Abstract:When dynamic properties of structures in vibration are considered, their elastic modulus and damping properties are emphasized. One of the best ways for true measurement of damping is the use of a beam with free-free end conditions. The aim of this study is to investigate dynamic properties of composites by using the vibrating beam technique. The composite specimens with free-free end conditions were vibrated at their fundamental nodes. An electro-magnetic shaker was used to vibrate the specimens by means of a… Show more
“…An alternating current through one coil was used as vibrators whilst the motion of the other coil as transducer. The composite specimen with high flexural modulus lowers specific damping capacity [16]. From the above review, it is concluded that the work presented in this paper has not been done anywhere in the past.…”
The vibration behaviour of polymers can be modified by the particulates and natural fibres which are interesting study to the design engineers. A study has been carried out to investigate the tensile, flexural and vibrational behaviour of vinyl ester composites reinforcing with woven kenaf and glass fibres. Vibration behaviour of composite was further enhanced by the addition of hexagonal boron nitride (2&4% hBN) particles. The fibres were chemically treated to improve its adhesion to matrix. The tensile strength of fabricated composites was marginally reduced with increase in hBN particles. The vibration behaviours of composite were studied by electro-dynamic shaker. The experimental results were clearly showed that natural frequency of composite decreases with increasing particulate content. The hBN particles inclusion in the treated kenaf laminate has increased damping ratio by dissipating by more local vibration energy. This is due to combined effect of chemical treatment of fibre and local relaxing behaviour of secondary hBN particles. The two fold increase in damping ratio obtained by adding four times of hBN particle. Dynamic mechanical tests proved that hBN, a secondary particle, is improving vibration damping characteristics. Hence, it potentially benefits the composite as an engineered material.
“…An alternating current through one coil was used as vibrators whilst the motion of the other coil as transducer. The composite specimen with high flexural modulus lowers specific damping capacity [16]. From the above review, it is concluded that the work presented in this paper has not been done anywhere in the past.…”
The vibration behaviour of polymers can be modified by the particulates and natural fibres which are interesting study to the design engineers. A study has been carried out to investigate the tensile, flexural and vibrational behaviour of vinyl ester composites reinforcing with woven kenaf and glass fibres. Vibration behaviour of composite was further enhanced by the addition of hexagonal boron nitride (2&4% hBN) particles. The fibres were chemically treated to improve its adhesion to matrix. The tensile strength of fabricated composites was marginally reduced with increase in hBN particles. The vibration behaviours of composite were studied by electro-dynamic shaker. The experimental results were clearly showed that natural frequency of composite decreases with increasing particulate content. The hBN particles inclusion in the treated kenaf laminate has increased damping ratio by dissipating by more local vibration energy. This is due to combined effect of chemical treatment of fibre and local relaxing behaviour of secondary hBN particles. The two fold increase in damping ratio obtained by adding four times of hBN particle. Dynamic mechanical tests proved that hBN, a secondary particle, is improving vibration damping characteristics. Hence, it potentially benefits the composite as an engineered material.
“…An instrumented impact hammer was used to hit the specimen, and the response signal was sensed and measured by the accelerometer and the data acquisition card (DEWESoft, Dewteron Corp., Austria); the observed data were then transmitted to a PC where the natural frequencies were determined. Further, the loss factors, η were estimated by the half power bandwidth method, used elsewhere 17–25 ; the expression for the same is as follows Figure 4.Schematic representation of impulse testing.…”
This paper reports the effect of temperatures (30 C to 80 C, with incremental steps of 5 C) and orientations of the glass fibers (0 , 30 , 45 , 60 and 90 ) on the dynamic properties (the loss factors and the natural frequencies) of polypropylene honeycomb sandwich composites. The impulse technique has been employed to calculate the natural frequency and loss factor of the sandwich specimens under different temperatures. The natural frequency and loss factor values have also been calculated theoretically using Blevins's formulae for natural frequency, and Yim et al.'s transverse shear effect, respectively. The values of damping loss factor and the natural frequency/stiffness are the maximum at 0 fiber orientation in the skins of the sandwich specimen. The loss factor of the same oriented specimen increases sharply with the increase in temperature. The main reasons for the above are the higher in-plane strength of skins and lower transverse shear strength of the honeycomb core. Hence, the 0 fiber oriented sandwich specimen is more desirable than the other fiber oriented specimens at all temperatures. A good agreement is observed between the experimental and theoretical values.
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