F.M. Haggag

Nondestructive determination of tensile properties and fracture toughness of cold worked A36 steel

Abstract Tensile and fracture properties of ASTM grade A36 steel have been studied using nondestructive Stress–Strain Microprobe™ system (SSM), which is developed on the basis of automated ball indentation (ABI) technique. Tests have been carried out on as-received, and cold worked (4, 8 and 12%) materials at several temperatures in the range −150°C–+200°C at a constant strain rate. Tensile properties determined from ABI tests agreed well with the results from conventional tensile tests. The elastic–plastic fracture toughness parameter K JC was estimated from the ABI data. As expected, cold working resulted in increase in strength, decrease in fracture toughness and increase in ductile to brittle transition temperature. ABI is a reliable nondestructive technique for determining tensile and fracture properties of materials and has potential applications in the nuclear industry particularly to determine toughness degradation due to aging in service.

INDENTATION-ENERGY-TO-FRACTURE (IEF) PARAMETER FOR CHARACTERIZATION OF DBTT IN CARBON STEELS USING NONDESTRUCTIVE AUTOMATED BALL INDENTATION (ABI) TECHNIQUE

Integrity of structures in various technologies depend on the fracture behaviors of materials, and in general the fracture characteristics of s tructural m aterials are evaluated using destructive tests, such as Charpy, fracture toughness, and other such techniques. However, for evaluating the material condition inservice, it is often not feasible or practical to cut samples from operating structures and nondestructive techniques are employed to determine the mechanical properties from which fracture behaviors are conjectured. Although many techniques, such as magnetic strength, Berkhausen noise, hardness, etc., were used in correlating the respective properties with fracture energ y measur ed from Charpy or fractu re toughness tests, these methodologies are essentially empirical with no real underlying technical justification. Recent advances using Automated Ball Indentation (ABI) technique clearly demonstrated the feasibility of obtaining, with excellent accuracy, the true stress-strain behaviors of ferritic steels and their weldments as well as heat-affected-zones (HAZs), stainless steels as well as electronic solders (SnSb, AgSn, etc.). We demonstrate here the application of the ABI technique in evaluating the energy to fracture in terms of a new parameter named Indentation Energy to Fracture (IEF). The new IEF parameter clearly depicts the DBTT (ductile-to-brittle-transition-temperature). ABI Technique The Automated Ball Indentation (ABI) has been demonstrated to measure the stress-strain behaviors of many structural metals such as ferritic steels, stainless steels, aluminum alloys, electronic solders, etc. (1) While the idea of ball indentation is not new, (2) the uniqueness of ABI lies in the fact that this technique does not require post measurement of the diameter of indentation using elaborate profilometry, optical interferometry, etc., which render the traditional methodology unsuitable for on-line monitoring of the mechanical properties of structures in-service. Based on thi s pri nciple, a porta ble/in-situ Stress-Strain Microprobe™ (SSM) system was developed by Advanced Technology Corporation (ATC) to test minimal material and to determine several mechanical properties (e.g. yield strength, flow properties, strain-hardening exponent, strength coefficient) of metallic structures including their welds and heat-affected zones.(3) The SSM system and test methods are based on well demonstrated and accepted physical and mathematical relationships which govern metal behavior under multiaxial indentation loading. (4)

Characterization of gradients in mechanical properties of SA-533B steel welds using ball indentation

Abstract Gradients in mechanical and fracture properties of SA-533B steel welds were studied using ball indentation technique. The local stress–strain behaviors of different microstructural zones of the weld were determined at various temperatures. Gradients in the strength of the base metal, weld metal and the different positions in the heat affected zone were observed to be consistent with the changes in the microstructure. The maximum in yield and the corresponding minimum in indentation energy to fracture occurred at around 1xa0mm from the fusion line.

