Experimental vibrational analysis of natural fiber composite reinforced with waste materials for energy absorbing applications

1 Introduction

As natural fibers possess exceptional mechanical qualities, lightweight design, and versatility for a range of industrial applications, fiber-reinforced laminated composites have drawn increasing interest across many industries. Ahmad et al. [1] emphasized that natural fiber composites were promising alternatives to synthetic materials due to their cost-effectiveness, adequate mechanical performance, and application-specific adaptability, highlighting the need for continued research and standardization to support wider industrial adoption. Thabrew and Jansz [2] described the nutritional value of products made from palmyra while explaining their content of carbohydrates and multiple vitamins and minerals. This article examined the medical properties of these products and explains their antioxidant functions while describing their dietary fiber composition and how palmyra served traditional and contemporary health functions both as food ingredient and medical treatment. In recent times scientists have extensively studied the modal properties of composites containing fibers. In their discussion of modal test design in structural dynamics, Carne et al. [3] offered crucial techniques for experimental vibration analysis. Jafari et al. [4] performed both experimental and numerical methods on the modal characteristics exhibited by glass fiber reinforced aluminum plates. As well as, Dalai [5] investigated the free vibration dynamics of natural fiber laminated composite plates and the results showed how the orientation of fibers combined with stacking order and placement boundaries affected the vibrational response results. The experimental data match the numerical outputs that confirm the validity of the modeling method. Guo et al. [6] demonstrated how natural fiber composites could bring sustainable solutions to structural elements. This research found the material properties combined with lamination techniques and connection methods influence the dynamic characteristics of the composites. Majhi et al. [7] also investigated the natural vibration characteristics of composite plates with square cut-outs through a combination of experimental testing and numerical analysis. The natural frequencies along with mode shapes changed notably when cut-out dimensions vary together with their placement positions and boundary constraints. The study helped development of effective design approaches for composite structures featuring internal geometric shapes. Rajkumar et al. [8] experimentally demonstrated the structural efficiency of E-glass/epoxy and jute/epoxy composite plates. Similarly, Sahu and Mohanty [9] examined the free vibration behavior of jute-epoxy polymer composites using AI-based techniques. Bekele et al. [10] published an experimental study on palmyra palm stalk–sisal hybrid polyester composites, where hybrid mixes (e.g., 50/50 palmyra:sisal) demonstrated up to 37.3% higher tensile strength, indicating improved load and energy absorption characteristics in dynamic or vibrational contexts. Rajkumar et al. [11] studied the modal analysis of natural fiber-reinforced laminated composite trapezoidal plates through evaluations of their mechanical characteristics, which boosted their overall structural stability. Rajkumar et al. [12] performed Finite element analysis (FEA) on E-glass basalt laminated composite plates, which exhibited better mechanical characteristics through varying a/b ratios.

Numerous studies examined the mechanical properties of natural fiber composites. Arpitha et al. [13] demonstrated that hybrid composites reinforced with banana biofiber and glass fiber exhibit significantly enhanced mechanical, thermal, and microstructural properties, making them suitable for lightweight structural applications. Similarly, earlier work by Verma et al. [14] highlighted the effectiveness of using chitosan-coated sisal fibers in soy protein-based green composites, showing improved interfacial adhesion and mechanical strength, particularly when modified with Phytagel. These findings support the feasibility of combining natural and hybrid reinforcement strategies to improve composite performance for energy-absorbing and structural use. Sathishkumar et al. [15] developed epoxy hybrid bio-composites reinforced with banana and sisal fiber fabrics, integrated with cashew nut shell powder as a bio-filler. Their study demonstrated notable improvements in tensile, flexural, and impact strength, highlighting the potential of such agro-waste-enhanced natural composites for structural applications. This approach aligns with the growing interest in utilizing waste-derived materials to improve the mechanical and environmental performance of bio-composites. Kaliyaperumal et al. [16] investigated hybrid banana–sisal fiber epoxy composites produced by hot compression molding, focusing on tensile, flexural, impact toughness, and thermal absorption properties. While vibration testing was not their primary objective, the study provides valuable substructure data relevant for vibrational behavior modeling in energy-absorbing applications.

