1 Introduction

In modern decades, fiber-reinforced polymers are powerfully used in tribological elements such as cams, brakes, bearings, gears, etc., because of their improved wear resistance and a capability of self-lubrication. Polymer composites have a superior strength-to-weight ratio, which is useful in a range of applications in automobiles, aerospace, and various household appliances [3.9]. The deficiency of fiber-reinforced polymer (FRP) composites can be defeat productively by using various fillers like nano- or micro-sized particles. The effects of the addition of nanoparticles on these properties have been broadly studied and its usefulness is proved by the various researchers. The adding up of a few percent of nanoparticles by weight results in a major development in the mechanical properties [1,2,3,4,5,6,7,8,9].

The FRP composites always got a high mechanical performance because of fiber as a most effective reinforcement [12, 14]. It is found that carbon fiber reinforced composites have better properties such as enhanced thermal conductivity, better strength, higher Young’s modulus, and brilliant electrical properties [9,10,11,12]. By the use of inorganic nanoparticles, one can improve toughness, stiffness, other friction, and wear properties of FRP composites [1,2,3] and Deca et al. found that there is an enhancement in the Ultraviolet rays (UV) resistance and thermal stability of the polymers of wood with the incorporation of nanoZnO and nanoclay [4]. Rashmi et al. and Li Chang et al. studied the improvement in the wear resistance for short/regular-sized CFRP composites with the nanoparticles effect [5, 6]. As mentioned by Shazed et al., the carbon nanotubes are also supportive in convalescing the tensile and mechanical properties of carbon fibers with different fiber orientations [7]. David et al. derived that fracture toughness can be significantly improved by effect of the nanoparticles in the CFRP composites [8]. With the addition of fillers such as carbon nanotubes (CNTs), nanoZnO results in astonishing mechanical, electrical, and thermal properties of the host matrix/composite materials [9, 10].

As per research, there is enhancement in wear resistance and mechanical properties of polyester woven carbon fiber, jute fiber, and chopped carbon fiber with the additional effect of nanoZnO [11,12,13]. By using surface-grown hydrothermal ZnO, nanorods can be used to enhance the vibration damping of FRP as per Alipour et al. [14]. The characterization processing of ZnO-incorporated polymer composites are confirmed by Chuangqi et al. and Kyungil Kong et al. [12, 15]. Yasser Rostamiyan et al. have found that there is an improvement in the flexural strength, tensile, and impact strength up to considerable higher amount of the glass fiber-reinforced composite with addition of nanoclay as filler used in epoxy resin [16, 17]. Tripathi et al. have derived a method for optimal design of a FRP laminate by taking into account different parameters like ply angle, ply thickness, and focused on a procedure to get optimum composition of the friction liners material [18, 19]. The studies are carried out by using the RSM for the design of experiments. Sanes et al. [20] found that using ZnO nanoparticles as a filler increases the stiffness and the chain mobility enhances because of the IL phase addition which results in a plasticizing effect. Also, the friction coefficient gets reduced by 50% and the rate of wear by a considerable order of magnitude because of the IL lubricant effect. Bahadur et al. [21] focused on the wear characteristics of polyphenylene sulfide (PPS) added with inorganic nanoparticles like ZnO, CuO, TiO2, and SiC. Yingke et al. have premeditated the tribological behavior of nanosilica coating on epoxy resin composite, and coating composition on the wear and friction behavior illustrated in relation with their microstructure [22].

