Abrasive Wear Behaviour of Thermoplastic ... - Springer Link

INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 17, No. 6, pp. 755-763

JUNE 2016 / 755

DOI: 10.1007/s12541-016-0093-x

ISSN 2234-7593 (Print) / ISSN 2005-4602 (Online)

Abrasive Wear Behaviour of Thermoplastic Copolyester Elastomer Composites: A Statistical Approach Hemanth Rajashekaraiah1, Suresha Bheemappa2, Seung-Han Yang3, and Sekar Mohan1,# 1 School of Mechanical Sciences, Karunya University, Karunya Nagar, Coimbatore, Tamil Nadu, 641 114, India 2 Department of Mechanical Engineering, The National Institute of Engineering, Mysore, Karnataka, 570 008, India 3 Department of Mechanical Engineering, Kyungpook National University, 80, Daehak-ro, Buk-gu, Daegu, 41566, South Korea # Corresponding Author / E-mail: [email protected], TEL: +91-422-2614 432, FAX: +91-422-2615 615 KEYWORDS: Thermoplastic copolyester elastomer composites, Response surface method, Central composite design, Abrasion, Scanning electron microscopy

Design of polymer composites for tribological applications is a multi-criteria optimization problem. Two-body abrasive wear (2-BAW) behaviour of thermoplastic copolyester elastomer (TCE) reinforced with and without short glass fiber, filled with various fillers (short carbon fiber, polytetrafluoroethylene, silicon carbide and alumina) in different proportions were influenced by the properties of their constituents. 2-BAW behaviour of multi-phased TCE composites was evaluated using pin-on-disc apparatus. This paper presents an approach to establish the model for predicting the specific wear rate (Ks) of TCE composites. Three-factors and three-levels, facecentered central composite design was used for conducting tests. Response surface methodology was applied to derive the second order quadratic model with the selected parameters. The results indicated that the Ks increases with increase in fiber/filler content and decreases with increase in grit size of silicon carbide (SiC) abrasives and abrading distance. The investigation also revealed that the fiber/filler content is the most influencing factor, followed by grit size of SiC abrasives and abrading distance. The predicted results show close agreement with the experimental. Hence the developed model could be used to predict abrasion behaviour of multi-phased TCE composites satisfactorily. The worn surfaces of TCE composites were analyzed with the help of scanning electron microscope. Manuscript received: September 21, 2015 / Revised: January 6, 2016 / Accepted: February 1, 2016

1. Introduction The usage of fibers and fillers for enhancement of characteristics of neat polymers dates back to the earliest years of the polymer industry. Over the period of time, there has been significant attention in particulate (micro or nano-fillers) filled polymer composites, since the scattered particulate fillers can be expended to control the strength, stiffness, resistance to wear and impact strength of the resulting polymer composites. In contemporary, there has been an exceptional development in large scale production of fiber and/or filler-reinforced polymer matrix composites for industrial applications. Engineering polymers and polymer reinforced with fibers and particulate fillers are extensively used in innovative product design. These newly designed materials have various applications, for instance in the manufacture of sliding elements operated in automobile industries such as gears, wheels, bushes etc.. In certain environments, these tribo-components are exposed to abrasive wear either by sliding against a coarse surface or graze by hard specks. The ever-increasing usage of engineering 1

2,3

4

© KSPE and Springer 2016

polymers and their alloys in such realistic circumstances makes abrasive wear studies dictatorial from scientific and industrial point of view. In general, it is the mechanical load hauling competence and resistance to wear of the composites that administer their appropriateness in real-time usages. Various kinds and aggregates of fiber reinforcement and/inorganic fillers are renowned to enhance substantially many physical and/or mechanical characteristics of polymers, and their prospective in refining the resistance to abrasion is worth discovering. Wear is a complex material behavior and differs extremely on the method in which two surfaces perform. Wear due to abrasion is extremely imperative among the various methods of wear since it chip in about 63% of the aggregate expenses of wear. It is triggered off due to hard specks or lumps that are pried against and travel along a solid surface. These can occur as two-body abrasion wear (2-BAW) or three-body abrasion wear (3-BAW) or both. In 2-BAW process, wear is caused by hard protrusions on one surface which can only slide over the other. 2-BAW is normally carried under single-pass (SP) and or/multi-pass (MP) conditions. In SP 2-BAW 5

