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Abstract

A comprehensive analysis carried out on the mechanical and free vibration properties of woven natural fiber polymer composites is presented. Jute fabric with three different weave types (plain, basket and herringbone) and intra-ply woven jute-banana fabrics are considered for investigation of the effect of weave type of a fabric and its stacking sequence on mechanical, dynamic mechanical and free vibration properties. Enhancement of the properties is found with the number of layers of fabric and better properties obtained for four layers. Uniform stress distribution along warp and weft direction of fabric with basket weave type lead to better properties compared to other weave types for four-layered composites. Intra-ply hybridization of jute-banana also enhances the mechanical properties but slightly less than the jute-basket fabric composite. The investigations on effect of layer sequence of fabrics revealed improvement in mechanical properties. Layered composite with relatively strong intra-ply fabric as the facing layer and relatively weak jute plain fabrics as the core layer has higher tensile and flexural properties. Experimental modal analysis carried out on beam-like composite laminates reveal that natural frequencies and associated modal damping factor are significantly influenced by stacking sequence and weave type of a fabric. The density of the composite calculated based on Archimedes principle matches well with the theoretical values.

Keywords

Woven fabric weaving natural fiber intra-ply hybridization layer sequence experimental modal analysis mechanical Properties

Introduction

In recent years, natural fiber has been chosen as a good alternate material due to several advantages associated with natural fibers such as use of plant waste, environmental friendly, high strength to weight ratio, requirement of less energy to fabricate their composites makes them as an alternative material to conventional materials and synthetic fiber-reinforced polymer composites in several applications where load-sharing requirement of the structural component is vital [1,2]. In most of the cases, the natural fiber-based composite material can be successfully implemented for low and medium load application while in high load application, it has restrictions. In most of the cases, natural fiber-based composite material has tensile and flexural strength less than 100 MPa. This makes them not suitable with high load application. In general, natural fiber-based composite material can find use in home-based application (telephone stand), structural application (door) and packing application. Natural fiber along with synthetic fiber can be used in automobile industry. This helps reducing the weight of the final product such as outer body, door, etc. The adoption of natural fiber in the polymer composite, especially in automobile industry, increases the fuel efficiency. Lightweight natural fiber composite structure decreases the fuel consumption [3 –5]. A few researchers proved that natural fiber composite can be successfully used to replace the synthetic fiber composite with equivalent properties for low and medium load application [6,7].

The tremendous developments in the textile field such as weave type, braiding and knitting technologies have triggered improvements in the properties of composite material [8,9]. Several researchers have made analysis of natural fiber reinforcement in woven form in the polymer matrix and reported that woven fabric composite enhances the properties of composite material compared to composite with intimately mixed fibers [10,11]. Sapuan and Maleque [12] used woven banana fabric-reinforced composite for low load application to develop the telephone stand. Bledzki et al. [13] compared the mechanical properties of woven flax and jute composite. Their results revealed woven flax composite increases the mechanical properties of composite material compared to jute composite. Goutianos et al. [14] found that the properties of woven composite depend entirely on the nature of yarn twist. They report that yarns with low twist transferring minimum stress under loading as a result of the low strength of woven fabric. Pothan et al. [15] have compared the mechanical properties of plain, twill and matt woven sisal composite. They found enhancement of the mechanical properties of the composite material compared to twill and plain woven composite through matt type woven sisal composite. This arises as a result of poor stress transfer of plain and twill woven fabric which is the result of lower fiber volume percentage in the polymer matrix. Rajesh and Jeyaraj [16] have done analysis of the dynamic mechanical properties of different woven composites for banana and jute composite. They found the nature of weaving pattern having influence on the dynamic properties of composite material. They have also extended the analysis to intra-ply woven banana/jute hybrid composite by changing banana and jute yarns in the warp and weft directions. They found the orientation of fiber influence on the dynamic properties of composite material. The results reveal composite with relatively stronger jute fiber yarn along the warp direction has a higher storage modulus (3.5 E+09 Pa) compared to relatively weak banana yarn in the warp direction (2 E+09 Pa).

Several researchers have performed the analysis of the layering effect of natural fiber composite on mechanical, dynamic mechanical and free vibration properties and concluded that the number of sequential layers influences the properties of composite material. Jawaid et al. [17] analyzed the tensile properties of tri-layer oil-palm jute woven composite and showed that jute layer, when kept as skin layer, improves the tensile property of composite material by 48% compared to pure oil-palm composite. Bennet et al. [18] analyzed the stacking sequence effect of coconut sheath/sansevieria cylindrica polyester composite and found that coconut sheath/sansevieria cylindrica/coconut sheath composite enhances the natural frequency. Santulli et al. [19] have analyzed the mechanical behavior of jute cloth/wool felts hybrid composite using the intercalated and sandwich method and found composite with sandwich method increasing the mechanical properties of composite material. Ramesh et al. [20] have analyzed the mechanical properties of sisal/jute/glass reinforced polyester composite. They found the incorporation of sisal and jute in glass composite increases the mechanical properties of the composite material.

Natural fiber composite with improved mechanical properties can be used to replace structures made of metals and synthetic fiber-based composites in low and medium load applications. The major drawback associated with natural fiber composite is their short and random orientation form of reinforcement in the matrix which reduces the mechanical properties due to their amorphous nature. A few researchers have demonstrated a significant improvement in the mechanical properties of natural fiber composite through their reinforcement in woven form.

