Mechanical Properties and Delamination Factor Evaluation of Cellulose (Nettle) Fiber Reinforced Polymer Composites using RSM

This paper discusses on fabrication, testing and evaluation of delamination factor of nettle ber based composites for low duty applications. The randomly oriented nettle bers were used to fabricate the biocomposite by conventional hand lap up technique. Epoxy and Nettle based composite plates were developed by varying ber weight percentage from 5% to 25%. The exural, tensile, impact, chemical resistance and water absorption rate of developed nettle ber based biocomposite were examined for different ber weight fractions in the randomly oriented patterns as a unique and innovative attempt. During the investigation, exural strength and tensile strength were improved up to 20 wt% of ber addition and then it was decreased. This resulted in a continuous rise in impact strength with an enhancement in ber wt. %. The inuence of ber weight percentage on water absorption and chemical resistance of fabricated composite was examined in different environments. The result showed that the nettle bers can be used as an essential reinforcing material to design and fabricate mechanical and structural members for low duty application. The chemical behavior of nettle based composite was studied by the FTIR spectroscopy method and the presence of chemical functional group was conrmed. The drilling behavior of developed nettle/SiC/epoxy hybrid composites was evaluated by consider cutting process parameters like feed rate (0.125, 0.212 and 0.3 mm/rev), spindle speed (400, 600, 800 rev/min) and drill diameter (4, 6, 8 mm). Analysis of variance was used in designing experiments for the current investigation. Feed rate was found to be a very impressive factor in inuencing the delamination factor.