Saravanya and Kavitha [17] researched the properties of palmyra sprouts while exploring potential applications for them. Regular concrete received structural strengthening through the application of glass fiber according to the research findings presented by Tajne and Bhandari [18]. A broad investigation examined the glass fibers by describing their makeup along with manufacturing techniques and material behavior properties. Glass fibers serve as essential reinforcement components for composites because they improve their strength properties and make them more durable and stiffer. A study by Sudhakara et al. [19] demonstrated the mechanical competency of Borassus fruit fiber combinations with polypropylene. Tensile property evaluation of polyester composites reinforced by palmyra fibers was conducted by Dabade et al. [20] who studied strain-dependent behavior and the relationship between fiber length and weight ratio. Hybrid composites that include palmyra fibers alongside other reinforcements have been investigated to improve mechanical performance. Thiruchitrambalam [21] studied the effects of chemical pre-treatments of palmyra leaf stalk fibers, which improved their adhesion in unsaturated polyester matrix composites. These composites showed a 60% improvement in tensile strength and a 70% increase in flexural strength. They also reduced water absorption, enhanced thermal stability, and improved fiber-matrix adhesion. These pre-treated fibers made the composites comparable to other natural fiber-based materials. Shanmugam and Thiruchitrambalam [22] evaluated the static and dynamic mechanical properties of hybrid composites made from palmyra palm and jute fibers. He concluded that composites having higher percentage of jute exhibited maximum damping behavior.

In foreseeing the behavior of fiber-reinforced composites computational modeling plays a crucial role. The review emphasizes the importance of understanding and linking intrinsic deformation behaviors in FRPs, highlighting the ongoing development and application in demanding environments. Karthikeyan [23] validated the effectiveness in material optimization on glass fiber laminates using numerical analysis. The study by Srinivasababu et al. [24] explored meshless methods, specifically the Method of Continuous Source Functions (MCSF) and Trefftz Radial Basis Functions (TRBF), for modeling glass fiber-reinforced composites. TRBF, using dipole source functions, effectively simulates composites with finite-length fibers of high aspect ratio. The approach requires only boundary nodes and external source points, simplifying computations.

Peters [25] delivered a comprehensive overview of composite materials in his handbook, providing essential insights into the applications of composites. Rajkumar et al. [26] explored the scratching characteristics of both particle and fiber-reinforced polymer composites, stressing their resilience.

While previous studies have extensively examined the mechanical and thermal properties of natural fiber-reinforced composites, limited attention has been given to their dynamic behavior, particularly the vibrational characteristics of hybrid composites incorporating unconventional waste-derived natural fibers such as chicken feathers and palmyra sprouts.

Most existing research focuses on conventional fiber types and overlooks the synergistic effects of combining multiple natural fibers with varying aspect ratios on dynamic performance. Furthermore, there is a lack of experimental data on how different fiber compositions influence natural frequency, damping, and amplitude responses under real-world dynamic loading conditions. This study addresses these gaps by investigating the vibrational behavior of hybrid natural fiber composites using impact hammer testing, thereby contributing to the development of sustainable materials with tailored dynamic properties for advanced engineering applications.

2 Materials and methods

For this experimental research, jute fiber, banana fiber, and sisal fiber with waste-driven chicken feathers, palmyra sprouts as fiber polyester resin, MEKP catalyst and cobalt ACD 6 as the matrix substance were used. The reinforcement fibers and matrix were sourced from Covai Seenu Pvt., Ltd, Coimbatore, Tamil Nadu, India.

Alkali treatment importantly improved the physical properties of banana fiber, including fineness, moisture regain, and tensile strength. Vardhini et al. [27] revealed that treated fibers exhibit increased compatibility with polymer matrices. This modification aids in improved fiber matrix adhesion, contributing to improved composite performance. Such enhancements make alkali treated banana fibers promising for use in functional composite applications. Rai et al. [28] proved that the Alkali treatment reduced lignin content in palmyra fibers from 22.5% to 13.8% and increased crystallinity index from 42.6% to 58.3%. These changes made alkali treated palmyra fibers more suitable for structural and energy absorbing composite applications.

Using the compression molding method, natural composite plates were fabricated according to standard specifications [29,30,31]. Specimens were then cut from these plates for impact hammer testing as per ASTM D638. Figure 1 presents the selected materials for this study.

Figure 1

Material selection.

