(AGUIJST) 08, Vol. No., Jul-Dec e-issn: 55-09; p-issn: 55-808 STUDY ON FRICTION AND DRY SLIDING WEAR BEHAVIOR OF CENOSPHERE FILLED VINYLESTER COMPOSITES Sunil Thakur, S.R. Chauhan Department of Mechanical Engineering, AP Goyal Shimla University, (H.P.) 009, Department of Mechanical Engineering, National Institute of Technology, Hamirpur, (H.P)-005 *Corresponding author s e-mail address: sunilthakur.nith@gmail.com ABSTRACT In this paper the friction and wear characteristics of vinylester and vinylester composites have been investigated under dry sliding conditions for different applied normal load and sliding speed and sliding distance. The experiments have been carried on a pin on disc arrangement at normal temperature conditions. The influence of friction and wear parameters like normal load, speed, sliding distance and percentage of filler content on the friction and wear rate has been investigated. In this study, a plan of experiments, based on the techniques of Taguchi, was performed to acquire data in a controlled way. An orthogonal array L ( ) and Analysis of variance (ANOVA) were applied to investigate the influence of process parameters on the coefficient of friction and sliding wear behaviour of these composites. Keywords Cenosphere, Friction and wear behavior, Taguchi, Vinylester resin INTRODUCTION Composite materials have replaced metals in various engineering applications owing to their numerous advantages like high strength-to-weight ratio, low cost. There is always an increasing demand for use of these materials in defense applications like naval ships, warplanes, armored vehicles and sea vehicles [, ]. In production industry polymer and their composites are being increasingly employed in view of their good strength and low densities. Polymer composites have been used successfully for many decades as engineering materials. Polymer composites are the most rapidly growing class of materials due to their combination of high specific strength and specific modulus. They have been design and manufacture for various application such as aircraft, automobiles and civil structure [-5]. A number of matrix materials are available, including carbon, ceramics, glasses, metals and polymers. The primary means of improving engine efficiency are to take advantage of the high specific stiffness and strength of composites for weight reduction [, ]. Polymer composites exhibits excellent friction and wear characteristics even without external activations and can provide maintenance free operation, excellent corrosion resistance.
(AGUIJST) 08, Vol. No., Jul-Dec e-issn: 55-09; p-issn: 55-808 Taguchi technique is a powerful tool for the design of high quality systems [8]. The Taguchi approach to experimentation provides an orderly way to collect, analyze, and interpret data to satisfy the objectives of the study. In the design of experiments, one can obtain the maximum amount of information for the amount of experimentation. Taguchi parameter design can optimize the performance characteristics through the setting of design parameters and reduce the sensitivity of the system performance to the source of variation [9, 0]. This technique is a powerful tool for acquiring the data in a controlled way and to analyze the influence of process parameters over some specific parameters, which is unknown function of these process variables. Taguchi technique creates a standard orthogonal array to consider the effect of several factors on the target value and defines the plan of experiments. The experimental results are analyzed by using analysis of means and variance of the influence of factors [- ]. EXPERIMENTAL DETAILS A Materials Vinylester resin is the matrix material used for the present investigations. Vinylester is a hybrid form of polyester resin which has been toughened with epoxy molecules within the main molecular structure. Vinylester resins are stronger than polyester resins and cheaper than epoxy resins. The filler material used in this study is cenosphere. Cenospheres are inert hollow silicate spheres. The shape of cenosphere is spherical and the colour is light gray. The chemical composition of cenosphere is SiO- 55%, AlO- %, FeO-.5%, TiO-.%, Carbon dioxide- 0%, Nitrogen- 0%. Table Material and test condition Sam ples Composites specification C Pure vinylester C %cenosphe re + vinylester C 5% cenosphere + vinylester Densit y (gm/c m ) Tempera ture ( o C) Humid ity (%)..0.