However, exploration still remains to be done by way of detailed investigation on the influence of the nature of the weaving type of the fabric, the number of layers and stacking sequence of fabrics with different weaving type on the mechanical properties of a polymer composite. In the same way, it is very important to analyze the effect of intra-ply hybridization of two different natural fibers in a woven fabric on the mechanical behavior of the composite. The focus of this work is on the mechanical, dynamic mechanical and free vibration behavior of different woven fabric (plain, basket and herringbone) composites made of jute yarn and intra-ply hybrid composite made of jute and banana yarns.

Experimental details

Woven fabric and polymer preparation

Plain, basket, herringbone and intra-ply hybrid fabrics are considered in the present study for the investigation of the effect of weave type and its layering sequence on the mechanical, dynamic mechanical and free vibration characteristics. The different types of fabrics considered are plain jute, basket jute, herringbone jute and banana–jute intra-ply basket fabrics as shown in Figure 1. All the fabrics are prepared with a thickness between 0.8 mm to 0.9 mm. These fabrics are woven using a power loom to obtain the stiff woven fabrics and also to minimize the gap between the yarns.

Figure 1.

Different woven fabrics. (a) jute plain, (b) jute basket, (c) jute herringbone and (d) intra-ply.

In this work, unsaturated isophthalic polyester resin is used as a matrix material while methyl ethyl ketone peroxide (MEKP) and cobalt naphthenate are used as a catalyst and as an accelerator, respectively. Initially, one weight percentage of MEKP and cobalt naphthenate are taken and mixed uniformly with the unsaturated isophthalic polyester in the ratio of 1:1:10 by weight.

Based on the investigation of the effect of the number of layers of woven fabric on mechanical properties, it is decided to perform the layering sequence study on the four-layered sandwich composites. The different types of sandwich composites investigated are IPPI, IPI, BPPB, BPB, IPPB, PIIP and IBaBaI. Here, the extreme letters indicate the fabric associated with the bottom and top skin layers and the remaining alphabets indicate the core layers. Similarly, I indicates banana-jute intra-ply fabric, H indicates herringbone jute fabric, P indicates plain jute fabric, B indicates basket jute fabric and Ba indicates basket type banana fabrics.

Fabrication of composites

Composite laminate with different fabrics are prepared with the help of a compression moulding machine. For this purpose, a mould of size 250 mm × 250 mm × 4 mm has been prepared using stainless steel material. Initially, a sufficient amount of resin is poured inside the mould cavity. This is followed by placing multiple layers of woven fabrics over the poured resin. This is followed by the use of a roller for removing voids present in the composite. The natural fiber fabrics are wet in the matrix material and subsequently placed inside the mould. This wetting process increases the adhesion between fiber and matrix more than what is possible in the normal laying process. The remaining amount of matrix material is poured over the layer and the mould is covered by a plate. It is then compressed by 150 kgf/cm² pressure for 1 h with 80℃ curing temperature to obtain the uniform composite laminate. After the curing, the composite laminate is removed from the mould and sized according to ASTM standards for tensile, flexural and impact test, respectively. Figure 2 shows the experimental setup used in the study to prepare the composite laminate.

Figure 2.

Experimental setup used in the study.

Testing standards

In this study, tensile test for the woven composite specimen is carried out as per ASTM D-638 with a testing speed of 5 mm/min. For that dog-bone shaped specimen with dimension of 165 mm length, 19 mm width and 57 mm gauge length are prepared. ASTM D-790 is followed to find the flexural strength of composite specimen through three-point bending test with a testing speed of 1.7 mm/min. For that composite specimens are sized into 127 mm × 12.7 mm × 4 mm. Impact strength of composite is found using Izod test without notch. Impact specimens are prepared as per ASTM standard D-256 with dimension of 63.7 mm ×12.7 mm × 3 mm. Dynamic mechanical analysis is done using double cantilever system SEIKODMAI-DMSC 6100 at a frequency of 1 Hz in atmospheric condition in a nitrogen environment for a temperature range of 0℃ to 200℃ at 2℃/min to determine the storage modulus, loss modulus and loss factor of various composite specimens.

Results and discussion

As the first steps, a separate study has been carried out to find the number of layers of fabric which gives better mechanical properties of the composite. This has been done for all the fabrics through variation in the number of layers of fabric from one through four. The total number of layers of fabric has been restricted to four considering the thickness limitations of the test specimen according to the standards. Followed by this, the investigation of a four-layered sandwich has been done for different sequences of fabric layers. Apart from mechanical strength behavior, dynamic mechanical and experimental modal analyses are also performed.

Density measurement

Experimentally calculated density of the composite specimen is compared with the theoretical values in Table 1. Theoretical values are obtained from the ratio of mass to volume. The experimental value is obtained using Archimedes principle applied on a composite specimen prepared according to ASTM D-792. Table 1 reveals the variations between the values predicted by the two methods as insignificant. This also indicates that the matrix is free from voids.

Table 1.

Influence of weaving pattern architecture, number of layers, stacking sequence on density of the composites.

