Changing debris orbits using High Power Pulsed Laser Interaction (HP PLI) finds interest in the Low-Earth Orbit (LEO) due to space debris congestion. Laser facilities allowing both high energy and repetition rate of a short pulsed irradiation become available as provided by the high power HiLASE beamline facility (Prague, CZ) with BIVOJ (100J, 10ns, 10Hz, 1030nm). In order to illustrate such an application, originally Crookes radiometer concept was adapted to quantify the efficiency of repeated laser shots in increasing rotating speed according to laser matter interaction. Various materials, from model to space applicative materials, allowed to estimate the material response with various irradiation characteristics (single shots vs. repeated shots). Matter behaviors (ablation, cratering, spallation, perforation) bracketed the laser conditions suitable in the perspective of laser propulsion with limited creation of extra debris or irradiated structures damages. Next is to strengthen the robustness of the simulation/experiment dialog to use simulation as a predesign tool for laser space propulsion.
Spallation caused by shock waves in optical components such as those used in the Laser MegaJoule facility during laser operation leads to material fracture during a Laser-Induced damage event. One solution may be to use a viscoelastic thin film on these components to mitigate spallation, but it must have excellent optical, mechanical, and resistance to laser damage properties. Among the viscoelastic materials investigated were Nafion and polydimethylsiloxane-based Ormosil. These materials, as thin films deposited on a fused silica substrate, were studied under nanosecond pulsed lasers at 1064 and 532 nm with different diagnostics in situ and post-mortem. In particular, the effect of the films on spallation was studied using the laser shock technique. Preliminary results showed that these thin films have interesting properties that could help to reduce mechanical damage to optical components.
In this paper, damage produced by lightning strike, laser shock and electron beam deposition on a protected Carbon Fiber Reinforced Plastic composite laminate is studied in order to find analogies of effects and damage between these experimental means. As lightning strike physics on CFRP coated with a Lightning Strike Protection and paint is not fully understood, these analogies could be able to enhance lightning strike modelling by potentially uncoupling the physics at hand and having access to additional measurement instruments. The different experimental setups are briefly described before analyzing the damage response of the aeronautical CFRP protected using an Expanded Copper Foil and coated in aeronautical paint. Eventually the results are compared to build potential analogies able to enhance lightning strike modelling.
Laser-assisted surface structuring was developed at CERN for the treatment of the inside wall of the vacuum system of the Large Hadron Collider (LHC). 50-µm-deep grooves were created by material ablation while the laser scanned the surface. A part of this material was redeposited as micrometer-size particle aggregates. This two-scale rugosity efficiently traps electrons. During the operation of the LHC, the surface is submitted to high electromagnetic forces and cooling cycles which might deteriorate its performances. Accelerations of the surface in the order of 350 000 g are expected to be induced by these electromagnetic forces. The LAser Shock Adhesion Test (LASAT), initially developed to assess the adhesion of coatings by spallation, was used to accelerate the surface of treated samples, in order to reproduce stress states similar to those generated by the electromagnetic forces. Pressure shock waves generated by nanosecond laser irradiation produce sharp velocity variations of the surface. Decelerations and, therefore, applied inertial forces were evaluated from the dynamics of the sample macroscopic surface, whose velocity evolution was measurement by VISAR (Velocity Interferometer System for Any Reflector) with a time resolution smaller than 1 ns. Once the test set-up was calibrated, the collect and the analysis of detached particles allowed the quantification of ejected material as a function of the applied mechanical stresses.
Spallation effects caused by shock waves in optical components such as those used in the Laser MegaJoule facility during laser operation can lead to material fracture. One solution could be to use a viscoelastic thin film on these fused silica components to reduce the reflection of shock waves from the rear surface, but it must have excellent optical, mechanical, and power-handling properties. Among the viscoelastic materials investigated were Nafion and polydimethylsiloxane-based ormosil, with ormosil synthesized using a sol-gel process. The materials were characterized optically and especially tested for acoustic attenuation. These materials, as thin films deposited on a fused silica substrate, were studied under shock wave propagation using the laser shock technique. Preliminary results showed that these thin films have interesting properties that could help reduce mechanical damage to optical components.
Composite materials are commonly used in many branches of industry. One of the effective methods to join CFRP parts is to use adhesives. There is a search of effective methods for quality assurance of bonded parts. There is a need for pre- and post-bond inspection to ensure proper bonding and verify its quality. Research reported here focuses on post-bond inspection of bonded CFRP parts. In this paper we report investigations of samples that were modified in order to simulate the conditions that can be encountered during the bonding repair processes. The modifications were made before adhesive bonding, and their effect on the quality of the bond is studied. The first case was the thermal treatment. It was made by exposure of samples to elevated temperatures. This case accounts for parts that may be exposed to external heat source or lightening impact. Second of the investigated cases was deicing fluid contamination prepared by dip-coating of clean CFRP plates. When cleaning the aircraft for a repair this fluid can be transported to bonding areas and weaken the joint. The third type of modification was faulty curing of the adhesive. It was prepared by local pre-curing of the adhesive. Pre-curing causes irregularities in the curing of the adhesive joint. Apart from single modifications, also mixed cases were studied, as well as scarf bonding. The samples were studied in non-destructive approach. It was shown that for some of the cases the detection is possible.
