Low weight additive manufacturing FBG accelerometer: design, characterization and testing

Structural Health Monitoring is considered the process of damage detection and structural characterization by any type of on-board sensors. Fibre Bragg Gratings (FBG) are increasing their popularity due to their many advantages like easy multiplexing, negligible weight and size, high sensitivity, inert to electromagnetic fields, etc. FBGs allow obtaining directly strain and temperature, and other magnitudes can also be measured by the adaptation of the Bragg condition. In particular, the acceleration is of special importance for dynamic analysis. In this work, a low weight accelerometer has been developed using a FBG. It consists in a hexagonal lattice hollow cylinder designed with a resonance frequency above 500 Hz. A Finite Element Model (FEM) was used to analyse dynamic behaviour of the sensor. Then, it was modelled in a CAD software and exported to additive manufacturing machines. Finally, a characterization test campaign was carried out obtaining a sensitivity of 19.65 pm/g. As a case study, this paper presents the experimental modal analysis of the wing of an Unmanned Aerial Vehicle. The measurements from piezoelectric, MEMS accelerometers, embedded FBGs sensors and the developed FBG accelerometer are compared.Ministerio de Economía y Competitividad BIA2013-43085-P y BIA2016-75042-C2-1-

Fabrication of Water- and Ice-Repellent Surfaces on Additive-Manufactured Components Using Laser-Based Microstructuring Methods

Laser patterning techniques have shown in the last decades to be capable of producing functional surfaces on a large variety of materials. A particular challenge for these techniques is the treatment of additively manufactured parts with high roughness levels. The presented study reports on the surface modification of additive-manufactured components of Ti64 and Al–Mg–Sc (Scalmalloy), with the aim of implementing water- and ice-repellent properties. Different laser-based microstructuring techniques, using nanosecond and picosecond pulses, are combined to create multiscale textures with feature sizes between ≈800 nm and 21 μm. The wettability could be set to static water contact angles between 141° and 153° for Ti64 and Al–Mg–Sc, respectively. In addition, surface free energy is analyzed for different surface conditions

Fiber Bragg grating application to study an unmanned aerial system composite wing

Structural health monitoring consists of structural integrity assessment by means of data acquisition and analysis from on-board sensors. Fiber Bragg grating–based monitoring is increasingly attracting the scientific community working on structural health monitoring due to its multiple advantages such as electromagnetic immunity, negligible weight and size, and multiplexing availability. However, the integration of fiber optics within a structure still requires new procedures and signal treatment techniques for increasing technology reliability and exploiting its full potential. In this article, five embedded Fiber Bragg grating sensors are installed in an unmanned aerial system wing for correlating operational conditions with structural strain in real time. Sensor locations are determined by a finite element model accounting for manufacturing limitations of the fiber line. The developed Fiber Bragg grating system and processing techniques are used in static and dynamic tests showing the capacities of this powerful technology. The assessment includes deflection shape estimation, strain cycles counting, audible and visual strain alarms, aileron control based on strain levels, and structural resonance response detection.Ministerio de Economía y Competitividad BIA2016-75042-C2-1-RMinisterio de Economía y Competitividad BIA2013-43085 -

Direct patterning of polystyrene–polymethyl methacrylate copolymer by means of laser interference lithography using UV laser irradiation

The fabrication of functionalized surfaces on polymericsubstrates is of importance in chemistry, biology,physics, and material science. Examples of functionalsurfaces are micro/nano periodic arrays that can befabricated using different methods. However, many ofthese techniques require several fabrication steps. Inthis communication, we report the fabrication of advancedarchitectures in poly(methylmethacrylate)?polystyrene(PMMA?PS) copolymers using direct laserinterference patterning. Because of the mixed opticalproperties of the copolymers, a different type of periodicarchitectures could be fabricated when comparedwith traditional pure polymers. This new type of periodicstructures results from the local swelling of thecopolymer due to the formation of gaseous productsinduced by the laser radiation. Additionally, relativelylow laser fluences are necessary to initiate the ablationprocess of the copolymers.Fil: Lasagni, A.F.. Universitat Saarland; AlemaniaFil: Acevedo, Diego Fernando. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Universitat Saarland; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Barbero, César Alfredo. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Mücklich, F.. Universitat Saarland; Alemani

Fatigue behaviour of PBF additive manufactured TI6AL4V alloy after shot and laser peening

Additive manufacturing (AM) of metallic parts is a relatively new manufacturing procedure. Many industry sectors, such as the aerospace or automotive sectors, have started to apply this technology to produce some elements, thus reducing costs and weight. Several metallic alloys have been employed for AM. Due to the high strength-to-density ratio, Ti6Al4V alloy is probably the alloy most used for AM in the aerospace industry. This alloy usually shows good static strength properties. However, the presence of internal defects and the surface roughness result in a fatigue strength that is clearly lower than that of materials produced by traditional processes. Moreover, the scatter of the fatigue results is generally higher than in the case of wrought pieces. Different treatments have been proposed to improve the fatigue behavior by reducing internal defects and roughness or generating a favorable residual stress field. In this work, selected surface treatments were considered to improve the fatigue strength of AM parts, including shot and laser peening as well as a combination of shot peening plus chemical assisted surface enhancement (CASE®). Three groups of specimens, each with one of the surface treatments, were fatigue tested to compare the results produced by these treatments. The residual stresses, roughness and hardness produced by the treatments were analyzed. After testing, the fracture surfaces were also analyzed to better understand the fatigue process of the different groups of specimens. The results indicate that laser peening produced the best results, followed by shot peening plus CASE and shot peening. In all three cases, the fatigue strength was much higher than that of the reference group without surface treatment. It was also observed that all failures initiated from an interior defect in the shot peening plus CASE group, four out of six failures in the laser peened group, but only one failure in the case of shot peened group and none in the reference group. Failures of specimens with initiation from internal defects started from defects located deeper than the compressive residual stress layer produced by the treatments