Introduction
Natural ber composites have evolved as a lightweight and good strength material at the starting of twentieth century and their popularity has increased in recent time for various applications [Gholampour and Ozbakkaloglu 2020). The growth of natural bers was seen in a very short period and various industries like automobile, sports and aerospace were in a race to utilize its potential. India is a great resource of natural bers and many researchers are working to utilize its potential to develop structural and mechanical members of biocomposites. India holds second place in terms of bamboo resources in the world and scientists are continuously working to develop bamboo ber composites (Dev et al. 2020).
Plant based bers are categorized into three types namely mineral bers, animal bers and plant bers: amongst these, plant bers are famous for reinforcement in polymer resins. Figure 1 shows the graphical abstract of ber and epoxy and its fabricated samples.
Fibers from plants can be obtained from leaves, stems and stalk through chemical or mechanical extraction techniques (Paul et al. 2020). Plant ber like nettle, jute, hemp and ax were traditionally used to make ropes for domestic applications from ancient times. In the 21st century, nettle was used as a raw material for clothes and paper making. Nettle ber is considered as the best reinforcement constituent in thermoplastic because of its higher relative comparative strength as compared to other plant based bers. Many experimental and analytical studies have revealed that the inclusion of nettle bers as ller member will improve the mechanical performance of the neat polymers (Buyukkaya and Demirer 2020). The presence of cellulose and hemicellulose in nettle bers are the main responsible factors for higher strength and hydrophilic nature respectively; also the presence of lignin and pectin yields thermal stability and biodegradability to the bers (Viju and Thilagavathi 2019) The interfacial linkage between natural ber and polymer resin plays an important role in deciding the mechanical and thermal performance of the natural ber composites. Since the natural bers are obtained from natural process, so they have inherent moisture quantity. Due to the moisture content natural bers have poor wettability with polymers, which need to be improved by various chemicals techniques . Tensile and exural strength of biocomposites improves with the addition of ber content up to a certain limit and beyond that limit it decreases.
Uttrakhand state in India, possess a variable physiographic diversity which makes it fertile land for various ber plants. Himalayan nettle grows up to a height of 3 meters and is found in various places in Uttrakhand state in India. Fibers extracted from Himalayan nettle plants looks like a silky white thread which can be used for various application like clothing and domestic purpose. There was a time when nettle ber was considered as a discarded articles in Uttrakhand but now a days it is harvested by local communities for making crafts, textile products, to enhance their economic and nancial conditions (Srivastava and Rastogi 2018).
Many researchers have developed epoxy based composite added with plant bers and has shown that the mechanical and thermal performance of natural ber added composite are better as compared to the unreinforced materials (Adesina et al. 2019) An enhancement in tensile and impact strength was reported with the reinforcement of woven Himalayan nettle bers into polyester resin. The highest tensile strength of 31.39 MP was observed for 15 wt% ber content; while the maximum impact energy of 29 joules was observed for 20 wt% ber lling (Pokhriyal, Prasad, and Rauri 2018). The other aspect of natural bers were observed where a decrease in young's modulus and tensile strength of single nettle ber was observed when the ber diameter was increased but overall outcomes were good in terms of biodegradability and better mechanical performance (Mahendrakumar et al. 2015). The mechanical properties can be improved via introducing particulate reinforcement into natural hybrid composites. The exural strength and tensile strength and increased when a hybrid composite of kevlar and sisal was introduced with nano silica (Chowdary et al. 2020). In another study, when silicon carbide content was varied from 5-15%: a signi cant enhancement in tensile strength and hardness was detected for jute based composite (Patnaik and Nayak 2018). The effect of jute ber as a ller material used in epoxy resin was studied to evaluate the chemical form and mechanical properties through Fourier-transform infrared spectroscopy. Natural bers showed hydrophilic nature which limited their use in higher load and marine applications, but still, ample research is occurring on to reduce moisture absorption behavior of the plant bers. The phenomena of moisture absorption was studied when sisal bers were reinforced into polypropylene (Maurya et al. 2021). The moisture absorption was high for natural ber based composite as compared to the synthetic bers (Chandramohan et al. 2019). A comparative study of water absorption in composites of ax/epoxy and Jute/hemp/epoxy was done and it was found that ax ber based composite had low water absorptions as compared to the Jute/hemp ber based composites (Chaudhary et al. 2020). Water absorption can be decreased by chemical treatment of bers and by controlling composites fabrication parameters. Reduction in water absorption was reported when the Luffa cylindrical ber based composites were processed at higher temperatures (Pires et al. 2020). The water absorption rate was high for untreated juli ora ber and decreased when NaOH concentration increased from 5-15% (Reddy et al. 2019). It has been reported that the moisture absorption rate for a hybrid composite of kenalf and sisal was 3.2% while for kenalf ber it was 5.3%. Thus the development of hybrid composite can reduce the water absorption rate for marine applications (Ramasubbu and Madasamy 2020). Through literature ndings, it has been concluded that very little work has been presented in fabrication of nettle ber based composites. The prediction and evaluation of mathematical modelling for drilling of SiC/nettle/ epoxy hybrid composite is not reported by any researcher yet. Therefore nettle ber based composites were fabricated to study the mechanical performance and drilling behavior of developed composites for this this research work.

Materials And Method
The Fabrication of natural ber composites is as follows

Material used
In the presented research study, epoxy LY 556 was used as a matrix and hardener HY 991 as a curing agent. The density of epoxy was 1.3 g/cm 3 .Nettle ber was used as the reinforcement into epoxy resin which was obtained from the Uttrakhand bamboo development board, India. To create better bond strength, epoxy and hardener was used in the ratio of 10:1. Nettle bers which were obtained in random oriental format from bamboo development board are shown in gure 1 (b). High duty silicon spray was used as the releasing agent.

