The effect of heat treatment on mechanical properties of pulsed Nd:YAG welded thin Ti6Al4V

Pulsed Nd:YAG has been adopted successfully in welding process of thin (0.7 mm) Ti6Al4V. Laser welding of such thin sheet requires a small focal spot, good laser beam quality and fast travel speed, since too much heat generation can cause distortion for thin sheet weld. The microstructures of Ti6Al4V were complex and strongly affected the mechanical properties. These structures include: a´ martensite, metastable ß, Widmanstätten, bimodal, lamellar and equiaxed microstructure. Bimodal and Widmanstätten structures exhibit a good-balance between strength and ductility. The microstructure of pulsed Nd:YAG welded Ti6Al4V was primarily a´ martensite, which showed the lowest ductility but not significantly high strength. A heat treatment at 950 followed by furnace cooling can transform the microstructure in the weld from a´ martensite structure into Widmanstätten structure

The effect of frequency on both the debris and the development of the tribologically transformed structure during fretting wear of a high strength steel

It is well established that damage to the first bodies in fretting wear gives rise to a hard and brittle tribologically transformed structure (TTS) which can influence both wear and fatigue. While the existence and significance of TTS has been established through extensive study, the underlying physical mechanisms of its formation and their dependence on fretting conditions are still not clear. The aim of this work is to investigate the role of frequency in the evolution of tribologically transformed structures in a high strength steel subjected to fretting. In this work, fretting tests in the gross slip regime were conducted using self-mated high strength steel pairs employing a cylinder-on-flat geometry to produce a line contact, across a range of fretting frequencies. The nature of the debris (both particle size and composition) expelled from the fretting contact was not affected by the fretting frequency. Examination of worn specimens using SEM and EBSD was conducted to characterise the formation of TTS and to allow its role in the development of wear to be understood. It was found that at low frequencies, the fretting scar consisted of an oxide debris bed on top of a largely undeformed martensite sub-structure. However, at higher frequencies, the appearance of the sub-surface worn damage layer was very different, consisting of a debris oxide, a severely damaged / fragmented metallic layer and a plastically deformed martensitic sub-structure. A phenomenological model is presented (based upon the basic physical processes of oxide formation at the fretting surface and subsurface deformation below the contact) which accounts for the complex observations made

Microstructural characterisation of subsurface deformation and the degradation of Stellite 6 induced by self-mated sliding contact in a simulated PWR environment

© 2021 Elsevier Ltd Stellite 6 (Co-29.5%Cr-5%W-1.2%C in wt%) is traditionally used as a hardfacing material in the primary circuit of pressurised water reactors (PWRs) due to its good corrosion and wear resistance in water at up to 300 °C. In this study, pin-on-disc type sliding contact tribocorrosion testing was conducted on HIPed Stellite 6 at 20 °C and 250 °C using a bespoke tribometer to simulate a primary circuit environment. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterize, for the first time, the material affected by tribocorrosion. Whilst the material loss increases by 16–39 times when the test temperature is increased from 20 °C to 250 °C, the mechanisms of degradation and deformation remain largely unchanged. Furthest from the sliding contact, strain is principally accommodated by the deformation-induced transformation of the γ Co-based matrix to ε-martensite. Closer to the sliding contact, the ε-martensite phase accommodates further strain via twinning and dislocation slip. At the sliding contact the intense deformation generates a nanocrystalline structure. The tribologically affected material is resistant to plastic strain localisation; this confines wear to the nanoscale where the synergistic effects of chemical degradation and mechanical deformation permit the removal of nanoscale particulates (corrosion enhanced nanowear (tribocorrosion)). The increased wear rate at 250 °C is attributed to a temperature dependent increase in corrosion enhanced nanowear. The degradation mechanisms revealed are important for the design of future hardfacings

The Randomised Evaluation of early topical Lidocaine patches In Elderly patients admitted to hospital with rib Fractures (RELIEF): feasibility trial protocol

Background: Topical lidocaine patches, applied over rib fractures, have been suggested as a non-invasive method of local anaesthetic delivery to improve respiratory function, reduce opioid consumption and consequently reduce pulmonary complications. Older patients may gain most benefit from improved analgesic regimens yet lidocaine patches are untested as an early intervention in the Emergency Department (ED). The aim of this trial is to investigate uncertainties around trial design and conduct, to establish whether a definitive randomised trial of topical lidocaine patches in older patients with rib fractures is feasible. Methods: RELIEF is an open label, multicentre, parallel group, individually randomised, feasibility randomised controlled trial with economic scoping and nested qualitative study. Patients aged ≥ 65 years presenting to the ED with traumatic rib fracture(s) requiring admission will be randomised 1:1 to lidocaine patches (intervention), in addition to standard clinical management, or standard clinical management alone. Lidocaine patches will be applied immediately after diagnosis in ED and continued daily for 72 hours or until discharge. Feasibility outcomes will focus on recruitment, adherence and follow-up data with a total sample size of 100. Clinical outcomes, such as 30-day pulmonary complications, and resource use will be collected to understand feasibility of data collection. Qualitative interviews will explore details of the trial design, trial acceptability and recruitment processes. An evaluation of the feasibility of measuring health economics outcomes data will be completed. Discussion: Interventions to improve outcomes in elderly patients with rib fractures are urgently required. This feasibility trial will test a novel early intervention which has the potential of fulfilling this unmet need. The Randomised Evaluation of early topical Lidocaine patches In Elderly patients admitted to hospital with rib Fractures (RELIEF) feasibility trial will determine whether a definitive trial is feasible. ISRCTN Registration: ISRCTN14813929 (22/04/2021)

