Effect of particle velocity, temperature and impingent angle on the erosive wear behavior of polymer matrix composites.
When solid particles impinges against a target surface and causes local damage combined with material removal, this kind of wear is generally referred to as erosion . Polymer composite materials have generated wide interest in various engineering fields, particularly in aerospace applications because they exhibit high specific strength and stiffness as compared to monolithic metal alloys. Polymer composite materials are therefore finding increased applications under conditions in which they may be subjected to solid particle erosion. Examples of such applications are pipe line carrying sand slurries in petroleum refining, helicopter rotor blades pump impeller blades, high speed vehicles and aircraft operating in desert environments, water turbines, and aircraft engine blades [2, 3, 4]. However, polymer composite materials exhibit poor erosion resistance as compared to metallic materials. It is also known that the erosive wear of polymer composites is usually higher than that of the unreinforced polymer matrix . Solid particle erosion of polymers and their composites have not been investigated to the extent that it has for metals or ceramics. Many researchers have evaluated the resistance of various types of polymers and their composites to solid particle erosion. Materials that have been studied include nylon, epoxy, polypropylene, polyethylene, UHMWPE, PEEK and various polymer based composites. Theoretically it is assumed that erosion damage can be expressed on two factors, one for repeated deformation and one for the cutting action, defined by a trigonometric function as - E=k [(Asin[alpha]).sup.n1] [(B-Csin[alpha]).sup.n2], where E is erosion rate expressed in units of [mm.sup.3] /kg, [alpha] is impact angle and k.A,B,C.n1 and n2 are constants and exponents which are affected by impact conditions. Theoretical analysis for predicting erosion damage caused by solid particle impact was introduced by Finnie and Bitter, equations for the two processes is the gradual removal of material caused by repeated deformation were derived as a function of mass, impact velocity, impact angle and mechanical and physical properties of the particles and materials.
Efficiency can be used for identifying the brittle and ductile erosion response of various materials to solid particle erosion. The erosion efficiency can be obtained from the following equation -
[eta] = 2EH/[[rho]v.sup.2]
Where E is the steady-state erosion rate, H the hardness, [rho] is the density of the target material and v is the impact velocity. Ideal micro-ploughing involving just displacement of material from the crater without any fracture (and hence no erosion) has zero erosion efficiency. Alternatively, incase of ideal micro-cutting, erosion efficiency is unity.
When erosion occurs by the formation of a lip and its subsequent fracture, the erosion efficiency is in the range 0-1. In contrast, as happens with brittle material, if the erosion takes place by material spalling and removal of large chunks (e.g. by interlinking of lateral or radial cracks) then the efficiency may be even greater than 100%. Ductile behavior is characterised by maximum erosion rate and generally occurs at 15-30[degrees]. Brittle behavior is characterized by maximum erosion rate at 90[degrees]. Semi-ductile behavior is characterized by the maximum erosion rate at 45-60[degrees]. The influence of impingement angle on steady-state erosion rate of epoxy and its composites were studied. It was observed that maximum erosion occurs at 60[degrees] impingement angle for all the materials tested. Hence the erosion behavior is semiductile. [6-7].
Erosive wear performance most probably depends on following parameters:Operating parameters-
* Angle of impingement, Impinging velocity, Particle flux (mass per unit time)
* Single/multiple impact direction of impingement with respect to the fiber direction in the case of composites Erodent.
* Abrasivity, Size, Shape, Nature of erodent, Hardness Polymer and composite target.
* Molecular structure, Mechanical properties, Morphology, Type and amount of reinforcement
* Fiber matrix adhesion Environment -
* Temperature, Dry/wet lubricated condition.
* Chemical interaction of erodent with the target.