Composite Fabrication
Five different composites were fabricated by changing the ber and resin weight percentage. All the sampled were fabricated through the reinforced of untreated nettle bers. The weight proportion of matrix and epoxy resin is speci ed in Table 1. The conventional hand layup practice was performed to prepare the composite specimens. Epoxy and hardener were mingled properly in the ratio of 10:1 and was slowly stirred to remove the air bubbles formed while mixing. The short randomly oriented bers were placed inside the mixture of epoxy resin and were thoroughly mixed for better wettability. The dimension of the steel mould was 250 x 200 x 4 mm which was designed in solid works and fabricated by welding the steel plates to the desired size.
Te on sheets were placed inside the steel mould and high duty silicon spray was used to avoid sticking of the epoxy with mould. The mixture of nettle ber and epoxy was then carefully poured inside the mould. It was then gently spread precisely inside the mould and rollers were used for removing the air bubbles. Te on sheet sprayed with high duty silicon was then placed on the top and covered with a steel plate. A load of 150 N was placed on the whole assembly and was retained for curing up to24 hours.
After complete curing, the composite was detached from the mould and for each weight fraction ratio, three specimens were fabricated and its average values were considered. The fabrication of composite was done by varying ber weight percentage as 5%, 10%, 15%, 20% and 25%. Composites (Z1-Z5) of different composition are prepared. Developed composites for various testing are shown in gure 1 (c). The samples for tensile, exural, impact and water absorption testing were prepared according to ASTM standards. Composites were converted into powders for studying its chemical form through fourier transform infrared (FTIR) spectroscopy.

Mechanical characterization
The natural ber based composite can be fabricated by various processing techniques according to the designed size and use. The most important aspect is to check its quality and mechanical properties so that it can perform e ciently without failure at the desired loading conditions. The various mechanical testing adopted for the developed composites is explained further. Tensile strength testing When a mechanical member is applied with an axial tensile load, it is expected from that member to withstand those loading conditions. This property named tensile strength can be evaluated by tensile testing of standardly prepared samples. For the present research work samples were prepared as per the ASTM D638 standard and tested on the universal testing machine.

Flexural strength testing
Flexural strength is one of the important properties to be evaluated for mechanical members under bending conditions. To measure exural strength of prepared composite for this study has been evaluated using 3 point bend test and samples were prepared as per the ASTM D790 standard. The exural strength test was done at room temperatures and the average value of three samples were taken as its nal exural strength. Impact strength testing The toughness of prepared samples were calculated by performing an impact test on the impact testing machine. Specimens were fabricated by following ASTM D256 standards and were subjected to impact loading. Three impact test for each ber wt. % were performed and the average was considered as the nal value.

Fourier Transform Infrared Examination (FTIR)
FTIR is one of the popular and best technique to validate the dispersion of functional group and bond category in the composites. The chemical form of composites can be easily examined through FTIR technique. To perform this examination powder form of the prepared composited was placed under the instrument and the results have plotted a graph. Water Absorption rate Water absorption performance of nettle ber reinforced polymer composite was studied according to ASTM D570-98 standards. Samples with different ber loading were dipped inside the glass of water to observe the water absorption characteristics. The change in weight of samples was measured after equal intervals of 24 hours. The samples were cleaned properly with tissue paper before weighing in precise electronic measuring equipment. The water intake of the composite samples was calculated by following formulae.
Water absorption percentage = Where W2 represented the initial weight of the sample before water dipping and W1 represent the nal weight of the sample after water dipping.

Chemical Resistance
The natural ber composites should have the capability to work under severe conditions and impart long duration functional properties for practical applications; therefore, it was very important to study the effect of distinct environmental conditions on biocomposites and many researchers are examining composites under various environmental conditions. In this respect, to design and fabricate a commercial storage tank of composite material for chemicals, the evaluation of chemical resistance is obligatory. In this study chemical resistance test of untreated nettle plant ber reinforced polymer composites was done according to ASTM D543-87 standard. In each investigation, the samples were weighed and dipped in an aqueous solution of KOH (10%), NaHCO 3 (10%) and NaOH (10%). The specimens were removed from the aqueous solution and cleaned properly to remove any water droplet adhered to the composite surface. Then the composites were measured precisely to calculate the weight loss/gain (Ashok et al. 2010). All the experimentation was done at room temperature and three specimens of each weight% were studied. The chemical resistance behavior of the prepared composite specimens was calculated by the following formulae.
Chemical resistance percentage = Where C1 denoted the initial weight of the specimen before chemical dipping and C2 denoted the nal weight of the specimen after chemical dipping. Evaluation of delamination factor All drilling operations were performed on drilling machine to analyze the delamination factor during drilling operation of SiC/nettle hybrid polymer composites. The hybrid composite was fabrication by reinforcing 3% SiC with nettle bers in the epoxy resin. The dimensions for drilling operation were selected as 180 mm x 90 mm x 6 mm. High speed steel drill with variable diameters (4mm, 6mm and 8mm) was used to perform the drilling operation. The three factors namely, drill diameter, spindle speed and feed were selected at three levels each during this investigation as shown in Table 2. Drilling was accomplished dry, at spindle speeds of 400, 600 and 800 mm/rev and three feed rates of .125, .212 and .3 mm/rev. The samples with drilled holes were scanned with digital microscope and obtained images were imported to imageJ software. The threshold feature was adjusted to measure the delamination around the hole.
Two concentric circles were drawn to divulge delamination around the hole. While drilling plant ber based polymer composites, the delamination is one of the predominant defect. The delamination factor for the evaluation of damage was evaluated via the given equation: Where D max is the enlarged diameter due to drilling and D is the nominal diameter.

