Work programme organization 

 

Each problem examined by the network is tackled by creating a dedicated Task Group (TG), which undertakes measurement and modelling round robin studies and the interpretation of their results.

By 2018 NeT has initiated seven Task Groups (TGs) on welding residual stress investigation since its formation. All of these TGs are studying model cases of “simple” geometry welds applied on different nuclear grade structural materials, i.e. steels, Ni base alloys and Al alloys. All Task Groups encompass the preparation of the specimens in such a way that the production data needed for the subsequent stress investigations are made available. Where necessary, the partners in the TG obtain materials data for the welding simulations. NeT has undertaken the following Task Group activities since its formation:

 

TG1: Single Bead-on-Plate Weldment (Stainless Steel)

TG2: Letter Box Repair Welds (Ferritic Steel)

TG4: 3-Pass Slot Weld (Stainless Steel)

TG5: Edge Welded Beam (Ferritic Steel)

TG6: 3-Pass Slot Weld (Ni alloy)

TG7: Electron beam weld on a high strength Al alloy

TG8: Letterbox dissimilar metal weld on ferritic steel

 

In addition, NeT is running Task Group 3 (TG3) on the application of Small Angle Neutron Scattering (SANS) in order to obtain supplementary information on the materials under investigation at a (sub-) microscopic scale.

 

 

Measurement Techniques
  • Neutron and X-ray diffraction

  • Small angle neutron scattering (SANS)

  • Surface and deep-hole drilling, contour method

  • Metallography, SEM, TEM, EBSD

  • Monotonic and cyclic stress-strain testing

  • Thermocouples (standard and micro-arrays)

  • Strain gauges, DIC, ESPI and hardness mapping

 

Modelling
  • FE thermo-mechanical weld residual stress analysis

  • 2-D, 3-D and moving heat source models

  • Cyclic hardening and annealing

  • Phase transformation effects

  • Use of diverse FE codes

  • Statistical analysis of measured data

 

Network modes of operation

The NeT modes of operation adopted ensure/facilitate efficient interdisciplinary collaboration. This has proved to be pivotal in reconciling predictions with measurements.

The network has adapted to long time-scales and recognized the need to ensure that new Task Groups have a committed long-term sponsor and dedicated resources to collate, understand and report results. On the practical side Net has provided significant insight about the importance of specimen manufacture (witnessing, photographs and recording), specimen tracking, the need for access to sufficient materials data and many measurement issues (for example, knowing the exact location of measurements).

The NeT partnership thrives on the synergy created by the need to reconcile predictions with measurements originating from diverse academic and industrial communities. This interdisciplinary interaction has stimulated new ideas, novel research studies, improved measurement practices and in particular, significant advances in residual stress prediction methods.

Network on Neutron Techniques Standarization for Structural Integrity