Safety Critical Components Research Articles

Finite element analysis of the mechanical behaviour of insulated rail joints due to impact loadings

Insulated rail joints (IRJs) are safety-critical components in the signalling system of rail corridors. They are subjected to dynamic loads generated by heavy rolling-stock/track- system interactions and degrade faster than the other components of the rail track. Degraded IRJs diminish the reliability of the signalling system, thus posing a serious threat to the safety of rail operations. Therefore, there is a pressing need to closely examine the failure mechanisms of the end posts made of insulated material and inserted into the discontinuity in the rail at IRJs with a view to improving their service life, reliability and efficiency. Only a limited literature is available that examines different materials for IRJ end posts, and these primarily focus on contact pressure and contact stress distributions in the vicinity of the end post, disregarding the damage to the rail ends and end post materials. In this paper, a detailed three-dimensional finite element analysis procedure is carried out to quantify plastic deformation and material damage to the end post and railhead materials of IRJs due to a wheel load above that of the shakedown limit of rail steel. A modified Hertzian contact pressure distribution is considered in this simulation. A 5 mm thickness of an end post is considered at the discontinuity in the rail, which is required to form the six-bolt IRJ. Three popular IRJ end post materials are considered in this study: fibreglass, polyhexamethylene adipamide, and polytetrafluoroethylene. A total of 2000 cycles of a 174 kN dynamic wheel load (in pressure format over the wheel/rail contact patch) are applied on the top of the rail’s surface in the vicinity of the IRJ. Equivalent plastic deformations along with vertical and longitudinal plastic strains for unloaded conditions are presented. The strain plots depict damage of end post materials and ratchetting failure of rail ends. The ratchetting failure modes follow the established trend of decay in ratchetting rate in successive wheel load cycles. Comparisons of strain and stress on the railhead surface and in the railhead sub-surface considering all three different end post materials are put forward. Out of the three end post materials, fibreglass is the optimal material considering the ratchetting mode for the damage of the railhead material.

Advances in multi-megawatt lower hybrid technology in support of steady-state tokamak operation

It has been demonstrated that lower hybrid current drive (LHCD) systems play a crucial role for steady-state tokamak operation, owing to their high current drive (CD) efficiency and hence their capability to reduce flux consumption. This paper describes the extensive technology programmes developed for the Tore Supra (France) and the KSTAR (Korea) tokamaks in order to bring continuous wave (CW) LHCD systems into operation. The Tore Supra LHCD generator at 3.7 GHz is fully CW compatible, with RF power PRF = 9.2 MW available at the generator to feed two actively water-cooled launchers. On Tore Supra, the most recent and novel passive active multijunction (PAM) launcher has sustained 2.7 MW (corresponding to its design value of 25 MW m−2 at the launcher mouth) for a 78 s flat-top discharge, with low reflected power even at large plasma-launcher gaps. The fully active multijunction (FAM) launcher has reached 3.8 MW of coupled power (24 MW m−2 at the launcher mouth) with the new TH2103C klystrons. By combining both the PAM and FAM launchers, 950 MJ of energy, using 5.2 MW of LHCD and 1 MW of ICRH (ion cyclotron resonance heating), was injected for 160 s in 2011. The 3.7 GHz CW LHCD system will be a key element within the W (for tungsten) environment in steady-state Tokamak (WEST) project, where the aim is to test ITER technologies for high heat flux components in relevant heat flux density and particle fluence conditions. On KSTAR, a 2 MW LHCD system operating at 5 GHz is under development. Recently the 5 GHz prototype klystron has reached 500 kW/600 s on a matched load, and studies are ongoing to design a PAM launcher. In addition to the studies of technology, a combination of ray-tracing and Fokker–Planck calculations have been performed to evaluate the driven current and the power deposition due to LH waves, and to optimize the N∥ spectrum for the future launcher design. Furthermore, an LHCD system at 5 GHz is being considered for a future upgrade of the ITER Heating and Current Drive systems, with a power capability of 20 MW coupled to the plasma using a PAM launcher. An R&D programme is being conducted at CEA/IRFM to develop a BeO vacuum window which is a safety critical component of the transmission line. In addition, a mock-up of a TE10–TE30 mode converter at 5 GHz, designed for a rectangular transmission line, has been manufactured and successfully tested on Tore Supra at low RF power.