Results And Discussions
The results and discussion on the conducted experimental study is discussed further.

Tensile strength testing
The practical applications of different natural ber composites is possible when they exhibit the desired tensile strength and tensile modulus properties. The optimum ller content is very important to nd out the lower or higher ller contents and their deterioration in respect to the load carrying performance of composites. At lower ller content, the mechanical performance of biocomposites is low because of its lower loading capacity and at larger ller content failure occurs because of the occurrence of higher voids and low ber/matrix wettability. The tensile strength of the composites was calculated from the tensile test and the result values are shown in Figure 2. It was concluded from the results that specimen number four (20% nettle ber and 80% epoxy) had superior tensile strength (23.26 MP) as compared to other samples. The lowest value of tensile strength was recorded for the rst sample (5% nettle ber and 95% epoxy). The tensile strength of composite with 20% nettle ber was 86.08% greater than the composite with 5% nettle ber. The maximum tensile strength of the developed composite of this study was 159.12% greater than the pineapple ber based composite (Sivasubramanian et al. 2020). It is perceived from the tensile strength results that the tensile strength continued to increase with a rise in the ber wt%. This improvement in tensile strength retained up to 20 wt% and after that reduced, which speci ed that the superior stress transfer takes place between ber and epoxy for optimum ber reinforcements (Rashid et al. 2016). The decrease in tensile strength above 20% was because of the poor wettability between polymer and bers as the inadequate ow of polymers occurs around the bers (Pankaj et al. 2021) Flexural strength testing The exural strength of nettle ber added epoxy composites specimens were evaluated using 3 points bending and the trend are displayed in gure 3. Flexural strength is combined properties of shear and compression. The same pattern was followed in tensile strength as it was observed in exural strength for variations in weight percentage of bers. After 20 wt % of ber addition, a drop in exural strength was seen. During the fabrication of composites, various defects were observed. These defects formed stress concentration sites at bers-ends and higher concentrations at these sites was the main cause of crack propagation due to its failure. As discussed earlier in the tensile strength segment, at higher content of ber (20 wt. %) the resin was unable to cover the entire surface area of ber and hence caused a reduction in the exural strength. The presence of voids, faults in composite processing and lack of interfacial strength were also the common reasons for the drop in its exural strength (Suriani et al. 2021). As the ber addition (up to 20 wt.%) increased the exural strength and after that it decreased; similar results were also reported for different ber content when jute, sisal and elephant grass based composites were fabricated (Gunti et al. 2018). The increase in ber concentration also made the composites brittle, because of the irregular load distributions between ber and polymers. The exural strength primarily affected by the binding e cacy between the matrix and its reinforcement. Poor binding e cacy induces lack of exural strength between the polymers and its ller content (Harish et al. 2009).