	Density (g/cm³)				Density (g/cm³)
No. of layer	Composite	Measured	Theoretical	No of layer	Composite	Measured	Theoretical
1	Plain	1.2083	1.1903	4	Plain	1.1923	1.1741
	basket	1.2174	1.1108		basket	1.2188	1.1382
	Herringbone	1.2333	1.1393		Herringbone	1.2333	1.2075
	Intra-ply	1.2000	1.2105		Intra-ply	1.1818	1.2456
2	Plain	1.1818	1.1365	Sandwich	IPPI	1.2414	1.1777
	basket	1.1667	1.5773		IPI	1.2083	1.1336
	Herringbone	1.2273	1.0453		BPPB	1.2414	1.0854
	Intra-ply	1.2273	1.1588		BPB	1.2105	1.2094
3	Plain	1.2222	1.0524		IPPB	1.2143	1.1701
	basket	1.1667	1.1770		PIIP	1.2414	1.1090
	Herringbone	1.2258	1.2222		IBaBaI	1.2143	1.1943
	Intra-ply	1.1923	1.2122

Mechanical properties

Table 2 shows the influence of the different types of woven fabrics on mechanical properties such as tensile, flexural and impact properties. The influence of the nature of the weave type and the number of layer and stacking sequence of different woven fabrics on the mechanical properties of the composite material are observed. The results also reveal lower tensile properties of jute plain composite and high tensile properties for jute basket and jute herringbone woven fabric composites. It is due to higher crimp between the yarns in the warp and the weft directions of the plain woven fabric which creates more stress, and results in poor tensile properties compared to basket and herringbone woven fabric composites. In the case of the basket woven fabric composite, crimp between the yarns in the warp and weft direction is less than in the case of plain and herringbone woven fabrics which results in a uniform stress distribution in both the directions during loading. In the case of the herringbone woven fabric, the crimp between warp and weft is smaller compared to the plain woven fabric. This is confirmed by conducting a tensile test on individual woven fabric according to ASTM 5034 standard. The tensile moduli of different woven fabrics such as jute plain, jute herringbone, jute basket and jute-banana intra-ply fabric are 102 MPa, 130 MPa, 154 MPa and 280 MPa, respectively. The jute-banana intra-ply fabric has better tensile properties than the other fabrics. This indicates that intra-ply hybridization of banana and jute fiber yarns in a fabric improves the tensile characteristics of the fabric. Another observation from Table 2 is that the number of layers in the polymer composite influences the tensile properties of the woven fabric composites. This is due to the increase in fiber loading with number of layers of fabric. The increase in fiber loading with increase in number of layers of fabric can be clearly observed from Table 3.

Table 2.

Influence of weaving pattern architecture, number of layers, stacking sequence on mechanical properties.

No. of layer	composite	Tensile strength (MPa)	Tensile modulus (GPa)	Flexural strength (MPa)	Flexural modulus (GPa)	Impact strength J/m
1	Plain	06.88 ± 0.62	0.85 ± 0.11	21.05 ± 1.31	1.31 ± 0.48	58 ± 27
	basket	11.76 ± 1.16	0.90 ± 0.10	31.20 ± 8.71	1.41 ± 0.42	129 ± 50
	Herringbone	15.92 ± 2.56	1.02 ± 0.18	33.40 ± 7.66	1.44 ± 0.32	94 ± 25
	Intra-ply	10.78 ± 2.70	1.10 ± 0.16	23.20 ± 9.01	1.76 ± 0.48	64 ± 40
2	Plain	15.16 ± 1.17	0.74 ± 0.23	29.08 ± 4.91	1.92 ± 0.52	62 ± 20
	basket	22.04 ± 1.39	1.00 ± 0.26	41.16 ± 9.35	1.77 ± 0.60	178 ± 37
	Herringbone	24.94 ± 3.08	1.05 ± 0.21	40.33 ± 6.81	2.49 ± 0.71	146 ± 20
	Intra-ply	27.36 ± 5.90	1.50 ± 0.10	41.37 ± 11.71	1.66 ± 0.51	168 ± 20
3	Plain	24.78 ± 1.49	1.11 ± 0.37	33.42 ± 5.16	1.31 ± 0.32	153 ± 32
	basket	42.08 ± 3.01	1.05 ± 0.39	56.02 ± 10.30	2.02 ± 1.11	224 ± 47
	Herringbone	35.70 ± 2.72	1.20 ± 0.31	53.86 ± 13.74	2.44 ± 0.58	186 ± 33
	Intra-ply	41.21 ± 2.32	1.36 ± 0.47	58.70 ± 3.53	2.57 ± 0.11	207 ± 26
4	Plain	30.42 ± 3.89	1.18 ± 0.23	33.77 ± 7.68	1.39 ± 0.58	206 ± 36
	basket	43.60 ± 2.40	1.02 ± 0.18	69.54 ± 11.66	3.43 ± 1.11	250 ± 26
	Herringbone	37.00 ± 7.00	1.27 ± 0.33	64.20 ± 15.88	3.18 ± 0.65	194 ± 23
	Intra-ply	44.32 ± 2.24	1.31 ± 0.32	72.80 ± 6.53	3.12 ± 0.25	234 ± 44
Sandwich	BPPB	43.28 ± 7.08	1.59 ± 0.16	56.07 ± 14.42	1.55 ± 0.56	234 ± 74
	IPPI	46.35 ± 5.49	1.59 ± 0.38	74.48 ± 8.675	2.51 ± 0.35	281 ± 144
	BPB	35.78 ± 3.02	1.35 ± 0.21	60.28 ± 13.33	1.74 ± 0.52	187 ± 20
	IPI	35.06 ± 1.32	1.32 ± 0.06	65.18 ± 14.79	2.45 ± 1.03	177 ± 22
	PIIP	41.95 ± 2.95	1.62 ± 0.35	53.12 ± 4.90	1.78 ± 0.29	225 ± 90
	IPPB	38.02 ± 1.09	1.15 ± 0.43	55.43 ± 5.29	1.98 ± 0.38	354 ± 132
	IBaBaI	41.07 ± 4.42	1.49 ± 0.31	48.60 ± 5.18	1.47 ± 0.17	272 ± 83

