Investigation on solid particle erosion behaviour of polyetherimide and its composites

The present investigation reports about, the solid particle erosion behaviour of randomly oriented short E-glass, carbon fibre and solid lubricants (PTFE, graphite, MoS₂) filled polyetherimide (PEI) composites. The erosion rates (ERs) of these composites have been evaluated at different impingement angles (15–90°) and impact velocities (30–88 m/s). Mechanical properties such as tensile strength (S), ultimate elongation to fracture (e), hardness (H_V), Izod impact strength (I) and shear strength (S_s) seems to be controlling the erosion rate of PEI and its composites. Polyetherimide and its glass, carbon fibre reinforced composites showed semi-ductile erosion behaviour with peak erosion rate at 60° impingement angle. However, glass fibre reinforced PEI composite filled with solid lubricants showed peak erosion rate at 60° impingement angle for impact velocities of 30 and 88 m/s, whereas for intermediate velocities (52 and 60 m/s) peak erosion rate observed at 30° impingement angle. It is observed that 20% (w/w) glass fibre reinforcement helps in improving erosive wear resistance of neat PEI matrix. Erosion efficiency (η) values (0.23–8.2%) indicate micro-ploughing and micro-cutting dominant wear mechanisms. The morphology of eroded surfaces was examined by using scanning electron microscopy (SEM). Possible erosion mechanisms are discussed.     

Abrasive wear performance of carbon fabric reinforced polyetherimide composites: Influence of content and orientation of fabric

Dry abrasive wear performance of five plain weave carbon fabric (CF) reinforced Polyetherimide (PEI) composites, developed with increasing CF contents (in the step of 10 vol%) is reported in this paper. It was observed that composite reinforced with 65 vol% CF (IP₆₅) exhibited the best tensile and shear strength and closely followed the leader (IP₇₅) in flexural strength. IP₆₅ when abraded against silicon carbide paper showed highest wear resistance (W_R) and lowest friction coefficient (μ) among all composites. The composites IP₈₅ and IP₄₀ containing highest and lowest amount of CF respectively showed least enhancement in strength properties and poorest wear performance. Parallel studies on the influence of fabric orientation with respect to the sliding plane and direction, on W_R showed that when CF was oriented parallel to the sliding plane, it had poorest wear resistance. The performance improved for the composites when fabric was oriented normal to the plane. The parallel or anti-parallel orientation of warp or weft fibers with respect to sliding direction showed marginal changes in friction and wear performance. Wear mechanisms were suggested and strongly supported by worn surface analysis using SEM.Efforts were also done to investigate the wear-property correlation. It was observed that the W_R was directly proportional to the product of interlaminar shear strength (I_s) and elastic modulus (E). Fairly good linearity was shown for specific wear rate (K₀) as a function of factor (μP/I_sE) where μ is coefficient of friction and P is the normal pressure (N/mm²).     

Analysis of interlaboratory test results of solid particle impingement erosion

During the development of a standard method for solid particle impingement erosion testing of materials, a number of interlaboratory test comparisons were conducted. In this paper the results of four test series involving twelve laboratories in total are described. The measurements were carried out with considerable care using the gas jet type of erosion tester, involving nearly the same conditions and test parameters on two different materials, a low carbon steel and a stainless steel. The final results indicated a high degree of within-laboratory precision and a moderate degree of between-laboratory precision of erosion loss determinations. A need for standard materials was identified to control sources of measurement bias between laboratories. The principal source of random error in these studies was believed to be associated with the measurements of particle impact velocity.     

The erosion of aluminum by solid particle impingement at normal incidence

A rotating arm apparatus was used to study the erosion of polycrystalline aluminum by 1.58 mm diameter WC-6% Co spheres impinging at normal incidence. Dynamic hardness values were obtained from measurements of the impact craters and compared with corresponding quasi-static values. In addition, material removal was monitored gravimetrically, and quantitative information was obtained on threshold and incubation phenomena and steady state erosion behavior. The variation of the velocity dependence of erosion with the number of particle impacts was derived from these data. Supporting scanning electron microscope studies suggest that the mechanism of material removal responsible for ductile erosion at near normal incidence is somewhat different from that which operates at shallower angles. The similarities and differences between these mechanisms are discussed, and it is suggested that together they account for the characteristic variation of ductile erosion with angle of impingement.     