State Detection of Bond Wires in IGBT Modules Using Eddy Current Pulsed Thermography

Insulated gate bipolar transistor (IGBT) modules are important safety critical components in electrical power systems. Bond wire lift-off, a plastic deformation between wire bond and adjacent layers of a device caused by repeated power/thermal cycles, is the most common failure mechanism in IGBT modules. For the early detection and characterization of such failures, it is important to constantly detect or monitor the health state of IGBT modules, and the state of bond wires in particular. This paper introduces eddy current pulsed thermography (ECPT), a nondestructive evaluation technique, for the state detection and characterization of bond wire lift-off in IGBT modules. After the introduction of the experimental ECPT system, numerical simulation work is reported. The presented simulations are based on the 3-D electromagnetic-thermal coupling finite-element method and analyze transient temperature distribution within the bond wires. This paper illustrates the thermal patterns of bond wires using inductive heating with different wire statuses (lifted-off or well bonded) under two excitation conditions: nonuniform and uniform magnetic field excitations. Experimental results show that uniform excitation of healthy bonding wires, using a Helmholtz coil, provides the same eddy currents on each, while different eddy currents are seen on faulty wires. Both experimental and numerical results show that ECPT can be used for the detection and characterization of bond wires in power semiconductors through the analysis of the transient heating patterns of the wires. The main impact of this paper is that it is the first time electromagnetic induction thermography, so-called ECPT, has been employed on power/electronic devices. Because of its capability of contactless inspection of multiple wires in a single pass, and as such it opens a wide field of investigation in power/electronic devices for failure detection, performance characterization, and health monitoring.

Frequency domain reflectometry for remaining useful life estimation of instrumentation and control cables

As the existing fleets of nuclear power plants age, a greater emphasis has been placed on technologies to quantify the remaining useful life of safety-critical components and to ensure that these systems will operate as intended when called upon, especially in emergency situations. Some of the most important, yet often overlooked components, are the cables that provide the signal paths for instrumentation and control systems used to ensure safe and efficient operation of nuclear power plants. Instrumentation and control cable aging, in particular, is primarily concerned with degradation of the polymer material by thermal oxidation while exposed to heat, humidity, radiation, and other environmental stressors. Consequently, as the polymer becomes embrittled, it cracks and becomes susceptible to moisture intrusion that can cause shorts and shunts in the cable circuits. This article describes the development of two prognostic models to estimate the remaining useful life of nuclear power plant cables. The first model uses data compiled in an existing polymer aging database as background for introducing the remaining useful life model development methodology. The second model uses data generated from accelerated cable aging experiments performed by the authors and explores the use of in situ electrical measurements such as frequency domain reflectometry for predicting the remaining useful life of instrumentation and control cables typically found in nuclear power plants.

Children’s pedestrian route selection: Efficacy of a video and internet training protocol

ObjectiveThis randomized controlled trial examined one aspect of child pedestrian behavior, route selection across intersections, to evaluate whether a combination of widely-available videos and websites effectively train children in safe pedestrian route selection compared to active pedestrian safety control training and a no-contact control group. MethodsA sample of 231 seven- and eight-year-olds were randomly assigned to one of four groups: training with videos and internet websites, active control groups of individualized streetside training or training within a virtual pedestrian environment, or a no-contact control group. All training groups received six 30-min training sessions. Pedestrian route selection was assessed using two strategies, vignettes accompanied by illustrations and tabletop models of intersections, on three occasions: prior to intervention group assignment, immediately post-training, and six months after training. ResultsAlthough there were differences in route selection over time, no time by condition interaction effects were significant (ps>.05), suggesting children in the video/internet training group did not learn pedestrian route selection skills at a rate different from those in the other training groups or those in the no-contact control group. ConclusionSafe route selection is a critical component of pedestrian safety. Our results suggest children may not learn route selection from widely-available videos or websites. Explanations for the null finding and implications for both research and future practice are discussed.

