Development of Silicon Carbide Substrates for Aerospace Applications

2012 ◽  
Vol 1373 ◽  
Author(s):  
Antonio J. Abdalla ◽  
Álvaro J. Damião ◽  
Elson Campos ◽  
Jerusa G.A. Santana ◽  
Marcelo C. Vicentini ◽  
...  
Keyword(s):  
Organic Material ◽  
Mechanical Tests ◽  
Argon Atmosphere ◽  
Optical Systems ◽  
High Tech ◽  
Laser Confocal Microscopy ◽  
Optical Surfaces ◽  
Aerospace Applications ◽  
Sintering Additive ◽  
National Boundaries

ABSTRACTPayload and high-tech are important characteristics when the goals are aerospace applications. The development of the technologies associated to these applications has interests that transcend national boundaries and are of strategic importance to the nations. Ultra lightweight mirrors, supports and structures for optical systems are important part of this subject. This paper reports the development of SiC substrates, obtained by pressing, to be applied on embedded precision reflective optics. Different SiC granulometries, having YAG as sintering additive, were processed by: ball milling, drying and deagglomeration, sift, uniaxial and isostatic pressing, and, finally, argon atmosphere sintering at 1900°C. Different porosities were obtained according to the amount of organic material added. Into one side of the samples pellets of organic material were introduced to generate voids to reduce the weight of samples as a whole. The substrates were grinding and polished, looking for a SiC surface having low porosity, as porosity is directly related to light scattering that should be avoided on optical surfaces. Laser surface treatments were applied (using or not SiC barbotine) as a method to improve the surface quality. The samples were characterized by optical and laser confocal microscopy, roughness measurements and mechanical tests. The results are very promissory for future applications.

Mechanical characterization of a woven multi-layered hyperelastic composite laminate under uniaxial loading

2021 ◽  
pp. 002199832110115
Author(s):  
Shaikbepari Mohmmed Khajamoinuddin ◽  
Aritra Chatterjee ◽  
MR Bhat ◽  
Dineshkumar Harursampath ◽  
Namrata Gundiah
Keyword(s):  
Composite Materials ◽  
Energy Function ◽  
Strain Energy ◽  
Strain Energy Function ◽  
Mechanical Tests ◽  
Stress Strain ◽  
Aerospace Applications ◽  
Envelope Material ◽  
The Individual ◽  
High Dielectric

We characterize the material properties of a woven, multi-layered, hyperelastic composite that is useful as an envelope material for high-altitude stratospheric airships and in the design of other large structures. The composite was fabricated by sandwiching a polyaramid Nomex® core, with good tensile strength, between polyimide Kapton® films with high dielectric constant, and cured with epoxy using a vacuum bagging technique. Uniaxial mechanical tests were used to stretch the individual materials and the composite to failure in the longitudinal and transverse directions respectively. The experimental data for Kapton® were fit to a five-parameter Yeoh form of nonlinear, hyperelastic and isotropic constitutive model. Image analysis of the Nomex® sheets, obtained using scanning electron microscopy, demonstrate two families of symmetrically oriented fibers at 69.3°± 7.4° and 129°± 5.3°. Stress-strain results for Nomex® were fit to a nonlinear and orthotropic Holzapfel-Gasser-Ogden (HGO) hyperelastic model with two fiber families. We used a linear decomposition of the strain energy function for the composite, based on the individual strain energy functions for Kapton® and Nomex®, obtained using experimental results. A rule of mixtures approach, using volume fractions of individual constituents present in the composite during specimen fabrication, was used to formulate the strain energy function for the composite. Model results for the composite were in good agreement with experimental stress-strain data. Constitutive properties for woven composite materials, combining nonlinear elastic properties within a composite materials framework, are required in the design of laminated pretensioned structures for civil engineering and in aerospace applications.

scholarly journals Mechanical Studies of Injection Molded Composites with Polypropilene Matrix

2018 ◽  
Vol 1 (2) ◽  
pp. 105-109
Author(s):  
Ráthy Istvánné ◽  
Pinke Péter ◽  
Huszák Csenge
Keyword(s):  
Mechanical Tests ◽  
High Tech ◽  
Test Results ◽  
Processing Technologies ◽  
Standard Specimens ◽  
Glass Fibre Reinforced ◽  
Injection Molded ◽  
Polypropylene Matrix ◽  
Reducing Costs ◽  
New Processing

Abstract The wide use of composite materials is mainly due to their excellent strength / mass ratio, corrosion resistance and relatively low price. Approximately 35-40% of the fibre-reinforced composites are made of thermoplastic polymers in which fibreglass, carbon or natural fibres are most often used as reinforcement, while the remaining 60 – 65% is made up of high-tech carbon or glass fibre-reinforced thermosetting composites. Most of them are used in the transport and electronics industries. New processing technologies not only improve the properties of the products but also contribute to reducing costs. In this paper, we compare the results of mechanical tests with molded standard specimens with polypropylene matrix and test results from cut-outs from injection molded products.

