Sand Erosion Tests Research Articles

Sand Erosion Resistance and Failure Mechanism of Polyurethane Film on Helicopter Rotor Blades.

Polyurethane is widely used on the surface of composite materials for rotor blades as sand erosion protection materials. The failure mechanism investigation of polyurethane film under service conditions is useful for developing the optimal polyurethane film for rotor blades. In this article, the sand erosion test parameters were ascertained according to the service environment of the polyurethane film. The sand erosion resistance and failure mechanism of polyurethane film at different impact angles were analyzed by an infrared thermometer, a Fourier transform infrared spectrometer (FTIR), a differential scanning calorimeter (DSC), a field emission scanning electron microscope (FESEM), and a laser confocal microscope (CLSM). The results show that the direct measurement method of volume loss can better characterize the sand erosion resistance of the polyurethane film compared to traditional mass loss methods, which avoids the influence of sand particles embedded in the polyurethane film. The sand erosion resistance of polyurethane film at low-angle impact is much lower than that at high-angle impact. At an impact rate of 220 m/s, the volume loss after sand erosion for 15 min at the impact angle of 30° is 57.8 mm3, while that at the impact angle of 90° is only 2.6 mm3. The volume loss prediction equation was established according to the experimental data. During low-angle erosion, the polyurethane film damage is mainly caused by sand cutting, which leads to wrinkling and accumulation of surface materials, a rapid increase in roughness, and the generation of long cracks. The linking of developing cracks would lead to large-scale shedding of polyurethane film. During high-angle erosion, the polyurethane film damage is mainly caused by impact. The connection of small cracks caused by impact leads to the shedding of small pieces of polyurethane, while the change in the roughness of the film is not as significant as that during low-angle erosion. The disordered arrangement of the soft and hard blocks becomes locally ordered under the action of impact and cutting loads. Then, the disordered state is restored after the erosion test finishes. The erosion of sand particles leads to an increase in the temperature of the erosion zone of the polyurethane film, and the maximum temperature rise is 6 °C, which does not result in a significant change in the molecular structure of the polyurethane film. The erosion failure mechanism is cracking caused by sand cutting and impact.

Solid Particle Erosion Performance and Damage Mechanism of AlTiN Coating

Aircraft, when operating in a sandy environment, can experience severe solid particle erosion damage to gas turbine engine components, such as compressor rotor blades, vanes, and impeller blisks/wheels, due to sand particle ingestion into the engine. Material removal from these components as the result of erosion not only leads to significant aerodynamic losses, but also results in their structural weakening. Applying erosion-resistant coatings on airfoil surfaces has been proven effective in extending the serviceable life of engine components. In this study, cathodic arc evaporated AlTiN was explored for its potential as an erosion-resistant coating for the compressor blades and helicopter impellers applications. AlTiN coating, along with baseline TiN coating, was subjected to gas jet sand erosion testing under different particle impingement angles and velocities. The erosion rates of the AlTiN coating were found to be much lower than those of the TiN coating in the entire range of the tested conditions. While the TiN coating mainly suffered from severe brittle erosion damage through coating chipping, the AlTiN coating exhibited only mild erosion damage through microcutting by sand particles. To include the aerodynamic effect on airfoil erosion in the consideration, dynamic wind tunnel sand erosion testing was also performed on AlTiN- and TiN-coated propeller blades. The results of these tests also confirmed superior erosion resistance of the AlTiN coating over that of the TiN coating.

On the stress dependency of sand production coefficient in hydro-dynamical sanding criteria

