Ground-based Simulation Facility Research Articles

The use of the Open-Loop Onset Point (OLOP) to predict rotorcraft pilot-induced oscillations

The Open-Loop Onset Point (OLOP) criterion has, for many years, been successfully used as a method to predict quasi-non-linear pilot-induced oscillations (PIOs) for fixed-wing aircraft. Only limited research has been conducted using the criterion for prediction of PIOs occurring in rotorcraft. This paper details a study to extend the application of OLOP to rotorcraft, using the combination of control inputs appropriate for the task and a suitable pilot model. Results are compared between pilot subjective opinion and OLOP predictions, from tests performed in a ground-based simulation facility. Using ‘task-specific’ application of OLOP, results obtained in the investigation are encouraging, whereby the objective predictions reflect subjective pilot assessment. From results obtained, a modified boundary is presented.

A ground-based test facility for airborne magnetic gradient tensor instruments simulating calibration flights

Progress is slow in terms of the research and evaluation of calibration algorithms for full tensor magnetic gradient instruments using airborne tests. The main reason is that, based on knowledge gained by actual calibration flights, problems exist regarding high risk, high costs, and long development cycles. In this paper, we describe a ground-based simulation facility for calibration flights which combines the nonlinear aerodynamic model with a magnetic interference model. Environmental magnetic fields can be calculated and produced by tri-axial coils, which are measured by the magnetic tensor gradiometer in calibration flights. Influence from systematic errors and magnetic interference can be extracted from the simulated calibration flight provided by the facility. Compared to system evaluation in airborne operation, this method has the benefit of zero risk, low costs, and short duration of evaluation cycles. In view of ground-based multi-degree of freedom motion platforms, it has the advantages of simple manufacture, good dynamic characteristics, and adaptability to different aircraft types.

Proton irradiation effects on the structural and tribological properties of polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) was irradiated with protons in a ground-based simulation facility to study the effects of proton irradiation on the structural and tribological properties of PTFE. The structural changes were characterized by X-ray photoelectron spectroscopy (XPS) and attenuated total-reflection FTIR (ATR-FTIR), while the tribological properties were evaluated by friction and wear tests. It was found that proton irradiation induced the degradation of PTFE molecular chains, resulting in the increase of C concentration and the decrease in F concentration on the sample surfaces, and the surface chemical structure and morphology of the samples changed, which affected the friction coefficient and decreased the wear rate of the specimens as the friction and wear tests revealed.

Effect of atomic oxygen irradiation on the structural and tribological characteristics of polytetrafluoroethylene and its composites

Based on the ground-based simulation facility, the effects of atomic oxygen (AO) irradiation on the structural and tribological properties of pure polytetrafluoroethylene (PTFE) and carbon fiber and MoS2-filled PTFE composites were studied by scanning electron microscopy, X-ray photoelectron spectroscopy, and a ball-on-disc tribometer. The results shown that AO irradiation had significant effects on the structural and tribological properties of pure PTFE, in which the surface morphologies, mass loss, friction coefficient, and wear rate had been changed greatly after AO irradiation. However, it was noticeable that the addition of carbon fiber and MoS2 filler to PTFE could improve the AO resist capacity and tribological properties of PTFE composites significantly. Copyright © 2016 John Wiley & Sons, Ltd.

Effect of Atomic Oxygen Irradiation on the Structural and Tribological Properties of the MoS<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub>/PI Composites

Polyimide (PI) composites have been widely used in a space science due to extraordinary properties, such as excellent mechanical and electrical properties, good thermal stability and chemical inertness, as well as high wear resistance. However, atomic oxygen (AO), as one of the main radiated constituents in low earth orbit, had an important influence on the structrural and tribological properties of the polyimide matrix. To investigate the mechanism of AO erosion on polyimide, MoS2/Al2O3/PI composites were fabricated by means of a hot-press molding technique and irradiated by AO in a ground-based simulation system. The chemical composition change of the irradiated surface was examined by X-ray photoelectron spectroscopy (XPS). Then, the friction and sliding wear behavior against GCr15 steel balls were evaluated in a ground-based simulation facility using ball-on-disk tribology test rig. The worn morphologies and radiated surfaces of the materials were observed by Scanning electron microscope (SEM) to reveal the wear mechanism. Experimental analysis indicated that oxidation induced by AO irradiation and degradation of PI molecular chains on the composite’ surface results in change in chemical composition and formation of “carpet-like” structures. Affected layer, gradually formed during the process of irradiation, plays an important role for wear performance of the materials increasing friction coefficient and wear rate. Incorporation of Al2O3 nanofibers and MoS2 nanoparticles is shown to be favourable for AO resistance, which is helpful for improvement in wear resistance of the PI.

