Mechanical properties analyses of bolted joint of Kusha and Nacha fiber composite laminates

Abstract

Researchers have been inspired to work on natural fibres as a replacement for man-made synthetic fibres in many lightweight, medium-load applications by the demand for environmentally friendly materials. In this research work, Kusha and Nacha fibre composite laminates have been made by using general-purpose polyester resin to study the possibility of using it as a new material. And its mechanical properties were evaluated. The fibre mat was fabricated by using a weaving setup tech nique and fabrication of laminates with [0°/0°, −45°/45°, and 0°/90°] degree orientations by hand lay-up. The mechanical properties like tensile, shear, and bearing strengths of bolted joints of Kusha and Nacha fibre composite laminates were investigated experimentally. The 18 different laminated composite plate specimens have been tested to observe the influences of joint geometry and stacking sequence on the failure mechanism. Comparisons have been made between the Nacha and Kusha composite fibre laminates in order to determine different failure modes. The mechanical properties of Kusha fibre laminates showed maximum average tensile strengths of 70.05 MPa, bearing strengths of 118.6 MPa, and shear strengths of 32.14 MPa. Whereas Nacha fibre laminates showed maximum tensile strengths of 101.6 MPa, bearing strengths of 149.9 MPa, and shear strengths of 40.2 MPa. Nacha fibre laminates showed more mechanical strength than Kusha fibre laminates. Generally, for this tensile, shear, and bearing strength test of [0°/0°], [−45°/45°], and [0°/90°] angle play for Nacha and Kusha fibres, [0°/90°] angle play has better bearing and shear strength than other angle arrangements.

Keywords:

• fibre composite laminates
• mechanical property
• shear strength
• tensile strength
• bolted joint
• fibre orientation

1. Introduction

Consumer awareness of new items made from renewable sources has increased significantly during the past few years. Consumers have been directed towards ecologically friendly outcomes by green marketing, new perspectives on recycling, social influence, and changes in cognitive values. To offer new products responsibly and sustainably while enhancing and adapting existing ones, composite materials are specifically being developed and modified.

Composites are designed to achieve unique mechanical properties and superior performance characteristics not possible with any of the component materials alone (Gon et al., 2012; Ramesh et al., 2017). Composites have a greater modulus than the polymer component but are not as brittle as ceramics. Two types of polymer composites are fibre-reinforced polymer (FRP) and particle-reinforced polymer (PRP). FRP is a common fibre-reinforced composite (Khalid et al., 2022). The most commonly used matrix materials are polymeric (Ullah Arif et al., 2022). In general, the mechanical properties of polymers are inadequate for many structural purposes. In particular, their strength and stiffness are low compared to metals and ceramics (Yasir Khalid et al., 2021). These difficulties are overcome by reinforcing other materials with polymers. Secondly, the processing of polymer matrix composites need not involve high pressure or high temperature (Yasir Khalid et al., 2022). Also, the equipment required for manufacturing polymer matrix composites is simpler. For this reason, polymer matrix composites developed rapidly and soon became popular for structural applications (Khalid et al., 2021). Composites are used because the overall properties of the composites are superior to those of the individual components, for example, polymer or ceramic (Chandramohan & Marimuthu, 2011; Yuhazri et al., 2011; Prasanna Venkatesh et al., 2016).

Polymers have recently gained popularity as materials for a wide range of applications thanks to their many distinctive technical characteristics, such as their light weight, high productivity, and affordability. Natural fibres have been discovered to be the most appealing throughout the past few centuries in terms of an economical and environmentally friendly method of producing fibre-reinforced polymeric composites. Engineers, scientists, and researchers are now researching renewable energy or alternative sources. Everyone is currently concentrating on finding sustainable technical solutions for the environment and the energy sector. The green environment spectrum spans a wide range of topics, including “green home,” “green energy,” “green living,” “green solution,” “green technology,” and “green materials” (Nirmal et al., 2015). Composite materials have taken the place of traditionally manufactured common materials with higher weight specifications. Polymeric materials are employed in tribological parts such as plastic gears, artificial joints, guide rails, sliding bearings, and so forth as an alternative to metals (Nozawa et al., 2009). This is a result of the polymers’ desirable properties, which include self-lubrication and noise reduction (Mylsamy & Rajendran, 2011). Glass and other synthetic fibres are still employed as reinforcement in polymer composites today, although they have some disadvantages, including high energy consumption, greater costs, and an inability to be recycled (Al-Oqla et al., 2015). Plant-based materials have taken over the role of synthetic materials because they have superior qualities, such as low abrasive impacts on processing equipment, high composite strength, low cost, simple manufacture, recyclable, and biodegradable (Nirmal et al., 2012). Additionally, there was a significant decrease in fuel usage, carbon dioxide emissions, and air pollution (Omrani et al., 2016).

