Use In Severe Environments Research Articles

Acceleration of Service Life Testing by Using Weibull Distribution on Fiber Optical Connectors

The service life assessment of previous fatigue stress has a fundamental role in estimating the reliability of products like fiber optical connectors, and should replicate use in severe environments in telecommunications systems. However, the vibration prediction models used in the literature present limitations in vibration life prediction. In this paper, we propose using the insertion loss fatigue life and including it in the Weibull distribution to determine the Weibull parameters ƞ and β to evaluate fiber optic connector reliability R(t) under environmental and mechanical testing stress. We analyzed the failure data of a standard telecommunication fiber optical connector under a program of service life stress testing against that of a fiber optical connector under only mechanical vibration stress testing. The fiber connectors were monitored during the vibration testing to review the transient change of the optical signal. Their results showed that the reliability of the fiber connectors submitted to the service life program was Rt=0.694, while that of the fiber connectors submitted to mechanical vibration only was Rt=0.970. In addition, the analysis showed that the service life testing consumed 70.2% of the product’s lifetime. We present in Numerical Validation the steps to determine the acceleration factors of the vibration test developed.

The Texas A&M University Hypervelocity Impact Laboratory: A modern aeroballistic range facility.

Novel engineering materials and structures are increasingly designed for use in severe environments involving extreme transient variations in temperature and loading rates, chemically reactive flows, and other conditions. The Texas A&M University Hypervelocity Impact Laboratory (HVIL) enables unique ultrahigh-rate materials characterization, testing, and modeling capabilities by tightly integrating expertise in high-rate materials behavior, computational and polymer chemistry, and multi-physics multiscale numerical algorithm development, validation, and implementation. The HVIL provides a high-throughput test bed for development and tailoring of novel materials and structures to mitigate hypervelocity impacts (HVIs). A conventional, 12.7mm, smooth bore, two-stage light gas gun (2SLGG) is being used as the aeroballistic range launcher to accelerate single and simultaneously launched projectiles to velocities in the range 1.5-7.0 km/s. The aeroballistic range is combined with conventional and innovative experimental, diagnostic, and modeling capabilities to create a unique HVI and hypersonic test bed. Ultrahigh-speed imaging (10M fps), ultrahigh-speed schlieren imaging, multi-angle imaging, digital particle tracking, flash x-ray radiography, nondestructive/destructive inspection, optical and scanning electron microscopy, and other techniques are being used to characterize HVIs and study interactions between hypersonic projectiles and suspended aerosolized particles. Additionally, an overview of 65 2SLGG facilities operational worldwide since 1990 is provided, which is the most comprehensive survey published to date. The HVIL aims to (i) couple recent theoretical developments in shock physics with advances in numerical methods to perform HVI risk assessments of materials and structures, (ii) characterize environmental effects (water, ice, dust, etc.) on hypersonic vehicles, and (iii) address key high-rate materials and hypersonics research problems.

Merging toughness and oxidation resistance in a light ZrB2 composite

A functionally graded composite based on ZrB2 and 0–50 vol% of short carbon fibres was prepared via a deliberately simple approach that involved creating a suitable stacking sequence of layers with different sintering agents and fibre contents. This led to an excellent combination of failure tolerance and oxidation resistance in a light material with a density below that of alumina. The graded architecture outperformed other related composites when tested at 1500 °C and, separately, achieved a toughness of 10 MPa m½. In addition, the composite withstood the ablation effect of an oxyacetylene torch at 2500 °C, undergoing minimal recession. Moreover, the true nature of the “tubular” zirconium oxide formed upon oxidation at extreme temperatures is reported for the first time. The functionally graded concept applied to a ultra-refractory matrix seems to be a promising route to obtain even complex shaped components with functional symmetry for use in severe environments.

Effects of annealing temperature on microstructure, mechanical properties and corrosion resistance of 30% Cr super ferritic stainless steel

A newly designed super ferritic stainless steel (FSS), i.e. 30Cr-4Mo-2Ni, was developed for use in severe environments, such as sulfuric acid. The annealing temperature had a significant effect on the precipitation behaviors of the steel, and ultimately on its mechanical properties and corrosion resistance. The results showed that the designed steel exhibits higher strength, higher hardness, lower elongation and far superior corrosion resistance than ordinary FSS. Detrimental Laves phases are readily precipitated in this steel, so suitable annealing parameters is necessary to change the precipitation behavior and promote the dissolution of Laves phases, and then render this economically produced steel, corrosion resistant to sulfuric acid.