Guidelines for the design of tyre sensor housings

The next generation of tyre sensors will be bonded directly onto the inner liner (IL) in order to measure important parameters such as strain, vehicle load, contact pressure, the tyre-road friction coefficient or wear. Sensor packages (SP) have a sensor node, which is bonded and kept in position by a specifically designed rubber housing (RH). Since the measurements they provide to the car control unit are used to improve the active or passive safety of vehicles, these packages can be considered critical safety components that should be dimensioned carefully. A tyre analysis, whether statical or dynamical, in which the complete structure is considered, under any load, inflating pressure or temperature working condition is mainly oriented towards defining the tyre product. The insertion of an SP inside such a complex tyre model, with the purpose of only analysing its behaviour, would be too time consuming considering the strong nonlinear behaviour of the tyre model. Therefore, this work presents a method that can be used to define a computationally lightweight finite element method (FEM) simulation, which is able to recreate the working conditions to which an SP is subjected. The basic idea behind this method is to separate the analysis of the SP from the structural tyre analyses; the latter is only run once, independently. The first task is to impose the deformed shape on a simplified model of the tyre with a bonded SP. All the deformation states that occur during rolling are computed in a static FEM simulation. The second task is to apply the inertial forces that act on the SP, whether computed or measured directly on the tyre, as external loads. These tasks are implemented in user-defined routines that are executed by the FEM solver. The method permits the stress concentration inside the RH material volume to be identified, at any angular position of the wheel. This information is then used, during the design process, to identify the most suitable geometry to level out the stress distribution. The resulting shape can be tested under different boundary conditions, by substituting the corresponding data arrays, but using the same FEM model. Since the deformed shapes and inertial forces are stored as simple text matrices (which are also used to form a test library), they can be easily interchanged in a flexible way. This more extended design process can reduce the costs of prototyping moulds. The proposed methodology has been developed and tested for the Pirelli Cyber TM Tyre project.

Speaking Up: An International Comparison of the Willingness of Radiation Therapists to Report Errors in Clinical Practice

Radiation therapy involves a complex, multi-step process of delivering treatment using the expertise of an interprofessional team. Errors occur rarely, but when they do occur they can cause significant negative consequences for the patient that can include permanent injury or even death. The detection and reporting of errors is therefore a critical component of patient safety and quality assurance (QA). There has been some recent significant work in Canada to develop national QA standards for radiotherapy quality assurance focusing on programmatic organization, competence and training of personnel, equipment quality control and department policies through the Canadian Partnership for Quality Radiotherapy (CPQR).

Feedback Loop: Hand Hygiene Database Leads to Sucess Staff Empowerment in a Hand Hygiene Program

Hand Hygiene is a critical component of patient and employee safety it is an essential measure in the prevention of health care-associated infections. Despite the availability of hand sanitizers at every room and reminders by Infection Preventionist, compliance with hand hygiene at our institution was forty percent.

A fracture condition incorporating the most unfavourable orientation of the crack

A fracture condition incorporating the most unfavourable orientation of the crack has been derived to improve the safety of loaded brittle components with complex shape, whose loading results in a three-dimensional stress state. With a single calculation, an answer is provided to the important question whether a randomly oriented crack at a particular location in the stressed component will cause fracture. Brittle fracture is a dangerous failure mode and requires a conservative design calculation. The presented experimental results show that the locus of stress intensity factors which result in mixed-mode fracture is associated with significant uncertainty. Consequently, a new approach to design of safety–critical components has been proposed, based on a conservative safe zone, located away from the scatter band defining fracture states. A postprocessor based on the proposed fracture condition and conservative safe zone can be easily developed, for testing loaded safety–critical components with complex shape. For each finite element, only a single computation is made, which guarantees a high computational speed. This makes the proposed approach particularly useful for incorporation in a design optimisation loop.

Analysis and Extension of Safety Mechanisms for Standardized Control Networks in Smart Grid

In smart grid, standardized control networks are typical safety critical components which are under the environments with strong noise and interferences. This paper focuses on the safety mechanisms of standardized control networks in smart grid. The underlying safety mechanisms of standardized wired control networks are analyzed deeply. More importantly, there are very few works considering the safety extensions for wireless control networks. To address this, we propose a combined cyclic redundancy check (CRC) based safety extension mechanism. In addition, key points and open issues of safety-related mechanisms are discussed. To evaluate the safety of the proposed combined CRC mechanism for wireless control networks, error correction capability simulation is performed, which validates the effectiveness of the proposed scheme under the typical noisy background in smart grid. The result supports the usefulness and feasibility of our scheme. To the best of our knowledge, this work is the first to focus deeply on the safety mechanisms for standardized control network in smart grid, especially for the safety extension scheme for wireless control networks.