Friction and wear properties of aligned carbon nanotube filled epoxy composites and short carbon fibers polyimide composites filled with microSiO2 and graphite were studied by Lei Yan et al. in their respective studies [23, 24]. Aluminum composites give an improved wear resistance and hardness with a filling of ZrO2 particles in an aluminum matrix as per the findings of Ramachandra et al. [25]. Shadpour et al. highlighted the ZnO filler effect on the morphology, thermal conductivity, and various properties of polymer nanocomposites [26]. Zhang et al. also expressed that nanoparticles as a filler results in reduction of the wear rate and friction significantly, and they can entail an improved tribological performance than the sub-micron particles [27]. Rajasekhar et al. presented their work on tribological behavior of Polyamide Jute Fiber filled with nanoZnO and found that both, the wear rate and friction coefficient of the nanocomposites, were lowered significantly than pure polyamide [13]. Sudeepan et al. studied friction/wear of polymer composite of ABS/ZnO by using the Taguchi method and found that the specific wear rate and friction coefficient are influenced by the increase of load, speed, and filler content [28]. Zhao et al. have focused on the micro/nanoparticles effect on the wear and friction properties of CFRP [29]. Senthil Kumar et al. have done a tribological analysis of nanoclay, epoxy, and glass fiber by using Taguchi’s technique [30]. Many researchers have focused on the effect of CNT/other nanoparticles on PEEK and other nanocomposites [31,32,33,34]. Shailesh Ambekar et al. successfully incorporated the use of nanoclay and nanoZnO for the enhancement and optimization of the CFRP flexural strength [35]. Zhou et al. have developed the fracture-based model to predict the wear damage due to chipping, the model was able to predict the size of the wear particles [36]. Liu, Zhou, and Wang et al. have focused their study on modeling and properties of 2D graphene nanoparticles and grain size effect on the mechanical properties of nanocrystalline carbon, respectively [37, 38] As before stated in literature review, the dry and sliding wear behavior of CFRP incorporated with hybrid combination of clay and NanoZnO is not studied till date. So, in the current study, the focus is on the experimental exploration of the influence of nanoparticles like nanoZnO, fiber angle, and nanoclay on the wear behavior of CFRP polymer composites. The new material, i.e., CFRP hybrid nanocomposites with incorporation of nanoclay and nanoZnO can be used in carbon–carbon disc brakes, friction clutches, various parts of the space craft, aeroplanes, and automotive gear box which nowadays are being used in racing cars and in fabrication of automobile variable transmission systems from these CFRP hybrid nanocomposites. The fiber orientation angle, wt % of nanoZnO and wt % of nanoclay montmorillonite nanoclay are chosen as independent variables and the wear rate performance carbon fiber reinforced polymers with the mixture of nanoclay and nanoZnO, new material system is derived with the application of fiber orientation angle as third variable their effect of on the rate of wear hybrid CFRP composite laminate has been investigated by using CCD in RSM. Central composite design (CCD) is the part of response surface design methodology that has been used to derive models as a function in terms of factors to forecast the wear rate of the newly fabricated CFRP hybrid nanocomposite. It has also been used to derive a mathematical model so as to develop the optimum design or structure of a new CFRP hybrid nanocomposite. The total 20 experiments were designed including six center point replicates as per the MATLAB. Accordingly, the samples were prepared and tested for wear rate of the CFRP hybrid nanocomposites with different fiber orientation angles and nanoclay, nanoZnO particles as filler.

2 Materials and Experimental Characterization

2.1 Materials

In the current study, Control sample was carbon fiber reinforced (CFRP) composites. The carbon fiber of 200 GSM, standard modulus of 3 K, and HCU200 code are used for the main reinforcement. Hinpoxy C epoxy resin is bisphenol‐A-based liquid-state material. HARDENER-B is a modified amine hardener, low viscosity, colorless liquid, with stoichiometric ratio of A:B = 10:3; the carbon fiber and the resin both were supplied by the Hindoostan Mills Ltd. Mumbai, India. Nano zinc oxide (ZnO) particles and montmorillonite nanoclay were used, supplied by Nano Research Lab. Jamshedpur, (Jharkhand), India. All the details of the properties are as given in Table 1.