Table 3.

Fiber volume fraction of different composites.

No. of layer	Composite	Volume fraction (%)	No. of layer	Composite	Volume fraction (%)
1	Plain	10.8	4	Plain	43.2
	basket	17.6		basket	70.4
	Herringbone	17.2		Herringbone	68.8
	Intra-ply	12.0		Intra-ply	48.0
2	Plain	21.6	Sandwich	IPPI	45.6
	basket	35.2		IPI	34.8
	Herringbone	34.4		BPPB	53.6
	Intra-ply	24.0		BPB	42.8
3	Plain	32.4		IPPB	49.6
	basket	52.8		PIIP	45.6
	Herringbone	51.6		IBaBaI	56.0
	Intra-ply	36.0

The strength of fiber reinforced composite depends on the fiber strength, amount of fiber, fiber length and weave type. Also the strength of composite dependent, stress transfer between fiber and matrix. It is evident from the results shown in Table 3 that amount of fiber in the composite influences the effective stress transfer. The composites with low fiber content are not able to transfer much load which leads to the failure of composite very early. However the composites with high fiber content are able to transfer much load hence has higher strength.

Table 2, clearly, shows a significant increase in the tensile properties with increase in the number of layers. Composites with four-layered basket type woven jute fabric are seen giving higher tensile properties compared to other fabric composites. The synergy effect of both high strength jute fiber and better load transfer between the basket weaving style woven fabric and matrix is the factor that improves the properties of composites. In the case of basket type woven fabric composite, higher resistance has been provided by the fabric against tensile loading as a result of the nature of arrangement of fiber yarns. Hence, additional load is required for breaking the composite material. Herringbone woven fabric composite has higher tensile properties compared to plain fabric composite but less than basket fabric composite. Further investigation has been done on jute-banana intra-ply hybrid woven fabric composite for tensile behavior and the results are compared with the individual jute basket fabric composite. The comparison shows intra-ply hybridization of banana and jute fibers yarns in basket type woven fabric resulting in better tensile properties compared to individual jute fiber fabric composites. Figure 3 shows the influence of the number of layers and the different types of woven fabrics on mechanical properties of the composite. Figure 3(a) reveals four-layered composite exhibiting better resistance against tensile loading than the other layered composites. Figure 3(b) brings out the fact of composite with basket weaving pattern providing more resistance against deformation and carries more load than other woven fabric composites. The basket weave type of woven fabric provides more restriction against the stretching of yarns in warp and weft direction thereby reducing the displacement of basket woven fabric composite. Another observation from Figure 3(b) is the failure of jute plain woven fabric composite earlier under low load with large deformation. This is the result of tightening effect between yarns in the warp and weft direction.

Figure 3.

Load vs. displacement diagram for woven composite under tensile load. (a) Influence of number layer and (b) influence of weaving pattern.

Indication from Table 2 is hybridization and stacking sequence of different woven fabrics influencing the tensile properties of the composite. Many researchers have proved that the stacking sequence of composite increases the mechanical properties of composite material [17,21,22]. They have suggested high strength fiber as skin layer and less strength fiber as core layer improves the mechanical properties. In a sandwich composite, the skin layers provide a higher resistance against deformation, while the core layer distributes the load uniformly. This is reflected in the results reported in Table 2. The layered sandwich composite has hybrid banana-jute intra-ply fabric as the skin layer, and plain jute fabric as the core layer (IPPI) has better tensile properties compared to the other layered composite sandwiches. Similarly, the layered composite BPPB has better tensile properties in comparison with other composites but less than IPPI composite due to the influence of basket jute skin layer. The poor tensile characteristics seen in three-layered BPB and IPI composite indicate the influence of core thickness. The higher core thickness associated with the four-layered BPPB and IPPI enhances the tensile properties of the layered sandwich composite. The four-layered sandwich composite PIIP has better tensile properties than IPPB but less than those of the four-layered IPPI and BPPB composite. This is the result of a non-uniform stress transfer behavior of intra-ply and basket-jute fabrics. Again sandwiching banana fabrics between the banana-jute intra-ply fabrics has also influenced in better tensile properties of the IBaBaI composite but less than those in IPPI and BPPB composites.

In the case of IPPI sandwich composites, hybridization of banana and jute natural fiber yarn in the warp and weft direction gives low deformation which increases the strength of the composite material. The stretching nature of fiber strands in the fabrics break at different times is independent, and individual breaking nature of fiber stands influences the tensile properties of sandwich composite material.