Automated Vision Inspection System for a Plastic Injection Mould Component

This paper presents an automated vision based defect inspection and sorting system for a plastic injection mould component called a Retractor Retaining Bush, which is an automotive safety critical component. The system identifies defects which usually occur in a plastic injection mould component. Various types of sensors and actuators were interfaced with the vision hardware and the part handling mechanism, to complete the total automated vision based inspection system.

On the low cycle fatigue failure of insulated rail joints (IRJs)

Insulated rail joints (IRJs) are safety critical components in the signalling system of railway corridors which provide a break in the continuity of the rail steel to locate trains. IRJs connect the two rail ends at the discontinuity to achieve geometric and mechanical requirements of rail. The bending stiffness of an IRJ is about one third that of continuous rail. As a result, the IRJs, especially those in heavy haul tracks, exhibit early failure predominantly due to ratchetting or alternating plasticity of railhead metal in the vicinity of the endpost insulators.A three-dimensional (3D) finite element numerical simulation is carried out to examine failures of railhead material in the vicinity of the endpost of an insulated rail joint considering high frequency dynamic wheel loading. A dynamic wheel load of 182kN is applied through a contact patch; the distribution of contact pressure is considered using a non-Hertzian formulation. A 12m long global IRJ model and a sub-model for localised analysis are employed. The shakedown theorem is employed in this study. Nonlinear isotropic/kinematic elastic–plastic material modelling is employed in the simulation. A peak pressure load lower than the shakedown limit is considered as the input load.The equivalent plastic strain plot for this load case lower than the shakedown limit demonstrates the railhead damage captured through a localised stress analysis in the vicinity of the endpost using the sub-modelling technique. The sub-surface plastic deformation of railhead material extends down to 8mm from the railhead top surface. The critical crack initiating stress components are at 2–4mm sub-surface depth. As such, the railhead material fails due to alternating plasticity through low cycle fatigue. Laboratory tests were performed to verify the simulation results and found that test and simulation results correlated well.

Variation in detection limits between bacterial growth phases and precision of an ATP bioluminescence system

To determine the detection limits of the SystemSure Plus, Escherichia coli and Staphylococcus aureus growth curve samples were taken in lag (1 h), log (6 h), stationary (12 h) and death phases (E. coli 144 h, Staph. aureus 72 h). At each time point, the log10 CFU ml(-1) was determined for the dilution where the SystemSure read 0 relative light units (RLU). Average detection limits were E. coli: lag 6·27, log 5·88, stationary 7·45 and death 6·88; Staph. aureus: lag 4·37, log 5·15, stationary 7·88 and death 7·57. Between-run precision was determined with positive control; within-run precision with positive control, lag and log growth for each bacteria. Within-run precision mean RLU (CV): positive control 274 (12%), E. coli lag 1 (63%), log 2173 RLU (19%), Staph. aureus lag 2 (58%) and log 5535 (18%). Between-run precision was 232 (16%). The precision is adequate with most values within the 95% confidence interval. The detection limit varied by 3·51 log10 for Staph. aureus and 1·47 log10 for E. coli. The lowest detection limits were during E. coli log and Staph. aureus lag phases; the highest was during stationary phase. These results suggest that organism identification and growth phase both impact ATP RLU readings. Surface hygiene is a critical component of food safety and infection control; increasingly, ATP detection by bioluminescence is used to evaluate surface hygiene and effective cleaning. This is the first study to show that the number of living and potentially infectious bacteria remaining when the device reads zero varies between the different bacterial life cycle phases: lag, log, stationary and death. ATP device users need to be aware of this information to use the devices appropriately.