(AGUIJST) 08, Vol. No., Jul-Dec e-issn: 55-09; p-issn: 55-808 B. Composite fabrication The filler material i.e. the Cenosphere of average size 90 µm mixed with vinylester resin in three different percentages (0 wt.%, wt%, and 5 wt.%) by conventional hand-lay-up technique and slowly poured in glass tubes so as to get cylindrical specimens (diameter mm, length 0 mm). Also.5 % of cobalt nephthalate (as accelerator) and.5 % of methyl-ethyl-ketone-peroxide (MEKP) as hardener is mixed thoroughly in composites materials. The mix is stirred manually to disperse the filler particles in the composites. The composites thoroughly stirred with the help of a glass rod and then the mould was kept for post-curing at room temperature for h. The hardened composite samples are extracted from the glass tube. Specimens of suitable dimension are cut using a diamond cutter for coefficient of friction test and specific wear test. The type of resin used in this work is vinyl ester ±resin (density. gm/cm ) supplied by Northan Polymer Ltd., Delhi, India and the Cenosphere (Hardness 5- MOH, Density 0.-0. gm/cm, ) supplied by Cenosphere India Pvt. Ltd. Table Levels of variables used in the experiments Factor A: Load B: Speed C: Sliding distance D: Roughness E: Filler content Level I II III Units 0 0 0 N 00 00 900 rpm 000 000 000 m 0.0 0. 0. µm 0 5 % C. Friction and wear measurements The friction and sliding wear performance evaluation of vinylester and its composites C, C and C under dry sliding conditions were carried out on a pin-on-disc type friction and wear monitoring test rig (DUCOM) as per ASTM G 99. During the test, friction force was measured by transducer mounted on the loading arm. The friction force readings are taken as the average of 00 readings every 0 seconds for the required period. For this purpose a microprocessor controlled data acquisition system is used. The environment condition in the laboratory was 0 C and % relative humidity. Weight loss method was used for finding the specific wear. For each condition, at least two tests were performed and the mean value of weight loss was reported. During these experiments initial and final weight of the specimens were measured. The material loss from the composite surface is measured using a precision electronic balance with accuracy ±0.000 mg. The specific wear rate (mm /Nm) is then expressed on volume loss bases
(AGUIJST) 08, Vol. No., Jul-Dec e-issn: 55-09; p-issn: 55-808 K S = M/ρLF N () Where Ks- is the specific wear rate (mm /Nm), M is the mass loss in the test duration (gm), ρ is the density of the composite (gm/cm), F N - is the average normal load (N). D. Experimental design The Taguchi method is a commonly adopted approach for optimizing design parameters. The method is originally proposed as a means of improving the quality of products through the application of statistical and engineering concepts. Since experimental procedures are generally expensive and time consuming, the need to satisfy the design objectives with the least number of tests is clearly an important requirement. In Table is indicated the factors to be studied and the assignment of the corresponding levels. The array chosen was the L ( ) which has rows corresponding to the number of tests (0 degrees of freedom) with columns at three levels, as shown in Fig. the factors and the interactions are assigned to the columns. The tests are conducted at room temperature as per experimental design given in Table, each column represents a test parameter whereas a row stands for a treatment or test condition which is nothing but combination of parameters levels. In the full factorial experiment design, it would require 5 = runs to study five parameters each at three levels whereas, Taguchi factorial experiment approach reduces it to only runs offering a great advantage in term of experimental time and cost. The plan of the experiments is as follows: the first column is assigned to load (A), the second column to speed (B), the fifth column to sliding distance (C) and the ninth column to roughness (D), the tenth column to filler content (E) the third and fourth column are assigned to (A B) and (A B) respectively to estimate interaction between load (A) and speed (B), the sixth and seventh column are assigned to (B C) and (B C) respectively to estimate the interaction between speed (B) and sliding distance (C), the eight and eleventh column are assigned to (A C) and (A C) respectively to estimate interaction between the load (A) and filler content (E) and the remaining columns are used to estimate experimental errors. The output to be studied is coefficient of friction (COF) and specific wear rate (W S ). RESULTS AND DISCUSSION A. Analysis of experimental results The experimental data for coefficient of friction and specific wear rate is reported in the Table. The data reported is the average of two replications. From Table the overall mean for the S/N ratio of the coefficient of friction and the specific wear rate are found to be 9.95 db and 08.8 db respectively. The analyses of the experimental data are carried using the software MINITAB specially used for design of experiment applications. Before analyzing the experimental data using this method for predicting the measure of performance, the possible interactions between control factors are considered.