Stacking sequence has a considerable influence on the flexural properties of different types of jute and jute-banana intra-ply woven fabric polyester composites as shown in Table 2. The significantly higher flexural strength in the IPPI-layered sandwich composite compared to all other layered composites is clear from Table 2. The IPPB sandwich composite has poor flexural strength compared to four-layered IPPI and three layered BPB and IPI sandwich composites. This indicates the enhancement of flexural strength arising out of a stiff layer of banana-jute intra-ply fabric. The lowest flexural strength of IBaBaI sandwich composite indicates that the flexural strength of a sandwich composite is not only influenced by nature of skin layer fabric but also influenced by the nature of core fabric. The weak banana fabric layers reduce the flexural strength of IBaBaI sandwich significantly.

In the case of IPPI, composite banana-jute intra-ply fabric is used as a skin layer which carries more load than other composites due to the nature of basket weaving and fiber count of jute and banana in the intra-ply fabric. The flexural strength of woven composite depends on fiber orientation, fiber strength, fiber–matrix interfacial bonding and fiber count [23,24]. Apart from this, weave type plays an important role in improving the properties of a composite material. The results lead to the observation that, during flexural loading, none of the specimen breaks completely at maximum load. This arises as an effect of weave type and continuous long fiber yarns which influence the flexural properties of sandwich composites [25]. The conclusion from this result is that flexural strength of sandwich composite material depends on the extreme outer layer strength which defines the flexural values of composite material.

Variations in impact strength with the layering sequence of different fabrics of the sandwich composite are detailed in Table 2. Similar to the tensile and flexural strengths, the impact strength of the four-layered basket jute fabric composite is higher than all other composites. Intra-ply hybrid fabric also yields better impact strength but less than that of basket jute fabric for the four-layered composite. The results of four-layered composites also indicate both the weave types of a fabric and material of the fiber yarn influencing the impact strength of the woven fabric composites. This is evident from the higher impact strength of basket jute fabric composite.

Impact strength of the layered fabric sandwich composite is enhanced whenever the facing layer is highly stiff compared to the core. This has been a clear observation for IPPB, IPPI and IBaBaI-layered composite sandwiches. In the case of IPPB sandwich composite, a combination of jute-banana intra-ply fabric and jute fabric as skin layers produces higher toughness and, in turn, withstands higher strain rates. Table 2 helps observation of poor impact strength for the three-layered sandwich composites such as BPB and IPI due to less core thickness associated with them.

ANOVA analysis, a form of statistical hypothesis test, has been performed on the mechanical properties and the results are given in Table 4. The ANOVA results divide the variance of tensile, flexural and impact strength into two components, i.e. between groups and within groups. Since the P-value obtained from the F-test is zero, which is less than 0.05, it can be concluded that there is a statistically significant difference between the tensile, flexural and impact strength of different composites with 95% accuracy in the confidence level. Here, 16 groups and 80 observations are used.

Table 4.

ANOVA test for mechanical properties of different woven composite.

Properties	Source	Degree of freedom	Sum of square	Mean square	F-ratio
Tensile strength	Between group	15	11328	755.19	47.26
Tensile strength	Within group	63	1007	15.98	47.26
Flexural strength	Between group	15	14416	961.07	12.41
Flexural strength	Within group	63	4879	77.44	12.41
Impact strength	Between group	15	134647	8976	4.32
Impact strength	Within group	63	130820	2077	4.32

Surface morphology study

Scanning electron microscope (SEM) is used for analyzing the tensile, flexural and impact fractured specimen for understanding the fiber–matrix adhesion and matrix damage due to loading. Figure 4(a) and (b) shows the SEM image of the fractured surface of four-layered and two-layered plain jute fabric composite, respectively, under tensile load. Figure 4(a) and (b) reveals the result of the poor stress transfer to matrix as a severe damage on matrix surface also. Figure 4(b) also indicates fiber pullout due to poor adhesion for the two-layered composite, but in the case of four-layered jute plain composite, it is not found. From this, it can be concluded that the addition of more number of layers in the polymer composite increases the rigidity of material. This resists the fiber pullout as a result of small extensibility of four-layer composite under tensile load.

Figure 4.

Microstructure of fractured surface of the composite. (a) Four-layer plain composite under tensile load, (b) two-layer plain composite under tensile load, (c) PIIP composite under flexural load, (d) four-layer intra-ply composite under tensile load, (e) four-layer jute basket composite under impact loading and (f) IPPI composite under impact loading.

Figure 4(c) shows the microstructure of PIIP composite under flexural load, indicating the severe damage near the fiber yarn in the matrix. It is due to poor stress transfer from outer weak layer to middle layer in the composite material. This causes severe damage in the matrix and allows the crack from fiber yarn to matrix material. No cracks are found in the case of four-layer intra-ply composite’s matrix. This is due to uniform stress transfer. A similar observation has been found in four-layer jute basket and IPPI composites under an impact load. This is shown in Figure 4(d) and (e). Figure 4(e) reveals that there is no crack and fiber pullout due to sudden impact loading. As a result of better fiber–matrix adhesion, it resists the crack propagation in the matrix as well as fiber pullout. Same observation has been found in IPPI composite under impact loading. Figure 4(f) shows that there is no crack in the matrix between outer intra-ply and middle jute plain woven fabrics. This is due to higher modulus of banana-jute intra-ply woven fabric. Hence, it resists the suddenly applied load and transfers the load. As a result, severe damage in the matrix material between the two layers is avoided.