GABES: A genetic algorithm based environment for SEU testing in SRAM-FPGAs

Testing of FPGAs is gaining more and more interest because of the application of FPGA devices in many safety-critical systems. We propose GABES, a tool for the generation of test patterns for application-dependent testing of SEUs in SRAM-FPGAs, based on a genetic algorithm. Test patterns are generated and selected by the algorithm according to their fault coverage: Faults are injected in a simulated model of the circuit, the model is executed for each test pattern and the respective fault coverage is computed. We focus on SEUs in configuration bits affecting logic resources of the FPGA. This makes our fault model much more accurate than the classical stuck-at model. Results from the application of the tool to some circuits from the ITC'99 benchmarks are reported. These results suggest that this approach may be effective in the inspection of safety-critical components of control systems implemented on FPGAs.

Analytical Modelling of Temperature Distribution Using Potential Theory by Reference to Broaching of Nickel-Based Alloys

Knowledge of temperature fields and heat flow evolving during metal cutting processes is of significant importance for ensuring and predicting the product`s quality. Furthermore, this knowledge enables an improved usage of resources, such as machine tools and tool deployment. The strength of the heat sources as a result of the process and the distribution of the temperature in the material directly influence the tool wear mechanisms, wear rate, thermo-elastic deflection of the tool centre point and the amount of heat flowing into the newly generated work piece surface. Especially the latter effect is of crucial importance when it comes to safety critical components as they are employed in aero-engines. In aviation industry, the surface integrity is used as a complex quality measure summarising several aspects at the machined surface and sub-surface out of which many issues are predominantly thermal issues (e.g. temperature driven hardening of the work piece material, re-cast and white etching layers as well as residual stress profiles).

A FEM-DBEM Investigation of the Influence of Process Parameters on Crack Growth in Aluminum Friction Stir Welded Butt Joints

Medium to high strength aluminum alloys, such as 2xxx, 6xxx, and 7xxx series, are actually considered of great interest in the transport industries. For aeronautical applications, the precipitation hardenable AA2024 (Al-Cu) alloy is gaining considerable attention, in particular for the realization of nose barrier beam or fuselage panels. In this context, remarkable research effort is currently focused on the application of the Friction Stir Welding (FSW) process, as a suitable alternative to fusion welding processes. The interest in aeronautical application of FSW process is also justified by the reduction of production costs and weight and by the increase of strength and damage tolerance with respect to riveted lap joints. The implementation of the technique in safety-critical components, however, requires a deeper understanding of static strength as well as of fatigue behavior of FSWed assemblies. In this sense some experimental results have already been presented in the inherent literature, relatively, for instance, to AA6082-T6 and AA6061-T6, AA6063-T6, AA2024-T351, AA2024-T8 alloys processed by FSW. Despite the unavoidable relevance of experimental testing, a numerical approach able to predict the mechanical behavior of FSWed assemblies is very desirable, in order to achieve time and cost compression and to implement computational optimization procedures. This paper deals with a numerical investigation on the influence of FSW process parameters, namely the rotating speed and the welding speed, on fatigue crack growth in AA2024-T3 butt joints. The computational approach is based on a combined Finite Element Method (FEM) and Dual Boundary Element Method (DBEM) procedure, in order to take advantage of the main capabilities of the two methods. In particular, linear elastic FE simulations have been performed to evaluate the process induced residual stresses, by means of a recently developed technique named contour method. The computed residual stress field has then been superimposed to the stress field produced by an applied fatigue traction load in a Dual Boundary Element Method (DBEM) environment, where the simulation of a crack, initiated and propagating along the previously mentioned cutting line, can be performed in an automatic way. A two-parameters crack growth law is used for the crack propagation rate assessment. The DBEM code BEASY and the FEM code ANSYS have been sequentially coupled in the aforementioned numerical approach by using a BEASY interface module and in house developed routines. Computational results have been compared with experimental data, showing a satisfactory agreement. The influence of process parameters on the residual stresses distribution has also been highlighted.

Friction stir welded joints of Al–Li Alloys for aeronautical applications: butt-joints and tailor welded blanks

