Abrasive wear behaviour of polymeric materials

Materials & Design Materials and Design 26 (2005) 705–710 www.elsevier.com/locate/matdes

Short Communication

Abrasive wear behaviour of polymeric materials H. Unal a, U. Sen a, A. Mimaroglu a

b,*

Faculty of Technical Education, University of Sakarya, Esentepe Kampusu, Adapazari, Turkey b Faculty of Engineering, University of Sakarya, Esentepe Kampusu, Adapazari, Turkey Received 25 February 2004; accepted 3 September 2004

Abstract In this study the abrasive wear behaviour of aliphatic polyketone (APK), polyoxymethylene (POM), ultrahigh molecular weight polyethylene (UHMWPE), polyamide 66 (PA66), and 30% glass fibre reinforced polyphenylenesulfide (PPS + 30%GFR) engineering polymers at room temperature were studied. Pin-on disc arrangement wear tests were carried out at 1 m/s test speed and load value of 10 N. Tests were carried out for 50, 100, 150 and 200 m sliding distances. Emery paper grid varying from 150 to 1200 grade were used as an abrasive disc surface. After each test the mass loss of the pin was recorded. Finally the specific wear rates were deduced from wear volume of the pin for test duration distances of 50, 100, 150 and 200 m. The results showed that the highest wear rate is for POM with a value of 8.5 · 10 4 mm3/N m and the lowest wear rate is for UHMWPE with a value of 3.36 · 10 5 mm3/N m. Furthermore, for all materials the wear rate increases linearly with increasing wear duration distance.
2004 Elsevier Ltd. All rights reserved. Keywords: Wear; Abrasive; Polymers; Thermoplastics

1. Introduction In design there are two main characteristics which make polymer and reinforced polymer attractive compared to conventional metallic materials. These are relatively low density value and reliable tailoring capability to provide the required strength and stiffness. One of the main important characteristics of materials are wear and friction. Wear is defined [1] as the damage to a solid surface, generally involving progressive loss of material, due to relative motion between that surface and contacting substance or substances. The five types of wear are abrasive, adhesive, erosion, fatigue and fretting. Abrasive wear has a contribution of at least 60% of the total cost due to wear [2]. Abrasive wear is caused by hard particles that are forced and moving along a solid surface [3]. In *

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2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2004.09.004

past many works were carried out for abrasive wear mechanism for polymers in general and polymer composite in particular [4–11]. In fact the abrasion involves the tearing away of small pieces of materials, therefore the tensile strength, fatigue life and hardness are important factors in determining the wear characteristics of a polymer [12]. Having said that there is a need to understand the basic phenomenon of two- and three-body abrasion [13–17] and the movement pattern of the dry and loose abrasive particles [18]. The abrasive wear of polymers is the interest and the subject of quite number of literature. In most cases the main test methods of abrasive wear are two- and three-body abrasion. Most test programmes have used two body abrasion tests. In a review of some of the literature concerning abrasive wear of polymers, Evans et al. [19] tested about 18 number of polymers, low density polyethylene exhibited the lowest wear rate in abrasion against a rough mild steel but the highest wear rate in abrasion with coarse corundum paper. Shipway and Ngao [20] investigated the abrasive behaviour of

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polymeric materials in micro-scale level. They concluded that the wear behaviour and rates of polymers depended critically on the polymer type. Furthermore, the wear was associated with indentation type morphology in the wear scar and low values of tensile strain to failure. Harsha and Rewari [13] investigated the abrasive wear behaviour of (polyaryletherketone PAEK) and its composites against SiC abrasive paper. They concluded that the sliding distance, load, abrasive grit size have a significant influence on abrasive wear performance. Liu et al. [21] investigated the abrasive wear behaviour of ultrahigh molecular weight polyethylene (UHMWPE) polymer. They concluded that the applied load is the main parameter and the wear resistance improvement of filler reinforced UHMWPE was attributed to the combination of hard particles which prevent the formation of deep, wide and continuous furrows. Bijwe et al. [22,23] tested polyamide 6, polytetrafluoroethylene (PTFE) and their various composites in abrasive wear under dry and multi-pass conditions against silicon carbide (SiC) paper on pin-on-disc arrangement. They concluded that the polymers without fillers had better abrasive wear resistance than their composites. Hironaka et al. [24–26] studied the behaviour of polyamide 66. They concluded that the water absorbtion and thermal properties affected the morphology of polyamides, which in turn affected the tribological properties of polyamides. Furthermore, the specific wear rates showed fairly good correlation with various mechanical properties such as ductility, fracture surface energy, tensile modulus and the time to failure under tensile stress.