Impact strength testing
The impact strength is the material capability to endure high speed stress or load, the experimental results showed that with a rise in the reinforcement of nettle bers in the epoxy resin, it improved the impact strength. When plastic deformation of composites took place then energy storage capacity increased in higher ber contents because larger energy was required to break the ber bundles (Devireddy and Biswas 2017). The results of the impact strength of nettle ber based biocomposites for the current investigation are displayed in gure 4. It was perceived from the results that the impact strength of biocomposite with 25 wt % was held the highest toughness as compared to other samples.
The impact strength of sample Z5 is 7.21 KJ/m2 which was 71.66% higher than sample Z1. The same pattern of increase in impact strength has been observed by the researchers when untreated luffa ber based composites were fabricated and the composites in the current investigations had higher impact strengths (Mohanta and Acharya 2016). This impact strength can be increased by different modi cation technique like the chemical modi cation of natural bers which enhanced the binding strength between reinforcement and polymer, a developing area in which many researchers are working (Debeli et al. 2017) (Kansal et al. 2020).

Water Absorption
The water absorption test of biocomposites is an essential parameter to be evaluated when the composite is exposed to marine environments. In the current study, water absorption behavior was studied for the same environmental conditions in the transient mode. The main parameters which affect the water resistance properties were the amount of ber contents, presence of hydroxyl groups and voids. The in uence of dipping time on water absorption rate in terms of moisture gain is illustrated in gure 5. An enhancement in water absorption rate was noticed while increasing the nettle ber lling, which represented the presence of a higher hydrogen bond between nettle bers with the retention of water molecules. The cause for the increase in water absorption seen in this study could be because of the occurrence of micro cracks and ber's nature to absorb water and voids. The same pattern of results was observed by many researchers during their previous studies (Gupta 2020) (Ramesh et al. 2020) ) ). The composite samples fabricated with epoxy and nettle ber proportion was 75:25 and they showed higher water absorption rates than 85:15, 90:10 and 95:5. The matrix material chosen was Epoxy which showed water resistant properties and nettle bers depicted water intake properties. The maximum of 10.96% water intake rate was reported for biocomposite made up of 25% nettle ber and minimum of 2.01% water intake rate was reported for biocomposite made of 5% nettle ber. When we require low water absorption the sample Z1 was best but in such cases, a compromise with the mechanical properties needs to be done.

Chemical Resistance
Chemical resistance is a scienti c technique used to nd out the capability of composites to survive the when exposed to alkalis and chemicals. The chemical resistance of fabricated composites was accomplished to nd out suitability for making chemical resistant articles. Chemical resistance of different composites for KOH (10%), NaHCO3 (10%) and NaOH (10%) in the graphical form is illustrated in gure 6. From this gure, it is clear that the weight gain was detected for all samples with different weight contents. It indicated that the prepared composites did not suffer any erosion as there was no weight loss. From another perspective view of point, the bers did not show any chemical resistance and this chemical resistance reduced with a rise in the ber content as a large number of chemicals came in contact with the chemicals. A higher absorption rate corresponds to the rich interaction between the bers and aqueous solutions. Conversely lower absorption rate corresponds to poor interactions between the bers and aqueous solution which is desirable for designing composite materials. Amongst all samples, sample Z5 showed maximum absorption rate and this absorption rate was absorbed maximum for the aqueous solution because bers showed hydrophilic behavior for aqueous solutions. Such ndings of an increase in absorption was stated in the case of bamboo ber lled epoxy composites (Gupta 2016).

FTIR analysis
The mechanical properties of biocomposites decreases because of the moisture absorption characteristics of natural ber composite due to the hydrogen bond formation between the water molecule and natural bers. The nettle bers were hydrophilic in nature and held hydroxyl groups in ber structures. When the percentage of O-H group was higher in bers, then bers showed a very attractive nature for water molecules and the overall moisture resistance decreased. This lead to the decrease in overall mechanical and thermal performance of the biocomposites (Hestiawan 2020). FTIR is a vital tool to examine the functional group of natural ber and biocomposites. The FTIR graph was divided into two groups: function group and ngerprint group. FTIR spectra of nettle ber reinforced epoxy composite in powder form was taken with FTIR spectrometer in the wavelength range 500-4000 cm −1 and the same is revealed in gure 7. High intensity and broader peaks near 3500 cm −1 represent stretching vibrations of hydroxyl groups for the tested powder sample of composites and this had been also represented by the FTIR analysis of the composite where the peaks formed between 3600 and 3000 cm −1 was consigned to O-H stretching (Celino et al. 2013). This peak con rmed that the natural bers had higher contents of O-H group and could easily absorb moistures. This peak can be decreased or we can decrease the percentage of O-H group by chemical treatment of natural bers (Jayamani et al. 2020). The band near 1600 cm-1 shown in gure 7 are because of the presence of water content in the fabricated nettle ber based composites which was speci ed by the peak formation between 1693 and 1607 cm-1 for the representation of water in natural bers (Ray and Sarkar 2001).The peaks near the 2800 to 3000 cm-1 were because of C-H stretching vibration in cellulose and hemicellulose which were also reported when jute bers were examined (Saha et al. 2010). The peak formed between 1100 and 1200 cm-1 denoted the bending present in the cellulosic and bonding structure of bers (De Rosa et al. 2010).

