Automated Ball Indentation Technique Research Articles

Evaluation of strength in stainless steel weld joints using ball indentation technique

In the present study, strength variations across the type 316LN stainless steel weld joints processed by advanced hot wire tungsten inert gas, activated tungsten inert gas, and hybrid laser metal inert gas welding processes were evaluated using automated ball indentation technique. The secondary dendrite arm spacing (SDAS) associated with welding heat input and welding thermal cycles strongly influenced the strength properties across the weld joints. The strength properties were lower at 823 K compared to 298 K because of thermally activated deformations. The hybrid laser metal inert gas welding process exhibited significantly narrower weld and higher strength in the weld and heat-affected zone due to finer SDAS and grain size, respectively, than the other weld joints.

Evaluation of bond interface characteristics of rotary friction welded carbon steel to low alloy steel pipe joints

In the present investigation, rotary friction weld joints were prepared between carbon steel and low alloy steel pipes. These types of similar and dissimilar configurations are in general, used for drill pipe joining. Low alloy steel for the friction welding in dissimilar configurations were used in two different microstructure state; a) as-received and b) quenched and tempered. The friction weld joints showed three distinct weld microstructure characteristics; a) radial plastic flow, b) axial plastic flow and, c) partial heat affected zone, for joining configurations. In general, microstructure characterization revealed grain size refinement and carbide precipitation in the vicinity of bond interface for all types of similar and dissimilar steel joining conditions. A characteristic bond layer width of ~2 μm was developed between the dissimilar steel weld joints whereas it was found to be absent for the similar weld joints. These weld joints were evaluated for their mechanical properties by using conventional tensile tests and furthermore by automated ball indentation technique. The study has also shown that in the case of dissimilar steel joints the mechanical properties of the bond interface can be obtained aptly by using an automated ball indentation technique. The quench and temper treatment given to the low alloy steel resulted in the improved bond interface strength. The improvement of the mechanical properties of the weld joints was attributed to the synergistic effect of grain size refinement and tempered martensite microstructure.

Quantitative evaluation of mechanical properties of machined surface layer using automated ball indentation technique

Machining-induced microstructure alteration in the machined surface layer possibly tends to result in the change of mechanical properties in this area that are different from the bulk material. It is very important to evaluate quantitatively mechanical properties of machined surface layer. In the present research, the nondestructive automated ball indentation (ABI) technique equipped with stress-strain microprobe system was employed to evaluate the mechanical properties of the machined surface layer generated by hard milling of AISI H13 steel. Through performing ABI tests, the mechanical properties including the true stress-strain curve, yield strength, ultimate tensile strength (UTS), strain hardening exponent and Brinell hardness were quantitatively acquired before and after hard milling. In addition, the fracture toughness can be determined by analyzing the continuous loading and unloading curves on the basis of the continuum damage mechanics (CDM). It indicates that the ABI technique can be exploited as a nondestructive technique for mechanical property evaluation of machined surface layer.

High temperature tensile properties of 316LN stainless steel investigated using automated ball indentation technique

Type 316LN stainless steel (SS) is the principal structural material for the components of sodium cooled fast reactors operating under elevated temperature conditions. In order to assess the degradation in strength of service exposed components using a small specimen testing technique such as automated ball indentation (ABI), it is necessary to carry out prior detailed ABI studies on the virgin material. In this investigation, the tensile behaviour of as-received 316LN SS were investigated at several temperatures in the range 298–973 K using ABI technique. The load-depth of indentation data measured from ABI tests was analyzed using semi-empirical relationships to obtain the tensile properties. The yield stress and the flow curves were determined by correlating ABI results with corresponding uniaxial tensile test results. Trend curve for tensile strength with temperature, as estimated from ABI tests, exhibited a plateau region in the temperature around 823 K, similar to uniaxial tensile tests. The variations of strength coefficient, strain hardening exponent, yield ratio, hardness and uniform ductility with temperature were evaluated from ABI tests. The ABI technique was found to estimate the influence of temperature on tensile properties sensitively.

Mechanical properties of bovine cortical bone based on the automated ball indentation technique and graphics processing method.