Solids production is a complex physical process which is controlled by several factors including mechanical failure from in-situ stresses and hydrodynamic erosion from fluid flow. Hydrodynamic models for the prediction of sand production involve sanding criteria based on filtration theories. Such models contain a constitutive model parameter, the coefficient λ, with dimensions of inverse length which is calibrated by sand erosion tests, but its nature and its dependencies have not been clarified to date. The aim of this work is an attempt to refine the hydrodynamic models by investigating the dependence of the sand production coefficient λ on the external stress conditions and on the plastic zone Λ that is developed on hollow cylinders tests and propose an expression describing its importance in the sand production prediction modelling. The aim of the work is obtained through simulations with finite elements by utilizing the well-established Arbitrary Lagrangian-Eulerian (ALE) analysis considering the poro-mechanical coupling of the fluid-solid system for simulating hollow cylinder tests. Best fitting experimental data estimated values for the sand production coefficient for various values of external stress are obtained through back analysis. The dependence of λ on the external stress turns out to be fairly smooth and a three-parameter model is proposed to describe that dependence: a scale parameter, an exponent, and a stress parameter defining the magnitude of stress at which erosion onset is predicted. It turns out that the stress parameter is associated with the minimum stress required for plastic yielding to occur, which was also estimated theoretically. This finding is in agreement with the physical assumption underlying the simulations that erosion onsets and progresses after the material reaches a critical plastic strain as a consequence of material plastic yielding. A power law model describing the dependence of λ on the plastic zone depth is also proposed and discussed.

Toughness enhancement mechanism of Ni-doped Cr2N

In this paper, experiments combined with density functional theory (DFT) are used to investigate the toughness enhancement mechanism of Ni-doped Cr2N coatings. The deposited Cr2-xNixN (x = 0–4.5 at%) coating exhibits a single trigonal structure identified as a Cr2N-Ni solid solution. The columnar structure of the Cr2N coating, with a width of approximately 80 nm, does not change with the doping of Ni. With 2.0 at% Ni alloyed, the hardness increases from 27 GPa for Cr2N to the maximum of 34 GPa. which is mainly due to an increase in residual compressive stress and dislocation density resulting from Ni doping. Interestingly, the elastic modulus shows a linearly decreasing trend as the Ni doping content increases, which indicates that Ni alloying improves the ductility of the Cr2N coating. The sand erosion test shows that the erosion rate of the Cr2N coating is significantly reduced when the Ni doping content is 2.0 at%, decreasing from 0.42 µm·min−1 to 0.15 µm·min−1. DFT results reveal that the metallic d-d state density increases with increased d-electron concentration contributed by Ni atoms, enhancing metallic interaction along the Ni-Cr stacking plane under shear loading, which leads to the improved ductility of the Cr2-xNixN coating.

Structure, mechanical, and sand erosion behavior of TiN/Ti coating deposited at various temperature

In this paper, the microstructure evolution, mechanical properties, sand erosion performance, and failure mechanism of multilayer TiN/Ti coatings deposited at different substrate temperatures (25 °C, 100 °C, 300 °C, and 500 °C) were investigated. TEM results showed the average columnar grain width of the TiN layer at the four deposited temperatures was 18.4 nm, 30.7 nm, 58.9 nm, and 86.9 nm, respectively. Additionally, a transition from columnar to equiaxed grain morphology was observed in the Ti layer when the deposition temperature was raised to 500 °C. The hardness of TiN/Ti coating decreased from 26 GPa at 25 °C to 22 GPa at 100 °C, 300 °C and 500 °C, which might be attributed to the decreased residual stress with the increase of the deposition temperature. The adhesion force of the deposited coating on the substrate increased firstly, peaked 72 N at 300 °C and then decreased. Sand erosion tests indicated that the sand erosion rate of the TiN/Ti coating initially decreased then rebound as the coating deposition temperature increased. The TiN/Ti coating deposited at 300 °C exhibited the optimal anti-erosion performance. Under a 45° sand erosion incident angle, the top TiN layer cracked and propagated parallelly to the incident angle and intersected, resulting in coating delamination. Under a 90°incident angle, the crack in the soft Ti layer intersected with the annular crack formed in the brittle TiN layer, leading to the removal of the coating.

