End Fittings Research Articles

Design and characterization of a pneumatic muscle actuator with novel end-fittings for medical assistive applications

Pneumatic muscle actuators (PMA) are a class of soft actuators known for their high power to weight ratio and inherent compliance. The pneumatic muscle's inherent properties make them very favorable for assistive applications (e.g., medical exoskeletons). This study presents a novel end-fitting design that makes the developed pneumatic muscle actuator lightweight, cost-effective, and modular, thus simplifying the process of assembly and maintenance. The pneumatic muscle actuator assembled using the novel end fittings achieves a shorter overall length without compromising its contraction. The pneumatic muscle actuator has been assembled using a commercial bladder and a braided sleeve alongside a pair of 3D printed novel end-fittings. The paper also details the developed actuator's characterization for force and deflection parameters at various operating pressures. A total of four muscle actuators of varying diameters with constant actuation length (100 mm) were developed and tested to showcase the effect of size on the muscle actuator's behavior. The study presented here also involved comparing three mathematical models developed for pneumatic muscles in order to find a model which closely resembles the developed muscle actuator. Finally, the developed pneumatic muscle actuator's behavior is compared with a commercially available muscle to determine the efficacy of the developed muscle's design. The tests showed that the muscle using a bladder of smaller volume but higher tensile modulus had a higher accuracy and stable performance. As the muscle is intended for medical applications, it was also put through an endurance test with realistic loading and pressure conditions, which revealed very promising results.

Deuterium Ingress at the Rolled Joints in CANDU Reactors: Where Does It Come From and How Can It Be Reduced?

AbstractSimple, small-scale, experiments demonstrate that the initial protium in stainless-steel end fittings contributes to the high deuterium concentrations found in the zirconium pressure tubes at CANDU rolled joints. This protium isotopically exchanges becoming deuterium that is then gettered by the zirconium pressure tube. We propose to reduce the concentration of hydrogen isotopes at the ends of pressure tubes in heavy-water nuclear reactors with yttrium getters placed in the outer regions of the stainless-steel end fittings away from the heat-transport heavy water. Simple, small-scale, experiments demonstrate the operating principle showing that yttrium can getter hydrogen isotopes from the zirconium through the stainless steel.

Effect of constitutive model on residual stress development in the pressure tube rolled joint

Being one of the most important joints in a pressurized heavy water reactor (PHWR), pressure tube rolled joint is critical during the construction and operation. This joint is formed through the roll expansion process that leads to an interference fit between the Zr 2.5%Nb pressure tube and stainless-steel end fitting. For integrity of this joint, a sufficient pull-out strength and leak tightness must be maintained, while having lower undesirable residual stresses, especially in the transition zone. The roll expansion process parameters are controlled to achieve optimum contact pressure and limit the tensile residual stress. The parameters of this roll expansion process are designed either through experiments or through numerical simulations. One important aspect that is often ignored in the numerical simulations is the effect of material constitutive behavior of the Zr 2.5%Nb alloy, particularly the anisotropic yield behavior and the cyclic stress-strain response. In this paper, these two aspects of constitutive behavior are investigated, using three-dimensional finite element simulations, to understand their influence on the residual stress development in the roll expansion process. The cyclic behavior was modelled using Chaboche nonlinear kinematic hardening model. The model parameters were extracted from low cycle fatigue experiments with the strain amplitude equivalent to that seen in roll expansion process. The results show that constitutive behavior, especially the cyclic behavior, has a significant impact on the residual stress. Anisotropic yielding of the pressure tube was also seen to affect the tensile residual stress and the contact pressure, although to a lesser extent. Finally, after comparison between four combinations of constitutive behavior, a simple isotropic yield with isotropic hardening model is suggested to predict the tensile residual hoop stress in the rolled joint, conservatively.

Characterization and nonlinear models of bending extensile/contractile pneumatic artificial muscles

Pneumatic artificial muscles (PAMs) are compliant fluidic actuators, usually consisting of a tubular bladder, a braided sleeve and end fittings. PAMs have been studied extensively by researchers; however, most previous researches are focused on the axial PAMs. Herein, a pair of nonlinear models were developed based on the principle of virtual work and the force balance analysis. And the two models are applicable to both bending extensile PAMs (BE-PAMs) and bending contractile PAMs (BC-PAMs). In this study, a cyclic bending moment loading experimental method were proposed and conducted with BE-PAMs and BC-PAMs to characterize their deformation and actuation performance and draw their overall relationships of actuation moment to bending curvature and inner pressure. With the experimental results, the validation analysis was carried out to demonstrate the validity of the two models. The energy model can get higher accuracy, while the force balance model could provide more details of the interior and interaction stress conditions. The combination of both can promote the comprehension of non-axial bending PAMs. Moreover, two three-finger soft grippers and a humanoid hand based on BE-PAMs and BC-PAMs were built and tested to investigate their performance on gripping objects. The BE-PAM gripper showed more accommodative gripping performance, whereas, the BC-PAM gripper owned higher gripping force. The humanoid hand combining the merits of both showed excellent flexibility, adaptability and decent load capability in gripping object with various sizes, shapes and materials.

