Natural fiber-reinforced polymer composites

Natural fiber-reinforced polymer composites: a comprehensive study on machining characteristics of hemp fiber-reinforced composites

2

Piyush Gohil1, Kundan Patel2 and Vijaykumar Chaudhary2 1 Mechanical Engineering Department, Faculty of Technology & Engineering, The M. S. University of Baroda, Vadodara, India, 2Mechanical Engineering Department, C.S. Patel Institute of Technology, CHARUSAT, Changa, India

2.1

Introduction

Nowadays, fiber-reinforced polymers (FRPs) have been widely used in many areas, such as research, industrial applications, etc. FRP materials are widely adopted by scientists, engineers, and researchers due to their superior properties. Due to their inherent superior properties, such as low weight, high strength-to-weight ratio, good corrosive and fatigue resistance, they can regularly replace conventionally used materials, such as metals and their alloys used in engineering applications [1]. In FRPs, synthetic and natural fibers are used as reinforcing material based on the desired applications. Composite material based on synthetic fibers possesses good mechanical and thermal properties and low water absorption capacity. Because of several environmental issues, disposal and recycling of synthetic fibers are dangerous and they can also create an adverse effect on the environment; in addition the cost of synthetic fibers is higher than that of natural fibers. Natural fibers may play an important role in developing biodegradable composite materials to overcome environmental problems [2]. The composites made from natural fibers have many advantages, such as less weight due to low density, better mechanical properties than synthetic fibers such as glass, carbon, and Kevlar, etc. Due to the superior properties of composites made from natural fibers, they are used in aerospace industries, automobile applications, and construction industries and are also used in goods-packing industries [3]. Hemp fibers have been increasingly used as reinforcement in polymer composites. In particular, their composites show higher specific stiffness than glass fiber composites in both tension and plate bending and only slightly lower values than carbon fiber composites in plate bending. Moreover, hemp fibers possess a much higher vibration-damping capacity, making them excellent candidates for Biomass, Biopolymer-Based Materials, and Bioenergy. DOI: https://doi.org/10.1016/B978-0-08-102426-3.00002-3 © 2019 Elsevier Ltd. All rights reserved.

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Biomass, Biopolymer-Based Materials, and Bioenergy

applications in sporting goods or musical instruments. The attraction of designers for these bio-based materials combined with the recent summary in the market of new, composite-oriented preforms of hemp fibers, are rapidly increasing the number and variety of composite products using hemp fibers as reinforcement [4]. Bourmaud and Baley [5] have shown that during such a recycling operation, hemp fibers do not fracture as easily as glass fibers, resulting in an almost constant aspect ratio for hemp
polypropylene (PP) injection-molded composites. Hence, the loss in mechanical properties in hemp
PP is negligible, whereas it is important in glass
PP [5,6]. When discussing the potential and advantages of flax and hemp fibers within the composites industry, a concern is often raised, namely that the variability of the fiber properties would be higher and it would be more difficult to control than in the case of manmade glass and carbon fibers [6]. Machining is an important process which is very necessary in the assembly of components made from FRPs. Various machining processes, such as drilling, milling, turning, and other unconventional machining processes, are used to achieve near net shape and size of product or component made from FRPs. Drilling is the most common and widely used machining operation for making holes in composite material for ease of assembly. The drilling mechanism for FRPs is quite different from drilling of metals and alloys because, in FRPs, the drill bit has to cut alternate layers of matrix and reinforcement material, which may cause damage around the drilled hole. The damage that occurs around the drilled hole depends on the torque and thrust force (TF) generated during the drilling operation. The TFs generated during the drilling operation should be minimized by selecting the proper cutting parameters such as spindle speed, feed rate, and also drill bit geometry [7].

2.2

Literature survey

The majority of research has been carried out for synthetic fiber-reinforced composites. Some researchers have investigated the drilling of natural fiber-reinforced composites using numerous input parameters. Bajpai and Singh [7] observed the effect of different drill bit geometries during drilling of sisal fiber-reinforced composite. They suggested that the trepanning type drill bit is most suitable for minimizing TF and damage during drilling. Debnath et al. [8] showed a comparison between two different types of sheet made from thermoset and thermoplastics resin having sisal as the reinforcing material. The study concluded that less TF and torque developed during drilling of composite sheets made from thermoplastics resin (polypropylene resin). Jayabal and Natrajan [9] performed a drilling operation on a coir fiberreinforced composite by varying the drill bit diameter (6
10 mm), spindle speed (600
1800 rpm), and feed rate (0.05
0.35 mm/rev). Based on their study they suggested that 6 mm drill tool diameter, 600 rpm spindle speed, and 0.3 mm/rev are optimum drilling parameters for coir FRP composites. Yallew et al. [10] studied the effect of drill bit geometry and cutting parameters on TF and torque produced during drilling of jute fiber-reinforced composite. They