Erosion Resistant Hydrophobic Coatings for Passive Ice Protection of Aircraft

Novel polymeric coatings, namely slippery polyurethane (SPU) coatings, with high surface hydrophobicity and superior erosion resistance against high speed solid particles and water droplets were successfully developed to protect the leading edge of fast moving aerodynamic structures, such as aircraft wings and rotor blades, against ice accretion. The coatings comprise newly synthesized surface-modifying polymers (SMPs) bearing fluorinated and polydimethylsiloxane branches at a loading level of 1–5 wt.%, based on the total resin solid, which showed good compatibility with the erosion-resistant polyurethane matrix (PU-R) and rendered effective surface hydrophobicity and slipperiness to the coatings, as evidenced by the high water contact angles of 100–115°. The coatings can be easily be sprayed or solution cast and cured at ambient temperature to provide highly durable thin coating films. X-ray photoelectron spectroscopy (XPS) investigation showed concentration of fluorine on the surface. The presence of 1–5 wt.% of SMPs in the polyurethane matrix slightly reduced the tensile modulus but had no significant impact on the tensile strength. All coating films exhibited good thermal stability with no material softening or degradation after heating at 121 °C for 24 h. DSC heating scans revealed no thermal transitions in the temperature range of −80 °C to 200 °C. Ice adhesion strength (IAS) tests using a static push rig in a cold room of −14 °C showed IAS as low as 220 kPa for the SPU coatings, which is much lower than that of PU-R (i.e., about 620 kPa). Sand erosion tests using 50 μm angular alumina particles at an impinging speed of 150 m/s and an impinging angle of 30° revealed very low erosion rates of ca. 100 μg/g sand for the coatings. Water droplet erosion tests at 175 m/s using 463 μm droplets with 42,000 impingements every minute showed no significant coating removal after 20 min of testing. The combination of the high surface hydrophobicity, low ice adhesion strength and superior erosion resistance makes the SPU coatings attractive for ice protection of aircraft structures, where the coatings’ erosion durability is of paramount importance.

Sand erosion and crack propagation mechanism of Cr/CrN/Cr/CrAlN multilayer coating

Herein, we have deposited Cr/CrN/Cr/CrAlN multilayer coatings with various modulation ratios on TC11 alloy substrate using cathodic arc system. The influence of various modulation ratios on microstructure and Al 2 O 3 sand erosion behavior of coatings is systematically studied. Results reveal that the coatings are about 200 nm per cycle and total thickness is 8 μm. Five groups of coatings exhibit high hardness (>3000 HV 0.025 ). The coating with modulation ratio of 12 adhesion can reaches 55 N. The residual stress increases with the decrease of the modulation ratio, but the increase is generally low (less than −2 GPa). In addition, according to sand erosion test, it is found that sand erosion resistance of multilayer coating is significantly around 5 times higher than TC11 alloy matrix. The erosion morphology shows that a large number of irregular cracks and layered spalling appear on the surface of the coating, indicating that the cracks are constantly initiated under the continuous impact of the sand and gravel，and finally gather together and then spalling. Moreover, dynamic response and stress field of the coating under the impact of single sand (Al 2 O 3 ) are studied by numerical simulations. It is determined that coating cracking is caused by high tensile stress under CrAlN layer. In addition, according to crack propagation morphology and influence of different interfaces between multilayered structures on crack tips, propagation/termination mechanism of cracks is analyzed in detail. Cracks are easy to initiate in hard CrAlN layer and consume a lot of energy after propagating into soft Cr layer, thereby ending at next soft and hard interfaces. These results provide experimental and theoretical support for the study of high tenacity and anti-erosion coating.

Synergetic Design of Transparent Topcoats on ITO-Coated Plastic Substrate to Boost Surface Erosion Performance

Transparent conductive films (TCFs) have received much research attention in the area of aeronautical canopies. However, bad wear, corrosion resistance and weak erosion performance of TCFs dramatically limit their scalable application in the next-generation aeronautical and optoelectronic devices. To address these drawbacks, three types of optically transparent coatings, including acrylic, silicone and polyurethane (PU) coatings were developed and comparatively investigated ex situ in terms of Taber abrasion, nanoindentation and sand erosion tests to improve the wear-resistance and sand erosion abilities of ITO-coated PMMA substrates. To elucidate the sand erosion failure of the coatings, the nanoindentation technique was employed for quantitative assessment of the shape recovery abilities under probe indentation. Results show that the PU topcoats can greatly enhance the sand erosion properties, which were superior to those of acrylic and silicone topcoats. This result can be attributed to the good toughness and self-healing properties of PU topcoats. Additionally, high hardness and good Taber abrasion properties of the ITO films and silicone topcoats did not have an obvious or affirmatory effect on the sand erosion abilities, based on their brittleness and irreparable properties under sand erosion.

