Papers by Keyword: Natural Frequency

Abstract: Hybrid composite laminates that combine Kevlar and glass fibers offer tailored performance, but the interaction between their progressive failure and vibrational behavior remains insufficiently understood. This study employs finite element analysis in ANSYS APDL to evaluate Kevlar/epoxy, glass/epoxy, and Kevlar–glass hybrid laminates with cross-ply and angle-ply stacking sequences, using layered shell elements and the Maximum Stress criterion. The study validates the model against published experimental data and applies it to assess first-ply failure (FPF), last-ply failure (LPF), and natural frequencies. Results show that Kevlar laminates provide the highest strength and natural frequencies, while glass laminates exhibit the lowest, with hybrids consistently demonstrating intermediate performance. Although hybrids record lower FPF than either constituent, their LPF exceeds that of GFRP, reflecting beneficial stress redistribution during damage progression. Natural frequencies decrease systematically with increasing fiber angle, with Mode 2 showing greater sensitivity to orientation. Among the hybrids, H4 provided the most balanced overall performance, pairing competitive LPF with stable modal behavior. This study establishes a clear correlation between failure progression and dynamic response, highlighting the governing role of fiber content and stacking sequence in determining the structural integrity and vibration resistance of hybrid laminates.

Abstract: Composites are materials designed to achieve superior mechanical or physical properties, and understanding both their failure and dynamic behavior is essential. Despite numerous past studies on understanding this behavior of composite materials, information on the interrelationship between these two aspects remains limited. The study aims to conduct a process innovation and provide detailed understanding of the effect of fiber orientation on the Graphite epoxy and E-glass epoxy composite laminates failure behavior and natural frequency and the relationship between the failure and dynamic behavior of these two materials. To achieve this, a process innovation of the simulation of failure analysis and vibration analysis of these composite laminates under uniaxial tensile loading was conducted on 8-ply composite laminates under a lamination scheme of (-θ/45/-45/θ/-θ/45/-45/θ), where θ from 0° to 90°. Finite element models for simulation were developed and validated to ensure the reliability and validity of findings in this study are trustworthy and useful. The results show that both failures loads, and natural frequencies are not much affected by the fiber orientation under this lamination scheme. These two behaviors are also identified to be closely related under specific modes of natural frequency. The detailed effects of failure and natural frequency under fiber orientation and its relation are successfully acknowledged. The findings are expected to support the optimization of laminate design and enhance the structural performance of composite materials in engineering applications and contribute to more informed material selection.

Abstract: This paper presents a comprehensive modal analysis of a 15-meter span footbridge constructed using fiber-reinforced polymer structures (FRPs) integrated with natural resource fibers and a partial bio-based resin. The bridge was erected at the Floriade Expo 2022 located in Almere, the Netherlands. The lightweight nature of FRPs, coupled with their sensitivity to vibrations, necessitates the satisfaction of specific design requirements to ensure the safety and comfort of pedestrians. The initial phase of this study entails determining the natural frequencies of the bridge via Finite Element Analysis (FEA). Comparative assessment between the footbridge's natural frequency and excitation frequencies evaluates the risk of resonance induced by pedestrian loading. The FEA employs a composite layup technique to replicate the same ply configuration as the actual bridge model. Following the initial assessment, a comprehensive analysis is undertaken to meticulously examine the dynamic response of the footbridge. This analysis prioritizes the evaluation of critical acceleration parameters under diverse conditions, encompassing scenarios such as walking, jogging, and crowded pedestrian traffic. Bridge peak acceleration is assessed and juxtaposed against design values based on site usage, route redundancy, and structural height, and for the target bridge is 0.77 m/s². The results indicate that the footbridge successfully fulfills the specified design criteria for ensuring pedestrian comfort under various dynamic loading conditions. This finding underscores the significance of including the footbridge in the building application process. This study underscores the successful application of FRPs, augmented with natural fibers and bio-based resin, in ensuring the structural integrity and comfort of footbridges subjected to real-world dynamic conditions.

Abstract: There are number of different methods and procedures in vibration analysis, where the natural frequencies of the specimen or the system are one of the key parameters. It is known that these frequencies can change under load, for example in response to pre-stressing, but the effect of residual stresses is less known. By developing a suitable method, natural frequencies can be used to predetermine residual stress, therefore this method can be used for example predicting whether it will cause deformation during machining of a part, whether it requires increased attention or how to set the parameters well for vibratory stress relief. The results can be significant cost and time savings, as well as the improvements of the quality. Natural frequency is the frequency of free vibration of an undamped linear vibration system, or in other words at which a system left alone will vibrate after excited by an external force [1]. Metal castings or welded structures may have several natural frequencies which appear as frequency bands or ranges on the measurement images. Based on these, to determine the natural frequency of a component or system, we need to excite a frequency as close as possible to the natural frequency for the resonance to occur. When the resonance is reached, the amplitude of the system is at its maximum, and the natural frequencies of the workpiece can be measured. Traditionally, sensors, usually accelerometers are used to measure the natural frequency. The continuous development of information technology has made it possible to replace these sensors with an acoustic diagnostic system. During this research, we have developed an acoustic diagnostic system and procedure, which can generate the acoustic measurement images. We have evaluated the measurement images in many ways, and many different types of components and materials (mostly iron alloys) were analyzed. In addition, the changes of natural frequencies show a similar pattern in the case of parts before treating with vibratory stress relief as for load tests.