Natural fiber-reinforced polymer composites

27

observed that the feed rate is a major factor, which has more influence on the TF and delamination factor (DF) value. They found that parabolic type drill bit geometry shows better cutting behavior than Jo and twist drill bit geometry. Balaji et al. [11] prepared four different types of composite sheet made from coir fiber. They used an high speed steel (HSS) twist drill for making holes in woven and nonwoven coir fiber-reinforced composite sheets. They observed that woven coir composite treated with alkali solution exhibited less delamination damage than the other three types of coir-reinforced composite sheets. Babu et al. [12] made a comparison of delamination damage between different natural fibers. They observed that less delamination damage occurred in hemp fiber-reinforced composite sheets. They also suggested that high spindle speed with lower feed rate are optimum parameters for making holes in composite sheets. Azuan [13] calculated the delamination damage value of coconut fiberreinforced composite. They observed that the delamination damage value is mainly affected by the feed rate. Naveen et al. [13a] carried out drilling on glass and hemp fiber-reinforced composite by varying the fiber volume fraction. They suggested that high spindle speed, lower feed rate, and 30% fiber volume fraction are optimum conditions to achieve less damage in glass and hemp fiber-reinforced composite sheets. Bajpai et al. [14] prepared a composite from sisal and Grewia optiva fibers with polyactic acid as the binder material. They performed drilling by taking twist, Jo, and parabolic type drill bits. They found that the Jo type drill bit caused more delamination damage on both composite sheets. They also observed that more TF developed during drilling of the ploy lactic acid / glass (PLA/G) type composite sheet. Venkateshkaran and ElayaPerumal [15] performed drilling on a banana fiberreinforced composite sheet using an HSS drill bit with 10 mm diameter. They observed that the cutting speed and feed rate have the same contribution to delamination damage during drilling. Babu et al. [16] measured the damage during drilling of an HFRP composite and also measured the residual tensile strength of drilled laminates. They observed that the residual tensile strength of drilled laminates is less affected by delamination damage that occurred during drilling. Chandramohan and Marimuthu [17] carried out drilling on banana, sisal, and roselle fiber-reinforced composite sheets using an HSS twist drill tool to study the effect of drill tool diameter on the TF and torque value. They observed that the feed rate and drill tool diameter are the main factors which have an influence on TF and torque value. Patel et al. [18] carried out a drilling operation on randomly oriented banana fiber-reinforced composite by varying the drill bit point angle. They suggested that low feed rate, high spindle speed, with low point angle of the drill bit are optimum conditions for minimizing TF and achieving high quality of drilled holes. Debnath et al. [19] developed a special drill bit having 10 mm diameter for drilling of sisal and nettle fiber-reinforced composites. They observed that a lower amount of TF and torque was produced when drilling is carried out using a specially designed tool. They also observed that the newly developed tool took less

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Biomass, Biopolymer-Based Materials, and Bioenergy

time to make a hole in composite and produced less damage as compared to a traditional twist drill. Chaudhary and Gohil [20] investigated the effect of drill bit point angle and cutting parameter on bidirectional cotton fiber-reinforced composite. The study concluded that low feed rate, low point angle of drill bit, and high spindle speed are optimum conditions for minimizing TF and damage during drilling. Vinayagamoorthy [21] observed the effect of drill tool diameter and drill bit point angle during drilling of a steel
jute hybrid composite. He also optimized the cutting parameters by using a Box
Behnken approach. He found that tool diameter, drill bit point angle, and feed rate are major factors influencing the TF value. Ramesh et al. [22] investigated the effect of different types of drill bits during drilling of sisal with S-glass hybrid composite. They observed that an HSS drill bit generates more TF and damage than solid carbide- and TiN-coated solid carbide drill bits. Chandrasekaran and Santhanam [23] studied the effect of fiber content on delamination and TF value during drilling of an E-glass hybrid composite. They suggested that 20% fiber volume fraction with 1400 rpm and 0.05 mm/rev are optimum parameters for drilling of chopped and woven-type hybrid composites. Jayabal et al. [24] suggested optimum parameters for minimization of TF, torque, and tool wear during drilling of glass
coir hybrid composites. The optimum parameters were 0.2 mm/rev feed rate, 8 mm drill bit diameter, and 1503 rpm spindle speed. Vinayagamorthy et al. [25] reported that the stacking sequence of reinforcement and spindle speed are important parameters which can affect the surface roughness and delamination damage value of an E-glass hybrid composite. Ramesh et al. [22] suggested that moderate spindle speed and low feed rate are preferable conditions for drilling of glass-sisal-jute hybrid composite.

2.3

Specimen preparation method

To fabricate composite, woven hemp fibers were cut into the required dimensions (300 3 300 mm) as shown in Fig. 2.1. Using a hand lay-up method pure hemp polyester composite was fabricated. The prepared composite specimen is shown in Fig. 2.2.

Figure 2.1 Woven hemp mats.

Natural fiber-reinforced polymer composites

29

Figure 2.2 Prepared composite specimens.

2.4

Mechanical characterization

Mechanical characterization was carried out at CHARUSAT, Mechanical Engineering Department, Chandubhai S. Patel Institute of Technology, Changa. A universal testing machine (Tinius Olsen/LSeries H50KL) was used for tensile and flexural testing. The set up for tensile and flexural testing is shown in Fig. 2.3. The samples were prepared for tensile testing according to ASTM D638 standard. The samples were prepared for flexural testing according to ASTM D790 standard. Table 2.1 shows the results of testing the tensile and flexural properties for the composite specimen.

2.5

Experimental design for drilling

The drilling input parameters selected for this study were drill geometry, spindle speed, and feed. The details of selected parameters are shown in Table 2.2. As little literature is available on drilling of hemp polyester composites, a general full factorial design is used for planning the number of experiments. Fig. 2.4 shows the test setup for performing these experiments.

2.6

Delamination determination method

In this investigation, the DF was measured using image analysis with the help of the MATLAB program. Fig. 2.5 shows a depiction of a DF. The images of drilled holes were taken using a 3D microscope (Mitutoyo, QS-L2010ZB), shown in Fig. 2.6. The images were taken at the same magnification and using ImageJ software they were converted into binary. Using MATLAB program the pixels were found for damaged areas as well as for hole area. The process for finding the DF is shown in Fig. 2.7.

Figure 2.3 Setup for mechanical characterization: (A) tensile test; (B) flexural test. Table 2.1 Flexural properties for different composite specimens Tensile strength (MPa)

Tensile modulus (MPa)

Flexural strength (MPa)

Flexural modulus (MPa)

76.5

1280

106

4070

Table 2.2 Process parameters and their levels Parameters/factors

Symbol/units

Levels

Drill geometry Spindle speed Feed

g s (rpm) f (mm/rev)

Plexi, center, parabolic 1000, 3000, 5000 0.06, 0.18, 0.3

Figure 2.4 Experimental setup.

Figure 2.5 Schematic representation of the delamination factor.

Figure 2.6 3D microscope.

Figure 2.7 Process for finding the delamination factor.