Crack resistance enhancement of gradient bias TiN/Ti multilayer coating by Ti sputtering

ABSTRACT In this study, monolayer TiN and multilayer TiN/Ti coatings involving different modulation ratios were deposited on Ti–6Al–4V substrate. Ti interlayers in the multilayer TiN/Ti coatings were prepared under gradient negative bias of –800, –600, and –400 V, with corresponding durations of 2, 2, and 1 min. Mechanical properties and crack' s resistance of the coatings were explored. Damage morphology of coating cross-section was characterized by the focused ion beam (FIB) method. Finite element modelling was used to analyse the stress field. Multilayer TiN/Ti coatings show better impact resistance than monolayer TiN coating. Tensile stress decrease with the increase of interfaces. Gradient bias Ti interlayers restrain crack propagation by cracks deflection and branch. Erosion resistance was evaluated by sand erosion test. Crack propagation and connection account for the coatings failure: the deeper the crack propagation, the higher the erosion rate.

Effect of Grain Refinement on Tribological Study of Low Carbon Steel

Tribological characteristics of low carbon steel (LCS) have been investigated on as-received coarse grains of 67 μm size and ultrafine-grained (UFG) microstructure of 0.2 μm size, which was prepared by equal-channel angular pressing (ECAP). Two-body abrasion tests have been carried out against silicon carbide abrasive papers at various loads. Furthermore, solid particle (silica sand) erosion tests were also conducted at normal particle impingement angles at various impact velocities. The ECAP process improved the resistance to abrasive and erosion wear of UFG LCS as compared to that of as-received coarse-grained steel. The abrasive and erosion wear resistances of UFG LCS were improved under severe conditions. The abrasive wear mechanism of as-received coarse-grained LCS was governed by micro-cutting, whereas it was microploughing in UFG LCS. The mechanism of material removal in erosive wear was brittle in as-received material in contrast to ductile in UFG steel.

Double Glow Plasma Nitriding Pretreatment of TiAlN-Coated TA15 Alloy for Enhancement of Bonding Strength and Mechanical Properties

As a classic hard coating, titanium aluminum nitride (TiAlN) coating is widely applied in the aviation field due to its extremely high hardness and strength. Unfortunately, the large difference in hardness and thermal expansion coefficient between the coating and the substrate could also lead to the reduction of bonding force. In this paper, Double-glow plasma nitriding (DGPN) pretreatment followed by RF magnetron sputtering was used to prepare DGPN-TiAlN coating on the surface of TA15 alloy. The adhesion and the bearing capacity of DGPN-TiAlN coating is characterized by scratch and indentation tests. The gradient hardness support and stress transition effect of the nitriding layer are significant, and the bonding strength of TiAlN coating and the substrate are significantly improved. In addition, the high temperature wear resistance and erosion resistance of DGPN-TiAlN coating were detected through high-temperature wear tests and sand erosion tests. At 500 °C, the surface of DGPN-TiAlN coating formes a dense Al2O3 lubricating film with good adhesion, and the friction coefficient is lower than that of TiAlN coating. Under different erosion speeds and erosion angles, the erosion rate of DGPN-TiAlN coating is lower than that of TiAlN coating, and the coating surface defects are less.

