Failure Assessment Diagram (FAD) analysis of fatigue test results for X65 welded joints

Offshore pipelines transfer oil and gas from seabed to production facility on the surface. The long pipelines are formed by welding of pipe segments, where these welded joints are a source of stress concentration and defects from which fatigue cracks can grow. This work aims to study the behaviour of deep fatigue cracks. In this current work, finite-element based on a parametric study of four-point bending is used to assess the stress intensity factors (SIFs) of deep surface cracks in X65 specimens, while considering local limit load the remaining load bearing ligament. These deep cracks take on a non-regular shape and have widths that exceed that of the specimen. They will be compared to empirical expressions from derived standards such as British Standards BS7910, which may be more conservative. The existing large flaw is also assessed via the failure assessment diagram (FAD). The effects of limit load solutions and reference stresses used to determine the FAD diagram will be discussed

Influence of Weld Toe Radii on Fatigue Life Prediction

A study was carried out to investigate the influence of the weld toe radii on the fatigue strength of butt welded joints loaded in bending and tension. Fatigue analysis starting from weld toe cracks in marine and offshore welded pipe specimens were conducted using cut-out four-point bend fatigue test specimens. Fatigue life can be enhanced by reducing the local stress concentration generated by weld toe radius effects. This study investigated the effect of different weld toe radii on the stress intensity factor at the region of the weld toe through Finite Element Analysis (FEA). FEA was used to model a butt welded steel plate extracted from a pipe subject to tension and four-point bend loading. Semi-elliptical surface (SESC) cracks were modeled at the weld toe region with different SESC crack depth and surface crack length. Four weld toe radii and two modes of loading were investigated. The stress intensity factors, weald toe magnification factors, or Mkc and Mka are reported and used for fatigue life prediction

Application of reinforcement learning in an open railway access market price negotiation

In an open railway access market price negotiation, it is feasible to achieve higher cost recovery by applying the principles of price discrimination. The price negotiation can be modeled as an optimization problem of revenue intake. In this paper, we present the pricing negotiation based on reinforcement learning model. A negotiated-price setting technique based on agent learning is introduced, and the feasible applications of the proposed method for open railway access market simulation are discussed.\ud \u

Finite element and experimental study on multiaxial fatigue analysis of rail clip failures

The rail clip fastening system is an important structural component of railway track systems providing flexibility and turnover resistance for running rails. High replacement frequency of fasteners was observed compared with other components because of fatigue failures of rail clips. In this study, implicit and explicit finite element (FE) models were developed for E-clip and Fast-clip with material and fatigue properties obtained from experimental testing. The fatigue loading experiments were conducted to determine the strain-life relationship. The assessments of the fatigue damage and fatigue life were analysed using the FE results for the rail clip strain/stress components with the Fatemi-Socie multiaxial fatigue criterion. A time-efficient smallest enclosing circle algorithm was developed to search the critical plane orientation and the maximum shear strain amplitude for fatigue analysis. This work provides a method for FE and experimental study of multiaxial fatigue analysis of rail clip failures subjected to dynamic loading

Structural fatigue investigation of transverse surface crack growth in rail steels and thermite welds subjected to in-plane and out-of-plane loading

This study investigates the structural fatigue crack growth behavior of observed transverse surface cracks in rail steel and thermite weld subjected to in-plane and out-of-plane loading. Stress Intensity Factor (SIFs) solutions were derived from finite element model analysis for transverse surface cracks located at five different crack initiation locations in the cross-section of rail steel and thermite weld. The SIFs were presented by the conventional geometry factor Y and weld magnification factor Mk solutions for rail steel and thermite weld. Fracture toughness and fatigue crack growth rate tests were conducted to determine the mechanical properties of thermite weld materials and are compared with reported data for rail steels (R260 and R350HT). Fatigue crack growth prediction algorithm was developed using the coupled root mean square integration approach and was compared with the conventional uncoupled two-degree of freedom approach for semi-elliptical surface crack growth in the depth and surface directions respectively. The fatigue crack growth algorithm and propagation life prediction provide valuable observations on the crack shape evolution. It proves that out-of-plane bending loading is a more significant failure mode as compared to in-plane bending loading for thermite weld joints at curve tracks. Fatigue crack propagation results provide fatigue stress range-life curves for weld-toe surface cracks initiated at the head-to-web region of thermite welded joint structure.Nanyang Technological UniversityNational Research Foundation (NRF)This research work was conducted in the SMRT-NTU Smart Urban Rail Corporate Laboratory with funding support from the National Research Foundation Singapore, SMRT Corporation Singapore and Nanyang Technological University, Singapore; under the Corp Lab at University Scheme

An integrated fatigue assessment approach of rail welds using dynamic 3D FE simulation and strain monitoring technique