32

2.7

Biomass, Biopolymer-Based Materials, and Bioenergy

Results and discussion

The values of responses as per full factorial design are shown in Table 2.3. An average of two experiment runs were taken for response values.

2.7.1 Effect of process parameters on TF The main effect plot of TF for tool geometry is shown in Fig. 2.8. It was observed that the higher TF is generated for the plexi point drill bit than the center and parabolic drills. The center and parabolic drills generated almost the same TF. This fact was due to steps in the diameter of the center drill bit and the parabolic flues allow chips to flow easily. The main effect plot of TF for feed is shown in Fig. 2.9. It is observed that the TF increases with an increase in feed. This was due to an increase in the cross-sectional area of undeformed chips. While drilling at greater feed, the Table 2.3 Experimental runs Sr. no.

Tool geometry

Speed (rpm)

Feed (mm/rev)

TF (N)

Torque (Nm)

DF at entry

DF at exit

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Plexi Plexi Plexi Plexi Plexi Plexi Plexi Plexi Plexi Center Center Center Center Center Center Center Center Center Parabolic Parabolic Parabolic Parabolic Parabolic Parabolic Parabolic Parabolic Parabolic

1000 1000 1000 3000 3000 3000 5000 5000 5000 1000 1000 1000 3000 3000 3000 5000 5000 5000 1000 1000 1000 3000 3000 3000 5000 5000 5000

0.06 0.18 0.30 0.06 0.18 0.30 0.06 0.18 0.30 0.06 0.18 0.30 0.06 0.18 0.30 0.06 0.18 0.30 0.06 0.18 0.30 0.06 0.18 0.30 0.06 0.18 0.30

47.18 59.39 83.81 47.18 71.60 74.65 44.13 65.50 80.76 31.92 53.29 77.71 34.97 50.24 74.65 34.97 50.24 71.60 34.97 50.24 71.60 34.97 56.34 68.55 38.03 56.34 68.55

0.1124 0.2233 0.2344 0.1429 0.1581 0.2192 0.0971 0.1581 0.2039 0.2039 0.3107 0.4175 0.1886 0.2649 0.3260 0.1429 0.2344 0.3146 0.0818 0.1124 0.1429 0.0818 0.0971 0.1124 0.0818 0.1124 0.1276

1.4088 1.6116 1.9062 1.4976 1.5078 1.6716 1.4548 1.4439 1.6371 1.4842 1.7216 2.2838 1.5636 1.5616 1.9721 1.4515 1.5232 1.9020 1.3656 1.4610 1.8052 1.4957 1.4490 1.7745 1.5342 1.4026 1.6476

1.4846 1.7139 1.7810 1.5213 1.5243 1.7171 1.4904 1.5634 1.5930 1.5853 1.8546 2.2632 1.4396 1.5455 1.8922 1.4368 1.5380 1.8459 1.3718 1.5567 1.9220 1.3666 1.5150 1.9666 1.3363 1.4546 1.7299

Natural fiber-reinforced polymer composites

33

Main effects plot for thrust force (N) Data means 65.0

Mean

62.5 60.0 57.5 55.0

Plexi

Center

Parabolic

Tool geometry

Figure 2.8 Main effects plot for tool geometry versus TF. Main effects plot for thrust force (N) Data means 80

Mean

70

60

50

40 0.06

0.18

0.30

Feed (mm/rev)

Figure 2.9 Main effects plot for feed versus TF.

resistance offered by work material in the direction of drilling is greater, thus leading to greater friction which increases the TF. Moreover, at greater feed, there is an improvement in the contact area flanked by the drill and the work material, which increases the TF [26]. The main effect plot of TF for speed is shown in Fig. 2.10. Within the cutting range tested, there is almost no effect of speed on TF. Many researchers have observed the same behavior [27
31]. ANOVA was carried out for TF in drilling of composites. Table 2.4 shows the ANOVA results for the TF. The P value from the ANOVA results represents that the drill geometry and feed have significant effects on the TF. The TF is not significantly affected by the speed. The drill geometry and feed affect the TF by 10.05% and 88.18%, respectively. The adjusted R2 value for TF (95.49%) suggests a satisfactory fitting of the model.

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Biomass, Biopolymer-Based Materials, and Bioenergy

Main effects plot for thrust force (N) Data means 60

Mean

58 56 54 52 50

1000

3000

5000

Speed (rpm)

Figure 2.10 Main effects plot for speed versus TF. Table 2.4 ANOVA table for TF Source

DF

Seq SS

Adj SS

Adj MS

F

P

% Contribution

g s f g s g f s f Error

2 2 2 4 4 4 8

663.18 0.69 5816.11 13.8 86.26 84.19 93.85

663.18 0.69 5816.11 13.8 86.26 84.19 93.85

331.59 0.35 2908.05 3.45 21.57 21.05 11.73

28.26 0.03 247.88 0.29 1.84 1.79

0 0.971 0 0.874 0.215 0.223

10.05 0.01 88.18 0.10 0.65 0.63

Total

26

6758.08

S 5 3.42514

3297.79 R 5 98.61% 2

R2 (adj) 5 95.49%

2.7.2 Effect of process parameters on torque The main effect plot of torque for tool geometry is shown in Fig. 2.11. It was observed that the higher torque is generated for the center drill bit than the plexi and parabolic drills. The parabolic drill generated the lowest torque. This was due to parabolic flutes allowing chips to flow easily. The main effect plot of torque for feed is shown in Fig. 2.12. It is observed that the torque increases with an increase in the feed. This was due to an increase in TF with an increase in feed. The main effect plot of torque for speed is shown in Fig. 2.13. It is observed that the torque decreases with an increase in speed. ANOVA was carried out for torque in drilling of composites. Table 2.5 shows the ANOVA results for the torque. The P value from the ANOVA results represents that the drill geometry, feed, and speed have significant effects on the torque. The drill geometry, feed, and speed affect the torque by 62.91%, 27.58%, and 4.12%,

Main effects plot for torque (Nm) Data means 0.28 0.26 0.24

Mean

0.22 0.20 0.18 0.16 0.14 0.12 0.10 Plexi

Center

Parabolic

Tool geometry

Figure 2.11 Main effects plot for tool geometry versus torque. Main effects plot for torque (Nm) Data means 0.24 0.22

Mean

0.20 0.18 0.16 0.14 0.12 0.06

0.18

Feed (mm/rev)

0.30

Figure 2.12 Main effects plot for feed versus torque.