Comparative Experimental Investigation of Erosion behaviour of AA2024/B4C and AA6061/B4C Metal Matrix Composites with Particulate coating

Different amounts of B4C reinforcement with 5% and 10% are coated with Nickel using Electroless coating technique and are used for reinforcement in Aluminium alloys to produce aluminium metal-matrix composites (AMC). The composites with/without nickel coating thus produced were tested for erosion rate at various pressure conditions and impinging angle. The addition of certain amount of nickel coating provides not only the wettability effect of B4C, it also increases the strength of parent materials (pure Aluminium, AA2024 and AA6061). SEM micrographs confirmed the formation of a Nickel layer on Boron Carbide. Sand erosion tests are designed using L27 orthogonal array with factors as four having three levels. External factors such as, type of matrix and the weight-percentage of particulate are selected. Internal factors viz., the pressure of the air/sand mixture and the angle of impingement. Three levels for every factor used in the experimentation and out of which, Impingement angle shows the predominant significant effect on the erosion rate. It is found that the impingement angle of level 1 (i.e. 30o) has the max influence of 39.75 % contribution on erosion rate. The Regression model is developed for estimating the erosion rate, in terms of the levels of all factor considered. From these models, it is observed that the 5% B4C reinforcement with nickel coating gives minimum erosion rate for aluminium alloys.

Anti-sand erosion and tribological performance of thick DLC coatings deposited by the filtered cathodic vacuum arc

In order to improve the abrasion and erosion resistance in severe environments, 50-μm-thick diamond like carbon (DLC) films with a hardness of 27.3 GPa were fabricated using filtered cathodic vacuum arc technique coupled with a high-voltage pulse power. The microstructures, mechanical properties and tribological and anti-sand erosion performance of DLC coatings with different thicknesses were evaluated. The increase in thickness from 3 to 50 μm, resulting the adhesion of the coatings increased from HF1 to above HF1 level. Radial cracks or delamination were not observed at the edge of the indentation of 50-μm-thick coating. The coefficient of friction (COF) was decreased but wear rate was increased as coating growing thicker due to the stacking of graphited debris between the asperities. Mechanical polish was carried out on the 50-μm-thick films, which lead to the COF and wear rate decreased from 0.079 to 0.067 and 14.7 to 6.78 × 10−8 mm3/N·m at 20 N. The sand erosion test demonstrated that as the increase in thickness from 3 to 50 μm, average mass loss rate significantly decreased from 0.81 to 0.035 mg/g. High load-bearing capacity and ability to restrain the initiation and propagation of cracks were responsible for the great erosion resistance for thick coating.

Dataset of wind blow sand erosion test on ultrasonic surface treated cementitious composites.

In this paper, we take cement mortar and paste as specimens, a novelty method named ultrasonic surface treatment(UST) was employed to form a hardening surface layer on cementitious specimens to improve its wind-blown sand erosion resistance, surface hardness and apparent density. The specimens with curing ages of 1-day, 3-days, 7-days, and 28-days were adopted. The wind blown sand erosion test was carried out in a wind-blown sand erosion test system, which simulated a wind blown sand environment of a wind speed of 30 m/s and a sand feed rate of 30 g/min. The erosion angle of 30°, 60°, 90° were adopted. The mass loss in erosion process was measured, then the erosion resistance was calculated. The surface hardness was tested with a Vickers micro hardness tester. The apparent density of cement paste was measured with mass volume method. The data provided reveal the improvement on wind blown sand erosion resistance, surface hardnenss and apparent density of cementitious materials with ultrasonic surface treatment. That may be used in the investigation on improving the erosion resistance and to evaluate the effectiveness of the UST method on cementitious materials.

Ultrasonic surface treatment for improving wind-blown sand erosion resistance of cementitious materials

In this study, we present a method that employed ultrasound to impose vibration on the surfaces of cementitious materials at the early stage of hydration to form a hardening layer and improve the surface hardness. The formation mechanism of the ultrasonic hardening layer (UHL) was analyzed, and the density and surface hardness of the UHL were measured. An experimental study was carried out to determine the effect of the UHL on improving the wind-blown sand erosion resistance of cementitious materials. Experimental data show that the UHL has a density 3.3% greater and a hardness 136% greater than that of the contrast samples after 28-days of curing. Wind-blown sand erosion tests data show that to the specimens with 28-days curing age, the UHL can improve the erosion resistance for 12.8–24.1% versus that of the contrast in a 30-min erosion procedure. • A layer known as the UHL can be formed by ultrasonic vibration applied on the surface of cementitious composites. • UHL had the characteristics of higher density and higher surface hardness. • In the UHL, the micro-structure of the composite was promoted. • The UHL improved the erosion resistance of the cement mortar specimens in a wind-blown sand erosion test.