Effects of atomic oxygen exposure on the tribological performance of ZrO2-reinforced polyimide nanocomposites for low earth orbit space applications

The effects of atomic oxygen exposure on pure polyimide and nano-ZrO2 reinforced polyimide composites were investigated in a ground-based simulation facility. The experimental results indicated that the surface structure of both pure polyimide and ZrO2/polyimide composites were destroyed by atomic oxygen attack, but the addition of nano-ZrO2 particles in polyimide could obviously decrease the mass loss, which showed that ZrO2 could enhance the atomic oxygen resistance. The results of ZrO2/polyimide composites before and after atomic oxygen exposure showed that atomic oxygen irradiation aggravated the friction and wear of the ZrO2/polyimide composites. The wear mechanism was mainly abrasive particles wear arising from the ZrO2-rich layer on the surface of composites. The ZrO2/polyimide composites with 1 wt% nano-ZrO2 owns the lowest varying rate of the friction coefficient and wear rate before and after atomic oxygen exposure, which showed stable friction and wear properties and was expected to become a kind of potential tribological materials for practical spacecraft designation.

The erosion effect of Kapton film in a ground-based atomic oxygen irradiation simulator

In order to investigate the effect of space environmental factors on spacecraft materials, a ground-based simulation facility for space atomic oxygen (AO) irradiation was developed in our laboratory. Some Kapton film samples were subjected to AO beam generated by this facility. The Kapton films before and after AO exposure were analyzed comparatively using optical microscopy, scanning electronic microscopy, atomic force microscopy, high-precision microbalance, and X-ray photoelectron spectroscopy. The experimental results indicate that the transmittance of Kapton film will be reduced by AO irradiation notably, and its color deepens from pale yellow to brown. Surface roughness of the AO-treated sample is already increased obviously after AO irradiation for 5 hours, and exhibits a flannel-like appearance after 15 hours’ exposure in AO beam. The imide rings and benzene rings in kapton molecule are partially decomposed, and some new bonds form during AO irradiation. The mass loss of kapton film increases linearly with the increase of AO fluence, which is resulted from the formation of volatile products, such as CO, CO2 and NO x . The breakage in structure and degradation in properties of AO-treated Kapton film can be attributed to the integrated effect of impaction and oxidization of AO beam. The test results agree well with the space flight experimental data.

Structural changes and tribological performance of thermosetting polyimide induced by proton and electron irradiation

The structural changes and tribological performance of thermosetting polyimide were investigated by electron, proton or both combined irradiations at 25 keV in a ground-based simulation facility. Three forms of irradiations could lead to the formation of the carbonized layer on the polymer surface that could increase the hardness and adhesive force of the material. Proton irradiation induced more extensive changes in structure and friction behavior than electron irradiation by reason of the higher linear energy transfer value, and combined irradiation resulted in the largest impact, but which was less than the sum of the radiation effects of electron and proton. Moreover, the experimental results indicated that the changes in friction behavior are closely related with the carbonized layer, which was easily worn out in friction process and could introduce a shift from adhesion wear to three-body abrasive wear that reduced the wear rate and the friction coefficient. The friction process of irradiated samples could be divided into the initial stage and the steady stage. Three forms of irradiations all induced the high friction coefficient in the initial stage and the low friction coefficient in the steady stage, and the wear rate of the irradiated samples decreased in the order: electron irradiation>proton irradiation>combined irradiation.

Shielding Kevlar fibers from atomic oxygen erosion via layer-by-layer assembly of nanocomposites

Highly uniform and defect-free multilayer coatings of montmorillonite (MMT) and poly (p-aminostyrene) (PPAS) on Kevlar fibers were generated to provide protection from atomic oxygen (AO) erosion, one of the greatest causes of degradation of polymeric materials used in the low earth orbit. The quantified protective MMT/PPAS layer was successfully deposited through a layer-by-layer assembly technique, as confirmed by Fourier-transform infrared spectroscopy and scanning electron microscopy. The accelerated AO durability was tested in a ground-based AO-effects simulation facility. The results show that the multilayers provide the Kevlar fibers an excellent protection from AO erosion.