Main effects plot for torque (Nm) Data means 0.21

Mean

0.20 0.19 0.18 0.17 0.16 1000

3000

Speed (rpm)

Figure 2.13 Main effects plot for speed versus torque.

5000

Table 2.5 ANOVA table for torque Source

DF

Seq SS

Adj SS

Adj MS

F

P

% Contribution

g s f g s g f s f Error

2 2 2 4 4 4 8

0.118573 0.007771 0.051986 0.0045 0.012535 0.002415 0.001648

0.118573 0.007771 0.051986 0.0045 0.012535 0.002415 0.001648

0.059286 0.003886 0.025993 0.001125 0.003134 0.000604 0.000206

287.86 18.87 126.21 5.46 15.22 2.93

0 0.001 0 0.02 0.001 0.091

62.91 4.12 27.58 1.19 3.32 0.64

Total

26

0.199428

S 5 0.0143511

0.094234 R 5 99.17% 2

R2 (adj) 5 97.31%

Natural fiber-reinforced polymer composites

37

Interaction plot for torque (Nm) Data means Plexi

Center Parabolic

0.06

0.18

0.30 0.3

Speed (rpm)

0.2

Speed (rpm) 1000 3000 5000

0.1 0.3

Tool geometry

0.2

Tool Geometry Plexi Center Parabolic

0.1 Feed (mm/rev)

Figure 2.14 Interaction plot for torque.

respectively. Also, the interactions between speed and geometry, and between geometry and feed, are significant. However, the effect of these interactions is much less compared to individual factors. The adjusted R2 value for torque (97.31%) suggests a satisfactory fitting of the model. The interaction plot for torque is shown in Fig. 2.14. It can be seen from the interaction plot between the geometry and speed that torque is almost the same for a parabolic drill at all speeds. Meanwhile, for center and plexi point drills, the torque decreases with an increase in speed. The maximum torque was observed for the center drill at all speeds than other tool geometries. The interaction plot between geometry and feed for torque shows that the torque increases as feed increases for all drill geometries used, but the increment in torque for the parabolic drill is less compared to the center and plexi point drills.

2.7.3 Effect of process parameters on DF at entry The main effect plot of DF at entry for geometry is shown in Fig. 2.15. It is observed that the lowest DF at entry occurred using a parabolic drill tool. Since the axial forces acting on the side of the drill tend to peel-up the first laminate of the composite, as the parabolic flutes allow chips to flow easily the axial force acting on the side of the drill will be less. The main effect plot of DF at entry for feed is shown in Fig. 2.16. It shows that, as the feed increases, the DF at entry value increases. The main effect plot of DF at entry for speed is shown in Fig. 2.17. It shows that the DF at entry decreases with an increase in speed. Table 2.6 shows the ANOVA table for DF at entry. The P value from the ANOVA results represents that the drill geometry, speed, and feed have significant effects on the DF at entry. The drill geometry, feed, and speed affect the DF at

Main effects plot for DF at entry Data means 1.725 1.700

Mean

1.675 1.650 1.625 1.600 1.575 1.550 Plexi

Center

Parabolic

Tool geometry

Figure 2.15 Main effects plot for tool geometry versus DF at entry.

Main effects plot for DF at entry Data means 1.9

Mean

1.8

1.7

1.6

1.5 0.06

0.18

0.30

Feed (mm/rev)

Figure 2.16 Main effects plot for feed versus DF at entry. Main effects plot for DF at entry Data means 1.675

Mean

1.650 1.625 1.600 1.575 1.550 1000

3000

Speed (rpm)

Figure 2.17 Main effects plot for speed versus DF at entry.

5000

Table 2.6 ANOVA table for DF at entry Source

DF

Seq SS

Adj SS

Adj MS

F

P

% Contribution

g s f g s g f s f Error

2 2 2 4 4 4 8

0.152982 0.06144 0.736233 0.032029 0.086154 0.100136 0.010428

0.152982 0.06144 0.736233 0.032029 0.086154 0.100136 0.010428

0.076491 0.03072 0.368117 0.008007 0.021539 0.025034 0.001303

58.68 23.57 282.42 6.14 16.52 19.21

0 0 0 0.015 0.001 0

14.39 5.78 69.29 1.50 4.05 4.71

Total

26

1.179403

S 5 0.0361034

0.531211 R 5 99.12% 2

R2 (adj) 5 97.13%

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Biomass, Biopolymer-Based Materials, and Bioenergy

Interaction plot for DF at entry Data means Plexi

Center Parabolic 0.06

0.18

0.30 2.00 1.75

Speed (rpm)

1.50 2.00 1.75

Tool geometry

Speed (rpm) 1000 3000 5000 Tool Geometry Plexi Center Parabolic

1.50

Feed (mm/rev)

Figure 2.18 Interaction plot for DF at entry.

entry by 14.39%, 69.29%, and 5.78%, respectively. The adjusted R2 value for DF at entry (97.13%) suggests a satisfactory fitting of the model. Also, the interactions between geometry and speed, geometry and feed, and speed and feed are significant. The interaction plot for DF at entry is shown in Fig. 2.18. It can be seen from the interaction plot between geometry and speed that maximum DF at entry was observed for the center drill tool at 1000 rpm and minimum DF at entry was observed for the plexi point drill tool at 5000 rpm. The interaction plot between geometry and feed for DF at entry shows that, as feed increases, DF at entry increases for all drill geometries. Maximum DF at entry is observed for the center drill bit at all feed levels. The interaction plot between speed and feed for DF at entry shows that as feed increases, DF at entry increases for all speed levels. The minimum DF at entry was observed for 0.06 mm/rev feed at 1000 rpm.