756 / JUNE 2016

INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING Vol. 17, No. 6

process, the test sample continuously encounters new abrasive specks: thus, the wear loss in terms of volume increases linearly with sliding distance and load. But, 2-BAW under MP process, which is likely a familiar case in real-time applications, the test sample is made to slide on the same wear path until the total sliding distance was attained. Generally the wear loss in SP situation is higher than in MP situation and the variation in the degree of wear is decided by the clogging effect. A number of researchers have examined the substantial changes in the tribological performances of polymers reinforced with fibers and particulate fillers. They investigated the 2-BAW behaviour of several polymers and polymer based composites and revealed that the wear rate increases with the addition of fibers and micron-sized fillers. However, it has been reported that inclusion of nano-sized fillers has enhanced the wear resistance of the polymer composite. Further, few investigators reported that the wear rate is influenced by individual factor such as abrasive particle size and applied load. However, the findings of Unal et al. and Harsha and Tewari revealed that the factors such as abrasive particle size, abrading distance, applied load and sliding velocity have substantial effect on abrasion performance of polymers and polymer composites. The main hitch of the above experimental investigations were that they do not elucidate the significances of the particular factors influencing the abrasive wear behaviour of polymers and polymer composites. In order to appreciate the contribution of significant factors, statistical tools like analysis of variance (ANOVA) with design of experiments (DOE) are to be implemented. Experimental investigations of researchers have adopted Taguchi method to determine the significance of the test parameters. The shortcomings of these investigations were that, they have not reported the mathematical model for the wear response data and its relation with wear control factors. These deficiencies could be enlightened by response surface method (RSM) approach encompassing face centered central composite design (FCCCD), an approach of DOE. Central composite design (CCD) is very effectual investigational technique in experiments containing large number of parameters, which has been discussed by researchers in the various disciplines of research. Oh et al. developed a mathematical model and simulated the hydraulic system of a top-hammer drill drifter. A second order polynomial equation for abrasive wear loss of bagasse fiber reinforced epoxy composites has been established and the relationship of abrasive wear loss with fiber concentration, applied load and sliding velocity has been successfully obtained by using RSM. Yoon et al. carried out geometric optimization of micro drills using Taguchi method and RSM. Thakre explored the erosion wear performance of polyetherimide (PEI) and its composites and discussed the parameters which affect the erosion rate. RSM was implemented and derived the second order quadratic model for erosion rate with control parameters and its interactions. Li et al. suggested the optimal design for cooling system of batteries using computational fluid dynamics (CFD) simulation and RSM. Song et al. studied the flushing capacities of 13 different designs of internal flow channels and selected the optimum design using RSM that analyses the relationship between design parameters and the simulation response. Experimental investigations of researchers has developed mathematical model for several wear response parameters such as wear rate, wear loss, K and coefficient of 6

7

Table 1 Materials used for the study Polymer/Filler Thermoplastic Copolyester Elastomer Polytetrafluoroethylene

Designation

Short glass fibre

SGF

Short carbon fibre

SCF

Silicon Carbide

SiC

Micro - Alumina

Al O

TCE PTFE

8-14

10

8,10

11

12

2

Table 2 Composites used in the present investigation Matrix material (% wt.) TCE (80) TCE (70)

9,13

15,16

17-25

17

18

19

20

21

22

23-25

s

3

Source and supplier DSM India Pvt. Ltd. Pune, India. Du Pont Co. Ltd. India. Fine organics, Mumbai, India. Fine organics, Mumbai, India. Carborundum Universal Ltd. Chennai, India. Triveni Chemicals, Gujarat, India.

TCE (60)

Fiber (% wt.)

Filler (% wt.)

SGF (20) SGF (17.5) + SCF (2.5)

PTFE (20) PTFE (10) PTFE (10) + SiC (5) + Al O (5) 2

3

friction (µ) of various metal matrix composites by implementing RSM. However, numerical assessment of the effect of different fibers and fillers on 2-BAW behaviour of TCE composites has not been explored till date. Hence, in the current work, experiments were carried out in order to assess the effect of incorporating fibers and fillers on 2-BAW behaviour of TCE based multi-phase composites. The main effect of fiber and filler concentration on the reliant variables were tested for statistical importance employing FCCCD approach.

2. Experimental Details 2.1 Materials and sample preparation In this study, Thermoplastic co-polyester elastomer (TCE) which is commercially available as Arnitel EM740 was considered as a matrix material, comprising of poly (butylene terephthalate) (PBT) as hard segments and poly (tetramethylene ether glycol terephthalate) as soft segments. Short E-glass fiber (SGF) was selected as reinforcement. Polytetrafluoroethylene (PTFE), short carbon fiber (SCF), silicon carbide (SiC) and alumina (Al O ) were selected as micron-scale fillers. The average diameter of the SGFs was approximately 12 μm with an average fiber length of about 4 mm. The average diameter of SCFs was approximately 7 μm with an average fiber length of about 100 μm. The size of PTFE particle was about 5 μm and around 5 to 10 μm for SiC and Al O . The sources and designation of these materials are listed in Table 1. The details of processing of TCE based multi-phase composites have been discussed elsewhere. The details of the composites manufactured for the current investigation are listed in Table 2. 2

2

3

3

2,3

2.2 Two-body abrasive wear tests A pin-on-disc setup as per ASTM G-99-05 (Make: Magnum Engineers, Bengaluru, India) was expended for 2-BAW test. The surface 8 mm × 8 mm × 3.2 mm of composite test sample is glued to a standard


JUNE 2016 / 757

Table 4 Control factors and levels for 2-BAW test Levels Low(-1) Middle(0) High(+1) 20 30 40 80 (165)* 200 (70)* 320 (31)* 20 40 60