Influence of weave of carbon fabric on abrasive wear performance of polyetherimide composites

Three composites of Polyetherimide (PEI) reinforced with carbon fabric (CF) of three weaves viz. plain, twill and satin-4 H were developed keeping the amount of fabric constant (55% by vol.). Studies on mechanical properties confirmed that the twill weave composite (T) showed the highest strength, modulus (both tensile and flexural) and interlaminar shear strength (ILSS) followed by satin (S) and plain weave (P) composites. The performance order, however, was reverse in the case of toughness and elongation to break. Specific wear rate in a single-pass, unidirectional and un-lubricated abrasive wear mode against SiC paper showed strong influence of weave in mild wear condition (load 10 N). Composite S showed the highest wear resistance (W _R) followed by composites T and P. With increase in load, the difference in performance diminished to the extent that at 40 N, it was almost similar for all the three composites. This was correlated with the difference in the length of the fibers between crossover points which, in turn, allowed the microdisplacement of fibers in the composites during abrasion. This was supported by the SEM.

The halo effect in jet impingement solid particle erosion testing of ductile metals

Two different areas of erosion occur on flat test specimens exposed to gas—solid particle erosive streams where the stream diameter is smaller than the specimen surface dimensions. The inner area accounts for the majority of the weight loss. This area sees the set test conditions of velocity and impingement angle. Erosion also occurs outside this area in an area designated the “halo area”. The weight loss in this area depends on the impingement angle of the particles and ranges from as high as 25% of the total weight loss at 15° to 3% of the total weight loss at 60°. A definite boundary was observed between the two areas. This halo erosion effect was found to be primarily due to the velocity distribution of the particles in a cone around the principal column of particles striking the specimen. A secondary effect is the change in the true angle of the particles striking the specimen from the set angle.     

Solid particle erosion of unidirectional carbon fibre reinforced polyetheretherketone composites

The solid particle erosion behaviour of unidirectional carbon fibre (CF) reinforced polyetheretherketone (PEEK) composites has been characterised. The erosion rates of these composites have been evaluated at different impingement angles (15–90°) and at three different fibre orientations (0, 45, and 90°). The particles used for the erosion measurements were steel balls with diameter of 300–500 μm and impact velocities of 45 and 85 m/s. The unidirectional CF reinforced PEEK composites showed semi-ductile erosion behaviour, with maximum erosion rate at 60° impingement angle. The fibre orientations had a significant influence on erosion rate. The morphology of eroded surfaces was examined by using scanning electron microscopy (SEM). Possible erosion mechanisms are discussed.     

Influence of content of carbon fabric on the low amplitude oscillating wear performance of polyetherimide composites

Tribo-potential of bi-directionally (BD) reinforced polymer composites is not yet adequately explored especially in low amplitude oscillating wear (LAOW)/fretting wear mode. Hence five composites of Polyetherimide (PEI) containing carbon fabric (plain weave) in the range 40–85 by vol% were developed by impregnation technique followed by compression molding. These composites along with unfilled PEI were evaluated for their LAOW performance on SRV Optimol tester under different loads using ball-on-plate configuration. The performance was compared with that of composite evaluated in earlier work but developed with different processing technique (hand lay up). With increase in load, specific wear rates of all the composites increased while friction coefficient (μ) decreased. It was concluded that carbon fabric inclusion in all amounts proved significantly beneficial for improving friction and wear performance and limiting load of PEI. Very high and very low amount of CF (85 and 40 vol%) proved least beneficial from strength and tribo-performance point of view. Composites with moderate amount of CF (65 and 55 vol%) proved most promising with almost similar potential in reducing μ and wear rate of PEI. Overall CF in the range of 55–65 vol% appeared to be the optimum range for tailoring the strength properties along with tribo-performance in fretting wear mode. The impregnation technique proved significantly better than the hand lay up technique for enhancement in strength and tribo-performance. SEM studies on worn surface proved helpful in understanding wear mechanisms.

Flux effects in solid particle erosion

Systematic measurements of the steady state erosion rate as a function of erodent particle flux were made for a range of different erosion conditions. A significant decrease in erosion rate with increasing flux was observed. A first-order particle collision model was developed that provides a physical basis for describing the flux effect. The data confirm the exponential dependence of the erosion rate on flux predicted by the model. Further analysis of the data within the context of the collision model also provides new insight into the particle impact process.     