Dynamic mechanical analysis

The influence of stacking sequence of fabrics with different weave types on dynamic mechanical properties such as storage modulus, loss modulus and loss factor of the composite is significant as seen in Figure 5. Figure 5(a) shows four-layer jute and jute-banana intra-ply composites having higher storage modulus value in both the glassy and rubbery regions than herringbone composite. Figure 5(a) also indicates increase in the storage modulus for four-layer composite in the order herringbone < basket < intra-ply fabrics. Storage modulus variation reveals weave type and fiber orientation in warp and weft direction having significant effects on the results. In the case of jute-banana intra-ply composite, the orientation of jute fiber in the warp direction and combination of both the fibers enhances the storage modulus, while the sandwich composites (BPPB, IPPI, PIIP) show lower storage modulus than the individual four-layer composite which arises as a result of variations in modulus of composite material. It is also evident from the mechanical properties of composite material shown in Table 2. The individual four-layer composite has a higher flexural modulus compared to sandwich composite. This increases the rigidity of composite material. In case of sandwich composites, the storage modulus variation is not significant in both the regions. Figure 5(b) shows the influence of different stacking sequences on loss modulus of the composite. This is similar to the storage modulus variation. It can be observed from Figure 5(b) that intra-ply composite has a higher loss modulus than other composites because the enhancement of frictional resistance of the composite increases the energy dissipation in the form of heat. In the case of the basket and the herringbone composites, much variation in loss modulus is not seen as it is the case for the sandwich composites also. In intra-ply hybrid fabric composite, combination of jute and banana fibers increases the frictional resistance. In the case of basket and herringbone fabric composite, only jute fiber influences frictional resistance. In the case of sandwich composite, frictional resistance of the composite may be less due to presence of two different woven fabrics in the composite layer upon layer.

Figure 5.

Influence of stacking sequence of fabrics on (a) storage modulus, (b) loss modulus, (c) damping factor and (d) Cole-Cole plot.

Variation in the loss factor with respect to different layered composites is shown in Figure 5(c). Figure 5(c) reveals the variation of loss factor of the composite for a different stacking sequence of the fabric as not significant. In general, the four layers of fabric reinforcement improve the stiffness of the layered composite while reducing the level of interaction between fiber to matrix and fiber to fiber which results in poor material loss factor.

Table 5 shows the damping curve peak height and glass transition temperature of different layered composites. This also reveals that the glass transition temperature obtained from Tan δ curve does not show any significant difference while the glass transition temperature obtained from the loss modulus curve shows deviation for intra-ply and PIIP composites. This is because the increase in the frictional resistance of both the composite materials enhances the glass transition temperature and the curve shifts towards the higher temperature side. Table 5 leads to the influence of T_g measured from the Tan δ curve being always higher than the T_g measured from the loss modulus. The loss modulus curve indicates the amount of energy dissipated during cyclic loading while in Tan δ curve, storage modulus also will influence the results. Tan δ is the ratio of the loss modulus to material storage modulus. Due to this reason, T_g calculated from Tan δ curve is always higher than the T_g measured from the loss modulus.

Table 5.

Peak height and glass transition temperature of different woven composites.

		Temperature (℃)
Type of composite	Peak height of Tan δ	Tg from Tan δ	Tg from loss modulus
Herringbone	0.1954	112.7	80.1
Intra-ply	0.2259	112.5	93.5
Basket	0.2170	112.7	84.9
BPPB	0.2276	110.6	87.3
IPPI	0.2195	110.4	88.4
PIIP	0.2267	112.7	98.3

Figure 5(d) shows the cole–cole behavior of composite material which reveals the homogeneous behavior of composite material in semi-circular form. In the composite material, the addition of fiber/filler in the polymer matrix changes the material behavior from homogeneous into heterogeneous reflecting an imperfect semi-circle in cole–cole plot.

Theoretical modelling

Several theories have been developed for the analysis of the different parameters such as the reinforcing effect and the volume percentage of fiber on mechanical properties of a composite material. Einstein [26] formulated the equation for analysis of the mechanical properties of composite material considering the reinforcing effect as given as

E_{c} = E_{m} (1 + 1 . {25 V}_{f})

(1)

Another relation given by Guth [27] is

E_{c} = E_{m} (1 + 2 . {5 V}_{f} + 14 . {1 V}_{f}^{2})

(2)

Several researchers have used the rule of mixture equation for predicting the tan δ or damping factor values of composite material to a certain extent [28,29].

tan δ_{c} = V_{f} tan δ_{f} + V_{m} tan δ_{m}

(3)

When reinforced materials are rigid, the first term of the above equation can be eliminated, and the equation can be rewritten as

tan δ_{c} = V_{m} tan δ_{m}

(4)

In the above expressions, subscripts c, m, and f indicate composite, matrix and fiber, respectively. Further equation (4) can be rewritten by introducing the stiffness parameter. Addition of stiffness term in the equation is based on the addition of fiber in the matrix which offers the stiffness of the composite material.

tan δ_{c} V_{m} (E_{m} / E_{c}) tan δ_{m}

(5)

Figure 6 shows the comparison of experimental storage modulus of different woven composites at 40℃ with Einstein and Guth theories. The results reveal the correlation of experimental value of different composites is in correlation with the Einstein equation rather than with Guth equation while damping factor experimental values, not matched well with theoretical values as the type of wove fabric influences the results.