Effect of machining parameters on delamination factor
The delamination factor was evaluated after performing experiments that were designed according to box-behnken design in the design expert software. The responses obtained during the investigation are shown in Table 3. A quadratic model was statistically suggested by the design expert software when experimental responses were analyzed in the design expert software. During the investigation, it was observed that the quality and appearance of drilled hole was signi cantly affected by the drilling conditions. The delamination phenomenon was predominantly intensive at the exit of the hole as compared to the entrance observed for various natural ber based composite plates (Belaadi et al. 2020) (Belaadi et al. 2019). Therefore, the current study was focused on the prediction of delamination behavior at the exit only. The characteristic curves revealing the in uence of the spindle speed, feed rate and drill diameter on delamination factors were plotted to evaluate the delamination damage that occurred during the drilling operation. Delamination was evaluated for the developed hybrid composites reinforced with SiC particulates. The state of the hole after at drilling conditions of spindle speed 800 rev/min, drill diameter 6 mm and feed rate 0.3 mm/rev is shown in gure 8. The maximum delamination factor during this investigation was observed as 1.301 (for the drilling conditions of spindle speed 600 rev/mm, feed rate 0.3 mm/rev and drill diameter 6 mm). The minimum delamination factor during drilling operation in the current study was observed as 1.096 (for the drilling conditions of spindle speed 800 rev/mm, feed rate 0.125 mm/rev and drill diameter 6 mm). The delamination factor at the exit of the hole creates various research opportunities for engineers, scientists and researchers; therefore, it is very di cult to compare the research work of this investigation with the literature because many experimental studies showed that the delamination factor gets affected by the composite manufacturing process (Rezghi et al. 2019), tool type and geometry (Suriani et al. 2021) and selection of machining parameters (Malik et al. 2021). For comparison, the delamination factor during the drilling of jute/polypropylene was found to be varied from 1.23-2.09 (Pailoor et al. 2021), while for the current investigation delamination factor was varied from 1.096-1.301. The output response as a delamination factor of our experimental study was higher than the delamination factor of drilling of the ax/polylactic acid (Lot et al. 2018).

Response surface methodology
Response surface methodology (RSM) is a useful technique that is used to predict and model the problems in which response is affected by the input parameters and in uencing parameters are optimized to get the desired response. The major mechanism of RSM consists of: (1) performing experiments and collecting data according to the experimental design (2) approximating the correlation between factors and responses by empirical modelling.
(3) Empirical model based optimization to obtain the best response. These models were used by many researchers in the estimation and optimization of response and process variables in the drilling of ber reinforced polymer composites. Response surface methodology using Box-behnken design was employed during the experimentation work to get a quadratic model consisting of 17 experiments. The experimental response in the terms of delamination factor was taken as an average value of two responses. The three independent process parameters and levels, drill diameter (D), feed rate (F) and spindle speed (N) were selected as displayed in Table 2. The empirical second-order polynomial equation was established for the delamination factor on the basis of experimental results shown in Table 3. The mathematical equation developed during experimentation by RSM is given below.  -5.14286 x 10 -4 x N x F+2.00000 x 10 -3 x D 2 +3.62500 x 10 -7 x N 2 +3.91837 x F 2