The solid particle erosion behavior of various polyetheretherketones (PEEKs) and their short fiber reinforced composites has been characterized. The erosion rates (ERs) of these composites have been evaluated at different impingement angles and impact velocities. Silica sand particles of size ranging between 150 and 212 [micro]m were used as erodent. Neat polyetheretherketone (PEEK) and 20% glass fiber (GF) reinforced PEEK showed peak erosion at 30[degrees] impingement angle whereas other PEEK matrix and their composites showed peak erosion at 60[degrees] impingement angle 
The erosive wear behavior of ultrahigh molecular weight polyethylene (UHMWPE) was tested by air-borne particle erosion equipment. The effects of impact angle, velocity and the particle hardness and the erosive wear of UHMWPE were determined. When the hard particles (silicon dioxide) act as the impingement particles, the erosion mechanisms of UHMWPE are micro cutting and microploughing at lower angles, while the mechanism is plastic deformation at higher angles. When the soft particles (coal powder) impact at higher angles, the mechanism is mainly micro cracking. [9 -10].Abrasion tests of polymers using slurries have also been conducted by Lowe and Marshall who concluded that the anti-erosion properties of polyethylene were superior to that of mild steel by 10%, and the erosion properties of all materials tested were correlated with several mechanical properties of the materials. Some papers have appeared in which the correlation between erosion damage and the impact conditions have been discussed for various polymeric material.
Walley, Field and Wang studied the erosion behavior of polyethylene at high impact velocities, showing that the maximum erosion when angle was low. Erosive wear resistance has been evaluated for neat epoxy, unidirectional glass and carbon fiber reinforced epoxy composites and bi-directional E-glass fabric reinforced epoxy composite at normal incidence .Bi-directional glass fiber reinforced epoxy composite showed better erosive wear resistance than unidirectional fiber reinforced composites The fiber content had a strong influence on the erosion rate of PEI composites. The erosion rate was higher in fiber reinforced composites than in neat matrix, whereas 20% glass fiber reinforcement to the PEI matrix has shown better wear resistance as compared to the other composites and also wear performance is on par with neat PEI matrix. Carbon fiber reinforcement to the PEI matrix does not result in better wear resistance; however it showed better wear resistance as compared to the composites. Fillers such as PTFE, graphite, MoS2 observed to be detrimental to erosive wear performance . Impingement angle of the particles is one of the important parameter that strictly affects the erosive wear characteristics of the material. The material wear mechanisms are in close relationship with the impingement angles. The morphologies of eroded surfaces observed by SEM suggest that the overall erosion damage of composites consists of matrix removal and exposure of fibers, fiber cracking and removal of broken fibers. . The erosion resistances of the composites first rises, until reaching a maximum, then declined, with content of the [Al.sub.2][O.sub.3] particles. R.Zhou have shown that the wear resistance of two composites first increased until reaching a maximum then decreased, with the increasing content of [Al.sub.2][O.sub.3] particles. The composite treated with sealan coupling agent A-1100 had higher wear resistance than those treated with sealan coupling agentA-187 due to the higher reaction activity of A-1100 with the matrix than A-187 .
Literature on solid particle erosion of PMCs reveals that the influence of impact velocity is quite significant on erosion rate. Undoubtedly, the fact is true but under the influence of other process parameters, impact velocity becomes comparatively less important. . The influence of impingement angle on erosive wear of both composites exhibited semi-ductile erosive wear behavior with a maximum wear at a 60[degrees] impingement angle. SEM studies revealed that erosion is characterized by a multiple matrix micro cracking and fiber matrix debonding . Slurry erosion tests of various materials have previously been carried out by Hocke and Wilkinson who showed that the damage to polyethylene was nearly half of that of mild steel at a flow velocity of 3.7 m/s and a particle concentration of 25%. The damage was, however, over twice of that of mild steel at a particle concentration of 40% . Fluid machinery including water turbines and pumps, used in the Yellow River regions experience serious slurry wear due to sandy river water. Such slurry wear leads to degradation of machinery performance and shortened service life .Factors that affect such slurry wear are flow velocity, impingement angle of the particles, and the concentration and diameter of slurry particles. The effect of the impingement angle has been studied by many researchers. Finnie et al. has reported that mass loss was maximized when the angle was approximately 200 for ductile and 90[degrees] for brittle materials. .