Composite materials have a wide range of applications because of their light weight, high strength-to-weight ratio, fatigue resistance, corrosion resistance, etc. compared to metals. Fibre-reinforced laminated composite materials have been gaining a wide application area in the aircraft, aerospace, automobile, and marine industries because of their advanced properties. In building complex structures, several parts must be joined together. Bolted and pinned joints are used to connect composites either to other composites or to metal (Muthukumar et al., 2011; Sutharson et al., 2013). Most composite structure damage occurs at joints. Because of this, so many researchers are interested in bolted composite joints. It is important to determine the failure strengths and failure modes of these joints. The knowledge of the failure strength of a joint help in selecting the appropriate joint size in a given application (Rao et al., 2017; Sen & Pakdil, 2008). Today, many composite parts are made out of different orientations of prepared tapes and are being used extensively in applications where a joint is required. In composite structures, three types of joints are commonly used: mechanically fastened joints, adhesively bonded joints, and hybrid mechanically fastened and adhesively bonded joints. A major goal of bolted joint research is to ensure load transfer without failure of the joint and determine the effect of various bolting parameters on the bearing strength of the joint. These parameters include joint geometry (specimen width, end distance, and hole diameter), loading condition (tension, compression, or combined static and/or fatigue loading), and material parameters (stacking sequence, fibre shape, matrix type, fibre volume fraction) (De Sousa et al., 2016; Retnam et al., 2014; Singh et al., 2017; Sridevi, 2014; Whitworth, 2003).

Natural fibres are used in the automotive industry and are sustainable on a worldwide scale. Additionally, these sectors took the initiative to enhance the production of automobile parts by including the use of plant-based fibres and composites in the fabrication of car components (Balasubramanian et al., 2022; Dass & Chellamuthu, 2022; Faruk et al., 2014; Nagappan et al., 2022; Selvaraj, Chapagain, et al., 2023, Selvaraj, Pannirselvam, et al., 2023). Over the last few years, there has been a dramatic increase in the use of plant fibres for making sustainable, eco-friendly, and biodegradable materials. Fibres from plants such as cotton, hemp, jute, sisal, pineapple, ramie, bamboo, banana, etc., as well as wood and the seeds of flax, are used as reinforcement in polymer matrix composites. Fibres extracted from plants are a type of renewable source and a new generation of reinforcements and supplements for polymer-based materials (Engineering, 2016; Hossain et al., 2013). These fibres are renewable, cheap, completely or partially recyclable, biodegradable, and environment-friendly materials. Their availability, low density, and price, as well as satisfactory mechanical properties, make them attractive alternative reinforcements to glass, carbon, and other man-made fibres (Mohammed et al., 2015; Samuel et al., 2012). Natural fibres, which originate from plants, have been used for thousands of years; they are naturally available resources that are popular among consumers who are highly health conscious, and these fibres are considered valuable raw materials for many applications and have also found use in gardening, pulp and paper production, and the cosmetic and food industries. Factors like poor wet ability, poor bonding and degradation at the fibre/matrix interface, and damage to the fibre during the manufacturing process are the main causes for the reduction of their strength (Babu & Gupta, 2016; Çıplak & Sayman, 2011; Deli, 2016; Tserpes et al., 2002). Therefore, plant fibres are not homogeneous in size, and different constituent scales must be accounted for when they are used for material reinforcement because of differences in various parameters, whatever the species studied, such as the fibre origin (for example, the part of the stem), the growth conditions of the plant, and the process to extract the fibres.

Despite the fact that a variety of factors influence the use of natural fibres in composites, their cost-competitiveness and renewability continue to entice businesses from all industries to look for ways to replace conventional materials with natural fibres. Given the vast number of problems that remain unsolved, study in this area is extremely valuable. Without a doubt, the proper design of natural fibre composites and selection of their manufacturing method will enable them to become one of the leading structural materials in engineering sectors.