Protocol for the development of a multidisciplinary clinical practice guideline for the care of patients with chronic subdural haematoma

Introduction: A common neurosurgical condition, chronic subdural haematoma (cSDH) typically affects older people with other underlying health conditions. The care of this potentially vulnerable cohort is often, however, fragmented and suboptimal. In other complex conditions, multidisciplinary guidelines have transformed patient experience and outcomes, but no such framework exists for cSDH. This paper outlines a protocol to develop the first comprehensive multidisciplinary guideline from diagnosis to long-term recovery with cSDH. Methods: The project will be guided by a steering group of key stakeholders and professional organisations and will feature patient and public involvement. Multidisciplinary thematic working groups will examine key aspects of care to formulate appropriate, patient-centered research questions, targeted with evidence review using the GRADE framework. The working groups will then formulate draft clinical recommendations to be used in a modified Delphi process to build consensus on guideline contents. Conclusions: We present a protocol for the development of a multidisciplinary guideline to inform the care of patients with a cSDH, developed by cross-disciplinary working groups and arrived at through a consensus-building process, including a modified online Delphi.</p

An experimental study on the key fretting variables for flexible marine risers

This paper presents an experimental investigation into the effects of contact conformity, contact pressure and displacement amplitude on the gross-slip fretting behaviour grease-lubricated cylinder-on-flat contacts in the context of flexible marine riser pressure armour wire, and compares behaviour with that observed in unlubricated conditions. Characterisation of friction and wear is critical to fretting fatigue life prediction in flexible risers since friction directly controls trailing-edge fretting stresses and hence fatigue crack initiation, on the one hand, and on the other hand, directly affects wear via relative tangential slip (displacement). Wear can have a beneficial or detrimental effect on fatigue crack initiation and propagation, depending on relative slip and slip regime. It is shown that friction and wear are higher for dry conditions than for grease-lubricated conditions. For grease-lubricated conditions, behaviour is determined by whether grease can be retained in the contact (as opposed to being extruded out). Retention (or replenishment) of grease in the contact results in low rates of wear and low coefficients of friction; these conditions are favoured by fretting displacements above a critical value, by low contact conformity, and by low applied loads.The authors would like to thank the Irish Research Council and Wood Group Kenny for funding of this project through the Enterprise Partnership Scheme (EPSPG/2013/638), the National University of Ireland for funding through a NUI Travelling Scholarship. We also wish to acknowledge the help and support we have received from Dr. Adrian Connaire and Mr. Kieran Kavanagh (Wood Group). The authors also wish to acknowledge the support of the Faculty of Engineering at the University of Nottingham where this research was conducted

A combined wear-fatigue design methodology for fretting in the pressure armour layer of flexible marine risers

This paper presents a combined experimental and computational methodology for fretting wear-fatigue prediction of pressure armour wire in flexible marine risers. Fretting wear, friction and fatigue parameters of pressure armour material have been characterised experimentally. A combined fretting wear-fatigue finite element model has been developed using an adaptive meshing technique and the effect of bending-induced tangential slip has been characterised. It has been shown that a surface damage parameter combined with a multiaxial fatigue parameter can accurately predict the beneficial effect of fretting wear on fatigue predictions. This provides a computationally efficient design tool for fretting in the pressure armour layer of flexible marine risers.The authors would like to thank the Irish Research Council and Wood Group for funding of this project through the Enterprise Partnership Scheme (EPSPG/2013/638), and the National University of Ireland for funding through an NUI Travelling Scholarship. We also wish to acknowledge the help and support we have received from Mr. Kieran Kavanagh (Wood Group Kenny), the NUI Galway Engineering Building technical staff; particularly Mr. Bonaventure Kennedy and Mr. Patrick Kelly and the Faculty of Engineering at the University of Nottingham

Comparison of the sliding wear behaviour of self-mated HIPed Stellite 3 and Stellite 6 in a simulated PWR water environment

Cobalt-based alloys such as Stellite 3 and Stellite 6 are widely used to protect stainless steel surfaces in primary circuit nuclear reactor applications where high resistance to wear and corrosion are required. In this study, selfmated sliding wear of Stellite 3 and Stellite 6 consolidated by hot isostatic pressing were compared. Tests were performed with a pin-on-disc apparatus enclosed in a water-submerged autoclave environment and wear was measured from room temperature up to 250 °C (a representative pressurized water reactor environment). Both alloys exhibit a microstructure of micron-sized carbides embedded in a cobalt-rich matrix. Stellite 3 (higher tungsten and carbon content) contains M7C3 and an eta (η) -carbide whereas Stellite 6 contains only M7C3. Furthermore, the former has a significantly higher carbide volume fraction and hardness than the latter. Both alloys show a significant increase in the wear rate as the temperature is increased but Stellite 3 has a higher wear resistance over the entire range; at 250 °C the wear rate of Stellite 6 is more than five times that of Stellite 3. There is only a minimal formation of a transfer layer on the sliding surfaces but electron backscatter diffraction on cross-sections through the wear scar revealed that wear causes partial transformation of the cobalt matrix from fcc to hcp in both alloys over the entire temperature range. It is proposed that the acceleration of wear with increasing temperature in the range studied is associated with a tribocorrosion mechanism and that the higher carbide fraction in Stellite 3 resulted in its reduced wear rate compared to Stellite 6