Table 1 Material properties
Full size table

2.2 Sample Fabrication

The CFRP nanocomposite laminates were manufactured by a hand layup method (as shown in Fig. 1a), succeeded by vacuum bagging the unidirectional carbon fiber was the main part of the reinforcement in the epoxy resin. Bisphenol A (DGEBA) resin was mixed with a hardener at a ratio of 100:30 by weight. The clay and Zinc Oxide nanoparticles were used as filler. For the suitable dispersion in the epoxy resin clay and Zinc Oxide nanoparticles, nanoparticles were dried prior to use for overnight at 75 °C in an oven. For attainment of a uniform dispersion of the Montmorillonite nanoclay and Zinc Oxide nanoparticles in the epoxy resin, magnetic stirring (as shown in Fig. 1b) and ultrasonication (as shown in Fig. 1c) were done for better mixing. The  %wt of nanoparticle content was used in the range 1 to 5 %wt with the epoxy resin and hardener mixture as per the results from OVAT analysis and previous research carried out. Ultra-sonic method was then carried out for 40 min at 40° C for uniform mixing of the nanoparticles in the epoxy resin. After ultrasonication, the said mixture was magnetically stirred for one and a half hour. The prepared mixture was then used for the composite preparation. The hand layup Fig.1(c) and vacuum bagging process (as shown in Fig. 1d) are used for the preparation test sample, the process of vacuum bagging is carried out for 4.5–5 h with application of constant vacuum pr. of 720 mm Hg. Fourteen plies were used and according to the coded levels, the combination of three factors was varied. The specimen was kept within the bag for 15–18 h at room temperature for curing. The post curing of specimen was then done in an oven for 5 h at 80 °C. Then the round specimens were cut from the laminates as per the required dimensions for wear test.

Fig. 1
figure 1

a Ultrasonication, b Magnetic stirring, c Hand Lay up of CFRP, d Vacuum bagging

Full size image

2.3 Experimental Procedure

For the wear test, a pin-on-disc tribo tester experimental setup, DUCOM, made in Bangalore was used to test the wear behavior of CFRP hybrid nanocomposite according to the ASTM G99 standard. The dry and sliding wear behavior was tested in the performed experiments The disc setup that was used was made from an alloy steel with 8 mm thickness and 165 mm diameter and of 62 HRC hardness. A surface specimen of size 10 mm in diameter and 3 mm thick was glued at the end of the pin of the mild steel. The total height of the specimen pin along with the sample piece was around 28 mm. Before start of the test, the disc was use to cleaned with acetone. The specimen was positioned in its holder normal to the steel disc. For each individual specimen, three trials were conducted on the pin-on-disc test setup and average reading values were used. Tests performed for the sample combinations as per the coded values given in Table 3. The weight of the pin assembly with the specimen was measured in an electronic balance of accuracy 0.0001 g. The weight loss was determined from initial wt and final wt after wear test of the specimen was recorded. The wear rate can be calculated from the ratio of weight loss and product of the sliding distance and the normal load by using Eq. 1. The coefficient of friction was taken directly from the setup. The wear rate was calculated for three different weights; 10 N, 15 N, and 20 N and the sliding velocity was at 2.09 m/s. According to the Archard equation, the model considers adhesive wear and assumes the sliding spherical asperities to deform fully plastically in contact. The area of contact then is circular with the contact area equal to πa2, where a is the radius. After the asperity slides, a distance of it is released from the contact and there is a probability K. The mean contact pressure in this case equals to hardness of the softer material, and thus = P/πa2. Then the wear volume per sliding distance 2a, W = Kπa2/3, πa2 = P/H×W = P× K/3H = k×P/H.

$$V_{T} = W \times s = k \times P/H,$$
$$V_{T} /A = W \times s = k \times P/A/H$$
$${\text{Wear rate}} = \frac{\text{weight loss}}{\text{normal load}} \times {\text{sliding distance}}$$
$$WR = \frac{w}{Fn \times L}$$
(1)

Experimental conditions

Parameters

Operating conditions

Temperature

Ambient conditions (temperature: 29° C)

Relative humidity

55(± 5) %

Test disc

Hardened ground steel (EN-31, hardness 60 HRC

Roughness of EN-31

1.6 m Ra

Duration of rubbing

600 s

Surface condition

Dry

Load

10 N, 15 N, 20 N

Sliding speed

2.09 m/s

Sliding distance

1500 m

Pin size (ASTM G99 Std.)