Single solid particle impact erosion damage on polypropylene

The literature on the erosion of polymers is reviewed. Single-particle impacts by spheres of 4 mm diameter have been carried out at various angles and speeds on polypropylene. The crater types are classified and plotted on a “deformation map”. High speed photography was used to record the impacts and any material loss. Both ductile (the drawing out of filaments) and brittle (the fracturing of blocks of polymer) erosion processes were observed. The surface finish of the specimens is an important variable in the latter mechanism.     

Carbon fabric reinforced polyetherimide composites: Optimization of fabric content for best combination of strength and adhesive wear performance

Polyacrylonitrile (PAN) based high strength carbon fabric (plain weave) reinforced polyetherimide (PEI) composites were fabricated using impregnation technique by selecting five different contents of carbon fabric, viz. 85, 75, 65, 55 and 40 vol.%. These bidirectional (BD) composites were evaluated for their mechanical strength as well as tribological behavior in adhesive wear mode. Dry adhesive wear studies were conducted on a custom designed wear tester in which high PV conditions can be simulated. Tests were conducted at various operating parameters such as load, temperature and orientation of fabric with respect to the sliding plane. Two important results were observed; firstly the moderate CF contents (75, 65 and 55 vol.%) proved to be the most effective in manifold increase in mechanical strength of PEI and secondly, the composites with fabric in the direction normal to sliding plane led to very high coefficient of friction (μ). When fabric was parallel to the sliding plane, significant improvement in the tribo-properties of PEI in terms of very high tribo-utility (up to 600 N), appreciably low μ and enhanced wear resistance (W_R) (in the range of 10⁻¹⁶ m³/N m) was achieved. The extent of improvement, however, strongly depended on the operating parameters and fabric content. A fairly good correlation was obtained between W_R and combination of mechanical properties such as ultimate tensile strength (S), and interlaminar shear strength (ILSS). Wear mechanism studies by SEM supported the observed wear performance of composites.     

Some aspects of solid particle erosion of cermets

The erosive wear resistance of cermets with different composition, structure and properties has been investigated. It was shown that the erosive wear resistance of cermets can not be estimated only by hardness, characterizing resistance to penetration. The differences in wear resistance between cermet materials with equal hardness levels can be attributed to differences in their resistance to fracture and fracture toughness. The mechanism of erosion depends first on testing conditions. The present paper discusses some features of the material removal process during particle-wall collision. Systematic studies of the influence of the impact variables on the collision process have been carried out.     

Solid particle erosion of unidirectional fibre reinforced thermoplastic composites

In the present study, the solid particle erosion behaviour of neat PEEK matrix and unidirectional glass fibre (GF) and carbon fibre (CF) reinforced polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) composites has been studied. The erosion experiments have been carried out by using silica sand particles (200 ± 50 μm) as an erodent. Steady state erosion rates of these composites have been evaluated at different impact angles and impact velocities. The neat PEEK exhibited peak erosion rate at 30° impingement angle whereas the composites exhibited a semi-ductile behaviour with peak erosion rate at 60° impact angle. The erosion rate of the glass fibre reinforced composites was higher than that of the carbon fibre reinforced composites. The results show that the fibre orientation has a significant influence on erosion rate only at lower impact angles. The erosion rate of the composites was higher when the particles impact perpendicular to the fibre direction than parallel to the fibres. The morphology of eroded surfaces was observed under scanning electron microscope and damage mechanisms were discussed.     

Correlation between solid particle erosion of cermets and particle impact dynamics

Since the erosion rate depends on energy exchange between particle and material, a reformulation and solution of the equations of two solid bodies collision is presented and adapted to the calculation of the energy absorbed by a material surface during impact of a spherical particle onto a plain target. It has been observed that energy loss is a strong function of dynamic coefficients named as coefficient of velocity restitution after impact, k, and coefficient of dynamic friction, f. The new method and experimental equipment for the coefficients determination are described. It was shown that energy consumption during application may be an appropriate guide for the material selection in the conditions of erosive wear.     