Control factors Fiber/filler content (A), in wt. % Abrasive grit size (B) Abrading distance (C), in m

( )* indicate the average abrasive grain size in µm of the SiC abrasive paper Table 5 Details of 2-BAW test combinations in coded factors and corresponding experimental and predicted results

Fig. 1 Schematic representation of pin on disc test rig

Table 3 2-BAW test conditions Parameters Load Speed of disk Track diameter Abrasive particles Abrasive grain size Abrading Distance

Test conditions 20 N (constant) 200 rpm (v = 0.31 m s ) 30 mm Silica sand abrasive paper 165 μm, 70 μm and 31 μm 20 m, 40 m and 60 m -1

dowel pin of φ 6 mm and 25 mm length, establishes a contact with water proof silicon carbide (SiC) abrasive paper attached on the rotating disc as shown in Fig. 1. During the test run, the sample remained on the same wear path and for each test sample a fresh abrasive paper was expended. Test procedure followed in the present investigation and determination of K has been discussed elsewhere. Before carrying out the DOE through RSM, pilot experimentations were carried out in order to have awareness of the effect of operating situations on wear loss and K . These inquiries not only provide the behavioral trend of each operating condition but also aid in fixing the factor levels. Experiments were conducted according to the parameters shown in Table 3. At least three specimens of each composition were tested. After wear test, the worn surface morphology of the composites was examined using scanning electron microscope (E-SEM, Quanta 200 model) instrument with voltage of 20 kV. 10,15

Run A order 1 0 2 1 3 1 4 0 5 0 6 1 7 -1 8 -1 9 0 10 0 11 0 12 -1 13 -1 14 0 15 0 16 -1 17 0 18 0 19 1 20 1 *Experimental K

s

B

* K (mm /Nm) 0.037200 0.104453 0.086277 0.036200 0.036100 0.058220 0.027600 0.013225 0.036300 0.035467 0.036200 0.023230 0.016388 0.034200 0.036100 0.015110 0.036300 0.047600 0.084391 0.076020 s(exp)

C

3

0 -1 -1 -1 -1 1 0 0 0 0 1 1 -1 -1 1 1 0 0 0 1 0 0 -1 1 0 0 1 0 0 0 1 -1 0 0 -1 0 0 0 1 -1 and predicted K

K (mm /Nm) 0.039713 0.104172 0.087180 0.036883 0.036883 0.060904 0.025428 0.014095 0.036883 0.030905 0.036883 0.023335 0.017976 0.030629 0.036883 0.014719 0.036883 0.049122 0.080753 0.075428 #

s(pre) 3

#

s

s

s

2.3 Design of experiments The experiments are designed based on RSM a mode of DOE. It is generally useful in contexts where retort of interest is affected by a number of variables and the purpose is to optimize this retort. The MINITAB 16 software package was used to form the investigational plan for RSM. A quadratic model of second order was planned to epitomize the correlation between K and wear control variables. The performance of the model depends on a large number of variables that can act and interact in a complex manner. In the current investigation, the fiber/filler concentration, abrasive grit size and abrading distance were considered as wear control factors and the response/output variable is the K . The fundamentals of RSM such as relation among the response and the independent variables, developing a quadratic model and test

17-25

factors coding are discussed elsewhere. The essential information for the quadratic models have been gathered by the experimentations established on RSM by exercising FCCCD. The factorial part of the CCD is the full factorial design with all permutations of the wear parameters at three levels (low -1, middle 0 and high +1) and compiled of eight star points and six central points which are the midpoints between the high and low levels. The star points at the face of the cubic portion on the design which relates to α value to 1 and this type of design are generally termed as the face centered. The three wear parameters at three levels with their ranges are bestowed in Table 4, and are implemented for RSM a mode of DOE. The experimental plan and the results obtained for 2-BAW are presented in Table 5.

3 Results and Discussion

s

s

3.1 Statistical examination of specific wear rate The results of the preliminary experiments revealed that increase in fiber/filler content increases the K of the TCE composites. Further, K decreases with increase in abrading distance. The experimental results against the plan of experimental runs in coded factors and levels are tabulated in Table 5. In the present investigation, statistical analysis s

s

758 / JUNE 2016


Table 6 ANOVA table for quadratic model for K

Table 8 Estimated regression coefficients for K

s

Source Regression model Linear factors A B C Square factors A B C Interaction factors AB AC BC Residual error Lack-of-fit Pure error Total 2

2

2

DF 09 03 01 01 01 03 01 01 01 03 01 01 01 10 05 05 19

Seq SS 0.01207 0.01090 0.00985 0.00085 0.00019 0.00091 0.00088 0.00001 0.00000 0.00025 0.00014 0.00011 0.00000 0.00007 0.00007 0.00000 0.01214

s

Adj MS 0.00134 0.00363 0.00985 0.00085 0.00019 0.00030 0.00042 0.00002 0.00000 0.00008 0.00014 0.00011 0.00000 0.00000 0.00001 0.00000