Apart from experimental studies several number of models which attempt to relate the abrasive wear resistance of polymers to some mechanical properties of the material such as hardness and tensile strength have also been proposed. Budinski [27], Larsen-Basse [28] and Rajesh et al. [26] examined five of such models. Budinski indicated that the correlations proposed by all models between the abrasive wear behaviour and other mechanical properties of 21 polymeric materials was poor. Larsen-Basse [28] argued that the mechanisms of wear differed depending upon the polymer type. Briscoe [29] in his review paper concluded that the models suppose a certain mechanism of material removal to prevail, and that changes in mechanism will tend to make the model predictions invalid. Budinski [27] notes that most of the studies on the abrasion resistance of plastics are inconclusive and tend to recommend further study. Thus, it can be seen that abrasive wear behaviour of polymeric material is complex and it is widely recognised that the processes of wear in polymers are not well understood [29]. In this work, an attempt has been made to understand and to obtain the wear behaviour of aliphatic polyketone (APK), polyoxymethylene (POM), ultrahigh molecular weight polyethylene (UHMWPE), polyamide 66 (PA66), and 30% glass fibre reinforced polyphenylenesulfide (PPS + 30%GFR) polymers under various external variables such as, external load of 10 N, sliding speed of 1 m/s, different discs with abrasive papers 150, 360, 800 and 1200 grit size and sliding distances of 50, 100, 150 and 200 m.

Fig. 1. Schematic illustration of the wear test apparatus.

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2. Experimental

140

Figs. 2–5 presents the loss in volume of the pin with sliding distance using emery paper with grit of 150, 360, 800 and 1200 grade, respectively. It is clear from these figures that for all polymers used in this study there is a linear loss in pin volume with sliding distance. This is an evident for a steady-state wear with a constant rate. For each polymer the loss in pin volume is higher at lower rank grit. The highest loss in volume is for POM and the lowest is for UHMWPE polymer. Apart from APK and PPS + 30%GFR all materials have kept their sequence in the figures. APK and PPS have swapped positions at 360 and 800 grit usage. In these figures for APK, POM, UHMWPE, PA66 and PPS + 30%GFR there is an average increase of 44%, 59%, 53%, 85% and 56% in pin volume loss for an

Wear volume, mm 3x10-3

1000 APK POM UHMWPE PA 66 PPS+30%GFR

800 700

Wear volume, mm 3x10-3

100 80 60 40 20 0 0

50

100

150

200

250

Sliding distance, m Fig. 3. Variation of wear volume with sliding distance using 360 grit emery paper.

80 APK POM UHMWPE PA 66 PPS+30%GFR

70

Wear volume, mm 3x10 -3

3. Results and discussions

APK POM UHMWPE PA 66 PPS+30%GFR

120

60 50 40 30 20 10 0 0

50

100

150

200

250

Sliding distance, m

Fig. 4. Variation of wear volume with sliding distance using 800 grit emery paper.

60

Wear volume, mm 3x10-3

In this study, pin samples from APK, POM, UHMWPE, PA66 and 30% glass fibre reinforced polyphenylenesulfide (PPS + 30%GFR) polymers were prepared in 6 mm diameter and 50 mm length. Wear test were carried out on in-house designed pin-on-disc arrangement test apparatus see, Fig. 1. To apply different abrasive conditions during each test, emery paper with grit grade of 150, 360, 800 and 1200 were fixed on the rotating disc surface and the pin is fixed in a holder. Before each test, each sample was cleaned by alcohol and dried in air. For each material the dry wear test was carried out for a sliding distances of 50, 100, 150 and 200 m and under load value of 10 N and at sliding speed of 1 m/s. After each test the loss in pin mass were recorded. The wear volume was computed from the mass loss of the pin. Furthermore, the microstructures of the worn surfaces were examined by using optical microscope.

900

707

APK POM UHMWPE PA 66 PPS+30%GFR

50

40 30 20

10 0

600

0

50

100

150

200

250

Sliding distance, m

500 400

Fig. 5. Variation of wear volume with sliding distance using 1200 grit emery paper.