2.7.4 Effect of process parameters on DF at exit The main effect plot of DF at exit for geometry is shown in Fig. 2.19. It is observed that the parabolic and plexi point drills generate lower DF at exit than the center drill. This fact was due to a lower point angle of the plexi point drill bit and the parabolic flues allow chips to flow easily. At a lower point angle the stresses and shear area are reduced. The main effect plot of DF at exit for feed is shown in Fig. 2.20. It shows that, increasing the feed resulted in an increase in the DF at exit. The reason may be an increase in TF. The TF increases with an increase in feed. When the drill tool moves toward the hole exit side, the uncut plies under the tool become more susceptive to deformation owing to a decrease in its thickness. This causes

Natural fiber-reinforced polymer composites

41

Main effects plot for DF at exit Data means 1.72 1.70

Mean

1.68 1.66 1.64 1.62 1.60 1.58 Plexi

Center

Parabolic

Tool geometry

Figure 2.19 Main effects plot for tool geometry versus DF at exit.

Main effects plot for DF at exit Data means 1.9

Mean

1.8 1.7 1.6 1.5 1.4 0.06

0.18

0.30

Feed (mm/rev)

Figure 2.20 Main effects plot for feed versus DF at exit.

delamination of the layer. The main effect plot of DF at exit for speed is shown in Fig. 2.21. It shows that increasing the speed resulted in a decrease in the DF at exit. Table 2.7 shows the ANOVA table for DF at exit. The P value from the ANOVA results represents that the drill geometry, speed, and feed have significant effects on the DF at exit. The drill geometry, feed, and speed affect the DF at exit by 8.07%, 69.35%, and 12.29%, respectively. The adjusted R2 value for DF at exit (96.46%) suggests a satisfactory fitting of the model. Also, the interactions between geometry and speed, geometry and feed, and speed and feed are significant. The interaction plot for DF at exit is shown in Fig. 2.22. It can be seen from the interaction plot between geometry and speed that maximum DF at exit was observed for the center drill tool at 1000 rpm and minimum DF at exit was

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Biomass, Biopolymer-Based Materials, and Bioenergy

Main effects plot for DF at exit Data means 1.75

Mean

1.70

1.65

1.60

1.55 3000

1000

5000

Speed (rpm)

Figure 2.21 Main effects plot for speed versus DF at exit.

observed for the parabolic point drill tool at 5000 rpm. The interaction plot between the geometry and feed for DF at exit shows that as feed increases, DF at exit increases for all drill geometries. Maximum DF at exit is observed for the center drill bit at 0.03 mm/rev. The interaction plot between speed and feed for DF at exit shows that as feed increases DF at exit increases for all speed levels. The DF at exit is almost the same for all speed levels at 0.06 mm/rev feed.

2.8

Regression analysis

The regression analysis helps to approximate the value of one variable from the given value of another. Regression modeling was carried out to propose empirical models for the TF, torque, and DF at entry and exit. The empirical models as determined by regression analysis to predict TF, torque, and DF at entry and exit are shown in Table 2.8.

2.9

Gray relational analysis

As each of the process parameters gives conflicting optimal solutions, it is important to arrive at an optimized solution. To optimize TF, torque, and DFs at the same time for improved productivity a gray relational analysis (GRA) is used. The methodology adopted for GRA is according to Rajmohan [32]. The distinguish coefficient was considered as 0.5. The first step in GRA includes linear normalization of the DOE data according to the type of performance response. It is desired that TF, and DF at entry and exit should be minimum so that the-lower-the-better performance responses were

Table 2.7 ANOVA table for DF at exit Source

DF

Seq SS

Adj SS

Adj MS

F

P

% Contribution

g s f g s g f s f Error

2 2 2 4 4 4 8

0.090712 0.138075 0.778801 0.067565 0.114381 0.041882 0.013562

0.090712 0.138075 0.778801 0.067565 0.114381 0.041882 0.013562

0.045356 0.069037 0.3894 0.016891 0.028595 0.01047 0.001695

26.75 40.72 229.7 9.96 16.87 6.18

0 0 0 0.003 0.001 0.014

8.07 12.29 69.35 3.00 5.09 1.86

Total

26

1.244977

S 5 0.0411737

0.561444 R2 5 98.91%

R2 (adj) 5 96.46%

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Biomass, Biopolymer-Based Materials, and Bioenergy

Interaction plot for DF at exit Data means Plexi

Center Parabolic 0.06

0.18

0.30 2.00

Speed (rpm) 1000 3000 5000

1.75

Speed (rpm) 1.50 2.00

Tool Geometry Plexi Center Parabolic

1.75

Tool geometry

1.50

Feed (mm/rev)

Figure 2.22 Interaction plots for DF at exit.

Table 2.8 Emperical models TF Plexi Center Parabolic

TF 5 35:7586 1 0:00095383 3 s 1 155:792 3 f 2 0:00529905 3 s 3 f TF 5 21:43 1 0:000445121 3 s 1 185:467 3 f 2 0:005299905 3 s 3 f TF 5 23:7192 1 0:00146254 3 s 1 155:792 3 f 2 0:00529905 3 s 3 f

S 5 3.40359

R2 5 97.09%

R2 (adj) 5 95.54%

PRESS 5 419.747

R2 (pred) 5 93.79%

Torque Plexi Center Parabolic

T 5 0:110015 2 4:71905 3 1026 3 s 1 0:499246 3 f 2 2:51315 3 1025 3 s 3 f T 5 0:182881 2 4:5495 3 1025 3 s 1 0:801378 3 f 2 2:51315 3 1025 3 s 3 f T 5 0:0614864 1 3:25212 3 1026 3 s 1 0:266128 3 f 2 2:51315 3 1025 3 s 3 f