Materials and Experimental Methods
Sample materials used are POM, PTFE and its composites. Three impingent angle (30,60,90[degrees]) and three velocities used are (45 60, 75 m/s).All the above materials are got manufactured /purchased from Perfect Packaging Pvt. Ltd,Pune.
Tests are done for the seven materials and their mechanical properties are as follows.
Erosive wear tests were done under small range of velocity and impingent angle at constant rate of [Al.sub.2][O.sub.3] particle as erodent. All the tests are done under relative humidity RH=60-65%, and ambient temperature condition of 32-33[degrees]C and also one test is carried out at high temp i.e. at 100[degrees]C .All the tests are carried out according to ASTM G76 on Air Jet Erosion tester at Ducom Instruments Pvt. Ltd.,Bangalore.
[FIGURE 2.1 OMITTED]
The angle of the specimen mount was adjustable to certain degrees, so that the impingement angle against the specimen could be changed in a range from 30[degrees] to 90[degrees].. Mass loss of the specimen was measured with a precision balance (accuracy: 0.001 g) after cleaning the test specimen with acetone in an ultrasonic cleaner and drying the specimen every specified test time.
[FIGURE 2.2 OMITTED]
The [Al.sub.2][O.sub.3] particles are passed through a ceramic converging nozzle of 1.5 mm diameter. These accelerated particles impact the specimen, which can be held at various angles with respect to the impacting particles using an adjustable sample holder. The feed rate of the particles can be controlled by monitoring the distance between the particle feeding hopper and belt drive carrying the particles to the mixing chamber. The impact velocity of the particles can be varied by varying the pressure of the compressed air. The velocity of the eroding particles is determined using rotating disc method. Square samples of size 25mmx25mmx3mm are cut from the plate for erosion tests. The conditions under which erosion tests have been carried out are listed in Table 03. A standard test procedure has been employed for each erosion test. The samples have been cleaned and weighed to an accuracy of .001g using an electronic balance, eroded in the test rig for 10 min and then weighed again to determine weight loss. The ratio of this weight loss to the weight of the eroding particles causing the loss (i.e. testing time, particle feed rate) is then computed as the dimensionless incremental erosion rate. This procedure is repeated till the erosion rate attains a constant steady-state value.
Result and Discussion
Part I: - Erosive wear as a function of impingent angle, impingent velocity.
[FIGURE 4.1 OMITTED]
Figure no. 4.1 shows erosive wear of pure PTFE at different velocity and impingent angles. It shows that as angle is constant and velocity increases from 45 m/s to 75m/s the mass loss of the material increases, there is rapid increase in the mass loss with velocity. This may be due to the direct striking of the erodent particles on the specimens .Graphs shows that as angle increases the mass loss decreases .the erosive wear at 60 degree and at 75m/s velocity it is .008g and at 30 degree it is .0 37 g. fig no.4.1 shows the mass loss at 90[degrees] angle of impact. But here it shows that the mass loss decreases as velocity increases at 75m/s velocity, loss of mass in ten minutes is just .001g.
[FIGURE 4.2 OMITTED]
Figure 4.2 shows the mass loss of PTFE +15% glass fiber composite. In fig. 4.4 mass loss increases with increase in velocity, but mass loss is more at 30[degrees] as compared to 60[degrees] and 90[degrees] . At 90 degree wear loss is very small and is almost constant at 60 m/s and 75 m/s. This may be because the [Al.sub.2][O.sub.3] particles cause the shearing of the material at 30[degrees] and deformation of the composite material takes place at 90[degrees] without loosing the material.
[FIGURE 4.3 OMITTED]
Figure 4.3 shows the mass (Erosive wear loss) of material PTFE with 25% glass fiber content. The graph shows that mass loss increases with increase in velocity .But with increase in angle mass loss at the same velocity decreases at 90[degrees] and at 75m/s velocity. There is very small increase in the erosive wear loss from 45m/s to 75m/s at an oblique angle.