Tensile properties of helical diamond fibres with platinum wire core

Helical diamond fibres of 218 μm diameter and up to ∼100 mm long have been made by chemical vapour deposition on to a 50 μm diameter platinum wire in coil form. The fibres had 43 vol.-% diamond and a spring index diameter ratio, coil diameter (D)/fibre diameter (d), of 3·3. Tensile load versus extension curves were determined for the diamond fibres. An extension value of up to ∼20 times that for a straight fibre was obtained. Failure occurred by shear fracture of the diamond coating. This often occurred at defects in the deposit. The highest average surface shear stress measured was 0·54 GPa, equal to 0·82 GPa after the Wahl correction for the maximum shear stress, which is in the reported fracture strength range for diamond. Shorter coils deformed plastically with up to ∼1% elastic strain. Initial coil stiffness values (K) were in the range 242–1367 N m-1.a The K values were increased by prestrain to 2950 N m-1. The effective coil shear modulus before correction was ∼300 GPa. Diamond in the form of a microcoil exhibited greater elastic extension by about a factor of 70 compared with a straight fibre, but this was obtained by sacrificing stiffness, which was about a factor of 70 greater for a straight fibre. The coil exhibited surprising damage tolerance with turns adjacent to fractured turns resisting fracture at higher loads. The results suggest helical fibres should enable free standing diamond microsensors to be produced that combine mechanical and physical properties and greater damage tolerance for use in severe environments.

Interpretation of friction and wear of ceramics in terms of surface analysis

Abstract Selected combinations of ceramic tribomaterials (SiC-SiC, Si 3 N 4 -Si 3 N 4 , h-BN-h-BN) were tested in an Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) analytical tribotester, under ultrahigh vacuum, and under partial pressures of gases (O 2 ,N 2 ,H 2 O, C 3 H 8 , air) respectively. The main purpose of the work was to clarify the correlations existing between the composition and microstructure of friction-induced interface films and the reduction of friction and wear of ceramics caused by ambient gases. In addition to conventional AES, XPS and secondary ion mass spectrometry analyses, electron microscopy (both transmission and STEM), electron energy loss spectroscopy, and extended electron energy loss fine structures were used to characterize the tribochemical reactions on the ceramic surfaces. Under ultrahigh vacuum, ceramic surfaces exhibit high friction ( f k >0.7) which is associated with friction-induced disorder in the interface material. Adsorbed gases did not “lubricate” these interfaces. Reactive gases (O 2 ) formed films in the contact region which provided lubrication and lower friction. This lubrication was observed with selected, carbon-containing systems and was associated with the formation of sp 2 -hybridized carbon in the interface films. The wide range of physical and chemical phenomena observed for sliding ceramic contacts and the implications for their use in severe environments is discussed.

Tribologie des céramiques et analyse de surface

Selected ceramic tribomaterial combinations (SiC/SiC, Si3 N4 /Si3 N4 , h-BN/h-BN) were tested in an AES/XPS analytical tribotester, under ultra-high vacuum, and under partial pressures of gases (O2 , N2 , H2 O, C3 H8 , air), respectively. The main purpose of this work is to clarify the correlations existing between the composition/microstructure of friction-induced interface films and the reduction of friction and wear of ceramics caused by ambient gases. In addition to conventional AES, XPS and SIMS analyses, electron microscopy (both TEM and STEM), Electron Energy Loss Spectroscopy (EELS), and Extended Electron Fine Structures (EXELFS) were used to characterize the tribochemical reactions on the ceramic suifaces. Under UHV ceramic surfaces exhibit high friction (fk > 0.6) that is associated with friction-induced disorder in the interface material. Adsorbed gases did not “lubricate” these interfaces. Reactive gases (O2 ) formed films in the contact region that provide lubrication and lower friction. Such lubrication was observed with selected, carbon containing systems and was associated with the formation of sp2 -hybridized carbon in the interface films. The wide range of physical and chemical phenomena observed for sliding ceramic contacts and the implications for their use in severe environments will be discussed.

Recent developments in photodetectors for use in severe environments

Several new types of photodetector have been developed for use in severe environmental conditions; four types of phototube are especially designed to be operated in high magnetic fields of several kilogauss or more. A photomultiplier which is designed for use under pressures as high as 600 atm has stable gain and energy resolution under such high pressures. And a 15 inch diameter spherical photocathode photomultiplier has also been developed for high pressure use when packed in a special strong glass housing. There is another photomultiplier which can be operated in temperatures over 175°C, such as in oil well logging works.