30 mm × 10 mm × 10 mm

The average contact pressure between the disc and specimen surface

0.3 MPa

2.4 Design of Experiments

The design of experiments was carried out by Response surface methodology (RSM), which is a mathematical and statistical technique of data collection. This technique is useful for design of experiments, to evaluate the effect of independent variables on final response, optimizing the processes and model building. In recent years, RSM has played important role in various fields of chemistry, biotechnology, nanotechnology, etc. It is important capability of RSM that it can develop quite true relationship function between the set of independent variables and response (Y) and following is the first-order model polynomial equation, which is used to describe a linear function between independent variables and response (Fig. 2).

Fig. 2
figure 2

Central composite design for three design variables at two levels

Full size image
$$Y = \, \beta_{0} + \beta_{1} X_{1} + \beta_{2} X_{2} + \cdots \cdots \cdots \cdots +_{k} X_{k}$$
(2)

where the independent variables are X1, X2...Xk and βk is the linear of the Kth coefficient factor, β0 is the constant coefficient, and ε is the error observed. If there is curve in the system, then the second-order polynomial model should be used. This model will take the form

$$Y = \beta_{0} + \mathop \sum \limits_{i = 1}^{k} \beta_{i} X_{i} + \mathop \sum \limits_{i = 1}^{k} \beta_{ii} X_{i }^{2} + \mathop \sum \limits_{i < j} \beta_{ij} X_{i } X_{j} + \varepsilon$$
(3)

2.4.1 Central Composites Design

Central composite design is RSM part set, which helps in design for fitting second-order models. The total experiment count for CCD is equal to 2k + 2k + η0, where 2k is the number of standard two-level factorial points, k is the number of design factors, 2k points are the star points which are located at “±α” from the center points of the domain of experiment, and the center point is η0 of domain which is to be replicated to estimate the “pure” experimental variance error. When the variance of variables is constant at all distances from the center point then the design is named as Rotatable central composite design named CCRD. Rotatability can be calculated from the equation given below

$$\alpha = \left( {2^{k} } \right)^{1/4}$$
(4)

For statistical calculation, Xi (experimental variables) has been coded as xi with the following transformation.

$$X_{i} = \frac{{X_{i} - X_{0} }}{{\Delta X_{0} }}$$
(5)

here xi is coded the dimensionless value of the ith variable of experiment, Xi stands for uncoded independent ith variable, X0 stands for the magnitude of Xi situated at center point, and ΔXi indicates the step change value for the real variable i.

In this experimental study, the Minitab software was used to analyze the data evaluation and to get results using CCD as methodology for experimental design. Here, nanoZnO wt%, fiber angle in degrees were used as inputs and the response was wear rate. Total 20 experimental levels for three factors were designed and at the center point with six replicates. Tables 2 and 3 show coded level and actual level of the design parameter and experiments generated and the corresponding wear rate for each test (Fig. 3).

Table 2 Actual and coded level of design parameter
Full size table
Table 3 Coded and actual values of factors
Full size table
Fig. 3
figure 3

Schematic diagram of pin-on-disc wear test setup

Full size image

In this experiment, the software of Minitab was used to interpret and analyze the data processing and to obtain results, and for the design of experiments CCD was chosen. Here, the input variables were nanoZnO wt%, nanoclay wt%, and fiber orientation angle and the response was the weight loss or wear rate. A total of 20 experimental levels were designed for three factors with six replicates at the center point. Tables 2 and 3 show the coded level and actual level of the design parameter, the experiments generated, and the corresponding wear results for each test.

3 Results and Analysis

As the input variables are nanoclay wt%, nanoZnO wt%, and fiber orientation angle which are denoted as A, B, and C, respectively, in analysis of variance, the response was wear rate of CFRP filled with nanoclay and nanoZnO. In this step, to evaluate the influence of these independent variables on corresponding response, analysis of variance was carried out by Minitab software according to the model of CCD and results determined based on considering the confidence level equals to 95% (α = 0.05). According to probability, P value significance of each term was evaluated. The probability value more than 95% (α ≤ 0.05) should be possessed by the significant terms.