Natural fibre plants like Kusha and Nacha are available in many parts of Ethiopia, such as Degadamot Wereda and Dembecha Wereda, where the fibres from these plants are mainly used for making traditional ropes. Much of this vegetation is burned off every year without even extracting the fibres. The literature reviews revealed that no research has been done on the mechanical properties like tensile, shear, and bearing strengths of bolted joints of Kusha and Nacha fibre composite laminates. The aim of this research work is to utilize the fibres from these plants for developing materials for certain engineering applications in order to replace the conventional structural materials.

2. Materials and methodology

Fabrication and testing of composite materials for mechanical properties has been selected as a broad field of research. The composite materials used in the production of the specimens include natural fibres such as Nacha and Kusha fibre, polyester resin, hardener, roller, thick glass plates, and metal shaving wax. The equipment used is a weighing balance, measuring cylinder, cutter, driller, and universal testing machine. The composite laminas were prepared by hand moulding between two thick glass plates at room temperature, and the specimens are prepared as per ASTM Standards D3039. Bearing, shear, and tensile tests were conducted on the specimens. The value of each property obtained for different composites was compared. Nacha and Kusha fibres were selected for this study because those materials are easily available and can be simply extracted from their stems. In this study, water washing and drying were used to prepare natural fibres that are Nacha and Kusha. The natural fibres, after being extracted, were allowed to dry in the sun for 7 days. Kusha was simply extracted from the back of their stems, while Nacha was immersed in water for 21 days and washed with water to remove gums. After which the fibres were changed into mats with very thin, small treads.

2.1. Extraction of Kusha and Nacha fibers

To extract fibres, first cut down the Nacha and Kusha fibre plants, as seen in Figure 1, from their vegetative origin by using a manual extraction process and drying them with sunlight for 3–6 days to remove the moisture. After drying, Nacha fibre plants were immersed in the water for 21 days to get clean, good fibres from their stems easily, but the dried Kusha natural fibres were not immersed in the water. It was simply extracted from the back of their stems. The Kusha and Nacha fibres were prepared as shown in Figures 2 and 3.

Figure 1. (a) Kusha fiber plant and (b) Nacha fiber plant.

Figure 2. Extraction of Nacha fibers.

Figure 3. Extraction of Kusha fibers.

2.2. Simple weaving set up tool

It is a simple type of tool that is prepared from simple materials, as shown in the following Figure 4.

Figure 4. Prepared fiber composites.

2.3. Preparation of Kusha and Nacha fiber mats

To fabricate mats, first select Kusha and Nacha fibres by using a weaving setup. The fibre mats were prepared with every thin thread in a perpendicular direction as shown in the following sample, as seen in Figure 5.

Figure 5. Weaved fabricated mat from Kusha and Nacha fibers.

2.4. Resin and hardener

The resin used for this study is polyester resin with the brand name GPP (general purpose polyester), as shown in Figure 6.

Figure 6. Polyester resin.

The ratio of polyester resin to hardener used for this study was based on their masses. In general, the ratio was calculated based on manufacturer guidelines, which was 27% hardener for 100% polyester. According to manufacturer guidelines, better mechanical properties of composites after the curing process are attained if and only if the above-mentioned ratio is correctly applied, irrespective of any environmentally determined conditions. Then, the mixtures were stirred for a few minutes using deep-stick material. In this work, MEKP (methyl ethyl ketone per oxide) hardener has been used, which is characterized by low toxicity and excellent moisture resistance, as seen in Figure 7.

Figure 7. Hardener.

2.5. Preparation of laminated structures

A laminate is constructed by stacking a number of laminates in the thickness (z) direction. Examples of a few special types of laminates and their standard lamination codes are given in Figure 8.

Figure 8. Laminated structures.