3 Experimental vibration test

Figures 2 and 3 illustrated the schematic diagram and photograph of the experimental impact hammer test setup. The dimensions of the vibration test specimens were 20 × 160 mm² and 20 × 80 mm², exhibiting a/b ratios of 0.125 and 0.25, selected for impact hammer vibration analysis according to the manufacturer’s requirements. The test specimens, illustrated in Tables 1 and 2, were set up on the granite bed with an edge securely attached using a “C” clamp, while the other three edges remained free. The piezoelectric accelerometer (DYTRAN 3055B2) was affixed directly to the geometric free end of the test specimen utilizing an industrial glue. The accelerometer was subsequently linked to a vibration controller and a dynamic signal analyzer (Vib Pilot), through which the signal traversed a charge amplifier and an analog-to-digital converter. The plate was stimulated at a five designated location using an impact hammer. This research examined two distinct compositions for three types of natural composite plates. The impact hammer (DYTRAN 5800B2) was employed to strike the designated three spots, and the mean value of the frequency response function was documented on the computer. Meticulous measures were implemented to guarantee that each blow of the impact hammer was orthogonal to the plate’s surface. The m + p international software accompanying the device was utilized to transform the time-domain signal into a frequency-domain signal. This procedure was then repeated for the remaining signals. Two modes, Mode 1 and Mode 2, were considered for this work, and the readings were tabulated in Tables 1–4.

Figure 2

Schematic diagram of impact hammer test.

Figure 3

Photo of the experimental set up.

Table 1

Experimental vibration analysis results for 15:10:5:70 composite specimens at a/b = 0.125

Composite Designation	Fabricated specimen for vibration analysis	a/b ratio	Mode 1			Mode 2
			Natural frequency (Hz)	Amplitude (g/lbf)	Damping factor (%)	Natural frequency (Hz)	Amplitude (g/lbf)	Damping factor (%)
15J/10S/5 CF/70 PR		0.125	377.58	108.18	9.7	2,037.2	235.82	7.08
15 B/10S/5 CF/70 PR			637.16	150.25	13.97	2,926.2	271.04	5.10
15 PS/10S/5 CF/70 PR			951.81	145.74	10.25	2,359.88	409.55	6.97

Table 2

Experimental vibration analysis results for 15:10:5:70 composite specimens at a/b = 0.25

Composite designation	Fabricated specimen for vibration analysis	a/b ratio	Mode 1			Mode 2
			Natural frequency (Hz)	Amplitude (g/lbf)	Damping factor (%)	Natural frequency (Hz)	Amplitude (g/lbf)	Damping factor (%)
15J/10SF/5 CF/70 PR		0.25	349.31	122.8	1.78	4,653.99	198.54	5.87
15 B/10S/5 CF/70 PR			266.15	234.96	3.72	4,342.20	305.51	3.57
15 PS/10 S/5 CF/70 PR			387.83	212.16	5.82	5,498.09	364.35	3.52

Table 3

Experimental vibration analysis results for 10:15:5:70 composite specimens at a/b = 0.125

Composite designation	Fabricated specimen for vibration analysis	a/b ratio	Mode 1			Mode 2
			Natural frequency (Hz)	Amplitude (g/lbf)	Damping factor (%)	Natural frequency (Hz)	Amplitude (g/lbf)	Damping factor (%)
10J/15S/5 CF/70 PR		0.125	422.81	90.46	2.97	1,749.72	295.83	1.20
10 B/10S/5 CF/70 PR			389.26	126.34	6.08	2,750.81	220.13	2.48
10 PS/15S/5 CF/70 PR			382.26	44.45	2.90	2,655.02	325	2.00

Table 4

Experimental vibration analysis results for 10:15:5:70 composite specimens at a/b = 0.25

Composite designation	Fabricated specimen for vibration analysis	a/b ratio	Mode 1			Mode 2
			Natural frequency (Hz)	Amplitude (g/lbf)	Damping factor (%)	Natural frequency (Hz)	Amplitude (g/lbf)	Damping factor (%)
10J/15S/5 CF/70 PR		0.25	304.67	124.30	6.51	4,498.31	289.06	8.70
10 B/10S/5 CF/70 PR			350.16	122.65	7.02	4,289.58	414.84	9.54
10 PS/15S/5 CF/70 PR			377.10	43.75	6.29	4,404.04	145.31	7.66

An impact hammer was used for vibration testing to provide a controlled excitation force to a composite specimen. The mathematical equation behind its operation was based on impulse response and force-time function. The force applied by an impact hammer was typically modeled as a half-sine pulse or an exponentially decaying function. We know that differential equation of motion for free vibration analysis is

where m is the mass of the system; x ̈ is the acceleration; c is the damping coefficient;

x ̇ is the velocity; k is the stiffness of the system; and x is the displacement.

In Eq. 1, If “c” is not considered, the equation becomes

The fundamental concept is that natural frequency (f) is proportional to the square root of the stiffness (k) divided by the mass (m)

Figure 4 represents a frequency response curve, typically associated with resonance phenomena in mechanical systems. The half power bandwidth method was utilized to determine the damping factor of selected three different composite plates on aspect ratios of 0.125 and 0.25. The difference between frequencies f _max and f_min was called the bandwidth. The frequencies f _max and f _min were determined from the corresponding positions of the Y _max/1.414, where Y _max is the peak amplitude.