3.1 Analysis of Variance and Fitting Regression Model

The ANOVA results of the analyses were as shown in Table 4. As seen, the fiber orientation nano and clay wt% angle had a significant value of P, probability greater than 95%. The wt% of nanoZnO was not significant probability, with a value less than 95% on the wear rate. From Table 4, it can also be seen that square values of the nanoclay wt% and fiber angle/orientation were most effective having a probability value of P ≥ 95%. With a probability value less than 95% from the square of nanoZnO, the wt% had no significant effect. It was observed that the interaction between nanoZnO and fiber orientation is the main interaction with good effective probability value. With a P value of about 0.552, an insignificant “lack of fit” indicates that the data satisfactorily fitted for the model; therefore the CCD was a best choice for the experiment design and the analysis of the results.

Table 4 Initial analysis of variance
Full size table

Regression Equation in uncoded units response surface regression: Wear rate (Y) versus A, B, C (nanoclay wt%, nanoZnO wt%, Fiber orientation angle)

$$Y = 0.3198 \, + 0.1556 A - 0.0262 B + 0.0602 C + 0.2413 A^{2} + 0.0352 B^{2} + 0.0398 C^{2} - 0.0075 AB + 0.0328 AC - 0.0557 BC\quad {\text{For initial analysis}}$$
$$Y = 0.3486 + 0.1556 A - 0.0262 B + 0.0602 C + 0.2378 A \times A + 0.0363 C \times C - 0.0557 B \times C\quad {\text{For final analysis}}$$

For the final analysis, the analysis process was then repeated by eliminating terms which were non-effective and the ANOVA results are displayed in Table 5. It is obvious that the P value of the significant terms and also the ‘‘Lack of Fit’’ magnitude increased after eliminating the insignificant terms. The above equation shows the reduced fitted model after eliminating the insignificant terms. Table 5 indicates the regression coefficients of the three independent variables, squares and interaction between factors.

Table 5 Final analysis of variance
Full size table

Moreover, Tables 6 shows the determination coefficient (R2) which is generated for ability of evaluation of the model in predicting the results, when this value is close to a 100%, it is capable to give more accurate results. The values of R2 were 95.01 and 92.99% for the first one overall model and the successor reduced model, respectively. These higher R2 values indicated that the model repressors could not explain only about 6% of the total variable values. The derived regression model is enabled for a good evaluation of response for the studied range.

Table 6 Regression coefficients and percentage of R2 for both steps of analysis of variance for wear rate
Full size table

Figure 4a and b displays the normal residuals probability plot for the initial and final analysis. These plots resolved by comparing different sample distributions, whether a particular distribution fits or not for the collected data. The two sections of this figure show that the closeness of points to the fitted distribution line, in both analyses, but it can be seen that the points for the final analysis fall closer to the distribution line than the points fitted for the initial one. So, for both the models, the distribution of the wear rate was close to normal distribution. The plot of residuals versus the fitted values for the initial and the final analysis of variance as shown in Fig. 5a and b indicate that the residuals on the plot scattered randomly for both the analyses. However, it can be observed that the tendency of the scattering in the first stage of analysis is much superior than the further one. Hence, it is found that the model proposed was satisfactory. Figure 6 shows the main effects plot of the variable inputs. This plot gives the significance of linear terms on the response and shows that the amount of the wear rate decreased with an increase in the nanoclay wt% from 1 to 2 wt%. The wear rate increased when the nanoclay wt% was between 3 and 4.2%. The effect of the nanoZnO can be seen and it shows that the wear rate decreased when the wt% of the ZnO was between 1 and 1.8%. The wear rate increased from 1.8 to 3% and then a decreasing trend was followed by the wear rate from 3% onwards. A similar kind of fashion trend is observed in the outcome of fiber orientation angle effect on the wear rate in the third part of the figure. From this, it can be consummated that all the results were in conformity with what was observed in the ANOVA tables and also an signal of the fitted regression coefficients.

Fig. 4
figure 4

Normal probability plots of residuals for a initial analysis, b final analysis of CFRP hybrid nanocomposites by RSM

Full size image
Fig. 5
figure 5

Residual versus fitted values for a initial analysis, b Final analysis of CFRP hybrid nanocomposites by RSM

Full size image
Fig. 6
figure 6

Main Effects plot of for wear rate

Full size image

3.2 2D Contour and 3D Surface Graphs for the Wear Behavior of CFRP Hybrid Nanocomposite

In this Section, 2D contour and 3D surface graphs have been used to demonstrate the dependence of the wear rate on the effectiveness of the parameters as design factors. Two of the factors should be varied while one of the factors should be held usually fixed or constant at zero level. Contours are drawn as a function of the two factors. These plots are useful for inspecting the effects of both, the interaction and main effects of factors on the wear rate.