Figure 6.

Comparison of experimental values with theoretical values for (a) storage modulus and (b) damping factor.

Free vibration analysis

Tables 6 and 7 show free vibration characteristics such as natural frequency and associated damping factor obtained for different composites under fixed-free and fixed-fixed boundary conditions using the experimental modal analysis. Experimental modal analysis has been carried out on different woven fabric composites using DEWETRON data acquisition system. Composite beams with a dimension of 170 mm × 17 mm × 4 mm are used for this purpose. In this analysis, the excitation of composite beam is done by a modally tuned impulse hammer (Kitsler 9722A2000), while a corresponding displacement signal is acquired using a single axis lightweight accelerometer (Kitsler 8778A500). In this experimental modal analysis, DEWE soft, modal analysis software is used for getting the frequency response function from which the natural frequency and modal damping factors are obtained. The modal damping factor of composite beam has been calculated using circle fit method using below equation

ξ = \frac{ω_{2}^{2} - ω_{1}^{2}}{2 ω_{0} [ω_{2} \tan \frac{α_{2}}{2} + ω_{1} \tan \frac{α_{1}}{2}]}

(1)

where ω₀ refers to the angular frequency at resonance, ω₂, ω₁ are angular frequencies, α₁, α₂ are angle between angular frequencies.

Table 6.

Influence of weaving pattern architecture, number of layers, stacking sequence on free vibration characteristics under fixed-free condition.

		Mode 1		Mode 2		Mode 3
No. of layer	composite	Nat. freq. (Hz)	Dam. fac.	Nat. freq. (Hz)	Dam. fac.	Nat. freq. (Hz)	Dam. fac.
1	Plain	29.3	0.0956	185.5	0.0515	498.0	0.0491
	basket	34.2	0.0781	224.6	0.0451	610.3	0.0300
	Herringbone	48.8	0.0474	297.8	0.0433	780.2	0.0298
	Intra-ply	43.9	0.0407	289.0	0.0497	805.6	0.0315
2	Plain	43.5	0.0639	234.0	0.0305	581.1	0.0301
	basket	58.6	0.0316	336.9	0.0253	917.9	0.0311
	Herringbone	48.8	0.0284	336.9	0.0247	932.6	0.0307
	Intra-ply	58.6	0.0342	366.2	0.0295	944.9	0.0376
3	Plain	43.9	0.0314	288.1	0.0281	786.1	0.0326
	basket	53.7	0.0356	351.0	0.0328	917.0	0.0370
	Herringbone	53.7	0.0304	332.0	0.0328	878.0	0.0314
	Intra-ply	53.7	0.0554	336.6	0.0368	893.0	0.0400
4	Plain	44.0	0.0427	273.4	0.0303	761.7	0.0324
	basket	68.4	0.0455	410.2	0.0353	1079.1	0.0364
	Herringbone	68.4	0.0455	410.2	0.0353	1079.1	0.0364
	Intra-ply	63.4	0.0331	371.0	0.0339	996.0	0.0375
Sandwich	IPPI	48.8	0.0299	312.3	0.0294	849.0	0.0333
	IPI	43.9	0.0449	302.7	0.0407	805.6	0.0404
	BPPB	48.8	0.0229	322.0	0.0307	854.0	0.0450
	BPB	39.1	0.0411	263.6	0.0413	712.1	0.0426
	IBaBaI	53.0	0.0382	322.1	0.0334	908.0	0.0390
	IPPB	53.7	0.0463	307.6	0.0446	834.0	0.0439
	PIIP	48.8	0.0384	327.1	0.0301	883.8	0.0395

Table 7.

Influence of weaving pattern architecture, number of layers, stacking sequence on free vibration characteristics under fixed-fixed condition.

		Mode 1		Mode 2		Mode 3
No. of layer	composite	Nat. freq. (Hz)	Dam. fac.	Nat. freq. (Hz)	Dam. fac.	Nat. freq. (Hz)	Dam. fac.
1	Plain	205	0.0504	634	0.0353	1137	0.0318
	basket	244	0.0333	693	0.0358	1250	0.0308
	Herringbone	312	0.0387	820	0.0354	1523	0.0496
	Intra-ply	268	0.0408	747	0.0304	1494	0.0371
2	Plain	205	0.0449	627	0.0296	1183	0.0349
	basket	307	0.0344	795	0.0348	1595	0.0396
	Herringbone	292	0.0376	756	0.0260	1464	0.0399
	Intra-ply	327	0.0367	772	0.0374	1548	0.0404
3	Plain	278	0.0386	742	0.0288	1401	0.0222
	basket	317	0.0476	810	0.0302	1608	0.0219
	Herringbone	297	0.0454	756	0.0378	1547	0.0227
	Intra-ply	292	0.0395	737	0.0337	1450	0.0246
4	Plain	283	0.0401	742	0.0382	1406	0.0244
	basket	341	0.0451	937	0.0398	1835	0.0333
	Herringbone	336	0.0409	864	0.0342	1655	0.0171
	Intra-ply	314	0.0478	864	0.0396	1708	0.0331
Sandwich	IPPI	351	0.0529	927	0.0304	1352	0.0385
	IPI	297	0.0452	776	0.0298	1406	0.0361
	BPPB	307	0.0513	810	0.0351	1372	0.0483
	BPB	278	0.0433	717	0.0217	1362	0.0301
	IBaBaI	288	0.0506	708	0.0314	1367	0.0283
	IPPB	317	0.0404	776	0.0458	1455	0.0336
	PIIP	317	0.0457	834	0.0295	1518	0.0162