Measurement of through-the-thickness variations of mechanical properties in SA508 Gr.3 pressure vessel steels using ball indentation test technique

Abstract The through-the-thickness variations of mechanical properties in SA508 Gr.3 pressure vessel steels were measured using the automated ball indentation (ABI) test technique. Key mechanical properties, such as the yield strength, ultimate strength, flow curve and hardness, were evaluated from indentation load-depth curves. The mechanical properties measured were location-dependent and the steepest gradients in the distributions of the mechanical properties appeared in the near-surface regions. The maximum through-the-thickness variations of the mechanical properties were in the range of 5–20% and they depended on the manufacturing process as well as the original wall thickness. It was concluded that the through-the-thickness variations in the mechanical properties were mainly caused by the location-dependent cooling rate during water quenching in the quality heat treatment which consisted of water quenching and tempering.

Effects of irradiation on the fracture properties of stainless steel weld overlay cladding

Abstract Stainless steel weld overlay cladding was fabricated using the submerged arc, single-wire, oscillating-electrode, and the three-wire, series-arc methods. Three layers of cladding were applied to a pressure vessel plate to provide adequate thickness for fabrication of test specimens, and irradiations were conducted at temperatures and to fluences relevant to power reactor operation. Post-irradiation test results of all cladding specimens show that, in the test temperature range from – 125 to 288°C, the yield strength increased by 40 to 5%, ductility increased insignificantly, and there was almost no change in ultimate tensile strength. All cladding exhibited ductile-to-brittle transition behavior during Charpy impact testing due to the dominance of delta-ferrite failures at low temperatures. On the upper shelf, energy was reduced up to 50% due to irradiation exposure. In addition, radiation damage resulted in 13 to 100 C shifts of the Charpy impact transition temperature at the 41 J level. Furthermore, irradiation exposure of 12.5 mm-thick compact specimens (0.5TCS), from the three-wire cladding to an average fluence of 2.41 × 10 19 neutrons/cm 2 (> 1 MeV ), resulted in decreases in the initiation ductile fracture toughness, J Ic , and the tearing modulus in the test temperature range from – 125 to 288°C. This is in agreement with the reduction in both the CVN upper-shelf energy and the CVN lateral expansion.

Statistical analyses of fracture toughness results for two irradiated high-copper welds

The objectives of the Heavy-Section Steel Irradiation Program Fifth Irradiation Series were to determine the effects of neutron irradiation on the transition temperature shift and the shape of the K{sub Ic} curve described in Sect. 6 of the ASME Boiler and Pressure Vessel Code. Two submerged-arc welds with copper contents of 0.23 and 0.31% were commercially fabricated in 215-mm-thick plates. Charpy V-notch (CVN) impact, tensile, drop-weight, and compact specimens up to 203.2 mm thick (1T, 2T, 4T, 6T, and 8T C(T)) were tested to provide a large data base for unirradiated material. Similar specimens with compacts up to 4T were irradiated at about 288{degrees}C to a mean fluence of about 1.5 {times} 10{sup 19} neutrons/cm{sup 2} (>1 MeV) in the Oak Ridge Research Reactor. Both linear-elastic and elastic-plastic fracture mechanics methods were used to analyze all cleavage fracture results and local cleavage instabilities (pop-ins). Evaluation of the results showed that the cleavage fracture toughness values determined at initial pop-ins fall within the same scatter band as the values from failed specimens; thus, they were included in the data base for analysis (all data are designated K{sub Jc}).

Results of irradiated cladding tests and clad plate experiments

Abstract Two aspects critical to the fracture behavior of three-wire stainless steel cladding were investigated by the Heavy-Section Steel Technology (HSST) Program: (1) radiation effects on cladding strength and toughness; and (2) the response of mechanically loaded, flawed structures in the presence of cladding (clad plate experiments). Postirradiation testing results show that, in the test temperature range from −125 to 288°C, the yield strength increased, and ductility insignificantly increased, while there was almost no change in ultimate tensile strength. All cladding exhibited ductile-to-brittle transition behavior during Charpy impact testing. Radiation damage decreased the Charpy upper-shelf energy by 15 to 20% and resulted in up to 28°C shifts of the Charpy impact transition temperature. Results of irradiated 12.5 mm-thick compact specimens (0.5TCS) show consistent decreases in the ductile fracture toughness, J Ic , and the tearing modulus. Results from clad plate tests have shown that: (1) a tough surface layer composed of cladding and/or heat-affected zone has arrested running flaws under conditions where unclad plates have ruptured; and (2) the residual load-bearing capacity of clad plates with large subclad flaws significantly exceeded that of an unclad plate.

INNOVATIVE NONDESTRUCTIVE METHOD DETERMINES FRACTURE TOUGHNESS OF IN-SERVICE PIPELINES

Applications of the innovative, patented Stress-Strain Microprobe (SSM) system, that utilizes an in-situ nondestructive Automated Ball Indentation (ABI) test technique to determine fracture toughness of in-service steel pipelines, are described in this paper. The ABI test provides the actual/current values of fracture toughness properties for base metal, welds, and heat-affected-zones. The ABI-measured key mechanical properties are used with other nondestructive measurements, such as crack/defect sizes (determined from in-line smart pigs or from on-line ultrasound instruments), to determine the safe operating pressure of the pipeline or to necessitate certain rehabilitation actions. The ABI test is based on progressive indentation with intermediate partial unloadings until the desired/required maximum depth (maximum strain) is reached, and then the indenter is fully unloaded. The ABI test is fully automated (using a notebook computer, data acquisition system, and a servo motor), and a single test is completed in less than two minutes. This paper describes two recent field investigations. The first investigation assessed a catastrophic failure that occurred in a natural gas plant on a cold winter night shortly following the leak of liquid natural gas into a natural gas pipeline. The combination of cold temperature and high strain rate near a crack resulted in the destruction of approximately a 12-meter section of a 508-mm (20-inch) diameter pipeline into several hundred small pieces. Since the remaining pieces from the exploded pipeline section were not sufficient to machine destructive tensile and fracture toughness specimens, the SSM system was used to measure the tensile and fracture toughness properties from multiple ABI tests on several pipeline pieces. The ABI-measured tensile and fracture toughness results provided the basis for the fitness-for-service assessment of the remaining pipeline sections of the natural gas plant. The second application involved a fire that occurred due to a leak from a 356-mm (14-inch) diameter Kerosene pipeline. The fire-damaged section of the pipeline was cut out and replaced. As part of the effort to prevent future accidents, the entire 7-km pipeline needed a structural integrity assessment. In-Situ ABI tests were conducted to measure the tensile and fracture toughness properies, from each ABI test, for the fitness-for-service assessment since the carbon steel pipeline had undocumented grade.© 2004 ASME

An investigation of the deformation mechanisms in sn5% sb alloy using tensile, creep and abi tests from ambient to 473k

Tensile, creep, and automated ball indentation (ABI) tests have been conducted to study deformation mechanisms in Sn5%Sb alloy between ambient and 473 K. A power law relationship was obtained between minimum creep rate and applied stress, with stress exponent,n=5 and activation energy,Q=12.6±1.1 kCal/ mole. At 473 K, a transition fromn=5 ton=3 was observed at low stresses. ABI tests showed a power law relationship between strain rate and ultimate tensile stress with values ofn=5 andQ=13.0±1.8 kCal/mole. Tensile results were in broad agreement with the creep and ABI data. A new deformation mechanism is proposed for then=5 region involving viscous glide of dislocations assisted by dislocation core diffusion.

Non-Destructive Evaluation of Deformation and Fracture Properties of Materials using Stress-strain Microprobe

Tensile deformation and fracture properties of several metallic materials, welds, and their heataffected-zones were determined non-destructively using the Stress-Strain Microprobe (SSM) system. The system is based on automated ball indentation (ABI) technique and involves straincontrolled multiple indentations at the same location on the material surface by a small spherical indenter. The technique permits evaluation of tensile deformation parameters such as yield strength, ultimate tensile strength, strength coefficient, and strain-hardening exponent, and a fracture energy parameter called indentation energy to fracture. ABI tests were conducted on carbon steels, stainless steels, nickel alloys, aluminum alloys, Zircaloys, electronic soldering materials and several nuclear pressure vessel steels (in the unirradiated, neutron irradiated, and irradiated and thermally annealed conditions). For all these test materials and conditions, the ABI-derived results were found to agree with the data from conventional standard test methods. In addition to the laboratory applications of SSM, it can be used as an in-situ testing instrument for non-destructive assessment of deformation and fracture properties of operating structural components.