TG6: 3-Pass Slot Weld (Ni alloy)
The Task Group 6 (TG6) round robin specimen is closely based upon the TG4 design, except that it is fabricated from nickel based alloys, namely Alloy 600 plate with Alloy 82 weld metal. It thus presents all the advantages and challenges of the TG4 specimen, namely, the generation of a complex 3D residual stress distribution in a compact, portable specimen that is amenable to rapid measurement of residual stresses by diverse techniques, with a significant volume of weld metal that undergoes multiple high temperature thermo-mechanical cyclic loads. The use of nickel-based alloys then adds considerable residual stress measurement challenges, while the slightly overmatched weld in AISI 316 is replaced by a significantly undermatched weld in alloy 82. The TG6 specimen is a 3-pass slot weld in Alloy 600 plate, made using a Tungsten-Inert-Gas welding process. The dimensions of the plate are 200 x 150 x 12 mm3, while the slot is 76 mm long and 5 mm deep, and is filled with three superimposed weld passes. As it was done in Task Groups 1 and 4 before, NeT Task Group 6 is undertaking parallel measurement and simulation round robins.
The TG partners have reported a number of neutron diffraction measurements which allowed a robust Bayesian estimation of the residual stresses and showed the systematic uncertainty that is associated with this non-destructive method for base and weld material individually . Detailed analyses and dedicated measurements have shown that the measurements suffered from a small position shift, which comes from the neutron attenuation in this nickel alloy plate shifting the effective gauge area . Comprehensive studies have also explored the thermo-mechanical material properties of both Alloy 600 base material and Alloy 82 weld metal  as well as the material characterization campaign of the weldments using both simple and analytical techniques . Finally, a simulation campaign has been conducted by six organizations members of the network using a protocol and adopting mixed isotropic-kinematic hardening models. The residual stress predictions and the robust Bayesian mean of measurements have been in good agreement [5, 6].
Akrivos, V., et al., On the neutron diffraction measurements of weld residual stresses in three-pass slot-weld (Alloy 600/82) and the assessment of the measurement uncertainty. Journal of Applied Crystallography, 2020. 53: p. 1181-1194 DOI: 10.1107/S1600576720009140.
Wimpory, R. C., et al., Precise Measurement of Steep Residual Strain Gradients Using Neutron Diffraction in Strongly Absorbing Materials with Chemical Compositional Gradients. Materials Performance and Characterization, 2018. 7 (4): p. 488-503 DOI: 10.1520/MPC20170114
Akrivos, V. and M.C. Smith, The thermo-mechanical behaviour of the Alloy 600 and Alloy 82 materials. Proceedings of the ASME 2018 Pressure Vessels and Piping Conference PVP 2018, 2018(84592) DOI: 10.1115/PVP2018-84592.
Akrivos, V. and M.C. Smith, Material Characterization on the Nickel-Based Alloy 600/82 NeT-TG6 Benchmark Weldments. Proceedings of the ASME 2019 Pressure Vessels and Piping Conference PVP 2019, 2019(94017) DOI: 10.1115/pvp2019-94017.
Akrivos, V., et al., A residual stress measurement and numerical analysis round robin on a three-pass slot nickel-base repair weld. Procedia Manufacturing, 2020. 51: p. 779-786 DOI: 10.1016/j.promfg.2020.10.109.
Fig. 1. TG6 – engineering drawing of specimen
Fig. 2. TG6 – macrograph of fusion zone
Fig. 3. TG6 – pad of weld material for the generation of weld specific materials data
Fig. 4. TG6 – quantifying gauge volume centre of gravity shift caused by attenuation; magnitude of shift depends on size of gauge volume and on neutron attenuation of the specimen material .
Fig. 5. TG6 – through thickness distribution of longitudinal and transverse residual stresses, simulation result compared to average of measurements (from , licensed under CC BY 4.0)
Fig. 6. TG6 – Gleeble testing, measurements of several thermo-mechanical load cycles compared to the corresponding simulations of the (a) base and (b) weld material response .