[FIGURE 4.4 OMITTED]
Figure 4.4 shows the graphs of mass loss with respect to velocity at various angles for PTFE with 35% glass fiber content. At 30[degrees] with increase in velocity wear increases and is almost proportional. At 60[degrees] with increase in velocity up to 60m/s wear increases and after that it decreases as the graph shows some bent .In between 60-75m/s at 90[degrees] wear loss decreases. From above graph it is found that at 75 m/s and at 30[degrees], 60[degrees], and 90[degrees] mass loss decreases from.046 g to .009g and .004g respectively.
[FIGURE 4.5 OMITTED]
Figure. 4.5 shows the mass loss of PTFE and 40% Bronze composite. At 30[degrees] with increase in velocity wear increases its value is .032g. At 60[degrees] it shows the same trend, where as at 90[degrees] with increase in velocity from 45m/s to 75m/s there is very small change in the wear loss.
[FIGURE 4.6 OMITTED]
Figure 4.6 shows the mass loss of PTFE and 60% Bronze composite. At 30[degrees] with increase in velocity wear increases its value is .036g. At 60[degrees] up to 60m/s it is almost constant and there is increase at 75m/s, where as at 90[degrees] with increase in velocity from 45m/s to 75m/s there is very small change in the mass loss.
[FIGURE 4.7 OMITTED]
Figure 4.7 shows erosive wear of pure POM (Polyoxymethelene) at different velocity and impingent angle. It shows that as angle is constant and velocity increases from 45 m/s to 75m/s the mass loss of the material increases, there is rapid increase in the mass loss with velocity at 30[degrees] angle of impingent .This may be due to the direct striking of the erodent particles on the specimens .Graphs shows that as angle increases the mass loss decreases .the erosive wear at 60 degree and at 75m/s velocity it is .009g and at 30 degree it is .0 041 g. Graphs also shows that at higher value of angle and with increase in velocity from 45m/s to 75 m/s the mass loss due to erosive wear is not that much determinant .
Part II: - Erosive wear as a function of impingent angle, impingent velocity, at temp. 100[degrees]C
[FIGURE 4.8 OMITTED]
Figure no 4. 8 shows erosive wear at high temperature i.e. at 100[degrees]C all the tests are carried out at constant angle of impact and at constant velocity of 60[degrees] and 60 m/s respectively. For pure PTFE it is .0049g but as % of glass fiber content increases the wear increases this may be because of the removal of glass fiber from the matrix material. But at high temperature i e.100[degrees]C with increase in % of glass content the wear decreases. Same thing has been found for bronze fiber content also. For 40% bronze content it is found.015g and for 60% bronze content it decreases and becomes.010g. The wear rate was predicted to increase with increasing temperature for a constant particle velocity and impingement angle as compared to wear of the materials at high temperature.
Part III: - Analysis of photo graphs of some Eroded specimens-Angle of impengent60[degrees] and Velocity - 60 m/s
[FIGURE 4.9 OMITTED]
All these above photographs are taken by using high resolution camera, which is commercially available. Figure no.4.9 shows the wear scar of various polymers and composites. By observing it is found that dia. of wear scar for the pure polymer is little more as compared to the wear scar of the composites, this shows that as the % of glass content increases the wear rate also increases. So it may be concluded that the material is semi -ductile in nature. Fig.4.21also shows the surface profiles of the specimens after the tests. All materials tested at an impingement angle of 60[degrees] and 60m/s velocity showed Circular-shaped (Wear scar) profiles. The pattern is the characteristics of wear caused by erodent. This is due to creation of a stagnation point near the jet center on the specimen surface. The deepest wear point of the circular profile was found approximately at the center. Some area away from the center showed little sign of damage and the damaged area is rough. The damage at higher impact velocity is more severe, because of excessive wear, and the fibers seems to be washed away from the surface.
[FIGURE 4.10 OMITTED]
Figure no.4.10 shows the Effect of hardness on the steady state erosive wear rate of polymer and polymer composites .Above figure shows the plot for constant impingent angle ( 30[degrees] ) and at various impingent velocity. It is observed that steady sate wear rate is almost constant up to D 64 Shore. Further there is increase and decrease.