(AGUIJST) 08, Vol. No., Jul-Dec e-issn: 55-09; p-issn: 55-808 Table Experimental Design using L array RU N Loa d (N) Spee d (rpm ) Slidin g distan ce (m) Roughne ss (µm) Filler Conte nt (%) 0 00 000 0.0 0 0 00 000 0. 0 00 000 0. 5 0 00 000 0.0 5 0 00 000 0. 5 0 00 000 0. 0 0 900 000 0.0 5 8 0 900 000 0. 0 9 0 900 000 0. 0 0 00 000 0.0 0 0 00 000 0. 0 00 000 0. 5 CO P 0. 0. 0.9 0. 0.9 0. 0. 0.5 0.5 0. 0. 0. 0 900 000 0.0 0. 0 900 000 0. 5 5 0 900 000 0. 0 0 00 000 0.0 5 0. 0. 0. 9 S/N Ratios (db).09.8 8 0.0.09 0.5 5.8 8.5.885 0 5.99.85 0.98.0 85.9 5.555.5 8.8 08 Specific wear rate (mm /N m) 0.000 0.0000 0.00005 0.00000 95 0.00008 0.0000 0.0000 5 0.000 0.0000 0.00000 9 0.0000 0.00000 0.00000 0.0000 0.0000 0.0000 S/N ratios (db).5 9 8.8 85.00 0.0 9 9.98 5 8.9 58 88.59 9.09 5 98. 9 8.0 5 8.8 9.89 9 08. 9.588 5 8.89 89.8 88 5
(AGUIJST) 08, Vol. No., Jul-Dec e-issn: 55-09; p-issn: 55-808 0 00 000 0. 0 8 0 00 000 0. 9 0 900 000 0.0 0 0 0 900 000 0. 0 900 000 0. 5 0 00 000 0.0 0 00 000 0. 5 0 00 000 0. 0 5 0 00 000 0.0 5 0 00 000 0. 0 0 00 000 0. 0. 0.5 0.5 0.5 0.5 0. 0. 0. 0.5 8 0. 0 0..5 5.885 9 5.99 5.5 5 5.885 9.9 0.8.5..9 5.8 0.00009 0.00000 9 0.00009 0.0000 0.00000 5 0.0000 0.00000 9 0.00009 0.0000 0.000058 0.0000 80.5 8.5 5 9.9 8.0 5 09. 8 8.90 8 0.9 90.5 8 9.90 8.8 9. 9 Table 5 (a) Analysis of variance for S/N ratios for coefficient of friction Source DOF Seq SS Adj MS A 9.09 9.55 B 9.5 9.59 C. 0.8 D 5..5 E 9.9.98 A*D.998.995 A*E 9.05. Residual 8 5.09.88 Error.88 Total F.. 0. 0.9 0. 0..8 P (%) 0.9.0 0.9.00 5. 0.. 0.0 00
(AGUIJST) 08, Vol. No., Jul-Dec e-issn: 55-09; p-issn: 55-808 Thus factorial design incorporate a simple means of testing for the presence of the interaction effects. Table 5 (b) Response table for S/N ratios for coefficient of friction Level A B C D E Delta Rank.5 5.5 5..8.8.8 5.8.989.80.85.9 0.5 5 5.0.8.0.0.88.98 5.5.5 Fig. and 5 shows graphically the effect of the five control factors on coefficient of friction and specific wear rate of the composite specimens C, C and C. The analysis of results gives the combination factors resulting in minimum coefficient of friction and specific wear rate of the composites. Analysis of these results leads to the conclusion that factors combination A, B, C, D and E gives minimum coefficient of friction as shown in the Figure. The interaction graphs are shown in Fig. (a, b). From these Fig. it is observed that the interaction A E shows significant effect on the coefficient of friction. Similarly the combination of factors A, B, C, D and E gives minimum specific wear rate as shown in the Figure 5. The interaction graphs for parameters of specific wear rate are shown in Fig. (a, b). It is observed that interaction A E also has significant effect on the specific wear rate. B. ANOVA and effects of factors It is done an ANOVA of the data with coefficient of friction and specific wear rate, with the objective of nalyzing the influence of normal load (A), speed (B), sliding distance (C), roughness (D) and filler content (E) on the total variance of the results. In order to understand the impact of various control factors and interaction on the response of experimental data it is desirable to develop the analysis of variance (ANOVA) to find the significant factors as well as interactions. ANOVA allows analyzing the influence of each variable on the total variance of the results. Table 5(a) shows the results of ANOVA for the coefficient of friction and Table (a) shows the results of ANOVA for the specific wear rate.