P-value 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.10 0.36 0.00 0.00 0.00 0.71

Term Coefficient SE Coefficient T P-value Constant 0.0368831 0.000940 39.243 0.000 A 0.0313885 0.000865 36.306 0.000 B -0.0092462 0.000865 -10.695 0.000 C -0.0044041 0.000865 -5.094 0.000 0.0124817 0.001649 7.571 0.000 A B 0.0029921 0.001649 1.815 0.100 -0.0015743 0.001649 -0.955 0.362 C AB -0.0042590 0.000967 -4.406 0.001 AC -0.0037247 0.000967 -3.853 0.003 BC 0.0003672 0.000967 0.380 0.712 S = 0.00273395; PRESS = 0.000553477; R-Sq = 99.38 %; R-Sq (pred) = 95.44%; R-Sq (adj) = 98.83% 2

2

2

SE: Standard error, T: the ratio of corresponding value under coefficientsand its standard error coefficients, P-value: test statistics

0.00

DF: Degree of Freedom, Seq SS: sequential sum of squares, Adj MS: adjusted mean squares, P-value: test statistics Table 7 Percentage contribution of significant factors affecting K of TCE composites s

Factor A % 81.11

B 7.04

C 1.60

A 7.32

AB 1.20

2

AC Others Error 0.91 0.2 0.62

were performed with the help of MINITAB16, a statistical evaluation software package, which is extensively used in many fields of engineering research. Wear responses were studied by ANOVA with a confidence limit of 95% or P-value (test statistics) of 0.05, indicating any factor with Pvalue equal to or less than 0.05 is significant. ANOVA result is presented in Table 6. The P-value of factors A (fiber/filler content), B (abrasive grit size), and C (abrading distance) are less than 0.05. Therefore, there is a significant linear effect for fiber/filler content, abrasive grit size and abrading distance, i.e., the K differs depending on the above said factors. The P-value of quadratic term of fiber/filler concentration (A ) is found to be less than 0.05. Therefore, there is a significant quadratic effects, i.e., the relationship between fiber/filler content and K follow a curved line, rather than a straight line. The P-value of AB and AC are found to be less than 0.05. Therefore, the effect of fiber/filler content on K depends on abrasive grit size and abrading distance. The percentage contributions of the wear control parameters are computed by dividing the sum of squares of a factor by the total sum of squares of all the factors. The percentage contribution of the significant wear control parameters is presented in Table 7. The contribution of fiber/filler concentration (81.11%) is highest followed by abrasive grit size (7.04%). The regression coefficients are presented in Table 8 for K of TCE composites under MP condition. The regression coefficient which possesses positive sign indicates an increase in K , whereas the negative sign symbolizes the reduction effect in K . The linear term A has positive sign resulting in increase in K (i.e., increase in fiber/filler content results in increase in K of TCE composites, which is evident from Figs. 2 and 5). However, terms B and C has negative sign indicating reduction in K (i.e., increase in abrasive grit size reduces the abrasive grain size s

2

s

s

s

s

s

s

s

s

Fig. 2 Contour plot for K with the change in fiber/filler content and abrasive grit size s

resulting in decreased K of TCE composites, which is evident from Figs. 2 and 6. Also, increase in abrading distance results in reduction of K of TCE composites, which is evident from Figs. 5 and 6). The quadratic terms A and B has positive sign indicating in increase in K of TCE composites. However, the term C has negative sign resulting in reduction of K of TCE composites. The interactions between fiber/ filler content and abrasive grit size (AB) results in the reduction of K . Whereas the abrasive grit size has detrimental effect but the fiber/filler content has encouraging effect on K . Hence, the influence of abrasive grit size over rules the fiber/filler content during interaction even though the percentage influence of abrasive grit size (7.04%) is quite less than that of fiber/filler content (81.11%). This is evident from the contour plot which is depicted in Fig. 2. Similarly, the interactions between fiber/filler and abrading distance (AC) results in the reduction of K . Whereas the abrading distance has detrimental effect but the fiber/filler content has encouraging effect on K . Hence, the influence of abrading distance over rules the fiber/filler content during interaction even though the percentage influence of abrading distance (1.6%) is quite less than that of fiber/filler content. This is evident from the contour plot which is depicted in Fig. 5. However, the interactions between the abrasive grit size and abrading distance (BC) has positive sign resulting increase s