Recognition of pollution layer location in 11 kV polymer insulators used in smart power grid using dual-input VGG Convolutional Neural Network

This paper portrays the application of a Partial Discharge (PD) signal combined with the dual-input VGG Convolution Neural Network (CNN) to predict the location of the pollution layer on 11 kV polymer insulators subjected to alternating current for smart grid applications. First, a non-uniform pollution layer artificially created for HV insulator with three straight shed ball end fitting in a laboratory setup and corresponding PD readings are measured. The wavelet transform is employed to represent the measured PD signal as scalogram patterns. In general CNN uses a single input pattern for feature extraction. If the pattern quality is low, it is easy to cause misclassification. Hence in this proposed work, the feature fusion of a dual-input Visual Geometry Group (VGG) based CNN is used for the classification of contamination layer. VGG 19 is a pretrained deep learning network used for extracting the rich features from the patterns. In continuation to that, hyperparameter (HP) play a vital role in deep learning algorithms because they directly manage the behaviours of training algorithms and have a significant effect on the performance of deep learning models. Hence, Bayesian Optimization (BO) is used for tuning the HP. At last, to check the practicality of the proposed algorithm, a new dataset is created for 11 kV polymer insulator with three alternate shed clevis end fitting and different pollution levels—acceptable results obtained by using dual-input CNN with the minimum quantity of data.

Production of hybrid tubular metal-fibre preforms: development of a digital twin for the draping process

Hybrid shafts or rods with a metallic end fitting and a load transmitting area made of fibre reinforced plastics possess a great potential in terms of lightweight design, e.g. in automotive industry or aviation. One essential and quality-defining process step in the manufacturing of such parts is the draping of dry braided fibre fabrics onto the shape of the metallic end fitting. To explore the immature draping process and to derive the draping tool geometry a digital twin based on finite element simulation has been developed and validated by first experiments.

Condition Monitoring Technologies for Steel Wire Ropes – A Review

In this research, we review condition-monitoring technologies for offshore steel wire ropes (SWR). Such ropes are used within several offshore applications including cranes for load handling such as subsea construction at depths up to 3-4000 meters, drilling lines, marine riser tensioner lines and anchor lines. For mooring, there is a clear tendency for using fiber ropes. Especially for heavy-lift cranes and subsea deployment, winches with strong ropes of up to 180 mm in diameter may be required, which has a considerable cost per rope, especially for large water depths. Today’s practice is to discard the rope after a predetermined number of uses due to fatigue from bending over sheaves with a large safety factor, especially for systems regulated by active heave compensation (AHC). Other sources of degradation are abrasion, fretting, corrosion and extreme forces, and are typically accelerated due to undersized or poorly maintained sheaves, groove type, lack of lubrication and excessive load.Non-destructive testing techniques for SWR have been developed over a period of 100 years. Most notably are the magnetic leakage techniques (electromagnetic methods), which are widely used within several industries such as mining and construction.The content reviewed in this research is primarily the developments the last five years within the topics of electromagnetic method, acoustic emissions (AE), ultrasound, X- and γ-rays, fiber optics, optical and thermal vision and current signature analysis. Each technique is thoroughly presented and discussed for the application of subsea construction. Assessments include ability to detect localized flaws (i.e. broken wire) both internally and externally, estimated loss of metallic cross sectional area, robustness with respect to the rough offshore environment, ability to evaluate both rope and end fittings, and ability to work during operation.