S 5 0.0162871

R2 5 97.74%

R2 (adj) 5 96.54%

PRESS 5 0.011976

R2 (pred) 5 93.99%

DF at entry Plexi Center Parabolic

DF at entry 5 1:26962 1 2:93333 3 1025 3 s 1 2:21736 3 f 2 0:000343889 3 s 3 f DF at entry 5 1:27105 1 1:0825 3 1025 3 s 1 3:33528 3 f 2 0:000343889 3 s 3 f DF at entry 5 1:16658 1 5:795 3 1025 3 s 1 2:18694 3 f 2 0:000343889 3 s 3 f

S 5 0.0973076

R2 5 86.35%

R2 (adj) 5 79.13%

PRESS 5 0.3729

R2 (pred) 5 68.38%

DF at exit Plexi Center Parabolic

DF at exit 5 1:41715 1 1:09752 3 1025 3 s 1 1:4711 3 f 2 0:000214997 3 s 3 f DF at exit 5 1:43083 2 3:48331 3 1025 3 s 1 2:78331 3 f 2 0:000214997 3 s 3 f DF at exit 5 1:16032 1 1:12244 3 1025 3 s 1 2:78916 3 f 2 0:000214997 3 s 3 f

S 5 0.0784940

R2 5 91.59%

R2 (adj) 5 87.13%

PRESS 5 0.2441

R2 (pred) 5 80.39%

Natural fiber-reinforced polymer composites

45

considered. The normalized data for responses are shown in Table 2.9, which are carried out as per the equation given below: xi ðkÞ 5

maxxði 0Þ ðkÞ 2 xði 0Þ ðkÞ

maxxði 0Þ ðkÞ 2 minxði 0Þ ðkÞ

where, xði 0Þ ðkÞ 5 original sequence xi ðkÞ 5 sequence after data processing maxxði 0Þ ðkÞ 5 largest value of xði 0Þ ðkÞ minxði 0Þ ðkÞ 5 smallest value of xði 0Þ ðkÞ

Table 2.9 Normalized data for responses Sr. no.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Tool geometry

Plexi Plexi Plexi Plexi Plexi Plexi Plexi Plexi Plexi Center Center Center Center Center Center Center Center Center Parabolic Parabolic Parabolic Parabolic Parabolic Parabolic Parabolic Parabolic Parabolic

Speed (rpm)

1000 1000 1000 3000 3000 3000 5000 5000 5000 1000 1000 1000 3000 3000 3000 5000 5000 5000 1000 1000 1000 3000 3000 3000 5000 5000 5000

Feed (mm/rev)

0.06 0.18 0.3 0.06 0.18 0.3 0.06 0.18 0.3 0.06 0.18 0.3 0.06 0.18 0.3 0.06 0.18 0.3 0.06 0.18 0.3 0.06 0.18 0.3 0.06 0.18 0.3

Smaller the better Thrust force (N)

Torque (Nm)

DF at entry

DF at exit

0.7059 0.4706 0.0000 0.7059 0.2353 0.1765 0.7647 0.3529 0.0588 1.0000 0.5882 0.1176 0.9411 0.6470 0.1765 0.9411 0.6470 0.2353 0.9411 0.6470 0.2353 0.9411 0.5294 0.2941 0.8823 0.5294 0.2941

0.9090 0.5786 0.5454 0.8181 0.7726 0.5908 0.9544 0.7726 0.6363 0.6363 0.3181 0.0000 0.6817 0.4544 0.2726 0.8181 0.5454 0.3064 0.9999 0.9090 0.8181 1.0000 0.9544 0.9090 0.9999 0.9090 0.8635

0.9530 0.7321 0.4112 0.8562 0.8451 0.6667 0.9029 0.9147 0.7043 0.8708 0.6123 0.0000 0.7844 0.7865 0.3395 0.9064 0.8284 0.4158 1.0000 0.8961 0.5212 0.8583 0.9092 0.5547 0.8164 0.9597 0.6929

0.8400 0.5926 0.5202 0.8004 0.7972 0.5892 0.8337 0.7550 0.7231 0.7314 0.4408 0.0000 0.8886 0.7743 0.4003 0.8916 0.7824 0.4502 0.9617 0.7622 0.3681 0.9673 0.8072 0.3200 1.0000 0.8724 0.5754

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Biomass, Biopolymer-Based Materials, and Bioenergy

Table 2.10 Deviation data for responses Sr. no.

Tool geometry

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Plexi Plexi Plexi Plexi Plexi Plexi Plexi Plexi Plexi Center Center Center Center Center Center Center Center Center Parabolic Parabolic Parabolic Parabolic Parabolic Parabolic Parabolic Parabolic Parabolic

Speed (rpm)

1000 1000 1000 3000 3000 3000 5000 5000 5000 1000 1000 1000 3000 3000 3000 5000 5000 5000 1000 1000 1000 3000 3000 3000 5000 5000 5000

Feed (mm/rev)

0.06 0.18 0.3 0.06 0.18 0.3 0.06 0.18 0.3 0.06 0.18 0.3 0.06 0.18 0.3 0.06 0.18 0.3 0.06 0.18 0.3 0.06 0.18 0.3 0.06 0.18 0.3

Deviation Thrust force (N)

Torque (Nm)

DF at entry

DF at exit

0.2941 0.5294 1.0000 0.2941 0.7647 0.8235 0.2353 0.6471 0.9412 0.0000 0.4118 0.8824 0.0589 0.3530 0.8235 0.0589 0.3530 0.7647 0.0589 0.3530 0.7647 0.0589 0.4706 0.7059 0.1177 0.4706 0.7059

0.0910 0.4214 0.4546 0.1819 0.2274 0.4092 0.0456 0.2274 0.3637 0.3637 0.6819 1.0000 0.3183 0.5456 0.7274 0.1819 0.4546 0.6936 0.0001 0.0910 0.1819 0.0000 0.0456 0.0910 0.0001 0.0910 0.1365

0.0470 0.2679 0.5888 0.1438 0.1549 0.3333 0.0971 0.0853 0.2957 0.1292 0.3877 1.0000 0.2156 0.2135 0.6605 0.0936 0.1716 0.5842 0.0000 0.1039 0.4788 0.1417 0.0908 0.4453 0.1836 0.0403 0.3071