Curing and lay-up processes were used to prepare composite materials, as seen in Figure 9. There are different types of lay-up processes, such as hand lay-up (wet lay-up), spray lay-up, and filament winding. Vacuum bagging, resin transfer moulding (RTM), and autoclaving pultrusion is grouped under curing processes. These processes depend on many factors, such as part size and shape, cost, schedule, familiarity with particular techniques, etc. To prepare this, all three components-G.P. polyester resin and hardener were mixed in the appropriate quantity and stirred well to obtain a homogenized mixture. The resin-to-fibre weight ratio for the prepared laminate was 1:3 in the present work. A hand roller had been used to remove trapped air in the laminate. The laminates were cured at room temperature (25 °C) for 24 hours. Thick glass plates were used to create each well laminate, and wax polish and PVA coating were applied smoothly and uniformly. The required quantity of 1/3 resin is spread on the glass plate, and the fibre mat is placed over it and also rolled. The second third of resin with hardener was distributed to the entire surface by means of a roller. The air gaps that formed between the layers during the processing were gently squeezed out. And also, the glass plate with the PVA or wax coating was placed on it. Excess resin would come out from the sides when the square plate with weights was placed over it. After these, the specimens were kept for several hours to get the perfect samples. Finally, it was taken out of the moulds, and rough edges were cut and removed as per the required dimensions. Figure 9 below shows the typical hand lay-up process. The matrix used to fabricate the fibre specimen was polyester of density 1.39 g/cm³ at 25 °C mixed with hardener MEKP. The weight ratio of mixing polyester and hardener would be as per the standard for 1 kg of polyester and 6 grammes of MEKP. Kusha and Nacha fibre laminates have been prepared by using the hand lay-up method. The thickness of the lamina was limited to 2.5 mm and 3 mm for Nacha and Kusha fibres, respectively. The size was 40 cm by 40 cm. During lamination processing, the following steps were used:

Figure 9. Hand lay- up method (Yasir Khalid et al., 2022).

First applying wax to the glass plate and implementing the first layer of resin with a brush over the wax. Positioning of the first fibre mate on the resin and applying the resin to the fibre mate by using a brush were followed. The air gaps formed between the layers were gently squeezed out by means of a hand roller, which eliminated the second layer of fibre mat on the resin. Application of the resin on fibre mates by using a brush and elimination of air bubbles by using the roller across the surface of the mould. Finally, these laminae were kept in press for over 24 hours to get the perfect shape and thickness. Excess resin would come out from the sides when the square plate with weights was placed over it. Nacha and Kusha fibre mat laminates were prepared by the hand lay-up method with general-purpose polyester resin in the form of sheets. The dimensions of compressed Nacha and Kusha fibre mat laminates were manufactured: width = 400 mm, length = 400 mm, and thickness = 5 and 6 mm, respectively, as shown in Figures 11–14, and divided into five samples with ASTM Number (D 5961) standards dimensions. The strength test was conducted in accordance with ASTM test method D5961 (Deli, 2016) as shown in Tables 1 and 2.

Table 1. Stacking sequences of laminated composite plates

Group	Stacking Sequence	Average Thickness of Kusha Laminate (mm)	Average Thickness of Nacha Laminate (mm)	Number of Stacked Lamina
1	[0°/0°]	6	5	2
2	[0°/90°]	6	5	2
3	[45°/-45°]	6	5	2

Table 2. Dimensional specification of ASTM D5961 for bolted joint specimens

ASTM D5961 standards
Dimensions	Values
Length (L)	210mm
Width (W)	36±1mm
Hole diameter (D)	6±0.003mm
Distance from the hole center to the edge (E)	18±1mm

2.6. Pin bearing strength testing

Many researchers have studied the strength of pin bearings (Sutharson et al., 2013), as seen in Figure 10, because it is a very crucial design parameter for bolted joints. There are different geometrical factors that determine the mode of failure of pin bearings. When the ratio of w/d is low, net tension initiates the failure, with cracks starting from the whole boundary. Shear-out failure occurs when the ratio of e/d is low. When net tension failure and shear out failure occur, then the composite laminate has a low load carrying capacity. But when the ratios of e/d and w/d are high, there is bound to be bearing failure. Factors such as the sequence of stacking and orientations of fibres and materials have a great influence on the ratios of e/d and w/d, which in turn affect the full bearing strength. Moreover, the ratio of d/h controls the shear and bearing strength of the produced specimens. There is a decrease in bearing strength when the ratio of d/h is increased. While observation of shear failure can be seen when the ratio of d/h is low. For full bearing strength to be developed, a ratio between 1 and 1.2 is required for d/h (Sutharson et al., 2013).

Figure 10. Pin bearing test and various failure modes (Sutharson et al., 2013).

Figure 11. Preparations of Kusha and Nacha laminates.

Figure 12. Shape and dimensions of Kusha and Nacha laminate samples.

Figure 13. Nacha fiber laminates.

