Wearable High Voltage Compliant Current Stimulator for Restoring Sensory Feedback

Transcutaneous Electrical Nerve Stimulation (TENS) is a promising technique for eliciting referred tactile sensations in patients with limb amputation. Although several studies show the validity of this technique, its application in daily life and away from laboratories is limited by the need for more portable instrumentation that guarantees the necessary voltage and current requirements for proper sensory stimulation. This study proposes a low-cost, wearable high-voltage compliant current stimulator with four independent channels based on Components-Off-The-Shelf (COTS). This microcontroller-based system implements a voltage-current converter controllable through a digital-to-analog converter that delivers up to 25 mA to load up to 3.6 kΩ. The high-voltage compliance enables the system to adapt to variations in electrode-skin impedance, allowing it to stimulate loads over 10 kΩ with currents of 5 mA. The system was realized on a four-layer PCB (115.9 mm × 61 mm, 52 g). The functionality of the device was tested on resistive loads and on an equivalent skin-like RC circuit. Moreover, the possibility of implementing an amplitude modulation was demonstrated

Experimental and numerical investigation of pressurized pipe elbows under strong cyclic loading

The present work examines the behavior of pipe elbows subjected to strong cyclic in-plane bending loading in the presence of internal pressure. In the first part of this work the experimental procedure is presented in detail. The tests are conducted in a constant amplitude displacement-controlled mode resulting to failures in the low-cycle fatigue range. The overall behavior of each tested specimen, as well as the evolution and concentration of local strains are monitored throughout the testing procedure. Different internal pressure levels are used in order to examine their effect on the fatigue life of the specimens. The above experimental investigation is supported by rigorous finite element analysis. Using detailed dimensional measurements and material testing obtained prior to specimen testing, detailed numerical models are developed to simulate the conducted experiments. An advanced cyclic plasticity material model is employed for the simulation of the tests. Emphasis is given on the local strain development at the critical part of the elbow where cracking occurs. Finally, the results of the present investigation are compared with available design provisions in terms of both ultimate capacity and low-cycle fatigue. Copyright © 2013 by ASME

Sull’identificazione del comportamento plastico di un acciaio a partire da misure a campo intero ottenute tramite correlazione digitale di immagini

In the present work a method to obtain a true stress-true strain curve of an alloy by a full field digital image correlation measurement of the specimen surface kinematics, is presented. A preliminary set of parameters of a plasticity law is obtained to start up an automatized search algorithm, that includes, for each step a FE analysis in 3D. It’s also proposed a dual approach of the same search problem

Modelling of Crack Arrestors on Gas-Pipelines

Design of gas pipelines implies demanding tasks such as the definition of material requirements in terms of ductile fracture propagation control. This task is especially challenging when high strength steels (like X100 and beyond), whose use is imposing as a result of the consolidated worldwide trend towards the realization of long distance/high pressure gas pipelines, are considered. In fact as recent research projects clearly demonstrated (Mannucci [1], Demofonti [2] and Papka [3]) it is not possible to rely on the self-arrestability of such a class of high strength steel and as a consequence new solutions must be adopted, especially when severe operating conditions (rich gas, low temperature, etc.) are envisaged. In this context, the adoption of additional mechanical devices, such as Crack Arrestors (CA), represents a valid alternative since, if properly designed, they can externally provide a structural positive contribution in terms of resistance opposed to ductile fracture propagation. Optimal design of CA presupposes the knowledge of the efficiency of each possible CA type, but also the influence of its main geometric parameters (thickness, radial clearance, axial length…) on the constraint applied on fracturing pipe, in the specific operative condition. The use of a specific finite element code named PICPRO, which was developed by CSM jointly with the University of Tor Vergata and actually used in the frame of a BP project, allows to perform numerical simulations of running shear fracture along a pressurised steel pipeline also considering the constraint applied to the running fracture by the crack arrestor; PICPRO was used to perform a rapid comparison within all the potential CA solutions and it allowed the successful identification of the best one for the case under consideration (Mannucci [1]). In the present paper some new algorithms, expressly developed to simulate crack advance inside a crack arrestor, are presented. Exploration of main CA design parameters imposes the use of algorithms different from those based on the search and application of contact elements, in order to reduce calculation time and to give the possibility to perform an higher number of simulations. Hence, two new algorithms are on purpose developed and hereby presented: the first one for the evaluation of the interaction pipe-CA and the second one for managing the fracture propagation criteria even if crack flanks cannot freely open because of crack arrestor presence

Crack arrestor design by finite element analysis for X100 gas transportation pipeline