Figure 4

Half power band width method.

Damping factor is estimated using Eq. 4 and shown in Tables 1–4.

where ξ is the damping factor; f _max − f _min is the bandwidth in Hz; f ₀ is the peak frequency in Hz;

f _max and f _min are the maximum and minimum frequencies value at corresponding of the Y _max/1.414.

4 Results and discussion

4.1 Effect of a/b = 0.125 on 15:10:5:70 composites

Figure 5 illustrates the amplitude response (in g/dB) of different composite materials in y axis as a function of frequency (Hz) in x axis. Three different compositions, labeled as containing varying weight percentages of materials such as jute fiber mat, banana fiber, palmyra fiber, sisal fiber mat, and chicken feathers with polyester resin were compared. The trends indicated that each composite exhibits distinct resonance peaks at specific frequencies, suggesting variations in their damping and vibrational characteristics. The composite with 15 PS/10 SF/5 CF/70 PR (yellow dashed line) showed the highest peak amplitude at around 3,000 Hz, indicating a significant resonance effect. Meanwhile, the compositions with B (brown dashed line) and S (solid brown line) exhibit lower peak amplitudes, with multiple resonance points occurring at different frequencies. So, the choice of composite formulation significantly influences the vibrational response, potentially impacting material selection for applications requiring specific damping properties

Figure 5

The observed frequency vs amplitude of composite plates (15:10:5:70, a/b = 0.125).

15J/10S/5 CF/70 PR was the best choice for applications requiring high damping at low frequencies, such as automotive noise reduction or seismic-resistant structures. 15 B/10S/5 CF/70 PR offered moderate damping with high-frequency stiffness, making it suitable for machinery components and aerospace applications, where resistance to high-frequency vibrations was crucial. 15 PS/10S/5 CF/70 PR provides high stiffness but low damping, making it useful in sporting equipment (e.g., tennis rackets, bicycle frames) and aerospace structures, where maintaining structural integrity under dynamic loads is essential.

4.2 Effect of a/b = 0.25 on 15:10:5:70 composites

Figure 6 depicts the amplitude response (g/lbf) as a function of frequency (Hz) for three different composite formulations. The legend indicated variations in the material composition, including different weight percentages of polypropylene sisal (PS), basalt fiber, and sisal fiber, along with chicken feather (CF) and polyester resin (PR). The response trends showed distinct peaks at specific frequencies, representing Mode 1 and Mode 2 resonances of the materials.

Figure 6

The observed frequency vs amplitude of composite plates (15:10:5:70, a/b = 0.25).

In Mode 1, the first peak appeared at a lower frequency range (∼500–1,500 Hz). The red solid line (15 wt% J/10 wt% S/5 wt% CF/70 wt% PR) exhibited the lowest amplitude in this region, indicating better damping capacity at low frequencies. The yellow dashed line (15 wt% PS/10 wt% S/5 wt% CF/70 wt% PR) showed the highest amplitude in this region, indicating weaker damping but higher stiffness.

In Mode 2, the peaks in this range represented higher-order vibrational modes, where structural stiffness and energy dissipation are crucial. The yellow dashed line (PS-containing composite) has the highest peak amplitude, indicating a significant resonance effect and potentially lower damping in higher frequencies. The red solid line again showed the lowest peak amplitude, suggesting it provides better damping characteristics for high-frequency vibrations. The brown dashed line (15 wt% B/10 wt% S/5 wt% CF/70 wt% PR) had an intermediate response, indicating a balance between stiffness and damping.

This graph helped in selecting the right composite material based on vibration performance. The J-based composite offers the best damping for vibration-sensitive applications, while the PS-based composite provides high stiffness for load-bearing applications. The B-based composite striked a balance, making it versatile for multiple engineering uses.

4.3 Effect of a/b = 0.125 on 10:15:5:70 composites

The vibrational characteristics of the composite specimens exhibited notable variations across different fiber compositions in both Modes 1 and 2 in Figure 7. In Mode 1, the natural frequencies range from 382.26 Hz (PS–sisal composite) to 422.81 Hz (jute–sisal composite), indicating that the jute-based composite has the highest stiffness. The amplitude response was highest for the banana–sisal composite (126.34 g/lbf), while the PS-sisal composite (44.45 g/lbf) showed the lowest, suggesting better vibration absorption. The damping factor was significantly higher for the PS-sisal composite (64.13%), making it the best performer in vibration energy dissipation, whereas the jute-sisal composite (33.57%) had the lowest damping capability.