The observation from the results is that the composite with three- and four-layered woven fabric reinforcement has higher a natural frequency compared to single- and double-layered composites which indicates that the addition of layers in the matrix increases the structural stiffness of composite material. Similarly, single- and double-layer composites have better damping factor of the composite laminate due to a large volume of matrix material in the composite and higher interaction between fiber–matrix. Even though three-layer composite increases the natural frequency of composite compared to single and double layer, the four-layer composite shows a significant increase in the natural frequency due to higher amount of fiber loading as seen in Tables 6 and 7.

In the case of four-layer composites, basket type woven jute fabric and jute-banana intra-ply woven fabric composites provide a higher natural frequency compared to jute plain woven fabric and jute herringbone fabric composites. Structural arrangements of yarns in the warp and weft direction in the woven fabric account for this. This is explained in the section on mechanical properties. The effect of stacking sequence of fabrics with different weave types influences the natural frequencies and modal damping of the sandwich composites. However, the natural frequencies of the sandwich composites are less than those of the four-layered composites such as jute basket and jute-banana intra-ply fabric composites. This can be attributed to the higher flexural modulus of the four-layered composites than the sandwich composites. In sandwich composite, IPPI and BPPB composite shows low damping factor which indicates better bonding between fiber–matrix as well as uniform stress distribution due to presence of two weak woven fabrics.

Finite element software ANSYS is used for comparison of the experimental value with numerical analysis, for which the composite beam has been modeled using four noded structural SHELL 181 element. The equivalent properties such as Young’s modulus and density of composite materials are found from three-point bending test and mass of the composite material. The expression used for analytical method given by [30] for bending mode frequency of ith mode based on Euler-Bernoulli hypothesis is

where E = Young’s modulus (N/m²), A = cross-section area of beam (m²), ρ =density of composite material (kg/m³), I = moment of inertia (m⁴), L = length of composite specimen (m), β value for first three modes of fixed-free condition is 1.875, 4.694, 7.854 and fixed-fixed condition is 4.73, 7.8532 and 10.995 [30]. Table 8 reveals the results obtained from analytical, numerical and experimental methods that show small deviations from each other which is due to the assumption of composite material as quasi-isotropic.

Table 8.

Comparison of experimental natural frequencies with theoretical and numerical results for IPPI sandwich composite.

	Natural frequency (Hz)
Mode	Experimental method	Theoretical method	FEM method
First	48.8	45 (7.78%)	44 (9.83%)
Second	312.3	287 (8.10%)	281 (10.02%)
Third	849.0	793 (6.59%)	805 (5.18%)

Conclusion

Influence of woven fabric reinforcement with different weave types and their stacking sequence on mechanical, dynamic mechanical and free vibration behavior has been investigated. The results revealed that jute woven basket composite has better mechanical, dynamic mechanical and free vibration characteristics than plain and herringbone woven fabric composites. Further jute-banana intra-ply basket type woven fabric composite results have been compared with jute basket woven composite. It is found that the intra-ply composite gives better properties compared to composites with jute woven fabric. The combined effect of jute and banana fibers enhances the properties of the composite material. It is also found that the four-layered composites give better properties. The density of composites calculated using the Archimedes principle revealed the absence of any porosity and fabrication damages in the composite. Further, sandwich composites are prepared using different combinations of strong woven fabrics and weak woven fabrics as skin and core material, respectively. Enhancement of the properties of composite as a result of effective stress transfer from matrix to fiber due to strong fiber–matrix interface are shown for IPPI composite, while PIIP (plain-intra-ply-intra-ply-plain) composite decreases the properties of composite material due to poor stress transfer from outer layer to middle layer. It is also observed that IPPI composite gives better properties than IPI composite due to better stress transfer and modulus value.

Footnotes

Acknowledgement

The authors wish to thank Material Characterization Lab, Department of Mechanical Engineering, NITK, Surathkal for allowing us to carry out tensile and flexural tests.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was funded by SERB-Department of Science and Technology, India. (SR/FTP/ETA-64/2012).

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Mechanical behavior of woven natural fiber fabric composites: Effect of weaving architecture,intra-ply hybridization and stacking sequence of fabrics

Abstract

Keywords

Introduction

Experimental details

Woven fabric and polymer preparation

Fabrication of composites

Testing standards

Results and discussion

Density measurement

Mechanical properties

Surface morphology study

Dynamic mechanical analysis

Theoretical modelling

Free vibration analysis

Conclusion

Footnotes

Acknowledgement

Declaration of Conflicting Interests

Funding

References