The interest of gas companies in the use of high grade steel pipes, equivalent to X100 and higher, for the construction of long distance gas pipelines has become a consolidated trend in the world; in response to this market demand, steel makers have successfully developed new classes of high grade steel for large diameter pipelines, but some limitations might occur to their application if important aspects related to their structural reliability, such as the resistance to ductile fracture propagation, are not completely clarified. Recent efforts spent in investigating this aspect, that is the ductile fracture propagation control, have demonstrated that the class of X100 large-diameter steel pipes being considered, when operated under severe operating conditions (high usage factor, rich gas, low temperature), may lie on the fracture propagation/arrest border line. In this case external mechanical devices, i.e. crack arrestors, may be required to ensure arrest of a propagating fracture This paper presents a crack arrestor design approach by finite element analysis for a X100, largediameter gas transportation line operating under severe conditions, such as those mentioned above. A CSM finite element model specifically developed for simulating dynamic ductile fracture propagation (PICPRO) has been used and implemented to consider the effect of crack arrestor constraint on the running fracture. Several types of crack arrestor have been considered, including a steel sleeve with or without grout, thickerwalled pipe and types of composite crack arrestor, and relevant design criteria have been obtained. Numerical predictions were also compared with the results of recent experimental full-scale burst tests carried out on X100 large diameter pipelines, demonstrating the capability of the model developed to correctly predict the crack arrestor performance

Modelling of Crack Arrestors on Gas-Pipelines

Design of gas pipelines implies demanding tasks such as the definition of material requirements in terms of ductile fracture propagation control. This task is especially challenging when high strength steels (like X100 and beyond), whose use is imposing as a result of the consolidated worldwide trend towards the realization of long distance/high pressure gas pipelines, are considered. In fact as recent research projects clearly demonstrated (Mannucci [1], Demofonti [2] and Papka [3]) it is not possible to rely on the self-arrestability of such a class of high strength steel and as a consequence new solutions must be adopted, especially when severe operating conditions (rich gas, low temperature, etc.) are envisaged. In this context, the adoption of additional mechanical devices, such as Crack Arrestors (CA), represents a valid alternative since, if properly designed, they can externally provide a structural positive contribution in terms of resistance opposed to ductile fracture propagation. Optimal design of CA presupposes the knowledge of the efficiency of each possible CA type, but also the influence of its main geometric parameters (thickness, radial clearance, axial length…) on the constraint applied on fracturing pipe, in the specific operative condition. The use of a specific finite element code named PICPRO, which was developed by CSM jointly with the University of Tor Vergata and actually used in the frame of a BP project, allows to perform numerical simulations of running shear fracture along a pressurised steel pipeline also considering the constraint applied to the running fracture by the crack arrestor; PICPRO was used to perform a rapid comparison within all the potential CA solutions and it allowed the successful identification of the best one for the case under consideration (Mannucci [1]). In the present paper some new algorithms, expressly developed to simulate crack advance inside a crack arrestor, are presented. Exploration of main CA design parameters imposes the use of algorithms different from those based on the search and application of contact elements, in order to reduce calculation time and to give the possibility to perform an higher number of simulations. Hence, two new algorithms are on purpose developed and hereby presented: the first one for the evaluation of the interaction pipe-CA and the second one for managing the fracture propagation criteria even if crack flanks cannot freely open because of crack arrestor presence

Onshore pipeline high-grade steel for challenge utilization

High pressure pipeline transportation is one of the key technologies to connect remote gas fields and deliver gas at competitive prices to consumption markets. Arctic regions will become more attractive in the near future as large gas resources are located there. Long onshore pipelines systems, characterized by high strength steels (above API 5L X80, i.e. exceeding 555 MPa Yield Strength) operated at high internal gas pressure (more than 10-12 MPa) in many cases appear to be the most convenient transportation option. This paper highlights the latest follow up coming from a long lasting R&D program launched by eni, together with industrial/technical partners, on the exploitation of commercial available options with high grade steels for onshore application even in harsh environments. The results obtained in this R&D program can be useful for applications even for arctic onshore/offshore scenario. Copyright © 2014 by the International Society of Offshore and Polar Engineers (ISOPE)

Crack arrestor design by finite element analysis for X100 gas transportation pipeline

The interest of gas companies in the use of high grade steel pipes, equivalent to X100 and higher, for the construction of long distance gas pipelines has become a consolidated trend in the world; in response to this market demand, steel makers have successfully developed new classes of high grade steel for large diameter pipelines, but some limitations might occur to their application if important aspects related to their structural reliability, such as the resistance to ductile fracture propagation, are not completely clarified. Recent efforts spent in investigating this aspect, that is the ductile fracture propagation control, have demonstrated that the class of X100 large-diameter steel pipes being considered, when operated under severe operating conditions (high usage factor, rich gas, low temperature), may lie on the fracture propagation/arrest border line. In this case external mechanical devices, i.e. crack arrestors, may be required to ensure arrest of a propagating fracture This paper presents a crack arrestor design approach by finite element analysis for a X100, largediameter gas transportation line operating under severe conditions, such as those mentioned above. A CSM finite element model specifically developed for simulating dynamic ductile fracture propagation (PICPRO) has been used and implemented to consider the effect of crack arrestor constraint on the running fracture. Several types of crack arrestor have been considered, including a steel sleeve with or without grout, thickerwalled pipe and types of composite crack arrestor, and relevant design criteria have been obtained. Numerical predictions were also compared with the results of recent experimental full-scale burst tests carried out on X100 large diameter pipelines, demonstrating the capability of the model developed to correctly predict the crack arrestor performance