scholarly journals Multifunctional contamination-resistant coatings

2019 ◽  
Vol 215 ◽  
pp. 02002
Author(s):  
Nadja Felde ◽  
Anne Gärtner ◽  
Stefan Schwinde ◽  
Sven Schröder
Keyword(s):  
Thin Film ◽  
Surface Roughness ◽  
Light Scattering ◽  
Structural Design ◽  
Optical Quality ◽  
Optical Systems ◽  
Optical Losses ◽  
High Optical Quality ◽  
Optical Surfaces ◽  
Laser Stability

Surface contaminations can critically affect the performance of optical surfaces, in particular with respect to light scattering, optical losses, and laser stability. Thus, avoiding contaminations and reducing contamination-induced effects is of particular interest in the manufacturing of optical systems. By combining a specific thin film design with a tailored structural design, contamination-resistant coatings with a high optical quality can be realized. Most important is the balance of self-cleaningand light scattering-relevant surface roughness components.

scholarly journals The Manufacturing of a Multi-surface Monolithic Telescope with Freeform Surfaces

2019 ◽  
Vol 215 ◽  
pp. 06004
Author(s):  
Todd Blalock ◽  
Brian Myer ◽  
Brittany Cox ◽  
Jessica Nelson
Keyword(s):  
Mechanical Stability ◽  
Optical Systems ◽  
Optical Performance ◽  
Freeform Surfaces ◽  
Optical Surfaces ◽  
Spherical Surfaces

Monolithic multi-surface telescopes combined with freeform optical surfaces provide improvements in optical performance in a smaller footprint as compared to systems with spherical surfaces, while providing superior mechanical stability to traditional telescope assemblies. Three different monolithic telescope concepts, in different configurations and optical performance were produced as proof of concepts. The results of the telescopes are presented as well as the unique manufacturing and testing challenges to produce these monolithic optical systems.

Imaging cellular dynamics using scanning laser confocal microscopy

1992 ◽  
Vol 50 (1) ◽  
pp. 12-13
Author(s):  
M.S. Cooper
Keyword(s):  
Confocal Microscopy ◽  
Laser Beam ◽  
Three Dimensional ◽  
Optical Systems ◽  
Scanning Laser ◽  
Fluorescent Light ◽  
Physiological Changes ◽  
Incident Laser ◽  
Laser Confocal Microscopy ◽  
Image Planes

In recent years, the ability to image morphological dynamics and physiological changes in living cells and tissues has been greatly advanced by the advent of scanning laser confocal microscopy. Confocal microscopes employ optical systems in which both the condenser and objective lenses are focused onto a single volume element of the specimen. In practice, galvanometer-driven mirrors or acousto-optical deflectors are used to scan a laser beam over the specimen in a raster-like fashion through an epifluorescence microscope. The incident laser beam, as well as the collected fluorescent light, are passed through pinhole or slit apertures in image planes that are conjugate to the plane of the specimen. This method of illumination and detection prevents fluorescent light which is generated above and below the plane-of-focus from impinging on the imaging system's photodetector, thus rejecting much of the fluorescent light which normally blurs the image of a three-dimensional fluorescent specimen.

Development of a metrology technique suitable for in situ measurement and corrective manufacturing of freeform optics

2019 ◽  
Vol 8 (3-4) ◽  
pp. 203-215 ◽  
Author(s):  
Dali Ramu Burada ◽  
Kamal K. Pant ◽  
Vinod Mishra ◽  
Mohamed Bichra ◽  
Gufran Sayeed Khan ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Tool Path ◽  
Optical Systems ◽  
Optical Fabrication ◽  
Optical Surfaces ◽  
Rotationally Symmetric ◽  
Freeform Optics ◽  
Slow Tool Servo ◽  
Metrology System

Abstract The applications of freeform optical surfaces in modern optical systems are providing unique solutions over rotationally symmetric surfaces. These surfaces offer higher degrees of freedom to the designer to enhance the high-end performance of the optical system. The precise metrology of freeform optics is one of the major bottlenecks for its use in imaging applications. Modern optical fabrication methods (i.e. fast or slow tool servo configuration) are, in principle, capable to meet the challenges to generate complex freeform surfaces if supported by precise metrology feedback for error compensation. In the present work, we have developed a Shack-Hartmann sensor-based metrology technique that can be used for quantitative in situ measurement of freeform optics. The sensor head is used to measure freeform optics in the reflection mode by following the CNC tool path in the offline mode. The measurements are used as feedback for corrective machining. Quantitative analysis is also performed to estimate the error budget of the metrology system. Further, the proposed in situ metrology scheme is validated by measuring freeform surface using a coherence correlation interferometric optical profiler.