s

2

2

s

2

s

s

s

s

s


Fig. 3 SEM image of 165 μm abrasive grain size SiC paper

JUNE 2016 / 759

Fig. 4 SEM image of 31 μm abrasive grain size SiC paper

in K of TCE composites. The contour plot (Fig. 2) reveals the K of TCE based multi-phase composites against the change in fiber/filler content and abrasive grit size and abraded to a distance of 40 m (hold value with middle factor level 0). The reduction in abrasive grain size from 165 μm (80 grit size with low factor level -1) to 31 μm (320 grit size with high factor level +1) has reduced the K (< 0.02 mm /Nm for 20 wt.% fiber/filler content), thus exhibiting its significance on the abrasive wear process. Bigger abrasive particles (80 grit size with factor level -1) has higher protuberances, resulting in greater area of surface contact with composite thus yielding to higher depth of penetration, ploughing, cutting and clogging leading to severe abrasion resulting in higher K (ranging from 0.02~0.04 mm /Nm for 20 wt.% fiber/filler content) compared to former. Further, it is evident from the Fig. 2 that increase in abrasive grain size (i.e., 165 μm with low factor level -1) with increase in fiber/filler content (40 wt.% with high factor level +1) has resulted in increase in K (> 0.08 mm /Nm). Clogging is the most discernible contribution to the abrasive grit size effect. Wear wreckages generated is accommodated in the depressions of the abrasive paper surface. The volume of inter-asperity slumps is directly correlated to the size of the abrasive particles. Simplistic arguments of geometrical resemblance reveal that the volume of the gorges is directly proportional to abrasive particle diameter, which is evident from Figs. 3 and 4. The wear debris in the form of long fibrils will be physically bounded within the abrasive slumps by the specimen surface. As the fibrils length increases, more energy will be consumed in deforming the specimen until breakage occurs. As the abrasive particle size decreases (high factor level +1), the relative length of the fibril increases, making its accommodations within the recesses more difficult. The fibrils are then more likely to rub against the specimen or interrupt itself among abrasive particles and sample under test, resulting in reduced K (< 0.02 mm /Nm). Also, increase in fiber/filler content (40 wt.% with high factor level +1) has boosted the K (in the range of 0.06~0.08 and > 0.08 mm /Nm) of TCE composite. This may be due to the fact that the higher concentration of fiber/filler in the matrix reduces the interfacial bonding strength, thus leading to fiber/filler debonding during abrasion. These debonded fibers/fillers on the wear track act as secondary abrasive particles, which increases the K , resulting in poor abrasion resistance. Fig. 5, depicts the contour plot for K of TCE composite against the s

s

3

s

s

3

Fig. 5 Contour plot for K with the change in fiber/filler content and abrading distance s

s

3

3

s

s

3

s

s

change in fiber/filler content and abrading distance. The interaction between fiber/filler content and abrading distance (AC) results in reduction of K . The term abrading distance has detrimental effect but the latter has encouraging effect which is over rid by the effect of abrading distance. Increase in abrading distance establishes continuous contact forces at the interface, leading to the clogging of wear debris and deterioration of abrasive particles by way of blunting, breakage or pull-out. The interaction between abrasive grit size and abrading distance (BC) has positive effect on K , but possess P-value of 0.712 which indicates its non-significant effect on K . Likewise, the quadratic terms B (abrasive grit size) and C (abrading distance) exhibits P-value of 0.100 and 0.362 respectively indicating its non-significant effect on K . Fig. 6 demonstrates the contour plot for K of TCE composites with the change in abrasive grit size and abrading distance. The K decreases (< 0.03 mm /Nm) with the increase in abrading distance and abrasive grit size (with high factor level of +1). Empirical model to forecast K are articulated by response surface regression analysis. Response surface and corresponding surface plots furnish broader perception to understand any problem in general, and to optimize the elements affecting the response in particular. Table 8 presents the results of response surface regression analysis of K of TCE composites subjected to 2-BAW. The regression model is represented s

s

2

s

2

s

s

3

s

s

21.24

s

760 / JUNE 2016


Fig. 6 Contour plot for K with the change in abrasive grit size and abrading distance s

Fig. 7 Correlation graph for K of TCE composites s

by equation: Ks = 0.0368831 + 0.0313885 × A – 0.0092462 × B – 0.0044041 × C 2

2

+ 0.0124817 × A + 0.00299218 × B – 0.00157432 × C

2

(1)

–0.004256 × A × B – 0.00372475 × A × C + 0.0036725 × B × C The determination coefficient R-Sq in Table 8 is a measure of the degree of fit when R-Sq approaches the unity, the best response model fits the actual data. The predicted R-Sq is equal to 95.44% and adjusted R-Sq equal to 98.83% is in good agreement with the actual R-Sq equal to 99.38%. Also, model is evaluated with the prediction error sum of squares (PRESS) value. The PRESS statistics is a measure of how well the model will predict new data. These values are computed and are shown in Table 8. A model with a small value of PRESS indicates that the model is likely to be a good predictor. The model developed in the present investigation has PRESS values of 0.000553477. This indicates that the full model would be expected to explain about 0.05% of variability in new data under MP condition. In addition to the significant terms indicated in Table 8, few insignificant terms are also included so that R-Sq (adj) is improved and the difference between R-Sq (adj) and R-Sq is minimized. This improves the prediction capability of the model. The predicted K of TCE composites are deduced from Eq. (1) and are presented in the last column of Table 5. Further, the coefficient of correlation ‘r’ was used to know how close the forecasted and experimentation values lie. The coefficient of correlation ‘r’ for the above developed model is found to be 0.9969, which signifies high correlation existence among the experimentation values and the forecasted values and this is additionally backed by correlation graphs, as shown in Fig. 7. Thus, the established model can be successfully used to forecast the K of TCE composites under MP condition. 26

