Critical issues of double-metal layer coating on FBG for applications at high temperatures

Use of fiber Bragg gratings (FBGs) to monitor high temperature (HT) applications is of great interest to the research community. Standard commercial FBGs can operate up to 600 ∘ C. For applications beyond that value, specific processing of the FBGs must be adopted to allow the grating not to deteriorate. The most common technique used to process FBGs for HT applications is the regeneration procedure (RP), which typically extends their use up to 1000 ∘ C. RP involves a long-term annealing of the FBGs, to be done at a temperature ranging from 550 to 950 ∘ C. As at that temperature, the original coating of the FBGs would burn out, they shall stay uncoated, and their brittleness is a serious concern to deal with. Depositing a metal coating on the FBGs prior to process them for RP offers an effective solution to provide them with the necessary mechanical strengthening. In this paper, a procedure to provide the FBG with a bimetallic coating made by copper and nickel electrodeposition (ED) is proposed, discussing issues related to the coating morphology, adherence to the fiber, and effects on the grating spectral response. To define the processing parameters of the proposed procedure, production tests were performed on dummy samples which were used for destructive SEM-EDS analysis. As a critical step, the proposed procedure was shown to necessitate a heat treatment after the nickel ED, to remove the absorbed hydrogen. The spectral response of the FBG samples was monitored along the various steps of the proposed procedure and, as a final proof test for adherence stability of the bimetallic coating, along a heating/cooling cycle from room temperature to 1010 ∘ C. The results suggest that, given the emergence of Kirkendall voids at the copper-nickel interface, occurring at the highest temperatures (700-1010 ∘ C), the bimetallic layer could be employed as FBG coating up to 700 ∘ C

Material and surface properties of LARES satellite

LARES (LAser RElativity Satellite) is a passive satellite put in orbit by the VEGA launcher the past 13th of February 2012. It is designed for the accurate test of the Lense-Thirring effect. This phenomenon is induced by the Earth rotation that according to Einstein General Relativity drags space-time and consequently the trajectory of orbiting objects. In order to reach the expected results of few percent accuracy in the measurement of that effect, some restrictive scientfic requirements have been imposed with regard to the material to be used for the satellite body (SB) and to the surface properties of the SB itself, giving special attention to the density of the SB (higher than 17900 kg/m3 ). Furthermore to reduce interaction with the magnetic field of Earth some upper limit to, the electrical conductivity of the alloy was specified. All those aspects along with some considerations on the manufacturing challenges of LARES will be reported. Finally the different methods evaluated for the finishing of the SB, so as to satisfy the scientific requirements such as the infrared emissivity (ε) and the solar absorptivity (α) of the surface will be analysed

Material and manufacturing issues of a laser ranged satellite

contenuti (Abstract) The LARES satellite is an Italian space mission funded by ASI, with CGS as prime contractor and Salento and Sapienza Universities as subcontractors. The LARES will be put into orbit by the European launcher VEGA during its maiden flight, foreseen in year 2011. The paper describes the general features of the material chosen for the manufacturing of the satellite and its components. Particular interest will be devoted to the manufacturing process and analysis of the screw

Use of FBG sensors for monitoring cracks of the equestrian statue of Bartolomeo Colleoni in Venice

The Bartolomeo Colleoni monument suffered for years damage from the local climate. The process of restoring the Colleoni equestrian statue, started in 2003, allowed to understand how the bronze statue was originally cast and manufactured and the techniques used in its construction. During this process a relevant crack on the right foreleg was investigated in correspondence of the cast-on joining the right foreleg to the front portion of the horse body. The crack was investigated experimentally by Fiber Bragg Grating (FBG) sensors, avoiding any modelling because of the very complex structure of the statue. An array of FBG sensors connected in series was glued on the crack with the aim of capturing live information about the effect of applying stress on the crack opening. The monitoring system was successfully tested during repositioning of the RIDER on the horse and is available for long term inspection of the crack opening evolution