CFD simulation of corium flow through an end fitting of a pressurised heavy water reactor

This study investigates the numerical simulation of corium relocation during a hypothetical accident, focussing on the modelling of core melt, its solidification and redistribution. This paper presents results of a high-fidelity computational fluid dynamics (CFD) simulation of an ex-vessel corium flow through a horizontal end fitting geometry, a pressurized heavy water reactor (PHWR) relevant configuration. The objective of this work is to simulate the corium progression within the end fitting of a PHWR to assess the suitability of two viscosity models using a CFD code; Siemens STAR-CCM+. This first-of-a-kind, exploratory study demonstrates the potential of the existing CFD models for modeling corium spreading within the end fitting geometry. Mixed convection turbulent corium flow in the end-fitting has been modeled in the three-dimensional CFD simulations. Transient simulations using the volume-of-fluid approach and melting-solidification models were performed to predict the corium melt spread within the end fitting. Two suitable temperature-dependant models for corium viscosity were tested, one being empirical viscosity model by Ramacciotti and the other mechanistic viscosity model available in STAR-CCM+. The unique flow features such as the Rayleigh-Bénard instability could be observed using the Ramacciotti empirical viscosity modelling approach. A qualitative assessment of the results was undertaken, showing that the CFD model has predicted the corium spreading behaviour that is consistent with the expectations based on engineering judgement and experience. This kind of simulations are expected to serve as a guidance in planning lab-scale experiments and aid in CFD-informed modeling improvements for integral (or system) codes going forward.

Creep damage in long-term grade 91 steel component tests

ABSTRACT This paper describes specific results from a unique study which involves design, manufacture and internal pressure testing of two Grade 91 steel vessels. The vessel results which are the focus of this paper relate to the creep behaviour of the closures and the associated pressure boundary welds. All the end fittings used in the vessels were consistent with arrangements allowed by typical design codes. Similar parts can be found in power boilers and other high energy components. The results are discussed in terms of creep crack initiation and the potential for fast fracture for the individual geometries.

Sealing Performance of the End Fitting of a Marine Unbonded Flexible Pipe under Pressure Penetration

The sealing performance of end fittings is very important for offshore oil and gas pipelines. To investigate the sealing behavior of a ring-shaped wedge seal, global and local numerical models of the ring–pipe interaction have been developed based on the finite-element method. First, the sealing process of the ring under pressure is simulated. Second, a criterion for the penetration of fluid pressure is applied in these models to assess how the sealing capacity changes along the contact surface. Finally, the contact magnitude of interference and the shape of the sawtooth heaves on the sealing ring are predicted and compared. The results show an interesting concentration of von Mises stress in the sealing ring and also that the peak contact pressure appears in the sealing zone. However, the penetration of fluid pressure has obvious effects on the distributions of von Mises stress and contact pressure. The best sealing performance is when the axial displacement of the sealing ring is 1.4 mm and the contact magnitude of interference is 0.3 mm. Given the sawtooth heave of sealing ring, semicircular heave gives the better sealing capacity compared with trapezoidal heave.

Microstructure and hydrides in the near rolled-joint regions of ex-service CANDU pressure tube

The regions of CANDU® pressure tubes near the rolled joint (RJ) are the un-supported portions of the inlet and outlet ends just inboard of where the tubes make contact with the 403 stainless steel end fitting sections. Compared to the main body of the pressure tube, in-service conditions are more complex with large gradients in the flux, significant hydrogen isotope concentration profiles and varying operating temperatures. In order to increase the amount of data related to microstructure evolution, the microstructures near rolled-joint regions from an ex-service CANDU pressure tube were investigated. The results show that irradiation-induced effects on the microstructure are more significant than the temperature influence near the inlet rolled-joint region (that operates at lower temperatures). Thermal effects play a more dominant role than the flux near the outlet region (that operates at higher temperatures). Zirconium hydrides aligned in both circumferential and radial directions of the tube have been observed. The zirconium hydrides have an orientation relationship of (0002)αZr//(1¯1¯1)ZrH, and [21¯1¯0]αZr//[011]ZrH with the α-Zr matrix; the hydride phases were identified as gamma (γ) hydride by observing superlattice reflections on the (110) planes in the electron diffraction patterns. The presence of γ hydrides at room temperature in the studied tube may have technical importance because in most of the previous research, δ hydrides were considered as the stable phase that would precipitate during cooling at reactor relevant rates. This assumption has been applied to both delayed hydride cracking (DHC) and fracture toughness experiments and during development of related models. It is critical to elucidate the phases of zirconium hydrides at relevant in-service conditions to enable representative experimental testing and modelling that can be used to verify and/or improve the predictive capability of material evolution and cracking behavior of zirconium alloys in nuclear reactors.