26

s

s

3.2 Worn surface morphology Figs. 8~10 present the SEM micrographs of worn surfaces of TCE composites subjected to 2-BAW under MP condition, abraded against 165 μm SiC abrasive paper, and 60 m abrading distance. The white arrow specifies the sliding direction. The infiltration of SiC hard asperities from the abrasive paper into the TCE composites surface during the abrasion activity would ensue in cutting, ploughing, plastic deformation and

Fig. 8 SEM image of TCE with 20 wt.% filler content abraded against 165 μm SiC paper, to an abrading distance of 60 m

surface breakage. Fig. 8 shows the furrows (indicated as DG) resulting in the formation of long fibrils (indicated as F) that are triggered by cutting and ploughing due to sliding action. Continued abrasion results in the separation of fibrils leading to the layer fragmentation (indicated as LF). The matrix material which is separated from the specimen in the form of debris (indicated as WD) can be seen adhering to the worn surface of the specimen at the end of the abrading distance. Initially the wear debris formed accumulates the space in between the asperities of abrasive papers thus making the abrasives inefficient after completion of certain abrading distance. The worn surface of the composite under applied normal load and on exposure to the ineffective abrasive particles of the SiC paper, results in the deformation of the fibrils (indicated as DF). Fig. 9 presents the SEM image of the worn surface of TCE composite filled with 30 wt.% fiber/filler. Grooves with higher depth than the earlier can be observed, which resulted in the fiber/filler debonding (indicated as SGF and PD) from the matrix material. The debonded fiber in the wear track establishes intermittent contact with the asperities, and experiences the applied normal load, leading to its rupture. These ruptured fibers in between the asperities at the counterface, acts as abrasive material and their by enhances the wear volume of the composite. The long fibrils formed during wear process indicate the


JUNE 2016 / 761

Fig. 9 SEM image of TCE with 30 wt.% fiber/filler content abraded against 165 μm SiC paper, to an abrading distance of 60 m

Fig. 11 SEM image of TCE with 20 wt.% filler content abraded against 31 μm SiC paper, to an abrading distance of 60 m



ductility of the matrix material. In Fig. 10, reveals the abrasive wear characteristics of TCE composite with 40 wt.% fiber/filler reinforcement. Debonding of glass and carbon fiber (indicated as SGF, SCF and FD) can be seen in the figure. Similarly, debonding of particulate fillers like PTFE (indicated as P), silicon carbide and aluminium oxide from the matrix material during the wear process is experiential. The debonded fibers are ruptured (indicated as BS) during the wear process. These ruptured fibers and the ceramic fillers occupy the space between the asperities and acts as abrasive particles (third body) and enhance the wear volume of the composite than the former in the study group. The fiber and particulate bonding (indicated as FB and AP); and short fibrils adhering to the fibers (indicated as MA), supports the existence of interfacial bonding between the fiber/filler and the matrix material. Figs. 11~13 demonstrates the SEM micrographs of worn surfaces of TCE composites subjected to 2-BAW under MP condition abraded against 31 μm SiC paper to a distance 60 m. The grooves formed and their geometric intensities are much smaller than the former causing the low wear volume in the study group. This is due to the reduction in the asperities height of the present with that of latter (i.e., with 165 μm SiC abrasive paper). This has supported the above experimental findings, i.e., decrease in abrasive particle size reduces the K of the composites under study. Fig. 13 depicts the worn surface of the TCE composite reinforced s


with 20 wt.% fibers and 20 wt.% fillers. It is evident from the figure that the fibrils are absent, which are present in the latter cases (indicated as F). The fibrils are formed due to the ploughing and cutting action of the abrasive particles and are fractured at the fiber/filler and matrix interface. Continued abrasion establishes a sliding between SiC abrasive particles against the fibers and ceramic fillers. This action reduces the thickness of fiber/filler surrounded by matrix and finally results in reduction of cross-section leading to its debonding from the matrix material. Also,

762 / JUNE 2016


Fig. 14 SEM image of debris deposited on 165 μm SiC paper abraded against TCE with 20 wt.% filler, to an abrading distance of 60 m