Effect of proton irradiation on the friction and wear properties of polyimide

Effect of 25keV proton irradiation with fluence of 2.25×1017ion/cm2 on the structural and tribological properties of polyimide blocks were investigated in a ground-based simulation facility. The changes in surface structure were characterized by FTIR-ATR, laser micro-Raman, contact angle measurement and nanoindentation. The experimental results indicated that the proton irradiation induced bond breaking to form the carbon-enriched structure on polyimide surface, and then increased the surface hardness and the surface energy. The irradiation depth was restricted within 514nm from the surface by TRIM simulation.The carbonized layer induced by irradiation was worn out in friction test, which was proved through Raman spectra analysis of the wear track. Proton irradiation increased the initial friction coefficient and decreased the steady friction coefficient of polyimide. In the initial stage, the friction coefficient was closely related to surface hardness of material, and the main wear mechanism was adhesive wear. In the steady stage, the main wear mechanism was three-body abrasion wear, three-body abrasion and the low surface energy could reduce the wear rate and the friction coefficient.

Phenylphosphine oxide containing polyimide matrix resins for atomic oxygen-resistant fiber-reinforced composites

Phenylethynyl-endcapped imide oligomers with different calculated molecular weights (calcd number average molecular weight ([Formula: see text])) and phosphorous (P) contents (P loading) were synthesized by the reaction of diethyl ester of 4,4′-oxydiphthalic acid, monoethyl ester of 4-phenylethynyl phthalic acid, and the P-containing diamines including [2,5-bis(4-aminophenoxy)phenyl] diphenylphosphine oxide and di(3-aminophenyl)methylphosphine oxide via in situ polymerization of monomeric reactant method. The amide–ester solutions were impregnated with carbon fiber (Cf) and quartz fiber (Qf) cloth to give high quality prepregs that were then thermally cured to yield the Cf-reinforced polyimide (PI) composite (Cf/PI) and Qf-reinforced PI composite (Qf/PI), respectively. The Cf/PI composites showed high mechanical properties with a flexural strength of 1554 ± 93 MPa, a flexural modulus of 112 ± 3 GPa and an interlayer shear strength of 90 ± 5 MPa, respectively. The atomic oxygen (AO) resistances of the neat resins and composites were evaluated on a ground-based simulation facility. Experimental results indicated that the P structures offer PIs with 55–75% lower weight losses and a self-healing property. The fiber-reinforced composites showed further lower erosion rates than neat resins. In addition, the effects of calcd [Formula: see text] and P loadings on the melt processabilities of the B-staged imide oligomers and the AO resistance of the cured PIs were systematically investigated.

Erosion Effects of Atomic Oxygen on Polyhedral Oligomeric Silsesquioxane-Polyimide Hybrid Films in Low Earth Orbit Space Environment

A novel polyimide (PI) hybrid nanocomposite containing polyhedral oligomeric silsesquioxane (POSS) had been prepared by copolymerization of trisilanolphenyl-POSS, 4,4'-oxydianiline (ODA), and pyromellitic dianhydride (PMDA). The AO resistance of these PI/POSS hybrid films was tested in the ground-based AO simulation facility. Exposed and unexposed surfaces were characterized by SEM and X-ray photoelectron spectroscopy. SEM images showed that the surface of the 20 wt% PI/POSS became much less rough than that of the pristine polyimide. Mass measurements of the samples showed that the erosion yield of the PI/POSS (20 wt.%) hybrid film was 1.2 x 10(-25) cm3/atom, and reduced to 4% of the polyimide film. The XPS data indicated that the carbon content of the near-surface region was decreased from 60.1 to 13.2 at% after AO exposure. The oxygen and silicon concentrations in the near-surface region increased to 1.96 after AO exposure. The nanometer-sized structure of POSS, with its large surface area, had led AO-irradiated samples to form a SiO2 passivation layer, which protected the underlying polymer from further AO attack. The incorporation of POSS into the polyimide could dramatically improve the AO resistance of polyimide films in low earth orbit environment.