Cause Analysis of the Crooked High Voltage End Fittings for a 220kV Composite Insulator in-service

The high voltage end fitting for an in-serviced 220kV composite insulator was found to be crooked by the transmission line inspector, and the deformed cause was then investigated by digital X-ray imaging, chemical composition analysis, metallographic observation and mechanical properties testing in this paper. The results indicated that both the material quality and mechanical properties of the composite insulator high voltage (HV) end fitting met the standard requirements. And the main reason for the crooking of HV end fitting was the effect of abnormal force, such as falling from high position, impact of heavy objects. At last, it was advised that the supervision on the installation quality of fittings and the inspection of in-service composite insulator fittings should be strengthened. In addition, composite insulator with deformed or fractured end fitting should be timely handled, avoiding similar metal section failures.

Numerical analysis of stress concentration factors on tensile armour wires inside the end-fitting of an axially tensed unbonded flexible pipe

ABSTRACT The present paper examines the case of a metal based unbonded flexible pipe under a number of axial tensile operational loads of varying intensity, expressly focusing on the response of the segments of the pipe’s tensile armour wires that lie inside the pipe’s End-Fitting (EF), with intent to track the development of high stress concentration areas there and assess the stress concentration factors (SCF) involved. Additionally, a parametric study is performed, to identify potential factors that might affect the maximum SCF values measured on these wire segments inside the EF. Based on the parametric study’s findings, an approximate relationship for evaluating the expected maximum SCF on the tensile wire inside the EF is developed. The paper adopts a numerical approach to the problem, based on the development of a two-dimensional finite element model for evaluating the wire’s response to axial tensile operational loads. The model considers both the effects the EF’s assembling procedure and the Factory Acceptance Test (FAT) have on the behavior of wire segments lying inside the EF. An analytical approach is employed as a benchmarking tool of the numerical model’s performance.

Design manufacture and testing of a composite support structure for spacecraft application

Abstract Spacecraft carries several electronic equipment, some of them have to be placed at a distance from the spacecraft panels with the help of a support structure. Such structures are subjected to significant vibration loads during the launch and also they have to be made with minimal mass. Support structure made of carbon fibre reinforced polymer (CFRP) is the best suited. In this work design, manufacturing and structural testing of a typical such support structure are addressed. The design of the support structure involves arriving at a suitable layup of CFRP plies. In addition to the launch loads manufacturing issues are also considered in the design. Design driver here is the natural frequency of the support structure and having an appropriate coefficient of thermal expansion. Considerable mass saving is achieved by using the composite material compared to conventional aerospace material aluminium. The composite support structure is attached to the spacecraft using end fitting which is made of aluminium. Two such support structures are manufactured from CFRP prepregs using autoclave curing. Tensile test carried out on the support structure showed slightly higher modulus than what is used in the design. The strains measured during the bending test are very good agreement with the strains computed using the modulus measured in the tensile test. But the deflections measured are higher. The natural frequency of the support structure in bending is determined through a resonance search experiment and found good agreement with the frequency determined from the measured deflections. The results show significance influence of the end fitting on the natural frequency.

Influence of Electric Field Distribution on 33kv Non-Ceramic Insulator with Different Shed Configurations using 3D Finite Element Method

In last decade, influence of electric field (E-field) distribution is plays a major concern in estimating the service life of Non-cermaic insulators. One of the foremost troubles met by the utilities is the breakdown of insulator owing toward high electrical stress on end fittings. The present work is intended to focus on the impact of different shed configurations on 33kV Non-Ceramic insulators by 3-Dimensional (3D) Finite Element Method (FEM). Totally seven different shed configurations of 3D simulation studies is performed on 33kV non-ceramic insulators. Optimum result is obtained by alternate shed configured insulator and the first shed near to the metal end fittings. It is whispered that obtained results will be helpful to the utility and design engineers.

An analytical method for the determination of molybdenum in the end fitting of PE flexible composite pipe

The flexible composite pipe is a new type of polymer composite pipe with excellent corrosion resistance. Based on the color reaction of molybdenum with sodium thiocyanate, a photometric method for the determination of molybdenum in flexible composite pipe joint samples was established. The sample is dissolved by a sulfuric acid-phosphoric acid mixed acid, and stannous chloride is used as a reducing agent in a sulfuric acid-perchloric acid medium, and an orange-red complex is formed between molybdenum and sodium thiocyanate, and the absorbance, absorbance and molybdenum content are measured in mass. The linear relationship is in the range of 0.30%∼1.18%. This method uses a standard steel solution closer to the real sample to establish a working curve. The experiment shows that the method is accurate and simple. The molybdenum in the end fitting of flexible composite pipe was measured, and the results were satisfactory.