Figure 14. Kusha fiber laminates.

The properties of KFRP and NRFP are shown in Tables 3 and 4 as seen below.

Table 3. Property of Kusha fiber and polyester resin

Material	Elastic modulus (GPa)	Mass(g)	Density(g/cm^3)	Volume (mL)	Poison ratio
Kusha fiber	58	386.5	0.841	459.67	.25
Polyester resin	4.9	896.5	1.399	815	.38

Table 4. Property of Nacha fiber and polyester resin

Material	Elastic modulus (GPa)	Mass(g)	Density(g/cm^3)	Volume (mL)	Poison ratio
Nacha fiber	31.7	390.5	1.261	309.48	.2
Polyester resin	4.9	901	1.399	819.1	.38

3. Results and discussion

Nacha and Kusha fibre-reinforced polyester laminates were done in 0°/0°, −45°/45°, and 0°/90° angle ply orientations with general purpose polyester resin. After getting six types of laminates, the specimens were prepared by being cut into the required size. The bolted joints have been tested using the Universal Testing Machine for the six types of laminated plates or specimens to determine the failure strengths such as tensile strength, shear strength, bearing strength, and maximum failure load of the prepared laminates. Specimen cutting is done according to ASTM standards for bearing, shearing, and tensile tests. The following picture shows the prepared specimens for different types of NFRP and KFRP. The cutting had been done using a jigsaw machine. Nacha and Kusha fibre-reinforced polyester composite laminates before and after the cut are shown in Figure 15.

Figure 15. Sample of Nacha and Kusha fiber composite laminate before and after cut.

3.1. Tensile testing

It is a computer-controlled electro-hydraulic machine with a capacity of 100 kN. During the test, the following initial parameters were fed to the computer: displacement 0.2 mm/min, load speed 0.1 kN/s (1 MPa/s), and extension 0.01 mm/s (0.02%/s). The tensile test was done to calculate the tensile strength of the spacemen’s and to find the young’s modulus of elasticity, which gives an indication to the toughness of the composite materials with various fibre volume fractions of Nacha and Kusha fibre mat.

3.2. Geometrical dimensions of Kusha and Nacha fiber composite specimens for testing

After getting six types of laminates, the specimens were prepared by being cut into the required size of the bolted hole with the help of a diamond cutter depending on the following parameters: For bearing strength, the ratio of (E/D) > 3, (W/D) > 6, and (D/t) is between 1 and 1.2. For shear strength, the ratios of (E/D) < 3, (W/D) > 6, and (D/t) are between 1 and 1.2. Tensile strength was determined by placing the bolted joint hole in the center of the specimen. And bolted joints were tested by using a universal testing machine for the six types of laminated plates or specimens in order to determine the failure strengths such as tensile strength, shear strength, bearing strength, and maximum failure load of the prepared laminates.

3.3. Strength test

In this research work, tensile, shear, and bearing strengths were tested experimentally. The test specimens are dimensioned according to ASTM (D 5961), and five specimens were tested for each condition. The test results presented are based on the average values of five specimens. The bearing, shear, tensile strength, and maximum failure load were also investigated experimentally. The specimens for each E/D and W/D ratio were tested for the experimental study. Bearing and shear strength values and failure loads were investigated for two variables: E/D ratio (1.3, 3) and W/D ratio (6.0) for bearing and shear strength, and (4.5) for tensile strength. The orientation angle of fibre for two stackings [0°/0°], [−45°/45°], and [0°/90°] was used in this study. The results of the tensile, shear, and bearing strengths of Kusha and Nacha fibre laminates with general purpose polyester resin are shown in Table 5–10. According to this experiment, three lamination cases were taken within the arrangement of [0°/0°], [−45°/45°], and [0°/90°] angle plays. The specimen has similar areas of 36 mm² and 30 mm² for the bearing strengths of Kusha and Nacha fibres, respectively. At [0º/0º] lamination, five samples were taken to measure their bearing strength. The average machine forces were 2.54 kN and 3.16 kN, and the corresponding bearing strengths for Kusha and Nacha were 70.6 kPa and 105.9 kPa, respectively. Similarly, the areas of the specimens for the tensile strengths of Kusha and Nacha were 168 mm² and 140 mm², respectively. The average machine forces were 11.75 kN and 14.26 kN, with corresponding tensile strengths of 70.05 kPa and 101.66 kPa. So, in this way, Nacha has better strength than Kusha fibre composite.