Surface modification of POSS–polyimide hybrid films by atomic oxygen using ECR plasma

A novel polyimide (PI) hybrid nanocomposite containing polyhedral oligomeric silsesquioxane (POSS) had been prepared by copolymerization of trisilanolphenyl-POSS, 4,4′-oxydianiline (ODA), and pyromellitic dianhydride (PMDA). The atomic oxygen (AO) resistance of these PI/POSS hybrid films was tested in the ground-based AO simulation facility. Exposed and unexposed surfaces were characterized by SEM and XPS. The SEM images showed that the surface of the 20wt.% PI/POSS became much less rough than that of the pristine PI. Mass measurements of the samples showed that the erosion yield of the PI/POSS (20wt.%) hybrid film was 1.2×10−25cm3/atom, and reduced to 4.3% of that of the PI film. The XPS data indicated that the carbon content of the near-surface region was decreased from 66.0 to 7.0at.% after AO exposure. The ratio of oxygen and silicon concentrations in the near-surface region increased to 2.08 after AO exposure. The nanometer-sized structure of POSS, with its large surface area, had led AO-irradiated samples to form a SiO2 passivation layer, which protected the underlying polymer from further AO attack. The incorporation of POSS into the PI could dramatically improve the AO resistance of PI films in low earth orbit environment.

Surface composition variation and high-vacuum performance of DLC/ILs solid–liquid lubricating coatings: Influence of space irradiation

In this paper, we fabricated a DLC/ionic liquid (DLC/ILs) solid–liquid lubricating coating and investigated the effect of atomic oxygen (AO), ultraviolet (UV), proton and electron irradiations on composition, structure, morphology and tribological properties of the DLC/ILs solid–liquid lubricating coatings. A ground-based simulation facility was employed to carry out the irradiation experiments. X-ray photoelectron spectroscope (XPS), Raman spectra, and Fourier Transform Infrared Spectroscopy (FTIR) were used to analyzed the structure and composition changes of DLC film and IL lubricant before and after irradiations. The tribological behavior of the DLC/ILs solid–liquid lubricating coating before and after irradiations was investigated by a vacuum tribometer with the pressure of 10−5Pa. The experimental results revealed that irradiations induced the structural changes, including oxidation, bond break and crosslinking reactions of DLC film and IL lubricant. The damage of proton and AO irradiations to lubricating materials were the most serious, and UV irradiation was the slightest. After irradiations, the friction coefficient of the solid–liquid lubricating coatings decreased (except for AO irradiation), but the disc wear rate increased compared with non-irradiation coatings.

Atomic oxygen-resistant and transparent polyimide coatings from [3,5-bis(3-aminophenoxy)phenyl]diphenylphosphine oxide and aromatic dianhydrides: Preparation and characterization

A novel meta-substituted aromatic diamine, [3,5-bis(3-aminophenoxy)phenyl]diphenylphosphine oxide (m-BADPO) was synthesized by the Williamson reaction of 3,5-difluorophenyldiphenylphosphine oxide (DFPPO) and meta-aminophenol. The diamine was then polymerized with several commercially available aromatic dianhydrides to afford a series of aromatic polyimides (PI-1–PI-4). The meta-substituted molecular skeleton and the pendant bulky phenylphosphine oxide (PPO) group endowed the PIs many desired properties for their potential applications in space environments. For instance, the solubility of the PIs was enhanced due to the synergic effects of meta structure and the bulky PPO groups, making it possible to fabricate the PI films via solution procedure. The films exhibited flexible and tough natures with light color and high transparency in the visible light region. The transmittance up to 87% at 400nm was achieved in the films. The atomic oxygen (AO) degradation behavior of the PI films in the ground-based simulation facility was investigated. The preliminary X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) measurement results indicated that the PI films exhibited good durability in AO-rich environments. Inert phosphorous-containing protecting layer might form at the surface of PI film during AO exposure. In addition, the intrinsic merits of typical high-performance PIs were maintained in the present polymers.

Atomic oxygen resistant phosphorus-containing polyimides for LEO environment

In this study, a series of polyimides had been prepared from bis-(4-aminophenoxyl) phenoxyl phosphine oxide (p-DAPO4) with corresponding dianhydrides via two-stage polycondensation method. The inherent viscosities of the polyamide acid were in range of 0.43–0.92 dL/g, and atomic oxygen (AO) exposure experiment was conducted in a ground-based atomic oxygen effects simulation facility with the filament charge and bound of magnetic field to determine the AO erosion-resistant properties of the polyimide films. Field emission scanning electron microscopy (FE-SEM), attenuated total-reflection Fourier transform infrared spectrometer and X-ray photoelectron spectrometer were employed to characterize the change on the surface of films after AO exposure, and the mass loss of some phosphorus-containing polyimide films reduced to about 20% that of Kapton® HN film as AO fluence of 4.14 × 1020 atoms/cm2. The morphologies of heave residues of the polyimide films acting as a barrier to further erosion could be obtained from FE-SEM. The results indicated that a phosphate-type layer was left on the surface of phosphorus-containing polyimide films after AO exposure.