Structural design for safety critical components, as airframes, requires comprehensive characterization of the materials and joints properties. This characterization must take into account a large amount of variables required for accurate design to ensure structural integrity during the different phases of the product life cycle of an aircraft. One of the most important variables in this characterization is fatigue behavior due to the cyclic loads during the life of an airframe.The application of welding processes to replace riveted joints in aeronautical structures is an attractive option, since it allows joints with less stress concentration points and might be applied efficiently without overlapping the two joining parts (with a butt-joint configuration), reducing the joint weight. This weight reduction can have a small impact in production costs, but has a huge impact in the life cycle costs. Friction stir is the most appealing welding process in aeronautical structures since it has been shown to produce joints with excellent properties when applied to aluminum alloys and can deal with hardened precipitated aluminum alloys, since it is a semi-solid state process. Furthermore, this joining process allows to join dissimilar materials and plates with different thicknesses, creating in this way tailor welded blanks, which support the manufacturing of optimized panels by tailoring their strength in function of their needs.This article presents a mechanical characterization of friction stir welds of last generation aluminum–lithium alloys, including tailor welded blanks with different thicknesses, with potential applications in aeronautical and aerospace components. Mechanical characterization with crack initiation and fatigue crack growth tests were included in this study for an enhanced assessment of these alloys behavior, and was preceded by welding parameter calibration.

Bentonite reactivity in alkaline solutions: interim results of the Cyprus Natural Analogue Project (CNAP)

AbstractBentonite is one of the more safety-critical components of the engineered barrier system in the disposal concepts developed for many types of radioactive waste. It is used due to its favourable properties (including plasticity, swelling capacity, colloid filtration, low hydraulic conductivity, high retardation of key radionuclides) and its stability in relevant geological environments. However, bentonite is unstable under alkaline conditions and this has driven interest in low-alkali cements (leachate pH of 10–11). To build a robust safety case, it is important to have supporting natural analogue data to confirm understanding of the likely long-term performance of bentonite. In Cyprus, the presence of natural bentonite in close proximity to natural alkaline groundwaters permits the zones of potential bentonite/alkaline water reaction to be studied as an analogy of the potential reaction zones in the repository. Here, the results indicate minimal volumetric reaction of bentonite, with production of a palygorskite secondary phase.

Optimal Group Configurations of Fibre Materials Based on Inclusion Modelling

The use of high performance composites is becoming increasingly common in safety critical components. The key driver behind this research is the need to develop a better understanding of through thickness stresses where fibres and matrix are not uniformly distributed throughout the thickness. Classical distribution of composite is not always possible due to problems associated with manufacturing processes. Poor fibre distribution through the thickness affects the through thickness properties and can compromise the structural integrity. This paper presents a semi-analytical tool that can be used for modelling of fibre group optimisation. It can be used for analysis at both microscopic (fibre resin interactions) and macroscopic (composite laminate) levels. At each level the components reactions to externally applied load have been investigated through its load transfer mechanisms. The effects of anisotropy, edge distance and pitch between fibres, numbers of rows and finally dissimilar fibre materials and fibre cross section have been considered.

Development and validation of a nurse-assessed patient comfort score for colonoscopy

Comfort during colonoscopy is a critical component of safety and quality. To develop and validate the Nurse-Assessed Patient Comfort Score (NAPCOMS). Prospective scale validation. Colorectal cancer screening centers in the United Kingdom and Canada. A total of 300 consecutive patients undergoing colonoscopy at participating colorectal cancer screening centers. The NAPCOMS was developed by using a modified Delphi process. During colonoscopy, two endoscopy room nurses independently observed and rated patient comfort and tolerability by using NAPCOMS. In addition, endoscopists reported global comfort scores and patients' reported global comfort by using visual 4-point Likert and National Health Service-United Kingdom Global Rating Scales. Reliability and validity of NAPCOMS was measured by using intraclass correlations (ICC) between nurse ratings of colonoscopies and between NAPCOMS, endoscopist ratings, and patient ratings of global comfort. The ICC for the overall NAPCOMS was 0.84 (95% confidence interval [CI], 0.80-0.87). There was high agreement between the NAPCOMS and endoscopist ratings of comfort (ICC = 0.77; 95% CI, 0.72-0.81), moderate agreement between the NAPCOMS and patient ratings (ICC = 0.61; 95% CI, 0.53-0.67), and moderate agreement between the endoscopist and patient ratings (ICC = 0.52; 95% CI, 0.43-0.60). NAPCOMS was validated in outpatients who received colonoscopy with minimal to moderate sedation as part of a screening and surveillance program, so performance among inpatients or those requiring deep sedation was not tested. NAPCOMS is a reliable and valid tool for assessing patient comfort in the setting of outpatient colonoscopy performed with minimal to moderate sedation.