But with respect to increase in impact velocity the steady state erosive rate increases irrespective of the material hardness.
After carrying out experimental erosive wear test on PTFE, POM and composites of PTFE with glass fiber and bronze fibers content, we have come to the following conclusions --
1) Erosive wear loss for pure PTFE and POM is approximately proportional to velocity at 30[degrees] angle of impact.
2) Erosive wear increases with increase in velocity at constant angle of 30[degrees] . It is also found that for all the polymer and polymer composite tested, erosive wear decreases with increase in velocity and also with increase in angle of impact.
3) At an angle of 90[degrees] with velocity range of 45m/ s to 75m/s there is not that much variation in the material loss for all composite tested.
4) For the PTFE composites with glass fiber content the mass loss due to erosive wear is more as compared to pure polymers.
5) In all experimental testing it shows that erosive wear of polymer composite material strongly depends upon the velocity and impingement angle.
6) One test for all polymer and PTFE composite s is carried out at higher temperature (100[degrees]C ) and at constant velocity and impingent angle of 60[degrees]and 60m/s.This test shows that at higher temperature for pure PTFE and POM wear is less and at the same time for the composite of PTFE wear is more.
7) From all the observations made and after making the analysis we have come to the conclusion that for pure polymer the erosive wear is less and increases with increase in velocity. Where as with the addition of fibers total wear of the composites for the prescribed time increases for the same velocity, angle of impact and temperature.
8) Also it is found that for the same velocity and impingent angle for all the materials tested at room temperature and at higher temperature of 100[degrees]C the erosive wear is more at higher temperature.
9) When [Al.sub.2][O.sub.3] particles are bombarded at higher velocity damages the surface of polymers significantly and resulted in excessive wear.
10) The extent of increase in wear however depends upon the materials, angle of impingent and velocity of impact.
11) The influence of impact velocity on erosion wear is more significant at an oblique angle of 30[degrees] than at normal impact angle.
12) On the other hand, chipping off of material by micro cutting and severe plastic deformation were observed prominent at the oblique angle of impact.
13) Steady state erosion rate is a function of hardness of the material. The steady-state erosion rate of polymer PTFE and its composites increased with increase in impact velocity from 45 to 75 m/s.
The authors would like to thank Dr. Madumurthy, HOD, Deptt. Of Mech. Engg., NIT, Warangal, for his valuable advice during the work and also Dr. Dhirendra, Principal Pravara Rural Engineering College, Loni. for his support in carrying out the experimental work .Also authors would like to thank Ducom Instruments Pvt.Ltd., Bangalore for providing the experimental facilities, DSC committee members for their guidelines and suggestions during this work.
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(1) Y. R. Kharde and 2K.V.Saisrinadh
(1) PhD. Scholar, Department of Mechanical Engineering, National Institute of Technology, Warangal (A.P.) E-mail: firstname.lastname@example.org
(2) Asst .Professor, Department of Mechanical Engineering, National Institute of Technology, Warangal (A.P.) E-mail: email@example.com
Table 2.1: Mechanical properties of materials Sr.no. Material Material Density Shore Tensile Designation (gm/cc) Hardness strength Mpa 1 A PTFE 1.86 57 25.01 2 B PTFE+ 15% 2.13 59 15.15 GF 3 C PTFE+ 25% 2.18 61 12.90 GF 4 D PTFE+ 35% 2.52 64 6.74 GF 5 E PTFE+ 40% 3..580 67 16.0 Bronze 6 F PTFE+ 60% 4.194 69 11.63 Bronze 7 G POM 1.4611 64 9.47 Table No. 2.2: Parameters used for experimental Investigation of materials. 1 Impingent angle ([[theta[.sup.0] 30 60 90 2 Impingent velocity (m/s) 45 60 75 3 Duration (Minute) 10 10 10
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|Author:||Kharde, Y.R.; Saisrinadh, K.V.|
|Publication:||International Journal of Applied Engineering Research|
|Date:||Dec 1, 2008|
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