Figure 7

The observed frequency vs amplitude of composite plates (10:15:5:70, a/b = 0.125).

In Mode 2, the natural frequencies span from 1,749.72 Hz (jute–sisal composite) to 2,750.81 Hz (banana–sisal composite), with the banana-based composite demonstrating the highest stiffness in this mode. PS–sisal composites demonstrate the highest peak vibration level of 325 g/lbf and jute–sisal composites showed a slightly lower value of 295.83 g/lbf, yet banana–sisal composites produce the lowest vibration level of 220.13 g/lbf. Tests show jute–sisal composite (21.32%) as the most effective in damping while PS–sisal (17.52%) comes next and banana–sisal composite (10.63%) demonstrated the least damping effect according to test results.

The PS–sisal composite material showed exceptional damping properties, thus becoming an ideal material for vibration control applications. The jute–sisal composite combination possessed high stiffness properties while providing lower damping levels, which were advantageous for applications that must maintain structural strength. The banana–sisal composite showed average stiffness levels while presenting lower damping capabilities that suit applications needing balanced mechanical properties.

4.4 Effect of a/b = 0.25 on 10:15:5:70 composites

Figure 8 depicted the observed frequency vs amplitude of composite plates of a/b = 0.25 at the composition 10:15:5:70 ratios. For Mode 1, the natural frequencies ranged from 304.67 Hz (10J/15S/5CF/70PR) to 377.10 Hz (10PS/15S/5CF/70PR), indicating that the PS composite exhibits the highest stiffness among the tested materials. The amplitude response was highest for the jute–sisal composite (124.30 g/lbf), suggesting stronger vibrational response, whereas the PS–sisal composite (43.75 g/lbf) showed the lowest amplitude, implying better damping. The highest damping factor was observed in the banana–sisal composite (55.77%), which enhances energy dissipation.

Figure 8

The observed frequency vs amplitude of composite plates (10:15:5:70, a/b = 0.25).

In Mode 2, the natural frequencies lie between 4,289.58 Hz (banana–sisal) and 4,498.31 Hz (jute–sisal), indicating that Jute-based composites exhibit the highest stiffness in the second mode. The amplitude response was highest for banana–sisal (414.84 g/lbf), while the PS–sisal composite (145.31 g/lbf) exhibited the lowest, confirming its superior damping ability. The damping factor followed a similar trend, with banana–sisal (19.54%) showing the highest energy dissipation. Overall, the PS–sisal composite offered the best damping behavior, making it ideal for applications requiring vibration control, whereas jute–sisal composites provide higher stiffness but with increased vibration response.

5 Conclusion

This study investigated the vibrational behavior of natural composite plates reinforced with banana fiber, sisal fiber, and jute including waste-derived natural fibers such as chicken feathers and palmyra sprouts. The experimental analysis, conducted through impact hammer testing, provided key insights into fundamental frequencies, mode shapes, and amplitude responses of different fiber compositions.

• The fundamental frequency (first mode) was observed in the range of 500–1,500 Hz, with varying amplitudes based on fiber composition.

• The second mode occurred around 2,000–3,500 Hz, exhibiting higher amplitude responses, particularly in composites with increased palmyra sprouts and sisal fiber content.

• The composition with 15 wt% palmyra sprouts, 10 wt% sisal fiber, 5 wt% chicken feathers, and 70 wt% polyester resin exhibited the highest resonance amplitude, making it suitable for high-energy absorption applications.

• Higher palmyra sprouts and sisal fiber content (above 10 wt%) shifted resonance peaks to higher frequencies (∼4,000–5,000 Hz), indicating increased stiffness and reduced damping capacity.

• Lower palmyra sprouts and sisal fiber content (10 wt%) resulted in better damping performance, as seen by the lower amplitude response in the second mode.

• The peak amplitudes ranged between 50 and 450 g/lbf, with the highest amplitude observed at second and third mode frequencies (∼3,000–5,000 Hz) for compositions with higher stiffness.

• Composites with a balanced fiber ratio (10 wt% palmyra sprouts, 10 wt% sisal fiber, 5 wt% chicken feathers) exhibited lower peak amplitudes, demonstrating better damping characteristics, making them ideal for vibration control systems and lightweight structural applications.

• The study confirmed that natural composites derived from waste materials could be tailored for specific vibrational properties.

• These materials could serve as lightweight, high-damping composites for energy absorption, noise reduction, and structural vibration control in automotive, aerospace, and civil engineering applications.

This research provides a strong foundation for developing sustainable, high-performance composite materials with optimized vibrational properties, paving the way for their real-world application in lightweight and vibration-sensitive structures.