Determination of key mechanical properties of welded components is essential for structural integrity evaluation and for life assessment of weld repairs. A novel portable/in-Situ Stress- Strain Microprobe (SSM) system was used to measure true- stress /true-plastic-strain behaviour of several metallic materials, welds, and their heat-affected zones (HAZs) in various metallurgical and damage conditions. The SSM system utilized an automated ball indentation (ABI) technique to measure elastic modulus, yield strength, stress-strain curve, strength coefficient, and strain-hardening-exponent (uniform ductility) in carbon steels, stainless steels, nickel alloys, aluminium alloys, zirconium, electronic soldering materials, etc. Numerous ABI tests were also conducted on several nuclear pressure vessel steels (NPVSs) in the unirradiated, neutron irradiated, and post- irradiated thermally annealed conditions. For all these test materials and conditions, the ABI-derived results were in very good agreement with those from conventional standard test methods. The ABI test results on few *steel weldments (e. g. A204 steel) demonstrated that the local stress-strain curve of a HAZ is not always bracketed by those for the weld and the base metal (it might be higher or lower than both neighbouring materials). Furthermore, the nondestructive ABI test results rigorously indicated the various levels of neutron-embrittlement damage and the amount of ductility recovery following thermal annealing of the NPVS specimens. In-situ nondestructive structural applications of the SSM system have been demonstrated by testing a circumferentially welded stainless steel pipe and a full- thickness section of a nuclear pressure vessel (using 90° V- blocks, and magnetic mounts for mounting the testing head of the SSM system on the pipe and the carbon steel section, respectively). All SSM tests were fully computer controlled and conducted easily and quickly (less than 1 second to several minutes, depending on the desired strain rate for an ABI test). The ABI technique of the SSM system is based on strain-controlled multiple indentations (at a single penetration location) of a polished surface by a spherical indentor (e. g. 0.25 to 1.57 mm diameter). The indentation depth is progressively increased to a maximum user-specified limit with intermediate partial unloading. The applied indentation loads and associated penetration depths are acquired during the ABI test and used to calculate the incremental stress-strain values based on elasticity and plasticity theories and some semi-empirical equations. A description of the ABI experimental and analytical procedures is presented along with sample results (on specimens and components) using a commercially available SSM system. In addition, results using a new single-cycle ABI test procedure, developed for high strain rate testing and continuous stress- strain measurement, are provided for electronic solder materials (Sn5%Sb). Potential future research areas for utilizing the SSM system to determine fatigue and creep damage as well as to measure residual stresses are briefly described in this paper.
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