Microstructure and Wear Behavior of MMC Coatings Deposited by Plasma Transferred Arc Welding and Thermal Flame Spraying Processes

In this study, two erosion protection MMC coatings with WC particles were deposited by the plasma transferred arc (PTA) welding. One of the coatings with tungsten carbide WC in the NiBSi matrix (WC/NiBSi), and the second coating WC in NiCrBSi matrix (WC/NiCrBSi) was deposited by the flame spray process on the same substrate material S235JR steel. Experiments were performed using a gas blast sand erosion test facility with high-velocity erodent particles impact (approximately 100 m/s) at different particle impact angles (20°–45°), with an objective to study erosion wear characteristics and mass loss of two MMC coatings. Microstructural characterization of MMC coatings was done by scanning electron microscope equipped with energy-dispersive X-ray spectroscopy, whereas X-ray diffraction analysis was used for identification of present phases. The hardness of coatings was determined by Vickers hardness measurements. WC/NiBSi obtained by the PTA process shows superior hardness and erosion properties.

Scalable and durable polymeric icephobic and hydrate-phobic coatings.

Ice formation and accumulation on surfaces can result in severe problems for solar photovoltaic installations, offshore oil platforms, wind turbines and aircrafts. In addition, blockage of pipelines by formation and accumulation of clathrate hydrates of natural gases has safety and economical concerns in oil and gas operations, particularly at high pressures and low temperatures such as those found in subsea or arctic environments. Practical adoption of icephobic/hydrate-phobic surfaces requires mechanical robustness and stability under harsh environments. Here, we develop durable and mechanically robust bilayer poly-divinylbenzene (pDVB)/poly-perfluorodecylacrylate (pPFDA) coatings using initiated chemical vapor deposition (iCVD) to reduce the adhesion strength of ice/hydrates to underlying substrates (silicon and steel). Utilizing a highly-cross-linked polymer (pDVB) underneath a very thin veneer of fluorine-rich polymer (pPFDA) we have designed inherently rough bilayer polymer films that can be deposited on rough steel substrates resulting in surfaces which exhibit a receding water contact angle (WCA) higher than 150° and WCA hysteresis as low as 4°. Optical profilometer measurements were performed on the films and root mean square (RMS) roughness values of Rq = 178.0 ± 17.5 nm and Rq = 312.7 ± 23.5 nm were obtained on silicon and steel substrates, respectively. When steel surfaces are coated with these smooth hard iCVD bilayer polymer films, the strength of ice adhesion is reduced from 1010 ± 95 kPa to 180 ± 85 kPa. The adhesion strength of the cyclopentane (CyC5) hydrate is also reduced from 220 ± 45 kPa on rough steel substrates to 34 ± 12 kPa on the polymer-coated steel substrates. The durability of these bilayer polymer coated icephobic and hydrate-phobic substrates is confirmed by sand erosion tests and examination of multiple ice/hydrate adhesion/de-adhesion cycles.

Structure and properties of CrSiCN coatings deposited by pulsed dc magnetron sputtering for wear and erosion protection