Structural and Tribological Properties of Polytetrafluoroethylene Composites Filled with Glass Fiber and Al2O3 in Atomic Oxygen Environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of polytetrafluoroethylene (PTFE) composites filled with both glass fibers and Al2O3 were investigated in a ground-based simulation facility, in which the average energy of AO was about 5 eV and the flux was 5.0 × 1015/cm2 s. It was found that AO irradiation first induced the degradation of PTFE molecular chains on the sample surface, and then resulted in a change of surface morphology. The addition of Al2O3 filler significantly increased the AO resistance property of PTFE composites. Friction and wear tests indicated that AO irradiation affected the wear rate and increased the friction coefficient of specimens. The PTFE composite containing 10% Al2O3 exhibit the best AO resistance and lower wear rate after long time AO irradiation.

Effects of proton and electron irradiation on the structural and tribological properties of MoS2/polyimide

To study the structural and tribological properties of MoS2/polyimide (MoS2/PI) composite under the irradiation environment of proton and electron, the MoS2/PI composites were investigated in a ground-based simulation facility, in which the energy of proton and electron was 25keV and the flux was 2.5×1014cm−2s−1. The experimental results revealed that the simplex and combined irradiation of proton and electron induced bond break and cross-link, proton irradiation can break the PI bond easier than electron irradiation and then formed the graphite-like structure at surface area of the samples. Irradiation decreased the friction coefficient and wear rate remarkably of the composites comparing with the pristine one. The wear rate increased with the increasing of the proton and combined radiation time, and decreased with the electron radiation conditions.

Effect of Atomic Oxygen Exposure on Polyhedral Oligomeric Silsesquioxane/Polyimide Hybrid Materials in Low Earth Orbit Environment

A novel polyimide (PI) hybrid nanocomposite containing polyhedral oligomeric silsesquioxane (POSS) had been prepared by copolymerization of octa(aminophenyl)silsesquioxane (OAP-POSS), 4,4’ -oxydianiline (ODA), and pyromellitic dianhydride (PMDA). The AO resistance of these POSS/PI hybrid films was tested in the ground-based AO simulation facility. Exposed and unexposed surfaces have been characterized by X-ray photoelectron spectroscopy and FTIR. The XPS data indicate that the carbon content of the near-surface region is decreased from 63.6 to 19.3 at% after AO exposure. The oxygen and silicon concentrations in the near-surface region increase after AO exposure. The data reveal the formation of a passive inorganic SiO2 layer on the POSS/PI hybrid films during the AO exposure, which serves as a protective barrier preventing further degradation of the underlying polymer with increased exposure to the AO flux. SEM images showed that the surface of the 10 wt% POSS/PI became much less rough than that of the pristine polyimide. The AO resistance of the POSS/PI hybrid films is up to several tenfold than that of the pristine polyimide.

Effect of Atomic Oxygen Exposure on Si Implanted Siloxane Coatings in Low Earth Orbit Environment

To improve the AO erosion resistance of siloxane coating, the Si ion implantation with nominal dosage of 7×1016 ions/cm2 in siloxane coatings on the polyimide substrate was carried out by using the plasma immersion ion implanter. The Si implanted siloxane coatings before and after AO exposure in the ground-based AO simulation facility were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS). The results of mass measurement shown that, in initial stage of AO exposure the implanted sample had a small mass change, and then was stabilized. The erosion yield of the implanted siloxane coating decreased by a factor of more than two orders of magnitude compared with that of the polyimide film, and decreased by a factor of more than an order of magnitude than that of unimplanted siloxane coatings. The results through SEM and XPS indicated that a continuous high-quality protective SiO2 surface layer was formed on the implanted siloxane coatings after the AO exposure. It can prevent further degradation of the underlying polymer with increased exposure to the AO flux and provide high-quality erosion protection for these materials. The Si implanted materials have a markedly increased erosion resistance than unimplanted siloxane coatings in AO environment.