300 200 100 0 0

50

100

150

200

250

Sliding distance, m Fig. 2. Variation of wear volume with sliding distance using 150 grit emery paper.

300% increase in sliding distance, respectively. Fig. 6 presents (shows a histogram) of comparative abrasive wear performance of APK, POM, UHMWPE, PA66 and PPS + 30%GFR. Again it is clear from Fig. 6 that the highest wear volume is for POM polymer.

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Fig. 6. Comparative abrasive wear volume of APK, POM, UHMWPE, PA66 and PPS + 30%GFR.

Fig. 7. Variation of specific wear rate of APK, POM, UHMWPE, PA66 and PPS + 30%GFR using 150 grit emery paper.

Fig. 7 presents the variation of specific wear rate–sliding distance–grit size for APK, POM, UHMWPE, PA66 and PPS + 30%GFR. At all sliding distances the highest wear rate is for POM with a value of 8.5 · 10 4 mm3/ N m and the lowest value of 3.36 · 10 5 mm3/N m for UHMWPE. For all polymers of this study the specific wear rate drops with the increase in sliding distance. There is a decrease of 97%, 75%, 37%, 39% and 127% in the specific wear rate for an increase of 300% in sliding distance of POM, PPS + 30%GFR, APK, PA66 and

UHMWPE for 150 grit abrasive paper, respectively. In comparison to UHMPE specific wear rate value, the wear rate of POM, PPS + 30GPR, APK and PA66 are 1025%, 300%, 125%, 25% higher rate for 150 grit abrasive paper. The specific wear rate value for UHMWPE varies between 3.36 · 10 5 and 7.54 · 10 5 mm3/N m, for PA66 9.58 · 10 5 and 1.28 · 10 4, for APK 1.26 · 10 4 and 1.71 · 10 4, for PPS + 30%GFR 1.87 · 10 4 and 3.26 · 10 4, and 4.32 · 10 4 and 8.5 · 10 4 for POM polymer. Fig. 7 also shows the

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Fig. 8. Microscopy of worn surfaces of (at 10 N load and 1 m/s, 360 grit abrasive paper): (a) APK, (b) POM, (c) UHMWPE, (d) PA66 and (e) PPS + 30%GFR.

variation of specific wear rate with the abrasive grit grade. Again, in this figure for all grit grades the specific wear rate is ranking as a highest for POM followed by, PPS + 30%GFR, APK, PA66 and UHMWPE. Optical micrographs of the abraded surfaces are shown in Fig. 8. In this, Fig. 8(a)–(e) shows the abrasive wear surfaces for APK, POM, UHMWPE, PA66 and PPS + 30%GFR polymers at 10 N load, 1 m/s sliding speed, 200 m sliding distance and using 360 grit abrasive surface. Fig. 8(a)–(d) shows the surfaces of APK, POM, UHMWPE and PA66 polymers. The deep furrows in the abrading direction due to the ploughing action by sharp abrasive particles are seen on the surface. The ductile APK, POM, UHMWPE and PA66 polymers matrix have a highly plastically deformed surface interspersed with many ploughed furrows parallel to the wear direction. Fig. 8(e) shows the worn surface for polymer composite (PPS + 30%GFR). In this figure the brittle fractures of the material due to the cutting action are apparent and the extend of damage to the matrix and fibre is severe.

4. Conclusions An experimental study of APK, POM, UHMWPE, PA66 and PPS + 30%GFR polymers at 10 N load and different sliding distance reveals the following conclusions:  The wear rate of APK, POM, UHMWPE, PA66 and PPS + 30%GFR decreases with the increase in sliding distance.  The highest wear rate is for POM polymer and the lowest wear rate value is for UHMWPE polymer.  The specific wear rate of UHMWPE, PA66, APK, PPS + 30%GFR and POM are ranging between 3.36 · 10 5 and 7.54 · 10 5 mm3/N m, 9.58 · 10 5 and 1.28 · 10 4, 1.26 · 10 4 and 1.71 · 10 4, 1.87 · 10 4 and 3.26 · 10 4, and 4.32 · 10 4 and 8.5 · 10 4 mm3/N m for 150 grit abrasive paper, respectively. For all polymer used in this investigation the specific wear rate decreases with the increase in grit grade number.

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 Optical studies of worn surfaces indicate cutting, ploughing, cracking wear mechanism under experimental conditions.

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