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The focus of this study is to experimentally investigate the effect of debonding stress, the interface between the fibers and the polymer matrix, on the damping properties of the short fiberglass reinforced polymer composites. In this study, short fiberglass reinforced polycarbonate composite materials were fabricated and characterized for their tensile properties by varying the fiberglass loading fraction. The debonding stress was evaluated by coupling the acoustic emission technique with the tensile testing. After the determination of the debonding stress was completed, dynamic cyclic testing was performed in order to investigate the effect of debonding on the damping properties of the polymer composites. It was experimentally observed in this study that the debonding can facilitate the stick-slip friction under cyclic loadings, which then gives rise to better damping performance in the fiberglass composites. [ABSTRACT FROM AUTHOR]

Abstract: A sandwich composite is typically designed to possess high bending stiffness and low density and consists of two thin and stiff skin sheets and a lightweight core. Due to the high stiffness-to-weight and strength-to-weight ratios, sandwich composite materials are widely used in various structural applications including aircraft, spacecraft, automotive, wind-turbine blades and so on. However, sandwich composite structures used in such applications often suffer from poor acoustic performance. Ironically, these superior mechanical properties make the sandwich composites “excellent” noise radiators. There is a growing interest in optimizing and developing a new sandwich composite which will meet the high stiffness-to-weight ratio and offer improved acoustic performance. The focus of this study is to investigate the structural–vibrational performance of carbon-fiber face sheet sandwich composite beams with varying core materials and properties. Core materials utilized in this study included Nomex and Kevlar Honeycomb cores, and Rohacell foam cores with different densities and shear moduli. The structural–vibrational performance including acoustic and vibrational damping properties was experimentally characterized by analyzing the wave number response, and structural damping loss factor (η) from the frequency response functions, respectively. It was observed that the relationship between the slopes of the wave number data for frequencies above 1000Hz is inversely proportional to the core material’s specific modulus (G/ρ). The analysis also showed the importance of using a honeycomb core’s effective properties for equal comparison to foam-cored sandwich structures. Utilizing analytical modeling, the loss factors of the core materials (β) was determined based upon the measured structural loss factors (η) for a frequency range up to 4000Hz. It was determined that low shear modulus cores have similar material damping values to structural damping values. However as the core’s shear modulus increases, the percent difference between these values is found to increase linearly. It was also observed that high structural damping values correlated to low wave number amplitudes, which correspond to reductions in the level of noise radiation from the structure. [Copyright &y& Elsevier]

Abstract: Due to their higher strength-to-weight and stiffness-to-weight ratios compared to metals, fiber reinforced composite materials are a great alternative for use in many structural applications. However these properties lead to poor acoustic performance as composite materials are excellent noise radiators. This is particularly true for sandwich composite structures. Therefore the focus of this study is to investigate the effect of a core thickness change on the vibrational properties of Rohacell foam/carbon-fiber face sheet sandwich composite beams. Four different foam core thicknesses were explored, using a combination of experimental and analytical methods to characterize sound and vibrational properties of the sandwich beams. First, the wave number responses of the beams were obtained, from which coincidence frequencies were identified. Second, from the frequency response functions the structural damping loss factor, η, was determined using the half-power bandwidth method. Experimental and analytical results show that the relationship between core thickness and coincidence frequency is non-linear. A drastic increase in coincidence frequency was observed for the sandwich beam with the thinnest core thickness due to the low bending stiffness. Moreover this low bending stiffness results in low damping values, and consequently high wave number amplitude responses at low frequency ranges (<1000Hz). [Copyright &y& Elsevier]

In this article we discuss the energy dissipation that occurs when the interfacial slip of nanoscale fillers is activated in a host matrix material. We consider both polymer (such as polycarbonate, PEO, PEG) and epoxy matrices. The nanoscale fillers considered are carbon nanotubes (both singlewalled and multiwalled) as well as fullerenes. The nano-composites are fabricated by using a solution mixing technique with tetra-hydro-furan as the solvent. The interfacial friction damping is quantified by performing uniaxial dynamic load tests and measuring the material storage and loss modulus. We study various effects such as impact of nanotube weight fraction, nanotube surface treatment (oxidation, epoxidation etc.), test frequency, strain amplitude, operating temperature, as well as effect of pre-strain or biased strain. The effect of geometry (i.e., aspect ratio) is also considered by comparing the damping response of fullerene-composites with that of nanotube-composites. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates strain dependent energy dissipation characteristics in carbon nanofiber (CNF) reinforced carbon fiber epoxy composites (multi-scale composites) by characterizing their viscoelastic properties and vibrational damping response. The air damping effect on the energy dissipation characteristics is also examined. The viscoelastic properties of epoxy containing two weight fractions (3 and 5wt%) of added CNFs were characterized using dynamic mechanical analysis. Carbon fiber layers were then infiltrated with the two epoxy resins containing the CNFs to form multi-scale composites. A strain dependent loss factor behavior of the multi-scale composites was observed in the dynamic cyclic testing due to CNF’s stick–slip friction, showing a 53% increase in loss factor for the composites containing 5wt% CNFs. The beam vibration test results also indicated an improvement in loss factor for the multi-scale composite beams relative to those without the CNF addition in the first two resonant frequencies. The multi-scale composite beams exhibit an increase in loss factor, up to 43%, at high amplitude excitation, while a reduction in loss factor was seen at low amplitude. These observed strain dependent damping characteristics seem to result from both the stick–slip friction and the air damping effect. [Copyright &y& Elsevier]

Abstract: Experimental evidence shows that some nanocomposites with special matrices and filler materials may achieve significant and simultaneous improvements in stiffness, fracture toughness, impact energy absorption and vibration damping, and these characteristics could be of particular importance in automobile or airplane structures. This paper reviews relevant literature which deals with various manifestations of energy absorption of composites from the nano to the macro-scale, with emphasis on the nano-scale. Energy absorption mechanisms in nanocomposites will be examined, along with important influence factors, such as shape, dimension and stiffness of particles, type of matrix, particle volume fraction, distribution of particles and the particle–matrix interfacial properties by both experiments and simulation methods. Relevant potential applications will be discussed, and the key related issues that need to be resolved in the future will be addressed. [Copyright &y& Elsevier]