. 2013), magnetic method, ultrasonic methods (Bray & Junghans 1995), and impact-indentation method (Zhu et al. 2015). The destructive techniques include hole-drilling and ring-core methods, and the destructive techniques include block removal, splitting, layering, and contour methods (Leggatt et al. 1996).

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.

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