The role of adiabatic shear in solid particle erosion

A comparison is made of the deformation produced when titanium and mild steel target specimens are impacted obliquely by flat-ended cylindrical projectiles. The impact process is studied by high speed photography; it is shown that whereas in mild steel material is not removed from the surface but merely displaced, in titanium, the displaced material detaches by a process involving the formation of adiabatic shear bands. Attention is drawn to the influence of susceptibility to adiabatic shear on resistance to solid particle erosion.     

Occurrence of melting during the solid particle erosion of copper

Copper single crystals were eroded by glass particles at a velocity of 133 m s^?1 and an incidence angle of 30°. After erosion, surfaces and debris were examined by electron microscopy. Clear evidence was obtained for localized melting of the surface layers; this is associated with embedded fragments of erodant. The most likely cause of melting appears to be the smearing of a thin layer of copper between the erodant particle and the embedded fragments. Under such conditions the layer may melt if the rate of heating during impact is sufficiently larger than the rate of thermal conduction through the low conductivity embedded and impacting glass erodant. The implication of these results for other studies and the erosion of two-phase microstructures is discussed.     

Particle size distribution effects on the solid particle erosion of brittle materials

The effects of distributions of projectile size and velocity on the erosion of brittle materials were assessed. Strong dependences of the steady state erosion rate on the width of the particle size distribution and on the velocity characteristics of the erosion equipment were predicted. The predictions were confirmed by experiment. The results indicate that careful design of controlled erosion experiments is essential in order to avoid misleading predictions of in-service erosion rates. The implications of the analysis for the interpretation of threshold effects and for experiments designed to verify erosion theories are also discussed.     

Solid particle erosion of CFRP composite with different laminate orientations

The solid particle erosion behavior of epoxy base unidirectional and multidirectional carbon fiber reinforced plastic composites was investigated. The erosion rates of these composites were evaluated at various impingement angles (15–90°) with a particle velocity of 70 m/s. Irregular SiC particles with an average diameter of 80 μm was used. The dependence of impingement angle on the erosive wear resembled the conventional ductile behavior with maximum erosion rate at 15–30° impingement angle. The erosion rate of unidirectional composites at acute impingement angle was higher for [90] than for [45] and [0] while the difference disappeared at normal impingement angle (90°). On the other hand, the erosion rates of multidirectional laminated composites ([0/90], [45/−45], [90/30/−30] and [0/60/−60]) were not much influenced by the fiber orientation except for 15° impingement angle.     

Erosion by solid particle impingement: experimentalresults with cast-iron,laser-treated surfaces

The surfaces of cast-iron specimens have been modified byCO₂ laser processing in order to enhance theirhardness, providing different surfaces for wear behaviourstudies. Various laser heat treatments were performed in order to generate distinct microstructures. Based on previous tests,interaction time and power density used were 0.5 s and 0.4kW/mm², respectively. Alloying with pure Cr allowedmicrostructure and the chemical composition of the material tobe modified in order to attain the desired properties. Chromium--iron carbides, (Cr,Fe)₇C₃, formed ``in situ', during laser surface melting, by reaction with carbon ofthe cast iron, change the wear properties. These carbides weredetected by conventional X-ray diffraction. The expected effectof a carbide-rich structure on the erosion behaviour is todecrease the mass loss by erosion mechanisms. Erosion was done by SiC erosive blast impingement tests. In this method the SiCparticles were accelerated in a compressed air stream along anozzle and projected against the surface to be eroded. After thelaser treatment, the erosion behaviour of material was evaluatedby measuring the weight loss. The wear test was complemented bySEM microstructural observations. Experiments performed in this work show that, in erosion, the mass loss of material does notdepend on hardness as proposed by the accepted tribologicaltheories. The worst behaviour was observed for laser-treatedsurfaces. Embedding of erodent particles plays a decisive rolein blast erosion performance of the surfaces studied.     

Measurement of erosion due to particle impingement and numerical prediction of wear in pump casing

Erosion damage of wear-resistant materials due to sand particle impingement is measured and correlated based on Bitter's erosion model to clarify the effects of particle impinging velocity and angle, particle size and concentration on the wear. Using the empirical formula for the correlation and calculating impinging velocities of sand particles on a casing wall of a pump, successive erosion of the wall is numerically calculated to demonstrate the viability of the prediction method proposed in our previous study.