Fatigue behaviour of PBF additive manufactured TI6AL4V alloy after shot and laser peening

Article number 106536Additive manufacturing (AM) of metallic parts is a relatively new manufacturing procedure. Many industry sectors, such as the aerospace or automotive sectors, have started to apply this technology to produce some elements, thus reducing costs and weight. Several metallic alloys have been employed for AM. Due to the high strength-to-density ratio, Ti6Al4V alloy is probably the alloy most used for AM in the aerospace industry. This alloy usually shows good static strength properties. However, the presence of internal defects and the surface roughness result in a fatigue strength that is clearly lower than that of materials produced by traditional pro cesses. Moreover, the scatter of the fatigue results is generally higher than in the case of wrought pieces. Different treatments have been proposed to improve the fatigue behavior by reducing internal defects and roughness or generating a favorable residual stress field. In this work, selected surface treatments were considered to improve the fatigue strength of AM parts, including shot and laser peening as well as a combination of shot peening plus chemical assisted surface enhancement (CASE®). Three groups of specimens, each with one of the surface treatments, were fatigue tested to compare the results produced by these treatments. The residual stresses, roughness and hardness produced by the treatments were analyzed. After testing, the fracture surfaces were also analyzed to better understand the fatigue process of the different groups of specimens. The results indicate that laser peening produced the best results, followed by shot peening plus CASE and shot peening. In all three cases, the fatigue strength was much higher than that of the reference group without surface treatment. It was also observed that all failures initiated from an interior defect in the shot peening plus CASE group, four out of six failures in the laser peened group, but only one failure in the case of shot peened group and none in the reference group. Failures of specimens with initiation from internal defects started from defects located deeper than the compressive residual stress layer produced by the treatments

Effect of surface treatment on the fatigue strength of additive manufactured Ti6Al4V alloy

Different alloys can be used for Additive Manufacturing (AM) with good structural strength. Among the titanium alloys, Ti6Al4V is the most used, especially for aerospace applications. There have been many analyses of the mechanical properties of additive manufactured Ti-6Al-4V with very good static strength results in general. However, there are still some difficulties to get fatigue properties close enough to the ones of specimens manufactured using traditional processes Considering the high effect of surface roughness on the fatigue strength of  AM specimens, this work deals with the effect produced by some surface treatments on the fatigue properties. Five treatments have been used for comparison. All specimens were annealed previously to reduce residual stresses, as well as sand blasted to reduce the roughness. The treatments considered are: 1) no treatment after annealing and sand blasting; 2) shot peening; 3) shot peening plus Chemical Assisted Surface Enhancement (CASE); 4) laser shock peening, and 5) HIP. After fatigue testing, a comparison of the results has been carried out. It was found that laser peening produced the best results, followed by shot peening plus CASE and shot peening, with the lowest strength produced by HIP as well as just sand blasting after thermal treatment

Strain monitoring on a composite aircraft cabin with fiber optic sensors

An integral composite aircraft cabin had been instrumented with two different technologies: distributed fiber optic sensors (DFOSs) and Fiber Bragg Gratings (FBGs). This structural test aims at strain field monitoring in any part of structure when cabin pressurization is applied in order to simulate flight conditions. The Distributed fiber optic network used is based on Rayleigh scatter ing using an Optical Backscatter Reflectometer (OBR). The OBR provides a large number of strain sensor s with high spatial and strain accuracy with a plain optical fiber. DFOSs prove to be the most suitable technology for this test due to their capability to cover large areas with an important amount of strain data. Moreover, the technology of Fiber Bragg Grating sensors has been also applied for the monitoring of the cabin structural integrity. This type of sensors enable a continuous monitoring during the pressurization tests. 24 FBG sensors in four fiber optic circuits were installed on cabin surface . This test allows to correlate distributed and discrete fiber optic sensors and evaluate their damage detection capabilities. Several static pressure tests were conducted in order to detec t structural damage and static loads at the cabin structure

The Dynamical State of the Didymos System before and after the DART Impact

NASA's Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the natural satellite of (65803) Didymos, on 2022 September 26, as a first successful test of kinetic impactor technology for deflecting a potentially hazardous object in space. The experiment resulted in a small change to the dynamical state of the Didymos system consistent with expectations and Level 1 mission requirements. In the preencounter paper, predictions were put forward regarding the pre- and postimpact dynamical state of the Didymos system. Here we assess these predictions, update preliminary findings published after the impact, report on new findings related to dynamics, and provide implications for ESA's Hera mission to Didymos, scheduled for launch in 2024 October with arrival in 2026 December. Preencounter predictions tested to date are largely in line with observations, despite the unexpected, flattened appearance of Didymos compared to the radar model and the apparent preimpact oblate shape of Dimorphos (with implications for the origin of the system that remain under investigation). New findings include that Dimorphos likely became prolate due to the impact and may have entered a tumbling rotation state. A possible detection of a postimpact transient secular decrease in the binary orbital period suggests possible dynamical coupling with persistent ejecta. Timescales for damping of any tumbling and clearing of any debris are uncertain. The largest uncertainty in the momentum transfer enhancement factor of the DART impact remains the mass of Dimorphos, which will be resolved by the Hera mission

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements