Elsevier

Wear

Volume 260, Issues 4–5, 24 February 2006, Pages 401-411
Wear

Influence of orientation and volume fraction of Aramid fabric on abrasive wear performance of polyethersulfone composites

https://doi.org/10.1016/j.wear.2005.02.087Get rights and content

Abstract

In case of fabric reinforced composites of specialty polymers influence of orientation of fabric and its volume fraction on tribo-behaviour is sparingly studied. In our earlier work, we have reported on the influence of amount of Aramid fabric (AF) in polyethersulfone (PES) on abrasive wear performance. However, orientation effect of fabric with respect to abrading plane was not investigated. In this work three orientations of composites of PES containing Aramid (Kevlar 29) fabric with three concentrations 64, 72 and 83 wt.% were selected to study the influence on abrasive wear performance. Composites developed by compression molding technique were characterized for their mechanical and physical properties. The abrasive wear performance of the composites was evaluated by abrading 10 mm × 10 mm × 10 mm sample against silicon carbide (SiC) paper under various loads and two grades of abrasive papers. The fabric reinforcement enhanced the abrasive wear resistance of PES significantly (approximately 1.35–9.46 times depending on the operating conditions). It was observed that 83% fabric composite showed the highest resistance to abrasive wear and impact along with the best tensile strength and elongation properties. Its flexural strength and ILSS values, however, were the lowest. Sixty-four percent fabric composite, on the other hand, showed an exactly reverse trend among the three composites. Among the three orientations, fibres in normal and parallel (N–P) and normal and anti-parallel (N–AP) direction with respect to sliding plane proved to impart maximum wear resistance. N–P was best for light loads while N–AP was best for high loading conditions. Orientation parallel and anti-parallel (P–AP) was least beneficial in this respect. Moreover, the extent of improvement very much depended on the operating parameters such as grit size and load. Benefits endowed due to reinforcement were higher at less coarse grade paper. With increase in load, however, wear rate of composites with N–P orientation increased and for other two orientations it decreased. Thus, for severe operating conditions, N–AP orientation proved to be most beneficial. SEM studies proved supporting for understanding the influence of orientation on wear performance.

Introduction

Fiber reinforced polymers (FRP) are extensively used in the sliding wear applications (bearings, slides, gears, seals, etc.) where resistance to adhesive and abrasive wear is one of the most important selection criteria. However, enhancement in abrasive wear resistance is very difficult to achieve. Literature indicates that particulate fillers such as PTFE, graphite, etc. and short fibers of glass and carbon enhance adhesive wear performance, but are detrimental for abrasive wear situations [1]. Rarely some marginal improvement due to short GF has been recorded [2]. Long fibers of carbon have been reported to enhance the abrasive wear resistance of PEEK marginally [3]. Fabric reinforcement appears to be the most promising in this respect though very few papers are available on this aspect [4], [5], [6]. Friedrich [4] studied the abrasive wear behavior of epoxy reinforced with fabrics of carbon (CF), glass (GF) and Aramid (AF) and reported the potential of fabrics in the order AF > GF > CF. Almost 2.5 times improvement in wear resistance of epoxy was recorded due to inclusion of AF. In the recent work by Bijwe et al. [5] on several composites of polyetherimide (PEI) with fabrics of glass (with weave variation), carbon and Aramid, it was reported that the potential of fabric for improving the wear resistance depended on the type of fabric, its weave and its two selected orientations with respect to abrading direction. Overall, AF proved to be significantly superior to other fabrics and reduced the wear rate of PEI by 6–7 times. CF did not help much and GF proved to be the least helpful and sometimes detrimental in this respect. However, in both papers, no efforts were put to investigate the influence of amount of fabric in the composite on the mechanical properties and abrasive wear resistance. This aspect was studied in the further work by the group on AF–PES composites [6]. Influence of fabric orientations, however, was not be highlighted in this paper. Hence, in this work three composites of polyethersulfone (PES) with varying amount of Aramid fabric were formulated, characterized and tribo-evaluated under varying operating conditions such as five loads, three orientations of fabric and two selected grades of abrasive papers.

Section snippets

Fabrication of the composites

Polyethersulfone was selected as a matrix for preparing the composites and was supplied in granular form, under the trade name Gafone (properties in Table 1) by Gharda Chemicals Ltd., India. Aramid fabric (Kelvar 29) was selected as a reinforcement. The thickness of each fabric was around 0.6 mm and 22 plies were used to get the composites of 7 mm thickness. The composites were prepared by hand lay-up process. The plies (300 mm × 300 mm) were cut from the fabric and dipped in the viscous solution of

Results and discussion

The histogram in Fig. 2 highlights the influence of fabric inclusion on various mechanical properties. The specific wear rates of composites as a function of load for two grades of abrasive papers are shown in Fig. 3. Wear rate of PES is also included in Fig. 3b. Histogram in Fig. 4 shows the specific wear rates of composites abraded against 80 grade paper as a function of load, amount and orientation of fabric while histogram in Fig. 5 is for 120 grade paper. Table 2 comprises the data

SEM studies on worn surfaces

Fig. 6 shows SEM of an Aramid fibre cut from the edge of the fabric along with a fibril generated during cutting. The approximate diameter of the fibre is 14 μm. Further SEM studies were carried out on the surfaces of A3 worn under 14 N load and are collected in Fig. 7, Fig. 8, Fig. 9 while that of SiC paper worn against A3 under 14 N load are shown in Fig. 10. SEM studies on PES surfaces are discussed in our earlier paper [6].

Micrographs (a–e) in Fig. 7 are for surfaces of A3 composite in N–P

Conclusions

It was concluded from these studies that inclusion of fabric in PES matrix in different amount affected all the properties very significantly, but not proportionately. Tensile strength, elongation to break, impact strength and resistance to abrasion were highest for 83% fabric composite. Its ILSS and hardness values, however, were the lowest. Sixty-three percent fabric inclusion led to highest tensile and flexural modulus but lowest wear resistance among AF composites. Seventy-two percent

Acknowledgement

We gratefully acknowledge Dr. P. D. Trivedi and Mr. Tushar Parida from Gharda Chemicals for supplying the PES material for these studies.

References (7)

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