Stress concentration induced by geometry irregularity was found near the weld toe of rail welded joints, leading to high risk of fatigue crack initiation. In this research, an integrated fatigue assessment method of rail welds based on the 3D dynamic finite element method (FEM) and onsite strain monitoring data has been developed. The 3D FEM considering wheel-track interaction has been built and the extracted stress and deformation results was analyzed using an implicit-explicit sequence approach. The FEM model was then validated and calibrated by strain monitoring results on a test track from strain gauges attached near the rail welds. A comprehensive investigation of fatigue behavior for rail welds under the dynamic loading condition has been conducted and it was found that the tensile peaks due to ‘reverse bending’ of the rail have a critical effect on the weld fatigue crack initiation. A further study of fatigue risk assessment using multi-axis fatigue theory revealed that the crack initiation risk is high for head-to-web transition region in gauge side

Development of salient medication reminders to facilitate information transfer during transition from inpatient to primary care: the Delphi process

Objective Transitional care is important to successful hospital discharge. Providing patients with a clear and concise summary of medication-related information can help improve outcomes, in particular, among older adults. The present study aimed to propose a framework for the development of salient medication reminders (SMR), which include drug-related risks and precautions, using the Delphi process.Design Identification of potential SMR statements for 80% of medication types used by older adult patients discharged from geriatric medicine departments, followed by a Delphi survey and expert panel discussion.Settings Medical and geriatric departments of public hospitals in Hong Kong.Participants A panel of 13 geriatric medical experts.Outcome measure A Likert scale ranging from 1 (strongly disagree) to 5 (strongly agree) points, scoring item relevance, importance and clarity. The minimum of 70% consensus was required for each statement to be included.Results The expert panel achieved consensus through the Delphi process on 80 statements for 44 medication entities. Subsequently, the SMR steering group endorsed the inclusion of these statements in the SMR to be disseminated among older adults at the time of discharge from geriatric medicine departments.Conclusions The Delphi process contributed to the development of SMR for older adult patients discharged from public hospitals in Hong Kong. Patient experience with and staff response to the SMR were assessed at four hospitals before implementation at all public hospitals

Ischemic postconditioning protects cardiomyocytes against ischemia/reperfusion injury by inducing MIP2

Cardiomyocytes can resist ischemia/reperfusion (I/R) injury through ischemic postconditioning (IPoC) which is repetitive ischemia induced during the onset of reperfusion. Myocardial ischemic preconditioning up-regulated protein 2 (MIP2) is a member of the WD-40 family proteins, we previously showed that MIP2 was up-regulated during ischemic preconditioning (IPC). As IPC and IPoC engaged similar molecular mechanisms in cardioprotection, this study aimed to elucidate whether MIP2 was up-regulated during IPoC and contributed to IPoC-mediated protection against I/R injury. The experiment was conducted on two models, an in vivo open chest rat coronary artery occlusion model and an in vitro model with H9c2 myogenic cells. In both models, 3 groups were constituted and randomly designated as the sham, I/R and IPoC/hypoxia postconditioning (HPoC) groups. In the IPoC group, after 45 min of ischemia, hearts were allowed three cycles of reperfusion/ischemia phases (each of 30 s duration) followed by reperfusion. In the HPoC group, after 6 h of hypoxia, H9c2 cells were subjected to three cycles of 10 minute reoxygenation and 10 minute hypoxia followed by reoxygenation. IPoC significantly reduced the infarct size, plasma level of Lactate dehydrogenase and creatine kinase MB in rats. 12 h after the reperfusion, MIP2 mRNA levels in the IPoC group were 10 folds that of the sham group and 1.4 folds that of the I/R group. Increased expression of MIP2 mRNA and attenuation of apoptosis were similarly observed in the HPoC group in the in vitro model. These effects were blunted by transfection with MIP2 siRNA in the H9c2 cells. This study demonstrated that IPoC induced protection was associated with increased expression of MIP2. Both MIP2 overexpression and MIP2 suppression can influence the IPoC induced protection

Global imperative of suicidal ideation in 10 countries amid the COVID-19 pandemic

Background: The novel coronavirus (COVID-19) has had a detrimental impact on individuals' psychological well-being; however, a multi-country comparison on the prevalence of suicidal ideation due to the virus is still lacking. Objectives: To examine the prevalence and correlates of suicidal ideation among the general population across 10 countries during the COVID-19 pandemic. Materials and methods: This was a cross-sectional study which used convenience sampling and collected data by conducting an online survey. Participants were sourced from 10 Eastern and Western countries. The Patient Health Questionnaire (PHQ-9) was used to measure the outcome variable of suicidal ideation. Ordinal regression analysis was used to identify significant predictors associated with suicidal ideation. Results: A total of 25,053 participants (22.7% male) were recruited. Results from the analysis showed that the UK and Brazil had the lowest odds of suicidal ideation compared to Macau (p < 0.05). Furthermore, younger age, male, married, and differences in health beliefs were significantly associated with suicidal ideation (p < 0.05). Conclusions: The findings highlight the need for joint international collaboration to formulate effective suicide prevention strategies in a timely manner and the need to implement online mental health promotion platforms. In doing so, the potential global rising death rates by suicide during the pandemic can be reduced