3.2.1 Effect of Nanoclay and NanoZnO on Wear Rate

Figure 7a and b displays the 3-D contour and 2-D surface graphs for the nanoclay and the nanoZnO. The value of fiber orientation angle was considered fixed at zero level (45°). The contour graph shows that the value of the wear rate increased with an increase in the nanoclay wt% from coded design parameter level 0 to 1.6817 and gets decreased from − 1.6817 to 0 level wt% of the nanoclay. The effect of nanoZnO wt% has a combined effect of increase and decrease of the wear rate with the % variation of the nanoZnO. The combined effect of these two variables demonstrates a clear effect on the response at same time and also interaction between them shows significant effect on the wear rate. Similarly from the surface chart it can be understood on which surface value of nanoclay wt% and nanoZnO wt% one can get the lesser wear rate. The area under the curve can be treated as the measure of the wear resistance for the given conditions.

Fig. 7
figure 7

a 3-D surface graph, b 2-D contour graphs, for effect of nanoclay and nanoZnO on wear rate

Full size image

3.2.2 Effect of Nanoclay and Fiber Orientation on the Wear Rate

2D contour and 3D surface graphs for fiber angle of orientation and wt% of nanoclay are displayed in Fig. 8a and b correspondingly. The value of wt% for nanoZnO was held constant at the zero level (i.e., 3%). As seen in these plots, the amount of the wear rate increased generally with an increase in the level of fiber orientation angle; the wear rate decreases until 3% wt of nanoclay, after which it increases with wt% values of nanoclay. In addition, it is noticeable that by varying the value of the two variables affected, the wear rate at the same time is in increasing trend. Also, it shows the mutual interaction effect between the nanoclay and the fiber angle of orientation. Similarly from the surface chart it can be understood on which surface value of nanoclay wt% and fiber orientation angle one can get the lesser wear rate. The area under the curve can be treated as the measure of the wear resistance for the given conditions.

Fig. 8
figure 8

a 3-D surface graph, b 2-D contour graphs, for the effect of nanoclay and Fiber angle on the wear rate

Full size image

3.2.3 Effect of Fiber Orientation and NanoZnO on the Wear Rate

Figure 8a and b describes the 3-D contour and 2-D surface graphs between the fiber orientation angle and nanoZnO and the nanoclay wt% was kept constant at zero level (3%). According to the surface and contour graphs, with an increase in the degree of the fiber angle of orientation, the wear rate decreases until 3% and then there is a slight increase in the wear rate. And the wt% nanoZnO increases the wear rate with its value. It can be seen from the contour graph that acceptable values of the wear rate can be obtained in the mid-portion of the values of fiber angle orientation and the wt% of nanoZnO displayed in the graph. Similarly from the surface chart it can be understood on which surface value of nanoZnO wt% and fiber orientation angle one can get the lesser wear rate. The area under the curve can be treated as the measure of the wear resistance for the given conditions.

The lowest value obtained for the wear rate was 2.22 mg/Nm which appeared in run no. 11 at coded levels nanoclay = 0, nanoZnO = 0, and fiber orientation angle = 0. The respective actual values were nanoclay = 3%, nanoZnO = 3%, and fiber orientation angle = 45°, respectively.

3.3 Optimization of Wear Rate

In the optimization stage, the wear rate was calculated by using response optimizer in the Minitab software. For this, the minimum value for the wear rate was targeted up to 3.0 mg/Nm with nanoclay, nanoZnO, and fiber orientation values at 3 %wt, 2.9 %wt, and 9° correspondingly. By considering to these values for the fabricating the specimens, which is optimzed variables value based sample. These specimens are then tested for wear rate, the average value of wear rate is obtained as 4.2 mg/Nm.