A three-dimensional explicit finite element analysis of rolled joint process by varying the roller path

In pressurized heavy water reactors, pressure tube to end fitting rolled joint is crucial for safe operation. The joint requires sufficient contact pressure for leak tightness and lower undesirable residual stress in the transition region of the tube. The objective of this work is to assess various paths of roller for roll expansion of tube such that the residual tensile stress is reduced while maintaining the required leak tightness. Consequently, three dimensional, explicit finite element simulations, of the roll expansion process are carried out. Several roller paths are considered in the simulation to vary the strain path of deformation. Results showed that with increase in number of rotations of the roller, the residual stresses decreased. In addition, the contact pressure is found to be within acceptable range for leak tightness. But, beyond a certain number of rotations, the stresses are found to saturate, hence putting an upper bound to their number.

Sealing Performance Analysis of an End Fitting for Marine Unbonded Flexible Pipes Based on Hydraulic-Thermal Finite Element Modeling

End fittings are essential components in marine flexible pipe systems, performing the two main functions of connecting and sealing. To investigate the sealing principle and the influence of the temperature on the sealing performance, a hydraulic-thermal finite element (FE) model for the end fitting sealing structure was developed. The sealing mechanism of the end fitting was revealed by simulating the sealing behavior under the pressure penetration criteria. To investigate the effect of temperature, the sealing behavior of the sealing ring under different temperature fields was analyzed and discussed. The results showed that the contact pressure of path 1 (i.e., metal-to-polymer seal) was 31.7 MPa, which was much lower than that of path 2 (metal-to-metal seal) at 195.6 MPa. It was indicated that the sealing capacities were different for the two leak paths, and that the sealing performance of the metal-to-polymer interface had more complicated characteristics. Results also showed that the finite element analysis can be used in conjunction with pressure penetration criteria to evaluate the sealing capacity. According to the model, when the fluid pressures are 20 and 30 MPa, no leakage occurs in the sealing structure, while the sealing structure fails at the fluid pressure of 40 MPa. In addition, it was shown that temperature plays a significant role in the thermal deformation of a sealing structure under a temperature field and that an appropriately high temperature can increase the sealing capacity.

Degradation behavior and aging mechanism of decay-like fractured GRP rod in composite insulator

Decay-like fracture is a new type of fracture of composite insulator that is different from normal fracture and brittle fracture. The fracture surface of the glass fiber reinforced polymer (GRP) rod in the decay-like fracture is like rotten wood. There are punctures on the silicone rubber housing and abnormal temperature rise is detected on the composite insulator before fracture. However, the cause and aging mechanism of the decay-like fractured composite insulator is still unknown. In this paper, the degradation behavior of the corroded GRP rod in a composite insulator with abnormal temperature rise was studied. The basic features of the GRP rod were obtained by optical microscope, SEM and TGA. Eroded gap and dendritic shadow in parallel light were found on the GRP rod. Degradation of the epoxy resin, fracture of the glass fiber and failure of the resin-fiber interface leads to the formation of an eroded gap and decreases the GRP-rod transmittance. Chemical reactions in the corroded GRP rod were studied by XPS and FTIR The reactions of ionic exchange and hydrolysis in the area of the dendritic shadow was weaker, but the oxidation under partial discharge was much stronger. The source of water is discussed and the aging mechanism of the GRP rod is revealed and divided into four stages; namely, deterioration of end fitting, hydrolysis and ionic exchange, oxidation of the epoxy resin, and rapid development. The speed of degradation of GRP rod increases stage by stage and the mechanical properties decreases sharply, which eventually leads to decay-like fracture of composite insulator.

Study on the optimisation of the end fittings of the DC disconnector

The disconnector is the key electrical equipment in DC field. In China, the ±1100 kV DC project uses the indoor DC field, where the switching impulse withstand voltage of the disconnector influences the clearance a lot. To improve the switching impulse withstand level of the ±1100 kV disconnector, first of all, the switching impulse test was carried out on the disconnector with traditional double-balanced ring structure and the 50% switching impulse discharge voltage was obtained. By analysing the discharge path, it is found that the grading ring did not effectively shield the upper part of the disconnector. Therefore, the structure of the end fittings of the disconnector was changed to the structure of the mushroom head. The electric field simulation was performed on the optimised shield，it is shown that the maximum field strength is lower than the control field strength. Then the switching impulse test was carried out on the optimised disconnector, it was found that the 50% impact discharge voltage was above 2400 kV which met the engineering requirements.