Q: What's the difference between ABI® and IIT?
A: Automated Ball Indentation ® (ABI® ) is a specific indentation test that uses a ball indenter and the Haggag partial unloading technique to accuratley measure the tensile and fracture toughness properties of metals. Instrumented Indentation Testing (IIT) is a general term for ultra low force nanoindenation using a Berkovich pyramidal indenter and is used to examine thin films and coatings for nano-hardness (Martens Hardness)
Q: Can I get a stress-strain curve from a linear geometry indenter?
A: Linear geometry indenters can only produce hardness versus depth, and you get one value of strain regardless of increasing depth. Nonlinear geometry (Ball) indenters produce increasing values of strain and stress as depth increases. In order to obtain macroscopic properties, such as a stress-strain curve, the indenter size should be several times the grain size of the material
Q: What are the key mechanical properties obtained from an ABI® test?
A: ABI tests are localized and nondestructive and measure the following key mechanical properties:
- Yield Strength
- True-Stress/True-Plastic Strain Curve
- Strain-Hardening Exponent (n)
- Strength Coefficient (k)
- Uniform Ductility
- Ultimate Strength
- Fracture Toughness Values
- Reference temperature and fracture toughness master curve analysis
Q: What are the advantages of ABI® testing?
Q: DOES INTERNAL PRESSURE OF AN IN-SERVICE PIPELINE AFFECT THE ABI® TEST?
Q: CAN YIELD STRENGTH BE
DETERMINED FROM HARDNESS
A: The advantages are many. Here’s a few.
- Testing can be performed directly on the component, thus eliminating the need to destroy the component and cut samples. We can design and manufacture custom fixtures if necessary, and we have a local machine shop to keep costs low.
- The nondestructive ABI® test provides a stress-strain curve and fracture toughness data [Haggag Toughness Method (HTM)] eliminating the need to perform Tensile and Fracture Toughness testing. And the test takes less than two minutes to perform.
- For failure analysis, new alloy development, or when testing at extreme high/low temperatures, only small amounts of material are needed. The smallest specimen size is 0.2" x 0.2" x 0.1" thick. The specimens need to be prepared for indentation testing with two parallel smooth (63 rms or better) surfaces.
- Small specimens can also be mounted in Bakelite (avoid epoxy since it is too soft and will affect the test results).
- Test specimens may also be the broken halves of traditional destructive specimens (e.g. tensile, Charpy V-notch, fracture toughness).
- The ABI® test technique is the only test that provides accurate stress-strain curves on small welds and their heat-affected- zones (HAZs). It can provide an overlay of the stress-strain curves from the base metal, weldment, and the HAZ for instant comparison of mechanical properties. Weld specimens should be properly etched to reveal the HAZ.
A: Internal pressure or a hoop stress condition creates ONLY elastic stress on the internal surface of an in-service pipeline. The maximum allowed hoop stress cannot produce yield strength of the pipe in order to avoid pipeline bulging and any potential failure. Hence, the elastic stress (which is lower than the yield strength by the margin of safety used in the MAOP) cannot affect the test results of the ABI test.
A: Yield strength cannot be measured by the hardness test. In pipeline steels yield strength (YS) is the stress at a small strain value of 0.5%. Any hardness number could be correlated empirically to ultimate tensile strength (UTS), which is the stress at 8-10% strain. UTS is usually much higher than YS and the two are not interchangeable.