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For the safe use of old facilities, it is necessary to accurately predict the lifespan through regular diagnosis of material properties.
We introduce the instrumented indentation technique.

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Instrumented Indentation Technique (IIT)

What Is the Instrumented Indentation Technique (IIT)?

In ASTM E 2546-07, IIT is defined as a mechanical test that measures the response of a material
to the stress and strain of a shaped indenter imposed by forcing the indenter into a material and
monitoring the force on, and displacement of, the indenter as a function of time during
a full loading-unloading test cycle. It is not restricted to specific test loads, displacement ranges, or indenter types.

What Are the Characteristics of IIT?

By applying an indenting load on the surface of target material, we can get an indentation load (L)-penetration depth (h) curve.
An indentation no deeper than 100 μm is usually suggested to avoid unnecessary indenting damage, since nondestructive testing is intended.
By analyzing the indentation loading-unloading curve using the interpretation of stress field beneath the indenter,
we can obtain various mechanical properties such as strength, fracture toughness and residual stress. Therefore,
we call this curve a fingerprint of the material. Of course, the accuracy of the data depends on the mechanical analysis of indentation curves.
When conventional mechanical testing is not available, for instance in in-field testing of on-site material nondestructively,
IIT can be a very good alternative. Also, IIT provides reliable mechanical output that is close to conventional mechanical data with less scatter.
The mechanical response measured by IIT is from a very small volume of a material close to the indentation site.
This locality of property measurement has the benefit of high-spatial-resolution testing and makes property mapping possible.
For instance, it allows testing of the heat-affected zones of weldments, which cannot be tested destructively because of their irregular shape and small volume.
When assessing the local properties of weld metal, heat-affected zone and base metal,
IIT can be an efficient and effective technique for mapping variations in local properties and finding the weak points.

Standards

ASTM E2546 concerns Instrumented Indentation Testing. This standard contains information about testing instruments,
indenter requirements, instrument compliance, etc. In addition, Instrumented Indentation Testing is used
in ASME Code Section IX as an alternative method to Vickers hardness testing in QW-290 (Code Case 2703).
Finally, Instrumented Indentation Testing is introduced in ISO as ISO TR 29381. This document mainly introduces
the evaluation of tensile properties using IIT but it also treats in an Annex the evaluation of residual stress using IIT.
In addition, the IIT residual stress evaluation algorithm was recognized, the ASME Code Case has been approved as Code Case N-881,
and more It has recently been selected to be published in ISO/TS 19096 (publication stage).

Standardization & Code Contents
KS B0950 (2002)
Metallic Materials - Instrumented Indentation test for Indentation Tensile Properties
KS B0951 (2005)
Instrumented Indentation tests on welds in steel-Measurement of residual stress on welded joints
ISO/TR 29831 (2008)
Measurement of mechanical Properties by instrumented indentation test: Indentation tensile Properties
ISO/TR 29831 annex (2008)
Measurement of the residual stress by instrumented indentation test
ISO/TS 19096(Publication stage)
Evaluation of stress change using indentation force differences
MDF A370 (2006)
Measurement of the mechanical properties and residual stress by instrumented indentation test
ASME Code case 2703 (2011)
Instrumented Indentation testing as Alternative Hardness Test for QW-290 Temper Bead Welding
Code Case N-881 (2017)
Exempting SA-508 Grade 1A From PWHT Based on Measurement of Residual Stress in Class 1 applications
ASME E2546-15
Standard Practice for Instrumented Indentation Testing

Structures built in the period of rapid economic growth in the 1970s are severely deteriorated due to over 30 years of use and have the potential for large industrial accidents.

Therefore, for the safe use of old facilities, it is necessary to accurately predict the lifespan through regular diagnosis of material properties.
Therefore, for the safe use of these old industrial facilities and facility management, in addition to the existing laboratory background mechanical property evaluation techniques, it is urgent to supplement the system that determines the timing of replacement and repair by securing/collecting data on material deterioration and life prediction, and determining the risk and inspection cycle of equipment through this by introducing technology to monitor material characteristics according to temperature aging in industrial sites. In order to utilize these developed materials in industries, it is necessary to secure the reliability of materials and parts based on the accumulation of accurate properties through the application of appropriate property evaluation techniques.
Uniaxial tensile and fracture mechanics tests, which are the existing standard methods for material property evaluation, provide a lot of information on deformation and fracture behavior. However, since standard specimens in bulk form are required, damage may be caused by notches in equipment and structures in the process of collecting specimens, which may rather harm the safety of the structure, and due to stress relief and damage during collection, standard specimens may have different properties from the original site structure.
In addition, looking at the requirements of the test technique for application to the property evaluation of micromaterials, first, it is necessary to evaluate the mechanical properties of only thin films having a thickness of at least several hundred Å, and in the case of nano-phases, grasp the mechanical properties of each phase. In order to do this, it is necessary to be able to limit the inside of the crystal grains to the area of the property evaluation.

As a solution to these problems, an automated indentation technique that can be used directly in the field because it is quasi-non-destructive and has a simple test method, and a nano indentation technique with an indentation depth of about nm with the application of extremely low loads were proposed.

These test methods are a method to calculate the continuous deformation behavior during the indentation test as an indentation load-displacement curve and to evaluate the mechanical properties related to various deformations and fractures based on this, unlike the existing hardness test that only obtains hardness. The automated indentation technique can evaluate not only hardness but also fracture characteristics based on appropriate modeling and flow characteristics of materials, including yield strength, tensile strength, and processing hardening index, such as uniaxial tensile tests, by analyzing the indentation situation during spherical indentation.
In addition, in the nano-indentation technique, where the study of evaluating the hardness and modulus of elasticity using a pointed indenter with a certain angle was mainly used to evaluate the properties of thin film materials and nanophase, recently, researches are underway to evaluate high-dimensional properties related to deformations such as flow curves by incorporating the techniques analyzed in the automated indentation technique. In addition, these property evaluation techniques can evaluate local weaknesses such as welds through changes in indenter size and shape, or even evaluate material behavior in various deterioration situations through attachment of an atmosphere device.