0.1600 0.4074 0.4798 0.1996 0.2028 0.4108 0.1663 0.2450 0.2769 0.2686 0.5592 1.0000 0.1114 0.2257 0.5997 0.1084 0.2176 0.5498 0.0383 0.2378 0.6319 0.0327 0.1928 0.6800 0.0000 0.1276 0.4246

The normalized values range between zero and one; the larger values yield better performance and the ideal value should be equal to one, x0(k) 5 1. The deviation values are shown in Table 2.10. After data preprocessing, a gray relational coefficient (GRC) can be calculated using the preprocessed sequences. The GRC is obtained from the following equation: GRC 5 where,

Δmin 1 ζΔmax Δ0i ðkÞ 1 ζΔmax

Δ0i ðkÞ 5 x0 ðkÞ 2 xi ðkÞ Δmax 5 max ’ jAi max ’ k x0 ðkÞ 2 xi ðkÞ

Natural fiber-reinforced polymer composites

47

Table 2.11 Gray relational coefficient and gray relational grades Sr. no.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Gray relational coefficient

GRG

Thrust force (N)

Torque (Nm)

DF at entry

DF at exit

0.6296 0.4857 0.3333 0.6296 0.3953 0.3778 0.6800 0.4359 0.3469 1.0000 0.5484 0.3617 0.8947 0.5862 0.3778 0.8947 0.5862 0.3953 0.8947 0.5862 0.3953 0.8947 0.5151 0.4146 0.8095 0.5151 0.4146

0.8460 0.5426 0.5238 0.7332 0.6874 0.5499 0.9165 0.6874 0.5789 0.5789 0.4230 0.3333 0.6110 0.4782 0.4074 0.7332 0.5238 0.4189 0.9998 0.8460 0.7332 1.0000 0.9165 0.8460 0.9998 0.8460 0.7856

0.9140 0.6511 0.4592 0.7767 0.7635 0.6001 0.8373 0.8543 0.6284 0.7947 0.5632 0.3333 0.6987 0.7008 0.4308 0.8424 0.7444 0.4612 1.0000 0.8280 0.5108 0.7792 0.8463 0.5289 0.7314 0.9254 0.6195

0.7576 0.5510 0.5103 0.7147 0.7114 0.5489 0.7505 0.6711 0.6435 0.6505 0.4721 0.3333 0.8177 0.6890 0.4547 0.8218 0.6968 0.4763 0.9289 0.6777 0.4417 0.9386 0.7217 0.4237 1.0000 0.7966 0.5408

0.7868 0.5576 0.4567 0.7136 0.6394 0.5192 0.7961 0.6622 0.5494 0.7560 0.5017 0.3404 0.7555 0.6136 0.4177 0.8230 0.6378 0.4379 0.9558 0.7345 0.5203 0.9031 0.7499 0.5533 0.8852 0.7708 0.5901

Δmin 5 min ’ jAi min ’ k x0 ðkÞ 2 xi ðkÞ ζ 5 distinguishing coefficient, ζA½0; 1

The gray relational grade is the weighted sum of the GRC. The gray relational grades are calculated by averaging the value of the GRC. The GRC and gray relational grades are shown in Table 2.11. The average gray relational grade for each factor level is shown in Table 2.12. From Table 2.12, the combination plexi point drill bit, 1000 rpm, and 0.06 mm/ rev are the optimal parameter combination for the current study where it is desired to reduce TF, torque, and DF at entry and exit.

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Biomass, Biopolymer-Based Materials, and Bioenergy

Table 2.12 Gray relational grades Levels

1 2 3

2.10

Factors Geometry

Speed

Feed

0.3588 0.2706 0.1573

0.3588 0.2706 0.1573

0.8195 0.6519 0.4872

Conclusions

This study emphasizes the drilling behavior of a hemp
polyester composite to simplify manufacturing of assembled components. The influences of feed, spindle speed, and drill geometry on TF, torque, and DFs were investigated using ANOVA and regression analysis. The optimum results of input parameters are attained through GRA. The main conclusions of studies on drilling of hemp
polyester composites are as follows: G

G

G

G

G

G

G

The TF increases with an increase in the feed rate, while there is no effect of speed on TF. Feed is the major determinant of the TF. Drill geometry is the major determinant for torque. The torque increases with an increase in feed, while it decreases with an increase in speed. Feed is the major determinant for DF at entry and exit. DF at entry and exit increases with an increase in feed. Empirical models for responses are developed using regressionand are influentially precise for estimation of the factors studied, within the boundaries. A distinguishable time can be saved by using these models. For minimization of TF, torque, and DF at entry and exit simultaneously, the feed of 0.06 mm/rev and plexi point drill tool, along with lower spindle speed of 1000 rpm, are essential for hemp
polyester composites.

Acknowledgments This work was carried out as a part of a research project sanctioned by the Science and Engineering Research Board (SERB), New Delhi (SB/FTP/ETA-113/2012 dated 10-29-2015).

References [1] Ramesh M, Palanikumar K, Reddy KH. Experimental investigation and analysis of machining characteristics in drilling hybrid glass-sisal-jute fiber reinforced polymer composites. In: 5th International and 26th All India Manufacturing Technology Design and Research Conference, 2014.