3.4 SEM Analysis of Worn Surfaces of CFRP Hybrid Nanocomposites

Figure 9 shows the SEM morphologies of the worn samples of CFRP hybrid nanocomposites sliding against the steel pin and at room temperature, with and without nanoparticles, tested under different loading conditions. The exclusion of the fiber in the composite without nanoparticles was also very much infuriated with an increase in applied pressure as compared with the nano partcles filled composite, which proves the enhancement in wear resistance of the composites filled with nanoparticles. It is seen that most of the carbon fibers are pulled out from the fabric matrix on the worn surface. The surface was observed to be rough and showed obvious signs of scuffing of the unfilled carbon fabric composite (as shown in Fig. 10a), which indicates that the pure carbon fabric composite undertook a large contact stress and experiences severe peeling off as it slided against the steel at room temperature. Opposite to the above, the worn surface of the carbon fabric composite filled with nanoparticles is smooth and the pulling-out and exposure of the carbon fibers are nearly invisible (as shown in Fig. 10b) at coded level 11, having nanoclay 3 %wt and ZnO 3 %wt at fiber angle 45°.

Fig. 9
figure 9

SEM morphologies of the worn surfaces of carbon fabric composites reinforced with different fillers a pure CFC; b CF with nanoZnO 3% + nanoclay 3%; c CF with nanoZnO 4.2% + nanoclay 1.8%; d CF with nanoZnO 3% + nanoclay 5%

Full size image
Fig. 10
figure 10

a 3-D surface graph, b 2-D contour graph, for effect of nanoZnO and Fiber angle on wear rate

Full size image

This indicates that the nanoparticles included in the carbon fabric composite effectively act to increase the interface bonding strength between the carbon fiber and the adhesive resin, and hence to increase the mechanical strengths and wear resistance of the carbon fabric composites filled with nanoparticles. Moreover, the worn surface of the carbon fabric composite filled with wt 1.8% nanoclay and 4.2% wt nanoZnO at coded level 8 and with wt 5% nanoclay and 3% wt of nanoZnO at coded level 1 is relatively smooth but still shows signs of carbon fiber pull-out, more rough and signs of scuffing (as shown in Fig. 10c and d), which agree well to the friction and wear behaviors of the composites filled with nanoZnO and nanoclay.

4 Conclusions

As in the studies of the past, it has been proved that the friction coefficient and wear rate can be significantly lowered with the application of nanoparticles [6,7,8,9,10]. In this study, the wear rate of the CFRP new hybrid nanocomposite material system has been investigated.

  1. (1)

    The new material, i.e., CFRP hybrid nanocomposites with incorporation of nanoclay and nanoZnO can be used in carbon–carbon disc brakes, friction clutches, various parts of the space craft, aeroplanes, and automotive gear box which nowadays are being used in racing cars and in fabrication of automobile variable transmission systems from these CFRP hybrid nanocomposites.

  2. (2)

    With the help of RSM and CCD design of experiments, one can find the optimum composition for wear rate.

  3. (3)

    The Analysis of variance (ANNOVA) results shows that the nanoclay and nanoZnO had a direct, i.e., improved effect on wear properties with the 2–3% of the each nanoclay and nanoZnO, while the fiber orientation had an undesirable effect on minimizing the wear rate.

  4. (4)

    The optimization result indicated that a minimum value for the wear rate from optimization given by the software was 3.0 mg/Nm. After manufacture and testing of the samples, the average value of the wear rate that was obtained was 4.2 mg/Nm which occurred in 2.9 wt% of nanoclay, 3 wt% of nanoZnO, and 0° of fiber angle of orientation. The optimization results also showed that the wear rate at the optimum value was much improved or minimized (about three times) than the controlled sample.

  5. (5)

    The addition of or nanoZnO, and nanoclay with optimum quantity can contribute to increase the resistance of wear and friction-reducing capabilities of the carbon fabric composites. The carbon fabric composite filled with nanoclay 3 %wt and ZnO 3 % demonstrates the least friction coefficient and the smallest wear rate. The differences in the wear and friction properties of various nanoparticle-filled CFRP and pure CFRP composites are related to their respective interfacial interactions with the resin adhesive.