(AGUIJST) 08, Vol. No., Jul-Dec e-issn: 55-09; p-issn: 55-808 Table (a) ANOVA Analysis of variance for S/N ratios for specific wear rate Source DOF Seq SS Adj MS A 05.0 5.55 B 8. 90.0 C.5.58 D 0. 0. E 9.. A*D. 5.0 A*E 8. 9.5 Residual 8.9 58.9 Error 089.8 Total F 0.89.5 0. 0. 5. 0.0.0 P (%) 5.0 8..0.9 0..5.88.55 00 It can be observed from the ANOVA table 5(a) for coefficient of friction that the (A) normal load (P=0.9%), and speed (P=.0%), the interaction between (A E) normal load and filler content (P=0.0%) have greater influence on the coefficient of friction and hence these are physically and statistically highly significant. Table (b) Response table for S/N ratios for specific wear rate Level A B C D E Delta Rank 88.9 89.80 9.9.0 8. 90.5 9.98. 89.80 9.5 89.. 5 9. 88.9 9..80 8.00 9.9 95.0.9 However sliding distance (P=0.9%), the interaction between normal load and roughness (A D) has (P=0.%) have lesser effect on coefficient of friction as error value (P=0.0%) is higher side hence less significant. From the analysis of ANOVA and response Table 5 (b) of the S/N ratio of coefficient of friction, it is observed that the control parameter normal load has major impact on coefficient of friction followed by speed, sliding distance, roughness and filler contents. In the same way from the ANOVA Table (a) for the specific wear rate it is observed that the load (P=5.0%), sliding distance (P=.0%), roughness (P=.9%) and filler content (P=0.%). The interaction between (A D) load and filler content (P=.88%) have great influence on the specific wear 8
(AGUIJST) 08, Vol. No., Jul-Dec e-issn: 55-09; p-issn: 55-808 rate and hence theses are physically and statistically highly significant. However the interactions (A D) between load and roughness (P=.5%) have lesser effect on specific wear rate as error value (P=.55%). From the analysis of ANOVA and response Table (b) of the S/N ratio for specific wear rate, it is observed that the roughness has major impact on specific wear rate followed by load, speed, filler content, sliding distance. I. Confirmation experiments The confirmation experiment is the final step in the design of experiments process. The confirmation experiment is conducted to validate the inference drawn during the analysis phase. The confirmation experiment is performed by considering the new set of factor setting A B C D and E to predict the coefficient of friction and for specific wear rate factor setting is A B C D E. The estimated S/N ratio for coefficient of friction can be calculated with the help of following predictive equation: η = T + (A - T) + (E - T) + [(A E - T) (A - T) (E - T)] + (B - T) + (C - T) + (D - T) () Where η is the predicted average, T is average results of runs and A E B C and D is the mean response for factors and interactions at designated levels. By combining all the terms equation () reduces to: η = A E + (B - T) + (C - T) +(D - T) (5) A new combination of factor levels A E B C and D are used to predict the S/N ratio of coefficient of friction through predictive equation and is found to be η = 9.95. For each of performance measures an experiment is conducted for different combination of factors and results are compared with those obtained from the predictive equation as shown in Table (a). Similarly a prediction equation is developed for estimating S/N ration of specific wear rate as given by the equation: η = T + (A - T) + (E - T) + [(A E - T) (A - T) (E - T)] + (B - T) + (C - T) + (D - T) () 9