Natural fiber-reinforced polymer composites

49

[2] Harish S, Michael DP, Bensely A, Lal DM, Rajadurai A. Mechanical property evaluation of natural fiber coir composite. Mater Charact 2009;60(1):44
9. [3] Chandramohan D, Bharanichandar J. Studies on natural fiber particle reinforced composite material for conservation of natural resources. Adv Appl Sci Res 2014;5 (2):305
15. [4] Pil L, Bensadoun F, Pariset J, Verpoest I. Why are designers fascinated by flax and hemp fibre composites? Compos Part A Appl Sci Manuf 2016;83:193
205. [5] Bourmaud A, Baley C. Rigidity analysis of polypropylene/vegetal fibre composites after recycling. Polym Degrad Stab 2009;94(3):297
305. [6] Bourmaud A, Baley C. Investigations on the recycling of hemp and sisal fibre reinforced polypropylene composites. Polym Degrad Stab 2007;92(6):1034
45. [7] Bajpai PK, Singh I. Drilling behavior of sisal fiber-reinforced polypropylene composite laminates. J Reinf Plast Compos 2013;32(20):1569
76. [8] Debnath K, Singh I, Dvivedi A. Drilling characteristics of sisal fiber-reinforced epoxy and polypropylene composites. Mater Manuf Processes 2014;29(11
12):1401
9. [9] Jayabal S, Natarajan U. Drilling analysis of coir-fibre-reinforced polyester composites. Bull Mater Sci 2011;34(7):1563
7. [10] Yallew TB, Kumar P, Singh I. A study about hole making in woven jute fabricreinforced polymer composites. Proc Inst Mech Eng Pt L J Mater Des Appl 2016;230 (4):888
98. [11] Balaji NS, Jayabal S, Kalyana Sundaram S, Rajamuneeswaran S, Suresh P. Delamination analysis in drilling of coir-polyester composites using design of experiments. Advanced materials research, vol. 984. Trans Tech Publications; 2014. p. 185
93. [12] Dilli Babu G, Sivaji Babu K, Uma Maheswar Gowd B. Determination of delamination and tensile strength of drilled natural fiber reinforced composites. Applied mechanics and materials, vol. 592. Trans Tech Publications; 2014. p. 134
8. [13] Azuan SS. Effects of drilling parameters on delamination of coconut meat husk reinforced polyester composites. Adv Environ Biol 2013;1097
101. [13a] Naveen PNE, Yasaswi M, Prasad RV. Experimental investigation of drilling parameters on composite materials. IOSR Journal of Mechanical and Civil Engineering 2012;2(3):30
7. [14] Bajpai PK, Debnath K, Singh I. Hole making in natural fiber-reinforced polylactic acid laminates: an experimental investigation. J Thermoplast Compos Mater 2017;30 (1):30
46. [15] Venkateshwaran N, ElayaPerumal A. Hole quality evaluation of natural fiber composite using image analysis technique. J Reinf Plast Compos 2013;32(16):1188
97. [16] Babu GD, Babu KS, Gowd B. Optimization of machining parameters in drilling hemp fiber reinforced composites to maximize the tensile strength using design experiments. Indian J Eng Mater Sci 2013;20:385
90. [17] Chandramohan D, Marimuthu K. Drilling of natural fiber particle reinforced polymer composite material. Int J Adv Res Technol 2011;1(1):134
45. [18] Patel K, Chaudhary V, Gohil PP, Patel K. Investigation on drilling of banana fibre reinforced composites. In: International Conference on Civil, Materials and Environmental Sciences (CMES 2015) 2015. London, UK: Atlantis Press; 2015 Apr 1, vol. 1, p. 201
205. [19] Debnath K, Sisodia M, Kumar A, Singh I. Damage-free hole making in fiber-reinforced composites: an innovative tool design approach. Mater Manuf Processes 2016;31 (10):1400
8. [20] Chaudhary V, Gohil PP. Investigations on drilling of bidirectional cotton polyester composite. Mater Manuf Processes 2016;31(7):960
8.

50

Biomass, Biopolymer-Based Materials, and Bioenergy

[21] Vinayagamoorthy R. Parametric optimization studies on drilling of sandwich composites using the Box
Behnken design. Mater Manuf Processes 2017;32(6):645
53. [22] Ramesh M, Palanikumar K, Reddy KH. Influence of tool materials on thrust force and delamination in drilling sisal-glass fiber reinforced polymer (S-GFRP) composites. Procedia Mater Sci 2014;5:1915
21. [23] Chandrasekaran M, Santhanam V. A study on drilling behavior of banana-glass fibre reinforced epoxy composite, Chenai, India. Indian J Appl Res 2014;4(11):194
9. [24] Jayabal S, Natarajan U, Sekar U. Regression modeling and optimization of machinability behavior of glass-coir-polyester hybrid composite using factorial design methodology. Int J Adv Manuf Technol 2011;55(1
4):263
73. [25] Vinayagamoorthy R, Rajeswari N, Vijayshankar S, Balasubramanian K. Drilling performance investigations on hybrid composites by using D-optimal design. Work 2014;60 (90):120. [26] Basavarajappa S, Venkatesh A, Gaitonde VN, Karnik SR. Experimental investigations on some aspects of machinability in drilling of glass epoxy polymer composites. J Thermoplast Compos Mater 2012;25(3):363
87. [27] Rawat S, Attia H. Wear mechanisms and tool life management of WC
Co drills during dry high speed drilling of woven carbon fibre composites. Wear 2009;267 (5
8):1022
30. [28] Faraz A, Biermann D, Weinert K. Cutting edge rounding: an innovative tool wear criterion in drilling CFRP composite laminates. Int J Mach Tools Manuf 2009;49 (15):1185
96. [29] Liu D, Xu HH, Zhang CY, Yan HJ. Drilling force in high speed drilling carbon fibre reinforced plastics (CFRP) using half core drill. Advanced materials research, vol. 102. Trans Tech Publications; 2010. p. 729
32. [30] Khashaba UA, El-Sonbaty IA, Selmy AI, Megahed AA. Machinability analysis in drilling woven GFR/epoxy composites: part I
Effect of machining parameters. Compos Part A Appl Sci Manuf 2010;41(3):391
400. [31] Khashaba UA, El-Sonbaty IA, Selmy AI, Megahed AA. Machinability analysis in drilling woven GFR/epoxy composites: Part II
Effect of drill wear. Compos Part A Appl Sci Manuf 2010;41(9):1130
7. [32] Rajmohan T. Experimental investigation and optimization of machining parameters in drilling of fly ash-filled carbon fiber reinforced composites. Part Sci Technol 2016. Available from: http://dx.doi.org/10.1080/02726351.2016.1205686.