Christopher E. Truman

This study introduces a Bayesian-informed framework for fatigue life prediction in shallow shell structures. The methodology focuses on inferring the Equivalent Initial Flaw Size Distribution (EIFSD), a critical parameter for structural durability. Bayesian inference, combined with a Co-Kriging surrogate model, enables statistically robust predictions while accounting for uncertainties in material properties, geometry, and loading. The Dual Boundary Element Method (DBEM) is employed for crack propagation due to its efficiency and re-meshing-free modelling. To improve inference efficiency, an iterative parameter space narrowing strategy is proposed. Instead of exhaustively sampling the entire space, the method begins with coarse discretisation to locate high-probability EIFSD regions, then refines them adaptively. A numerical example involving a fuselage window under cabin pressure demonstrates the method. Surrogate models trained on DBEM-generated data significantly reduce computational cost. The proposed strategy achieves high-precision inference, with only 0.059% error in the inferred mean and 5.2% in standard deviation, while reducing CPU time by 52% compared to dense sampling.

Steel components in the boilers of nuclear reactors are subject to high temperatures and varying loading conditions. This can introduce time-dependent and time-independent plasticity, which can interact with one another. Specimens of 316H austenitic stainless steel were heated to 550 °C and tensile pre-strained to 8%, 11% and 14% followed by 200 h, 280 MPa creep tests. These tests showed an increase in creep resistance with increasing tensile pre-strain. Macroscale simulations using RCC-MR deformation laws proved ineffective at predicting this interaction. Microscale crystal plasticity simulations proved effective at predicting the trends observed experimentally, hence demonstrating the potential of crystal plasticity as a predictive tool for structural integrity analysis.

Rectilinear blocks of the very high-strength aerospace aluminum alloy 7449 were solution treated and cold water quenched. They were then stress relieved immediately by cold compression. The amount of cold compression was systematically varied from 0 to 0.3 %. The amount of plastic strain was limited to well below the industrial standard of ~2 %. The blocks then received a stabilizing aging treatment. The residual stress distribution remaining in the blocks was characterized using neutron diffraction, with the aim of tracking how the through thickness 3-D residual strains and stresses change as cold compression progresses. Stress relief was of the order of 30–50 %, but there was no discernible systematic increase in stress relief as the plastic deformation magnitude was increased. It is suggested that this is mainly due to the differences between the samples being less than the experimental uncertainty of the neutron diffraction strain measurement technique.

Three rectilinear blocks of the aluminium alloy 7449 were characterised using neutron and X-ray diffraction. One block was heat treated normally and two blocks were subject to uphill quenching from −196°C to 100°C. Boiling water and steam were used to rapidly increase the temperature of the blocks to reverse the thermal gradients introduced by cold water quenching. It was possible to detect the beneficial influence of uphill quenching on residual stress using either fluid. The influence of steam was very effective but localised and limited to the surface in close proximity to the steam jet. For more uniform stress relief, multiple steam jets will be required to ensure the entire surface receives a significant thermal input.

High energy welding technologies, such as electron beam, have a number of potential benefits including: faster process time, smaller heat affected zone and potentially favourable weld residual stresses. Therefore, they are good candidates for manufacturing complex components for the next generation of nuclear power plants. However, before electron beam can be deployed on a wide scale, further work is required in a number of areas, including how these welds are treated in structural integrity assessments. As an example, the full extent of the effects of complex residual stress (RS) fields, arising from high energy welding technology, on the fracture behaviour of components has not been fully investigated. This understanding is essential for defect tolerance calculations using integrity assessment procedures. In this study, the fracture toughness of austenitic stainless steel 316L plates with various thicknesses (6mm to 25mm), joined by electron beam welding, is evaluated. Residual stresses were measured using non-destructive diffraction and mechanical relief methods (contour method). This is to examine the effect of welding residual stresses on the resistance of the welded component to fracture.

Residual stresses within welded components can redistribute when exposed to high temperatures and large levels of loading. The ageing process for a specimen attempts to replicate the temperature regime experienced during typical service use of the component, redistributing stresses from the as-welded condition to post-ageing. The aim of this investigation was to study the effects of ageing on weld residual stress redistribution and to evaluate the changes in the residual stress profiles before and after the pipe had been aged. In this investigation the through thickness residual stresses within a narrow gap girth TIG welded stainless steel 316L pipe were measured. The ageing of the pipe specimen involved heating to 400°C for 3000 hours. To measure residual stress the incremental Deep-Hole Drilling (iDHD) method was employed; two measurements were taken, once before and after ageing. Analysis of the measured pre and post-ageing residual stresses showed a consistent reduction in the magnitude of approximately 50 MPa, corresponding to the change in the yield stress of the material at room and elevated (400°C) temperatures; the maximum residual stress, of 450 MPa, was measured at 4 mm from the external surface of the pipe.

The residual stresses in heat-treated 7075 aluminum alloy blocks have been characterized using neutron diffraction, X-ray diffraction, and incremental center-hole drilling. Specimens were quenched to induce high-magnitude residual stresses, which were then stress relieved by the controlled application of plastic deformation using a cold compression technique. The experimental variables investigated were the quench water temperature and the postquench delay. This delay is considered to influence the final residual stress magnitudes because of hardening precipitation occurring by natural aging during the period between quenching and the application of plastic deformation. Cold compression significantly lowered the residual stresses in all specimens. Neutron diffraction measurements demonstrated a benefit to applying plastic deformation as soon as possible after quenching. However, this beneficial effect was not evident when characterizing surface residual stresses using hole drilling or X-ray diffraction.