Fig. 15 SEM image of debris deposited on 165 μm SiC paper abraded against TCE with 40 wt.% fiber/filler, to an abrading distance of 60 m

this action wears out the sharp asperities of SiC abrasives and thus reduces its efficiency. The worn out SiC abrasives are debonded from the paper and the ruptured fibers/debonded fillers acts as a third body (free to role and slide) and fractures the fibrils leading to increase in wear volume with respect to the latter. The fiber/filler surrounded by the matrix material presents the strong interfacial adhesion between them. The formation of fibrils significantly indicates the ductility which leads to increase in ultimate elongation to break of the composites. Figs. 14 and 15 depicts the TCE composite with 20 wt.% filler and TCE composite 40 wt.% fiber/filler respectively, abraded against 165 μm SiC abrasive paper to an abrading distance of 60 m. The white arrow indicates the abrading direction. The SiC abrasive (indicated as SA) possesses the cutting edge (indicated as E). This cutting edge engages in the wear process and removes the matrix material in the form of debris (indicated as SD for short volume debris and WD for high volume debris). Some of this debris occupies the space between SiC abrasives and rest are welded to the cutting edge of the abrasives. The high volume wear debris adhered to the SiC abrasive particles can be seen in Fig. 15. This action reduces the efficiency of the cutting edge. The ruptured glass and carbon fiber (indicated as SGF and SCF) are also present, which indicates increase in wear volume of the composite under wear test.

study group. • The fiber/filler content exerted the paramount effect on K followed by abrasive grit size of SiC paper and abrading distance. These results were further backed by the variations in the worn surfaces of the specimens after two-body wear testing, studied using SEM. • 2-BAW was chiefly reigned by the combination of micro-cutting, micro-cracking and micro-ploughing mechanism as demonstrated from the worn surface morphology. • Empirical model using response surface regression analysis is devised. The forecasted and the experimental values are satisfactorily close to each other which indicated that the devised empirical model can be successfully used for forecasting the K of TCE composites subjected to 2-BAW under multi-pass condition with 95 % confidence level. • The developed empirical model is applicable to predict the K of TCE composites prior to the actual experimental work with 95% confidence level. • Good correlations amongst the experimental and the forecasted value signify the adequacy of the developed model. • In regression coefficients, the interactions of wear control parameters have both statistical and physical significance, since error concomitant is more than percentage contribution of these interactions. • Furthermore, the use of multiple test specimens and testing of the differences in average values of variables between the composite systems by proper statistical analysis instead of relying on just numerical values are obvious strength of this qualitative investigation.

4. Conclusions Fiber and particulate reinforced TCE composites were successfully manufactured and investigated numerically the effect of fiber and filler constituents on 2-BAW behaviour under MP condition. SEM analysis of the worn surfaces was studied to explore the involved wear mechanisms of abrasive wear. Based on the study, the following major conclusions are drawn. • Addition of fibers and fillers to TCE significantly affects the K of the composites. The K was increased with the addition of SGFs (20 wt.%) and further increased with the addition of ceramic fillers (20 wt.%). • The K decreases with increase in abrading distance for all the composites. However, TCE with PTFE exhibited lower K at an abrading distance of 60 m than that of 20 m. Similarly TCE with 40 wt.% fiber and filler loading exhibited the similar trend in the

s

s

s

ACKNOWLEDGEMENT

s

s

s

s

The authors express sincere thanks to Dr. Pramoda Kumari Pallathadka, Senior Scientist I, Materials Processing and Characterization, Institute of Materials Research and Engineering, Singapore, for her kind assistance in characterizing the composites. The authors also like to express sincere thanks to Mr. Srinivas, HeadQuality, Brakes India Ltd. Nanjangud, India for his kind assistance in the fabrication of hybrid composites.


REFERENCES 1. Wang, R. M., Zheng, S. R., and Zheng, Y. P., “Polymer Matrix Composites and Technology,” Woodhead Publishing, pp. 29-30, 2011. 2. Rajashekaraiah, H., Mohan, S., Pallathadka, P. K., and Bhimappa, S., “Dynamic Mechanical Analysis and Three-Body Abrasive Wear Behaviour of Thermoplastic Copolyester Elastomer Composites,” Advances in Tribology, Vol. 2014, Article ID: 210187, 2014. 3. Hemanth, R., Suresha, B., and Sekar, M., “Physico-Mechanical Behaviour of Thermoplastic Co-Polyester Elastomer/ Polytetrafluroethylene Composite with Short Fibers and Microfillers,” Journal of Composite Materials, Vol. 49, No. 18, pp. 2217-2229, 2014. 4. Hutton, T. J., Johnson, D., and McEnaney, B., “Effects of Fibre Orientation on the Tribology of a Model Carbon-Carbon Composite,” Wear, Vol. 249, No. 8, pp. 647-655, 2001. 5. Neale, M. and Gee, M., “A Guide to Wear Problems and Testing for Industry,” William Andrew, p. 8, 2001.

