Free Vibration and Acoustic Responses of Partially Biodegradable Hybrid Composites: Numerical Analysis and Experimental Validation

This research numerically investigates the free vibration characteristics and sound radiation responses exhibited by a novel partially biodegradable hybrid composite material.

The composite synthesis involves NaOH-treated animal-based (human hair) and plant-based (Luffa cylindrica) fibers, epoxy resin, and variable proportions of Incense stick ash (ISA) as filler. The synthesis process involved stirring of the individual constituents using an ultrasonicator, and the composites are produced through hand lay-up method. Experimental assessments of densities precede the determination of elastic properties, employing a non-destructive impulse excitation technique (IET). Utilizing the experimentally acquired composite material properties, a higher order finite-element (FE) model is derived and executed within the MATLAB programming environment to compute the free vibration responses. The model is expanded in conjunction with the indirect boundary-element method (IBEM) to achieve coupling between the structure and its surroundings. Sound radiation responses are computed by solving the Helmholtz wave equation.

The efficacy of the developed model is evaluated by comparing the outcomes with the data obtained from laboratory experiments. From the parametric investigation, moderate ISA filled (10 wt.%) composites with higher aspect ratio and lower thickness ratio are observed to provide more significant resistance to resonant vibrations and less susceptible to sound radiation.

The functional inferences derived from this study will assist in designing imminent hybrid natural fiber composite structures for high-performance engineering applications where minimizing sound radiation into the surrounding medium is a critical design consideration.