S/N ratios Mean of S/N ratios Mean of S/N ratios AGU International Journal of Science and Technology (AGUIJST) 08, Vol. No., Jul-Dec e-issn: 55-09; p-issn: 55-808 Main Effects Plot for S/N ratios Data Means 95.0 A B C 9.5 90.0 8.5 85.0 95.0 0 0 D 0 00 00 900 000 000 000 E 9.5 90.0 8.5 85.0 0.0 0.0 0.0 0 5 Signal-to-noise: Smaller is better Fig. Main effect plot for S/N ratios for cof Main Effects Plot for S/N ratios Data Means 95.0 A B C 9.5 90.0 8.5 85.0 95.0 0 0 D 0 00 00 900 000 000 000 E 9.5 90.0 8.5 85.0 0.0 0.0 0.0 0 5 Signal-to-noise: Smaller is better Fig. 5. Main effect plot for S/N ratios for swr Interaction Plot for S/N ratios Data Means D 0.0 0.0 0.0 5 0 Signal-to-noise: Smaller is better 0 A 0 Fig. (a) Interaction graph for A D for cof 0
S/N ratios S/N ratios AGU International Journal of Science and Technology (AGUIJST) 08, Vol. No., Jul-Dec e-issn: 55-09; p-issn: 55-808 Interaction Plot for S/N ratios Data Means 8 E 0 5 5 0 0 0 A Signal-to-noise: Smaller is better Fig. (b) Interaction graph for A E for cof 98 9 9 Interaction Plot for S/N ratios Data Means D 0.0 0.0 0.0 9 90 88 8 0 0 0 A Signal-to-noise: Smaller is better Fig. (a) Interaction graph for A D for swr
S/N ratios AGU International Journal of Science and Technology (AGUIJST) 08, Vol. No., Jul-Dec e-issn: 55-09; p-issn: 55-808 05 00 Interaction Plot for S/N ratios Data Means E 0 5 95 90 85 80 0 Signal-to-noise: Smaller is better 0 A 0 Fig. (b) Interaction graph for A E for swr Where η is the predicted average, T is average results of runs and A E B C and D is the mean response for factors and interactions at designated levels. By combining all the terms equation () reduces to: η = A E + (B - T) + (C - T) + (D - T) () A new combination of factor levels A E B C and D are used to predict the S/N ratio of specific wear rate through predictive equation and is found to be η = 08.8. Table (a) Results of the confirmation experiments for the coefficient of friction Optimal control parameters Prediction Experiment % Error Level A E B C D A E B C D S/N ratio for COF (db) 9.950 8.5.5 For each of performance measures an experiment is conducted for different combination of factors and results are compared with those obtained from the predictive equation as shown in Table (b).
(AGUIJST) 08, Vol. No., Jul-Dec e-issn: 55-09; p-issn: 55-808 Table (b) Results of the confirmation experiments for the specific wear rate Optimal control parameters Prediction Experiment % Error Level A E B C D A E B C D S/N ratio for SW (db) 08.8 0.850. The resulting equations seem to be capable of predicting the coefficient of friction and specific wear rate to the acceptable level of accuracy. An error of.5 for the S/N ratio of the coefficient of friction and. for the S/N ratio of the specific wear rate is observed. However if number of observations of performance characteristics are increased further these errors can be reduced. This validates the statistical approach used for predicting the measures of performance based on knowledge of the input parameters. CONCLUSIONS Following conclusions can be drawn based on the experimental results of this study: Design of experiments approach by Taguchi method enabled successfully to analyze the friction and wear behavior of the composites with normal load, speed, sliding distance and filler content as test variable. The experimental results show that the load and filler content are the main parameters among the five controllable factors (load, speed, sliding distance, roughness, filler content) that influence coefficient of friction and specific wear rate. The experimental results show that load and speed have percentage contribution 0.9% and.0% for coefficient of friction respectively. In the case of specific wear rate the filler content significant parameters statistically as compared to other parameters. The percentage contribution of filler content is 0.%. The results showed that the inclusion of cenosphere as filler materials in vinylester resin the composites the coefficient of friction decreases with the addition of wt% to 5wt% and wear resistance is increases for the addition of wt% to 5wt% of cenosphere significantly.
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