Analysis of variance for delamination factor
The signi cance of each process variable and their interactions are analyzed through analysis of variance (ANOVA) details derived from the factorial investigational results. The sum of the square, probability, F-value, degree of freedom and mean square is shown in ANOVA Table 4. The F-value is helpful in predicting the qualitative in uence of each process variable and its effects. When any process parameter exhibits a larger F value then it means, that factor has a larger effect as compared to the error variance. On another aspect, the smaller p value speci es the signi cant effect of the process parameter on response.  Table 4 showing the linear coe cient process parameters (D, N and F) and quadratic term coe cients (F 2 ) were signi cant as they showed fewer P values (Prob. 0<.005). The other process parameter and their interactions were not signi cant because they had a larger p value (Prob. >.005). From Table 4, it could be wrapped up that feed rate (F) was the most in uencing parameter for the delamination factor while drilling developed composites during this investigation. The next effective independent process parameter is the spindle speed (N). The diameter of drill (D) was found to be a very less effective in uencing parameter. The coe cient, R 2 , also known as the coe cient of determination is the measure of the t degree in the analysis of variance (ANOVA) tables. The R 2 provides a good correlation between predicted and experimental results when it is nearing unity.  Figure 9 and 10 respectively.

Surface plots for delamination factor
Page 14/29 The relative in uence of process factors in 3D surface plots is displayed in gure 8. Since the modal is adequate, therefore the estimation of delamination factor for input parameters namely drill diameter, feed rate and spindle speed can be done by using these 3D surface plots. The modal predicted in this experimental investigation had three process parameters, each 3D plot was created by holding one variable constant at the central level. Figure 3 (a) shows the evolutionary relationship between spindle speed and drill diameter, while the feed rate was kept constant. It is clear from the gure that drill diameter has a substantial in uence on the delamination factor as compared to the spindle speed. Figure   3 (b) illustrates the impact of drill diameter and feed rate on the delamination factor. The gure depicts that feed rate and drill diameter had a substantial in uence on the delamination factor. The delamination factor was witnessed to be increased with the rise in feed rate and drill diameter. It has been noticed that, feed rate was more signi cant as compared to drill diameter. The larger feed rate escalates the thrust force in the machining area and the delamination factor increases which is not a desired effect among biocomposites while drilling. Therefore it is necessary to drill biocomposites at a lower feed rate. The 3D surface plot for the delamination factor at constant drill diameter and variable feed rate and spindle speed is presented in gure 3 (c). It is clearly illustrated by the gure that, feed rate increases the delamination factor and spindle speed decreases the delamination factor. This happens because larger forces are required for chip removal as a larger feed rate increases the region of the sheared chip.

Conclusions
Investigations of the in uence of ller loading on mechanical properties and chemical resistance of nettle ber based composites have been done successfully and stated in this paper. During the experimental investigation, it was noticed that Tensile and exural strength of developed biocomposites enhanced up to 20 weight% of ller loading and above that, it reduced.
In the case of impact strength, a continuous surge in strength was observed.
It was observed that tensile and exural strength enhanced by 1.86 times and 1.84 times respectively for 20% ber content as compared to 5% ber content.
The impact strength increased by 71.66% for 20% ber content as compared to 5%.
Because of the hydrophilic nature of nettle bers a gradual increase in water absorption rate in composites was observed and an approximate constant pattern was observed for water immersion from 192 to 240 hr.
When composites were placed in different environments least and maximum absorption was observed for NaHCO 3 and NaOH respectively.
No composite erosion was found and the trend for weight gain was observed.
The presence of a chemical functional group was con rmed when composite was observed by FTIR analysis.
Delamination factor in the drilling behavior in the SiC/nettle ber hybrid composites was found in the range of 1.096 -1.301.
Feed rate was observed as the most effect parameter in delamination factor of SiC/nettle ber hybrid composites.
The nding of this the conducted experimental study was that natural bers were good reinforcing elements in polymers and can emerge as environmentally friendly materials for various engineering elds like sports, automotive and aerospace for designing interiors as well as exterior components.