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Many components in conventional and nuclear power plant, chemical plant and aero engines may be subjected to severe loading conditions, i.e. loads which cause reverse plasticity and/or incremental growth (Ratchetting). If operating temperatures are high, creep strains may also be significant and may exacerbate the ratchetting process. Also the residual stress fields associated with the cycling of load in the plastic region for a material will influence the accumulation of strain during the dwell periods between cycles when steady loading is sustained. Some analytical solutions for the cyclic behaviour of simple components and loadings are available, however very little information on the effects of stress concentrations and complex loading conditions on ratchetting is published. A better understanding of the mechanisms of ratchetting for complex components and loadings is essential in order to identify characteristic behaviours which can be used to aid the design process for components in potential ratchetting situations. A range of component geometries, uniform sections and stress concentrations, and loading conditions have been analysed by the finite element method to investigate ratchetting mechanisms and to obtain ratchet and dwell period strain data. The effects of stress concentrations, material behaviour models, loading conditions and stress redistribution due to creep on ratchetting mechanisms and strain accumulations are described. Dwell period creep effects are bounded by the 'no creep' (zero dwell period) condition on the one hand and by complete redistribution between cycles at the other extreme. The results of the analyses have been successfully used to 'extend existing approximate design rules for simple components to these more complex components and loadings. It has been shown that reasonable estimates (in some cases exact solutions) can be obtained from either a limited finite element analysis or by using approximate methods of solution. Comparisons between experimental ratchetting data for two components made from a lead alloy material and equivalent finite element predictions are presented. Simple material behaviour models are used and the results highlight both the benefits and shortfalls of these models. Improvements to modelling techniques for more accurate predictions are suggested although it is shown that, in certain circumstances, more realistic material behaviour modelling is unwarranted.

Background: The prevention of errors and adverse effects from healthcare in hospitals is a global priority. The beliefs, values, and norms of an organisation can support patient safety and influence staff behaviours. Aim: To understand perceptions of, and influences on, patient safety culture within an Acute NHS Trust in England. Method: A case study of one acute NHS hospital Trust with embedded units of analysis (two medical wards). Semi-structured interviews were conducted with 16 staff at different levels of the Trust. Documentary analysis included patient safety metrics and organisational safety documents. Theoretical framework: Open Systems Theory. Findings: There were differing perceptions at the different levels about acceptable levels of risk and the compromises needed to manage pressures. There was a lack of opportunities for interaction and dialogue to establish common values around patient safety. Micro level staff perceived that a balance had to be struck between maintaining quality of care and reporting patient safety. There was little internal or externally facing examination and interrogation of safety metrics that would convey a commitment to a positive patient safety culture. Conclusions: A more nuanced understanding of how a system contributes to patient safety has emerged and some of the factors that act as enablers of, or barriers to, a positive patient safety culture. Staff at all levels believed that patient safety was important but patient safety culture was more about measurement of events and avoidance of specific measurable harms than a clearly articulated set of values about safety. Recommendations: Organisations should regularly evaluate the effectiveness of patient safety feedback loops so clinical staff voices, including healthcare assistants, become part of meso/macro level decision-making regarding how safe patient throughput can be managed. Healthcare organisations should recognise the role that shift co-ordinators play in keeping patients safe at ward level by providing training for junior nurses to step into this role. Safety training at all levels is necessary to create a shared dialogue about risk, safety, reporting and learning so organisations should embrace the safety syllabus and training for NHS staff that was introduced in May 2021 and ensure staff have protected time for this training.