Material and Manufacturing of LARES Satellite

Differently from all other laser ranged satellites, LARES is manufactured from a single piece bulk material. This choice offers a simpler design and will reduce thermal gradients on the satellite surface. To improve the surface-to-mass ratio, i.e., a parameter proportional to the intensity of most of the non gravitational perturbations, a high density material has been selected: tungsten alloy. A combination of data from two more satellites and a design of LARES aimed to reduce the non gravitational perturbations will allow the measurement of the Lense-Thirring effect with an accuracy never reached before. This effect is predicted by Einstein General Relativity. Tungsten alloys have never been used for the entire construction of a satellite. For this reason a first breadboard, representative of a small portion of the satellite has been manufactured. This allowed to pin point a problem with the small screws of the cube corner reflector mounting system. After a description of the material and the procured semi-finished parts, particular interest will be devoted to the manufacturing process for the screws and to the microscopic analysis of the tungsten alloy screws that broke during mounting. A different manufacturing process for the screw is finally proposed

A study of gas contaminants and interaction with materials in RPC closed loop systems

Resistive Plate Counters (RPC) detectors at the Large Hadron Collider (LHC) experiments use gas recirculation systems to cope with large gas mixture volumes and costs. In this paper a long-term systematic study about gas purifiers, gas contaminants and detector performance is discussed. The study aims at measuring the lifetime of purifiers with unused and used cartridge material along with contaminants release in the gas system. During the data-taking the response of several RPC double-gap detectors was monitored in order to characterize the correlation between dark currents, filter status and gas contaminants

Performance of the Gas Gain Monitoring system of the CMS RPC muon detector and effective working point fine tuning

The Gas Gain Monitoring (GGM) system of the Resistive Plate Chamber (RPC) muon detector in the Compact Muon Solenoid (CMS) experiment provides fast and accurate determination of the stability in the working point conditions due to gas mixture changes in the closed loop recirculation system. In 2011 the GGM began to operate using a feedback algorithm to control the applied voltage, in order to keep the GGM response insensitive to environmental temperature and atmospheric pressure variations. Recent results are presented on the feedback method used and on alternative algorithms

A study of asymmetric tensile properties of large area GEM foil

Gas Electron Multiplier (GEM) technology is being used in various applications, particularly in high energy physics experiments. The GEM is known as a reliable detector in high radiation environment which can maintain high temporal and position resolution. GEM foil is the basic part of the detector which consists of a composite material (polyimide and copper). Large size GEM foil has complex mechanical structure and asymmetries which mainly arises due to formation of the HV sectors in the foil. These asymmetries become very relevant when large size foils are stretched to build a detector. In this article asymmetry affects are presented that define the tensile properties of a large size segmented GEM foil

Smart Disaster Mitigation in Italy: A Brief Overview on the State of the Art

Italy is notoriously exposed to several natural hazards, from hydrological to volcanic and, above all, to seismic activity that affects a large part of the national territory. Historically the devastating effects of tsunamis have also been recorded, despite the peninsula is confined in the Mediterranean basin (i.e. Messina earthquake in 1908, and more recent the activity of the undersea volcano “Marsili”). Since Italy is particularly exposed to such hazards, many research institutions are involved in campaigns about monitoring, prevention and mitigation of the effects of such phenomena, with the aim to secure and protect human lives, and secondly, the remarkable cultural heritage. The present paper will first make a brief excursus on the main Italian research projects aimed at the mitigation of environmental disasters, referring to projects of national and international relevance, being implemented, such as the MOSE (for the containment of the tides and of high water, for the preservation of cultural and artistic heritage of Venice and of the entire ecosystem of the lagoon); the research in earthquake-resistant structures performed for instance by ENEA and finally the COSMO-SkyMed (CSK) program of the Italian Space Agency (ASI), which has among its purposes the environmental monitoring and surveillance applications for the management of exogenous, endogenous and anthropogenic risks. Furthermore in the paper, it will be described some new ideas concerning the use of smart materials and structures capable of self-monitoring and self-diagnosis of the risk of failure and adapting itself to environmental condition variations, in order to avoid catastrophic effects, thanks to an integrated network of sensors and actuators