Joining of Advanced Ceramics, Glasses and Composites at Politecnico di Torino, Italy

2010 ◽  
Vol 434-435 ◽  
pp. 197-201 ◽  
Author(s):  
Valentina Casalegno ◽  
Qiu Ling Chen ◽  
Qiu Ling Chen ◽  
Milena Salvo ◽  
Federico Smeacetto ◽  
...  
Keyword(s):  
Solid Oxide Fuel Cells ◽  
Foam Glass ◽  
Ceramic Matrix Composites ◽  
Mechanical Tests ◽  
Matrix Composites ◽  
Advanced Ceramics ◽  
Lab On Chip ◽  
Aerospace Applications ◽  
Cu Alloys ◽  
On Chip

An overview of the last 16 years of activity on joining of advanced ceramics, glasses and ceramic matrix composites at Politecnico di Torino (Italy) will be presented. Results on thermal assisted direct bonding (TADB) of glasses for lab-on-chip devices, C/C composites to Cu-alloys for nuclear fusion components (ITER), SiC and SiC/SiC joints for nuclear components (fusion and fission), glass joining of foam glass, C/C joints for aerospace applications, ceramics to stainless steels for Solid Oxide Fuel Cells (SOFC), will be shown. Mechanical tests on joined components will be discussed, in particular, the results of an experimental campaign on carbon/carbon and ceramic joints tested in pure and apparent shear by nine different configurations.

Simulation of segmented mirrors with adaptive optics

2019 ◽  
Vol 8 (2) ◽  
pp. 119-127
Author(s):  
Johannes Störkle ◽  
Luzia Hahn ◽  
Peter Eberhard
Keyword(s):  
Adaptive Optics ◽  
Optical Systems ◽  
Optical Aberrations ◽  
Optical Surfaces ◽  
Atmospheric Disturbances ◽  
Simulation Based ◽  
Segmented Mirror ◽  
Multidisciplinary Simulation ◽  
And Control ◽  
Optical Unit

Abstract This work deals with the simulation-based investigation and control of optical systems that are mechanically influenced. Here, the focus is on the dynamic-optical modeling of vibration-sensitive, segmented mirror systems, which are used, for example, in large astronomic telescopes. Furthermore, an adaptive optical unit usually compensates for the optical aberrations due to atmospheric disturbances. In practice, these aberrations are detected and corrected within a few seconds using deformable mirrors. However, to further improve the performance of these optical systems, dynamic disturbances in the mechanics, i.e. small movements and deformations of the optical surfaces, must also be taken into account. For the investigation of such cases, multidisciplinary simulation methods are developed and presented.

An assessment of approximating aspheres with more easily manufactured surfaces

1998 ◽  
Vol 5 (3) ◽  
pp. 814-816 ◽  
Author(s):  
Malcolm R. Howells ◽  
Joel Anspach ◽  
John Bender
Keyword(s):  
Surface Roughness ◽  
Synchrotron Radiation ◽  
System Performance ◽  
Three Dimensional ◽  
Lower Surface ◽  
Optical Systems ◽  
Conic Sections ◽  
Optical Surfaces ◽  
Elliptical Cylinders ◽  
Surface Figure

In designing optical systems for synchrotron radiation, one is often led to conclude that optimal performance can be obtained from optical surfaces described by conic sections of revolution, usually paraboloids and ellipsoids. The resulting design can lead to prescriptions for three-dimensional optical surfaces that are difficult to fabricate accurately. Under some circumstances satisfactory system performance can be achieved through the use of more easily manufactured surfaces such as cylinders, cones, bent cones, toroids and elliptical cylinders. These surfaces often have the additional benefits of scalability to large aperture, lower surface roughness and improved surface figure accuracy. In this paper we explore some of the conditions under which these more easily manufactured surfaces can be utilized without sacrificing performance.

scholarly journals Imperfections of Scalar Approximation in Calibration of Computer-Generated Holograms for Optical Surface Measurements

2021 ◽  
Vol 11 (15) ◽  
pp. 6897
Author(s):  
Yingying Bai ◽  
Zhiyu Zhang ◽  
Ruoqiu Wang ◽  
Tianbao Chen ◽  
Xu Wang ◽  
...  
Keyword(s):  
Measurement Errors ◽  
Grating Period ◽  
Optical Systems ◽  
Practical Significance ◽  
Etching Depth ◽  
Rigorous Evaluation ◽  
Optical Surfaces ◽  
Scalar Approximation ◽  
Surface Measurements ◽  
Computer Generated Holograms

Computer-generated hologram (CGH) null correctors are used as accuracy standards for interferometric measurements of optical surfaces and optical systems. Diffractive optics calibrators (DOCs) have been developed to evaluate the phase tolerance of CGHs based on scalar approximation by measuring variations in duty cycle and etching depth. However, if the grating period of a CGH < 5 λ, the scalar approximation is not accurate for phase analysis and reconstruction. In this study, the measurement errors of DOCs with small-period CGHs were investigated and experimentally verified. Results show that the imperfections of scalar approximation in CGHs cannot be ignored and the development of rigorous evaluation methods to improve the measurement accuracy of CGHs is of great practical significance.

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