JUNE 2016 / 763

No. 13, pp. 1221-1240, 2002. 15. Suresha, B., Ramesh, B. N., Subbaya, K. M., Kumar, B. R., and Chandramohan, G., “Influence of Graphite Filler on Two-Body Abrasive Wear Behaviour of Carbon Fabric Reinforced Epoxy Composites,” Materials & Design, Vol. 31, No. 4, pp. 1833-1841, 2010. 16. Pasha, B. A. M., Budan, D. A., Basavarajappa, S., Yadav, S. M., and Nizamuddin, B., “Studies on Wear Resistance of PTFE Filled with Glass and Bronze Particles based on Taguchi Technique,” Journal of Thermoplastic Composite Materials, Vol. 26, No. 2, pp. 243-259, 2013. 17. Oh, J.-Y., Lee, G.-H., Kang, H.-S., and Song, C.-S., “Modeling and Performance Analysis of Rock Drill Drifters for Rock Stiffness,” Int. J. Precis. Eng. Manuf., Vol. 13, No. 12, pp. 2187-2193, 2012. 18. Mishra, P., “Statistical Analysis for the Abrasive Wear Behavior of Bagasse Fiber Reinforced Polymer Composite,” International Journal of Applied Research in Mechanical Engineering, Vol. 2, pp. 7-11, 2012.

6. Harsha, A. P. and Tewari, U. S., “Two-Body and Three-Body Abrasive Wear Behaviour of Polyaryletherketone Composites,” Polymer Testing, Vol. 22, No. 4, pp. 403-418, 2003.

19. Yoon, H.-S., Wu, R., Lee, T.-M., and Ahn, S.-H., “Geometric Optimization of Micro Drills using Taguchi Methods and Response Surface Methodology,” Int. J. Precis. Eng. Manuf., Vol. 12, No. 5, pp. 871-875, 2011.

7. Bijwe, J., Indumathi, J., Rajesh, J. J., and Fahim, M., “Friction and Wear Behavior of Polyetherimide Composites in Various Wear Modes,” Wear, Vol. 249, No. 8, pp. 715-726, 2001.

20. Thakre, A. A., “Prediction of Erosion of Polyetherimide and Its Composites using Response Surface Methodology,” Journal of Tribology, Vol. 137, No. 1, Paper No. 011603, 2015.

8. Friedrich, K. and Cyffka, M., “On the Wear of Reinforced Thermoplastics by Different Abrasive Papers,” Wear, Vol. 103, No. 4, pp. 333-344, 1985.

21. Li, Z.-Z., Cheng, T.-H., Xuan, D.-J., Ren, M., Shen, G.-Y., and Shen, Y.-D., “Optimal Design for Cooling System of Batteries using DOE and RSM,” Int. J. Precis. Eng. Manuf., Vol. 13, No. 9, pp. 16411645, 2012.

9. Harsha, A. P. and Tewari, U. S., “Abrasive Wear of Glass Fibre Reinforced Polysulfone Composites,” Indian Journal of Engineering and Materials Sciences, Vol. 9, No. 3, pp. 203-208, 2002. 10. Kumar, B. R., Venkataramareddy, M., and Suresha, B., “Two-Body Abrasive Wear Behavior of Nano-Clay Filled LDPE/EVA Composites,” Journal of Reinforced Plastics and Composites, Vol. 28, No. 24, pp. 2999-3007, 2009. 11. Bijwe, J., Sen, S., and Ghosh, A., “Influence of PTFE Content In PEEK-PTFE Blends on Mechanical Properties and TriboPerformance in Various Wear Modes,” Wear, Vol. 258, No. 10, pp. 1536-1542, 2005. 12. Unal, H., Sen, U., and Mimaroglu, A., “Abrasive Wear Behaviour of Polymeric Materials,” Materials & Design, Vol. 26, No. 8, pp. 705710, 2005. 13. Harsha, A. P. and Tewari, U. S., “Tribo Performance of Polyaryletherketone Composites,” Polymer Testing, Vol. 21, No. 6, pp. 697-709, 2002. 14. Bijwe, J., Neje, S., Indumathi, J., and Fahim, M., “Friction and Wear Performance Evaluation of Carbon Fibre Reinforced PTFE Composite,” Journal of Reinforced Plastics and Composites, Vol. 21,

22. Song, C.-H., Kwon, K.-B., Park, J.-Y., Oh, J.-Y., Lee, S., Shin, D.Y., and Cho, J.-W., “Optimum Design of the Internal Flushing Channel of a Drill Bit using RSM and CFD Simulation,” Int. J. Precis. Eng. Manuf., Vol. 15, No. 6, pp. 1041-1050, 2014. 23. Kumar, S. and Balasubramanian, V., “Effect of Reinforcement Size and Volume Fraction on the Abrasive Wear Behaviour of AA7075 Al/ SiCp P/M Composites-A Statistical Analysis,” Tribology International, Vol. 43, No. 1, pp. 414-422, 2010. 24. Suresha, S. and Sridhara, B., “Effect of Silicon Carbide Particulates on Wear Resistance of Graphitic Aluminium Matrix Composites,” Materials & Design, Vol. 31, No. 9, pp. 4470-4477, 2010. 25. Chauhan, S. R. and Dass, K., “Dry Sliding Wear Behaviour of Titanium (Grade 5) Alloy by Using Response Surface Methodology,” Advances in Tribology, Vol. 2013, Article ID: 272106, 2013. 26. Montgomery, D. C., “Design and Analysis of Ewperiments,” Wiley, p. 251, 2007.