Study of Residual Stress Distribution in a Stainless Steel Bead-on-Plate Simulation Benchmark Sample

This paper summarizes the results of a neutron diffraction study of a single weld bead on a rectangular austenitic stainless steel plate. The measurement was carried out at SALSA, the engineering strain scanner at the ILL, Grenoble, France. The work has been carried out under the European NET project, and is a round robin exercise of residual stress simulation and validation benchmark in a stainless steel bead-on-plate (BOP) weldment. A monochromatic beam of wavelength 1.494 Å was used and the lattice spacing of {311} crystallographic plane was measured. The principal strain measured in the plate was corrected by measuring small cube sample of 3×3×3 mm3 as stress free reference. The measured strain was then used to calculate the principal stress distribution. Finally, the measured strain was compared with the strain measured in a similar specimen in a pulsed neutron source by the time-of-flight (TOF) technique.

The Effect of Plastic Anisotropy on the Residual Stress within a 316L Stainless Steel Bead-on-Plate Specimen

Plastic anisotropy can affect the strains measured by neutron diffraction. If this is not properly accounted for significant errors can result in the calculated stresses. This paper illustrates addresses this issue using measurements of the residual strain field around a 60 mm long single weld bead deposited on the surface of a 17 mm thick stainless steel plate. Measurements were made on ENGIN-X, the engineering spectrometer at the ISIS facility of the Rutherford Appleton Laboratory (UK). Diffraction spectra from these measurements have been fitted using both single and multi-peak fitting approaches. Both residual strain and stress results have been presented for (111) and (200) single peak fits and compared to a multi-peak fit (Rietveld) analysis. Results from these analyses have revealed significant anisotropy in the response of the individual lattice planes. This effect is most severe in measurements carried out in the normal direction and is shown to be predicted using an elasto-plastic self-consistent model.

Development of a Residual Stress Simulation Benchmark for a Single Bead-on-Plate Weldment

Finite element weld residual stress modelling procedures involve complex non-linear analyses where many assumptions and approximations have to be made by the analyst. Weld modelling guidelines for inclusion in the R6 defect assessment procedure are in preparation and will be accompanied by a series of validation benchmarks that can be used to evaluate the accuracy of weld modelling procedures and assess their suitability for use in fracture assessments. It is intended to base one of the benchmarks on a stainless steel bead-on-plate weldment that has been extensively studied by members of Task Group 1 of the NeT European Network project. This paper uses round robin residual stress measurements from the NeT project to derive a statistically based ‘best estimate’ distribution of transverse stress passing through the wall-section at mid-length of the bead-on-plate weldment. The accuracy of a state-of-the-art residual stress prediction is benchmarked against the best estimate measurements using a root mean square error analysis and comparisons of decomposed components of stress. The appropriateness of using the predicted residual stresses in fracture assessments is assessed by comparing stress intensity factors based on the measured and predicted distributions of stress. The results from these studies will be used to help establish accuracy targets and acceptance criteria for the welding benchmark.