Composite materials are commonly used in many branches of industry. One of the effective methods to join CFRP parts is the adhesive bonding. There is a search of effective methods for quality assurance of bonded parts. There is a need for pre- and post-bond inspection to ensure proper bonding and verify its quality. Research reported here focuses on post-bond inspection of bonded CFRP parts. In this paper we report investigations of samples that were modified with contamination that can be encountered during the manufacturing process of the CFRP parts. The contaminations were introduced before adhesive bonding, and the effect of the contamination on the quality bond is studied. First of the investigated cases was release agent contamination prepared by dip-coating of clean CFRP plates. The release agent is used during the production of composite elements and can contaminate the surface to be bonded. The second case was the moisture contamination. It was obtained by conditioning of the samples in humid conditions. Moisture contamination can be gained from water-coupled ultrasonics or during transportation of unprotected parts. The third type of contamination had more local character. It simulated fingerprints. Artificial sweat was used. The fingerprint contamination can be caused by improper handling of the parts. Apart from single contamination, also mixed contamination cases were studied, as well as curved samples. The samples were studied in non-destructive approach. It was shown that for some of the cases the detection is possible.
The behaviour of eco-composites, when subjected to laser or mechanical impact loadings, is not well known yet. A research was proposed looking at the behaviour of ‘green’ and synthetic composites under impact loading. The study was focused on composites reinforced with short, medium and long fibres. Short fibre composites were made of spruce fibres and ABS. The fibres were used both as received and after a thermal treatment. Another set of samples was made of 60 mm-long flax fibres. Two types of thermoplastic polymers were used as matrices: polypropylene and polylactide. Also a woven eco-composite was investigated. It was made of plain woven hemp fabric impregnated with epoxy resin. A fully synthetic woven composite, used as reference laminate for comparison with ‘green’ composites, was prepared by using a plain weave woven glass fabric impregnated with epoxy resin. Mechanical impacts were performed by means of a falling dart impact testing machine. The specimens were tested at different impact energy levels (from 1J to 5J) by keeping constant the mass of the impactor and varying the drop height. Laser impact tests were performed by means of a high power laser shock facility. All the samples were tested at six different laser shock intensities, keeping constant the shock diameter and the pulse duration. Six assessment techniques were employed in order to analyse and compare impact damages: eye observation, back face relief, terahertz spectroscopy, laser vibrometry, X-ray micro-tomography and microscopic observations. Different damage detection thresholds for each material and technique were obtained.
Structured Light Systems (SLS) give access, without contact, to a rich measurement of a cloud of points belonging to a same object surface. SLS received much interest in the past years and became a standard technique. The aim of this talk is to present the design of such a means, working in the visible spectrum, dedicated to shock physics (implying velocities up to several km/s) and to provide an example of measurements with a 3D reconstruction. A dedicated development is necessary (laser lighting, speckle smoothing, ambient light canceling, depth of field improvement), since commonly developed SLS don’t suit this field of study, mainly for three reasons: phenomena of interest (usually lasting a few microseconds) require extremely short exposure durations (few nanoseconds to few hundreds of picoseconds); the field of view ranges from millimeter for samples shocked by high power lasers to decimeter for high-explosive setups ; and finally, experimentations have single-shot acquisitions. The main domains of study are fragmentations, surface deformations and associated damages, like micro-spalling or ejected particle clouds.
The design of piezochromic pigments is a promising way to adjust smart painting and therefore to develop a “visual” impact detection coating. This paper deals with the possibility to use laser shock waves to test piezochromic coatings for impact detection. For that purpose, an experimental setup was developed in order to obtain compressive load in the coating thanks to the impedance mismatch between selected materials. An analytical modeling was used to validate the proposed method. The experimental investigation coupled with finite-element modeling on four smart coatings showed that these coatings can reveal impact location by a significant change of color if a relevant pressure threshold is reached. The results presented in this work are promising and demonstrate the ability of the proposed laser shock method for characterizing the pressure thresholds of piezochromic smart paintings. It opens the door for studying future smart paintings with different critical pressure levels, depending on the targeted application.
The paper is devoted to R&D of novel experimental technique - laser-driven shock tube (LST) for modeling of
Rayleigh-Taylor (R-T) and Richtmyer-Meshkov (R-M) hydrodynamic instabilities development at the contact surface of
two immiscible liquids under a shock wave (SW) passage. 100-J, 100-ns KrF laser facility GARPUN has been used to
irradiate some opaque liquids. A homogenizing focusing system combined multi-element prism raster and a lens to
provide non-uniformity less then few percents across a square 7*7-mm spot, laser intensities being varied in the range of
q = 0.004 - 2 GW/cm2. Surface plasma blow off produced a planar SW propagated into the liquid. SW amplitudes as
high as 0.8 GPa weakly damping with increasing thickness were measured in dibutyl-phthalate (DBP), which strongly
absorbed UV laser light. Test bench experiments were performed to produce standing acoustic waves as initial
perturbations at the interface between two immiscible liquids.
Two types of carbon materials after the powerful laser influence were studied. First - low grade pyrolitic graphite, second - 10 micron film of the amorphous line- chain carbon. The film was prepared by the method of Ar ion assisted deposition of carbon plasma. The samples were irradiated by a 1.06 micro wavelength Nd laser in vacuum 0.3 Pa. The energy of the laser pulse was approximately 70 J, the duration 580 ps and intensity 440 GW/cm2. After the experiments the samples were examined by means of transmission electron microscopy. Auger and Raman spectroscopy. The formation of carbyne crystals with lattice parameters 'a' 0.516 and 0.533 nm were detected in the shocked samples. A small amount of nanodiamond was detected, too. An interesting feature is the formation of large carbyne crystals in pyrographite. Raman spectra of recovered materials exhibit strong peaks at the frequencies corresponding to the oscillations of carbon atoms in line- chain structures.
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