Cortical bone provides the main form of support in humans and other vertebrates against various forces. Thus, capturing its mechanical properties is important. In this study, the mechanical properties of cortical bone were investigated by using automated ball indentation and graphics processing at both the macroscopic and microstructural levels under dry conditions. First, all polished samples were photographed under a metallographic microscope, and the area ratio of the circumferential lamellae and osteons was calculated through the graphics processing method. Second, fully-computer-controlled automated ball indentation (ABI) tests were performed to explore the micro-mechanical properties of the cortical bone at room temperature and a constant indenter speed. The indentation defects were examined with a scanning electron microscope. Finally, the macroscopic mechanical properties of the cortical bone were estimated with the graphics processing method and mixture rule. Combining ABI and graphics processing proved to be an effective tool to obtaining the mechanical properties of the cortical bone, and the indenter size had a significant effect on the measurement. The methods presented in this paper provide an innovative approach to acquiring the macroscopic mechanical properties of cortical bone in a nondestructive manner.

Characterization of Reactor Pressure Vessel Steel by ABI Testing

Microstructure of the base metal, the multilayer welding seam and the two-layer cladding was characterized through the thickness of the WWER 440 reactor pressure vessel wall. Mechanical properties were determined by performing a series of instrumented indentations across the weld at room temperature. The results were treated by so-called automated ball indentation technique. Mechanical properties obtained by instrumented indentation from the local stress-strain behavior were compared with minimum values required by the standard.

Evaluation of variation of tensile strength across 316LN stainless steel weld joint using automated ball indentation technique

Tensile strength variation across 316LN stainless steel fusion welded joint comprising of base metal, deposited weld metal and heat affected zone (HAZ) has been evaluated by Automated Ball Indentation (ABI) technique. Automated Ball Indentation tests were conducted on the various zones of the steel weld joint at 300, 523 and 923 K. The flow curves obtained from ABI results were consistent with corresponding conventional uniaxial tensile test results. The HAZ exhibited higher tensile strength than the other regions of the steel weld joint at all investigated temperatures. The ratio of ultimate tensile strength to yield stress (YS), which represents the work hardening behaviour, increased with an increase in temperature for the base metal and HAZ; whereas it remained nearly the same for the weld metal.

Mechanical property evaluation of an Al-2024 alloy subjected to HPT processing

An aluminum-copper alloy (Al-2024) was successfully subjected to high-pressure torsion (HPT) up to five turns at room temperature under an applied pressure of 6.0 GPa. The Al-2024 alloy is used as a fuselage structural material in the aerospace sector. Mechanical properties of the HPT-processed Al-2024 alloy were evaluated using the automated ball indentation technique. This test is based on multiple cycles of loading and unloading where a spherical indenter is used. After two and five turns of HPT, the Al-2024 alloy exhibited a UTS value of ~1014 MPa and ~1160 MPa respectively, at the edge of the samples. The microhardness was measured from edges to centers for all HPT samples. These results clearly demonstrate that processing by HPT gives a very significant increase in tensile properties and the microhardness values increase symmetrically from the centers to the edges. Following HPT, TEM examination of the five-turn HPT sample revealed the formation of high-angle grain boundaries and a large dislocation density with a reduced average grain size of ~80 nm. These results also demonstrate that high-pressure torsion is a processing tool for developing nanostructures in the Al-2024 alloy with enhanced mechanical properties.

Characterization of Local Stress-Strain Behavior in WWER 440 Weld and Base Metal by Instrumented Indentation Technique

15Ch2MFA (base metal) as well as 10ChMFT (weld) steels used for WWER 440 nuclear reactor pressure vessel manufacturing present a gradient in mechanical properties through the wall thickness, which can hardly be assessed by conventional testing such as tensile or Charpy tests. Mechanical properties in the weld and base metal were therefore determined by performing a series of instrumented indentations across the weld at room temperature. The results were treated by so-called automated ball indentation technique. Local stress-strain behavior obtained by instrumented indentation was correlated to the tensile test data and microstructure characterized by metallographic analysis.

A Study on the Effect of Tempering Temperature on Tensile Properties of P92 Steel by Automated Ball Indentation Technique

P92 steel was normalized at 1353 K for 30 minutes followed by air cooling and subs equently tempered at 1013, 1033 and 1053 K for 60 minutes each followed by air cooling. The effect of tempering temperatures on the tensile properties of P92 steel has been investigated using automated ball indentation technique (ABI) at different test temperatures in the range of 300 K-923 K. The yield strength (YS), ultimate tensile strength (UTS) and strength coefficient (K) were determined and these were found to decrease with increase in tempering and test temperatures. The decrease in strength was attributed to the increase in M 23C6 precipitate size and lath width with higher tempering temperatures. The strain hard ening exponent (n) decreased with increase in the test temperature which is confirmed by increased pile up around indentation. The ABI results were in good agreement with the results obtained from conventional tensile tests.

Evaluating the Mechanical Properties of HPT Processed Aluminium Alloys Using Automated Ball-indentation Technique

Al-Cu and Al-Zn-Mg alloys exhibit excellent physical and mechanical properties, and are widely used for aerospace applications. However, these properties may be further improved through high-pressure torsion (HPT) processing. HPT processing was carried out on Al-2014 alloy and Al-7475 alloy to investigate the improvement in mechanical properties. Disks of coarse-grained Al- 2014 alloy and Al-7475 alloy were processed up to two turns of HPT, and the mechanical properties were evaluated using automated ball indentation (ABI) technique. HPT processing was carried out at atmospheric temperature, under pressure of 6GPa. The results show that, for Al-2014 alloy the ultimate tensile strength at the edge of HPT disk increased by a factor of ∼ 4, after 2 turns of HPT processing. Since, ABI technique provides the capability of obtaining extensive mechanical data using only a very small sample; it is an ideal procedure for evaluating the mechanical properties of samples processed by HPT.

Use of Portable Automated Ball Indentation System to Evaluate Mechanical Properties of Steel Pipes

In this study, portable automated ball indentation technique (PABI) has been applied to evaluate the few mechanical properties of steel pipes and excellent correlation has been obtained with conventional test results. A PABI system, developed and fabricated at National Metallurgical laboratory, India, was used to evaluate the mechanical properties. The operational parameters were optimized for various materials to measure yield strength, ultimate tensile strength, true-stress versus true-plastic-strain curve, strength coefficient (K), strain-hardening-exponent (n), hardness (BHN) and fracture toughness (KJC). This unit can be mounted on components with curved or flat surfaces and properties of the material could be evaluated by making a very small indentation. Also it has provision to use small test specimens. Automation of the test, where a computer and test controller were used in innovative ways to control the test as well as to analyze test data made it simple, accurate, economical and highly reproducible. A LabVIEW BASED S/W was made to control the unit.

Non-destructive studies on tensile and fracture properties of molybdenum at low temperatures (148 to 423 K)

Tensile and fracture properties of molybdenum have been studied using the automated ball indentation technique. Tests have been carried out at several temperatures in the range of 148 to 423 K at a constant strain rate. Tensile properties determined from these tests agreed well with published results from conventional tensile tests. Temperature dependence of indentation energy to fracture, the fracture toughness parameter specific to this technique using critical stress-to-fracture concept, showed a sharp transition from brittle to ductile condition. These results complement the previous studies on pressure vessel steels, and clearly demonstrate that automated ball indentation technique is a reliable and non-destructive method for determining tensile and fracture properties of materials.

Compressive mechanical behavior of nanocrystalline Fe investigated with an automated ball indentation technique

Nanocrystalline (nc) iron was produced by mechanical attrition and compacted into near fully dense samples. Isothermal annealing at 800 K resulted in grain sizes between 15 and 24 nm. A newly available Automated Ball Indentation system was used to study the compressive mechanical properties of the samples. The ABI method proved useful in examining the mechanical properties of nc iron on a more quantitative level than previously possible by conventional hardness testing methods. Stress–strain curves were obtained which indicated a compressive behavior similar to that of perfectly plastic materials: low strain hardening at high flow stresses around 3 GPa and a low room-temperature strain-rate sensitivity. The flow stresses were independent of the grain size in the range of the present study. The deformation pile-up around the indentations seems to have formed inhomogeneously, exhibiting intense plastic deformation in localized shear bands.