Table 5. Experimental result of various angled lamina of NFRP for bearing strength

Nacha fiber bearing strength
Type		Force (KN)	Average Force (KN)	Area (mm2)	Ultimate Bearing Strength (MPa)	Average (MPa)
[0°/0°]	1	3.1	3.16	30	103	105.96
	2	3.2			107.7
	3	3.1			104.8
	4	3.4			113.8
	5	3.0			100.5
[−45°/45°]	1	3.2	3.5	30	106.6	116.67
	2	3.2			107
	3	3.4			112.4
	4	3.8			127.1
	5	3.8			127.1
[0°/90°]	1	3.9	4.5	30	129.3	149.94
	2	4.3			142.5
	3	4.5			151.2
	4	4.8			161.2

Table 6. Experimental result of various angled lamina of KFRP for bearing strength

Kusha fiber bearing strength
Type		Force (KN)	Average Force (KN)	Area (mm2)	Ultimate Bearing Strength (MPa)	Average (MPa)
[0°/0°]	1	2.1	2.54	36	58.9	70.6
	2	2.6			72.4
	3	2.6			72.7
	4	2.6			71.5
	5	2.8			77.5
[−45°/45°]	1	2.6	2.63	36	72.1	69.6
	2	2.63			69.6
	3	3.0			76.5
	4	2.3			60.3
[0°/90°]	1	3.4	4.26	36	93.4	118.62
	2	4.3			119.1
	3	4.4			121.5
	4	4.6			128.1
	5	4.7			131

Table 7. Experimental result of various angled lamina of NFRP for shear strength

Nacha fiber bearing strength
Type		Force (KN)	Average Force (KN)	Area (mm2)	Ultimate Bearing Strength (MPa)	Average (MPa)
[0°/0°]	1	2.0	1.88	80	24.9	23.16
	2	2.0			24.6
	3	1.8			21.9
	4	1.8			22.2
	5	1.8			22.2
[−45°/45°]	1	2.0	2.7	80	25.4	33.9
	2	2.9			36.5
	3	2.5			30.8
	4	2.6			32.9
	5	3.5			43.9
[0°/90°]	1	2.9	3.22	80	35.9	40.2
	2	3.1			39.2
	3	3.6			45.0
	4	3.3			40.7
	5	3.2			40.1

Table 8. Experimental result of various angled lamina of KFRP for shear strength

Kusha fiber bearing strength
Type		Force (KN)	Average Force (KN)	Area (mm2)	Ultimate Bearing Strength (MPa)	Average (MPa)
[0°/0°]	1	1.9	1.76	96	19.5	18.5
	2	1.9			20.2
	3	1.7			18.1
	4	1.6			16.5
	5	1.7			18.2
[−45°/45°]	1	2.2	2.42	96	22.6	25.14
	2	2.5			26.0
	3	2.3			24.2
	4	2.7			28.2
	5	2.4			24.7
[0°/90°]	1	3.2	3.10	96	33.3	32.14
	2	3.0			31.1
	3	3.0			31.1
	4	3.2			33.1
	5	3.1			32.1

Table 9. Experimental result of various angled lamina of NFRP for tensile strength

Nacha fiber bearing strength
Type		Force (KN)	Average Force (KN)	Area (mm2)	Ultimate Bearing Strength (MPa)	Average (MPa)
[0°/0°]	1	15	14.26	140	106.8	101.66
	2	15.2			108.3
	3	14.9			106.5
	4	12.7			90.6
	5	13.5			96.1
[−45°/45°]	1	3.9	3.48	140	28.2	24.88
	2	3.6			25.4
	3	3.6			25.6
	4	3.5			25.0
	5	2.8			20.2
[0°/90°]	1	7.5	7.82	140	53.5	55.9
	2	7.4			53.1
	3	7.1			50.9
	4	8.0			56.9
	5	9.1			65.1

Table 10. Experimental result of various angled lamina of KFRP for tensile strength