Abstract CrSiCN nanocomposite coatings were deposited by sputtering a chromium (Cr) target in a gas mixture containing argon, nitrogen, and trimethylsilane (TMS) using middle frequency pulsed dc magnetron sputtering (PDCMS). The coatings with different silicon (Si) and carbon (C) contents were obtained by varying the TMS flow rate from 0 to 12 sccm. Uniform depositions and high deposition rates (8–10 μm per hour) have been achieved. The microstructure of the coatings was studied by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. The lattice parameter of the coatings first increased with the addition of a small amount of Si (1.7 at.%) and C (5 at.%) by the formation of cubic solid solution, and then decreased with a further increase in the Si and C contents. The microstructure of the coating changed from columnar grains to interconnected fine grains, and finally to nanocomposite structure as the Si and C contents increased, in which cubic Cr(Si, C)N nanocrystallites were surrounded by an amorphous matrix consisting of SiC x , amorphous C, SiN x , and CN x . The volume fraction of amorphous phases increased as the Si and C contents increased. The mechanical properties, dry sliding wear resistance, and solid particle erosion (SPE) resistance of the coatings were analyzed using nanoindentation, ball-on-disc test, and air jet sand erosion test, respectively. As compared to the baseline CrN coating, the addition of a small amount of Si (1.7–5 at.%) and C (5–9.6 at.%) effectively improved the hardness and the H/E ⁎ and H 3 /E ⁎2 of the coatings. The strengthening mechanisms include solid solution hardening and grain boundaries strengthening via the formation of a thin amorphous layer. The improved mechanical properties contributed to excellent wear resistance and SPE resistance of the coatings against alumina at both 30° and 90° incident angles. However, as the Si and C contents were increased respectively to above 10.3 at.% and 16 at.%, the mechanical properties and wear and SPE resistance of the CrSiCN coatings all decreased.

Particle erosion on carbon nanofiber paper coated carbon fiber/epoxy composites

Carbon fiber (CF) woven fabric (52% by weight) reinforced epoxy composite and carbon nanofiber (CNF, 12% by weight) paper coated on the surface of the CF/epoxy composite were fabricated by resin transfer molding (RTM). The surface erosion characteristics of molded CF composites were investigated by sand erosion test using silica particles with a size around 150μm as the erodent. The eroded surfaces were examined by scanning electron microscopy (SEM) and weight loss. The CNF paper was able to provide a much stronger erosion resistance compared to the CF reinforced epoxy composites, which is attributed to the high strength of CNFs and their nanoscale structure. Finite element (FE) computer simulations were used to qualitative interpret the underlying mechanisms.

Solid Particle Erosion Testing of Helicopter Rotor Blade Materials

The Army Research Laboratory (ARL) was asked to participate in an OSD-funded erosion effort by the Coating Technology Integration Office at Wright Patterson Air Force Base. Solid particle (sand) erosion testing was conducted by the University of Dayton Research Institute to determine the erosion resistance of materials currently used on the leading edges of Army aviation rotor blades of aircraft in Southwest Asia (SWA). This testing and evaluation was important for two reasons; first, Iraq and Afghanistan are the primary locations of our current anti-terror operations, and second, the sands within these two countries are the worst in the world from an erosion standpoint (dry conditions + freshest grains of sand + predominantly angular quartz grains + blowing winds). The sand utilized herein is considered even more erosive than the sand from these two countries, since they contain a higher concentration of quartz than the SWA sand. In 2005, observations of actual SWA field failures of helicopter rotor blade protective tapes and coatings were compared to existing state-of-the-art, laboratory-based sand erosion data during a U.S. Army sponsored program. Laboratory-produced data did not match the severity of field-use damage, even under extremely high levels of particle loading. The need to test to erosive failure representative of this environment was determined to be paramount in establishing relative performance levels of erosion resistant protective systems being screened for potential field use. The goal of this effort was to provide two synthetic sand formulas capable of testing various polymer-based candidate rotor blade protective systems to failure. The test media was derived from characterization of sand and dust materials unique to SWA. The synthetic sand mixtures developed by this effort will be incorporated in a new test protocol for sand erosion to represent a truly “worst case” test, with extended application to other aerospace components susceptible to sand erosion damage applicable to Department of Defense activities in most dry—hot desert regions. Comprehensive post-test analysis performed by ARL included: visual examination, mass loss calculations, erosion rate determination, surface roughness testing, volume loss calculations, scanning electron microscopy characterization, and metallography. As a result of post-test analysis, many trends were observed, with the results documented herein. The results of this testing have been used as a baseline for future testing of alternative materials and coating systems, and to prepare a solid particle erosion test standard (MIL-STD-3033).