Abstract: The primary focus of this research is to investigate the eigen values and strain energy release rate (SERR) of delaminated adhesively bonded single lap joint (SLJ). To achieve this, the study utilizes finite element analysis (FEA) to calculate eigenvalues for the adhesively bonded joints. These predictions are then compared with published data to validate the accuracy of the FEA model. Experimental work is also conducted on intact and delaminated bonded joints to further verify the FEA model reliability. Furthermore, the virtual crack closure technique (VCCT) in ABAQUS software was used to determine SERR values around the delamination edge. Simulation solutions are obtained for various overlapping lengths (e.g., 25, 30, 35, and 40 mm) to predict the natural frequency under different boundary conditions, bond thickness ratios (a/h), and delamination shapes. Similarly, changes in the lamination scheme are considered to predict SERR values. It has been noted that the natural frequency response decreases with increase in bond thickness ratio. Furthermore, a higher number of end restrictions contribute to improved outcomes. There is no significant impact of delamination shape on the natural frequency response. Notably, the cross-ply lamination sequence exhibits higher SERR values around the delamination edge than other sequences.

Abstract: In this work, rectangular sheets of composite materials consisting of epoxy with a single layer of fiberglass were studied with the internal crack at angles (0°, 90°) with the x-axis in the presence of nanomaterial TiO₂ in proportions (1 wt%, 2 wt%, and 3 wt%), the study was experimental and numerical using the ANSYS. The sample mold was made from plastic using a CNC machine. One case was studied in both the experimental and numerical parts, which is clamped-clamped-free-free (CC-FF). After conducting the test, it was found that the crack negatively affects the rectangular composite plate, as it reduces the value of the natural frequency and increases the value of damping. However, in the case of adding the nanomaterial, it was found that the natural frequency increases with the increase in the percentage of nanomaterials, and the maximum value of the natural frequency was at 3% because it works to increase hardness rectangular plate stiffens and reduces damping. The error rate between the experimental and numerical parts did not exceed (9.717%).

Abstract: Modal analysis of a quasi-isotropic Fiber Reinforced Polymer (FRP) composite plates having different cut-outs is numerically investigated under free-clamped boundary conditions using ANSYS 2023 R1. First six natural frequencies & corresponding mode shapes are extracted from the simulation. To verify the numerical results, experimental modal analysis is carried out on a sample specimen made of epoxy/glass composite with traditional ‘strike method ‘to determine the frequency response functions and to measure the natural frequencies. Investigation was continued to understand the effect of fiber orientation and systematically altered length to breadth ratio (size ratio - a/b) on the natural frequencies and the respective mode shapes. Obtained results exhibited that the correctly chosen fiber orientation contributes to improved dynamic performance, which delivers greater flexibility in designing structures to meet the application requirements. Furthermore, optimization of cut-outs was performed to demonstrate that variation in cut-outs is a key parameter and can be used to attain essential vibration mode shapes and definite frequencies. It was found from the investigation that circular cut-out acts a vital role for attaining desired free modal characteristics.

Abstract: Fiber reinforced polymer composites made with glass fibers are among the oldest and most popular kinds of composites in use today. Glass fiber reinforced composites' key benefits are their adaptability for specific material applications, which allows them to give a number of design advantages relating to strength, chemical stability, impact damage tolerance, heat insulation, and low cost. The focus of this research is to investigate the role of hybridized ramie fibers in the assessment of enhanced vibrational damping capabilities in fiber glass reinforced composites, as well as in the initial assessment to verify their acceptability for real-time applications. Composite molding employing the hand layup technique was used to fabricate hybrid epoxy composites with ramie to glass fiber weight ratios from 0 to 50%. A free vibration test was performed to determine the hybrid composite's vibration dampening capabilities as a function of the ramie fiber filler content. The results demonstrated that the damping ratio was reduced when the percentage of ramie fiber in the GFRP composite was raised from 10% weight to about 50% weight. But adding up to 40% wt of ramie fiber to the hybrid composite had the biggest effect on the damping ratio, natural frequency, storage modulus, and loss modulus. This means that using ramie fiber in hybrid composites will be cost-effective and good for the environment.

Abstract: This paper describes an approach extended from Ritz method to analyze the free vibration of thin isotropic annular plates in good accuracy, and presents comprehensive lists of natural frequencies of the plate for all possible sets of classical boundary conditions. Analytical process is developed to introduce the boundary index that allows to accommodate any sets of free, simple supported and clamped edges along inner and outer boundary of the plate. Convergence and comparison studies are made to demonstrate numerical accuracy in the frequency parameters. Results are summarized for nine sets of boundary conditions and six different ratios of (inner radius)/(outer radius), and are intended to serve for uses of design data and comparison in relevant future papers.

Abstract: Taguchi based optimization of natural frequency of perforated stiffened hypars is performed to consider the role of fibre lamination, width/thickness ratio of shell and position of perforation centre along x- and y-direction. Natural frequency of stiffened shell is obtained for simply supported boundary condition using finite element procedure based on L27 orthogonal array (OA) considering three settings of each parameter. Main effect plot is analyzed to identify the significant parameters. Natural frequency becomes maximum for a combination of 45⁰ fibre lamination, width/thickness value of 20 and perforation centre position (0.4, 0.4). Interaction graphs identify the interaction parameters. ANOVA study provides the significant contribution of the parameters considered here. Present analysis identifies width/thickness as the most significant factor and other parameters yield very little significance while no interaction is found to be significant. Width/thickness value of shell yields major (98.64%) contribution to natural frequency and other factors yield very little significance. Residual analysis for natural frequency and confirmatory test validate the present study. S/N ratio gets improved by 38.3% at optimal condition compared to the initial parameter setting.