Kusha fiber bearing strength
Type		Force (KN)	Average Force (KN)	Area (mm2)	Ultimate Bearing Strength (MPa)	Average (MPa)
[0°/0°]	1	12.1	11.75	168	72.3	70.05
	2	12.1			72.3
	3	10.8			64.2
	4	12.0			71.4
	5	11.7			70.4
[−45°/45°]	1	4.1	4.26	168	24.4	25.34
	2	3.8			22.9
	3	5.0			29.7
	4	4.1			24.3
	5	4.3			25.4
[0°/90°]	1	7.7	7.36	168	45.9	43.84
	2	7.1			42.3
	3	7.2			43.1
	4	7.7			45.8
	5	7.1			42.1

In [−45º/45º] angle play, the average machine forces of Kusha and Nacha fibres are 2.63 kN and 3.5 kN, respectively, with corresponding bearing strengths of 69.9 MPa and 116 MPa in the same area. And also, the average tensile strengths of Kusha and Nach fibres were 25.34 MPa and 24.88 MPa, respectively, with corresponding average machine forces of 4.26 kN and 3.48 kN.

Similarly, for [0°/90°] angle play, the average machine forces of Kusha and Nacha fibres were 4.2 kN and 4.5 kN, with corresponding bearing strengths of 118.6 MPa and 149.9 MPa in the same area. And also, the average tensile strengths of Kusha and Nach fibres were 43.84 MPa and 55.9 MPa, with corresponding average machine forces of 7.82 kN and 7.36 kN. Generally, for this tensile, shear, and bearing strength test of [0°/0°], [−45°/45°], and [0°/90°] angle play for Nacha and Kusha fibres, [0°/90°] angle play has better bearing and shear strength than other angle arrangements.

For [0º/0º] laminates, failure in pin-bearing tests occurs by longitudinal splitting since such laminates have poor resistance to in-plane transverse stresses at the loaded hole. The bearing stress at failure for [0º/0º] laminates is also quite low. In this experiment, the general-purpose polyester resin is the same in each laminate. but the strand of fibres is not similar to the direction of the force. So, it has a great effect on the strength of laminates. The number of strands at [0º/0º], [−45º/45º], and [0º/90º] angle play is straight, off straight, and perpendicular, as seen in Figures 16–18.

Figure 16. Tensile strength of Kusha and Nacha fiber composite.

Figure 17. Shear strength of Kusha and Nacha fiber composite.

Figure 18. Bearing strength of kusha and Nacha fiber composite.

In [0°/0°] angle play laminate, the arrangement of fibres or the number of strands are totally in the force direction, so it has great strength, while in [0°/90°] angle play laminate, the half of the fibres are arranged in the direction of force, so it has better strength. And also, the last case is [−45°/45°] angle-play laminate, which has low strength because neither of the fibres arranged in the direction of force is arranged in the direction of force so that it has a better strength. Different kinds of failures were observed. Bearing and shear strength testing showed bearing and shear-out failure modes. While tensile strength testing showed net tension failure mode. Due to the arrangement of fibres in one direction, [0°/0°] angle-ply lamination showed cleavage failure mode. Figures 19–21 show the different failure modes of Kusha and Nacha composite fibre laminates at different angles of orientation.

Figure 19. Bearing strength test specimens of Kusha and Nacha after testing.

Figure 20. Shear strength test specimens of Kusha and Nacha after testing.

Figure 21. Tensile strength test specimens of Kusha and Nacha after testing.

4. Conclusion

In this research work, the tensile, shear, and bearing strengths of Kusha and Nacha fibre polyester composites were studied. The fibre composite laminates were manufactured by the hand lay-up method and tested according to the ASTM D5961 standard. From the obtained results, the following conclusions were deduced:

• Kusha and Nacha fibre polyester composites have better tensile strength at [0°/0°] orientation angle than [−45°/45°] and [0°/90°]. orientation.

• The bearing and shear strengths of Kusha and Nacha fibre polyester composites are better at [0°/90°] orientation angles than [−45°/45°] and [0°/0°].

• The tensile, bearing, and shear strengths of Nacha fibre polyester composite are better than Kusha fibre polyester composites.

• From the experimental results of Nacha fibre polyester composites, the [0°/0°] orientation angle has the highest tensile strength, which is 101.6 MPa, and can resist a maximum force of 14,260 N.

• Shear out, net tensile, bearing, and cleavage failure modes were noted throughout the test when the fibres were arranged at various angles. In [0°/0°] angle ply orientation for bearing and shear strength tests, cleavage failure mode was noted (Ramesh et al., 2017).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

All data used for this research is included in this manuscript.

Additional information

Funding

The authors received no direct funding for this research.