Damping Properties Of Composites Research Articles

Parametric Study of different Fiber Parameters and their Influence on Acoustics and Vibration Behavior of Jute Fiber/Polyester resin Composites

ABSTRACT Short natural fiber–based composites are becoming a viable alternative to short E-glass fiber–reinforced composites in a variety of applications, due to their better damping and sound absorption capabilities. Also, quasi-isotropic properties can be obtained with randomly oriented short natural fibers. However, identifying the optimum fiber length and weight content are important to obtain better mechanical properties. The effect of fiber parameters on acoustic and vibration properties of jute/polyester composites was investigated in this study. Compression molding was used to fabricate composite specimens with different fiber lengths (10, 15, 20, and 25 mm) and fiber loadings (5, 10, 15, and 20 wt%). Further, sound absorption and damping properties of composites were studied using the impedance tube method and a free vibration test in cantilever mode. The damping property increases with increasing fiber loading and decreases with increasing fiber length, according to the findings. The highest natural frequency was found with a fiber length of 5 mm and a fiber loading of 25%, but larger fibers resulted in improved sound absorption. The findings suggest that jute/polyester composites could be a more cost-effective, practical, and environmentally superior and therefore, an alternative to E-glass/polyester composites, particularly in damping-sensitive applications.

Phase structures, loss, storage, damping, voice-absorption, and mechanical properties: nano-carbon black/BWZT/RTV

Composites with damping–absorption performances and storage-loss behaviors were fabricated based on NCB (nano-carbon black), BWZT [Ba (W1/2Cu1/2)O3–Pb0.98Sr0.02 (Mg1/3Nb2/3)0.275(Ni1/3Nb2/3)0.10(Zr0.25Ti0.375)O3] and RTV (room temperature vulcanizing silicone rubber) employing three steps methods of ball-milling, three-roller milling and pressing. The effects of NCB on storage, loss and damping properties of composites were investigated by the method of DMTA and, absorption and mechanical performances are measured by the methods of standing wave tube and TG separately. The micro, chemical and phase structures of composites are characterized by SEM, XRD and IR. The results indicated that both doping of NCB and the combination of BWZT and RTV can be proposed to improve greatly the comprehensive performance of RTV matrixes and, there would be more excellent comprehensive properties in NCB/BWZT/RTV(NBR) with amount of 4–6 wt.% for NCB as d33 of 81 pC/N, storage modulus of 25003 MPa, loss modulus of 398 MPa, damping coefficient of 0.07–0.12, and absorption coefficients of 0.45–0.55 with the difference of frequency in the range of 400–1600 Hz. Lattice growth of BWZT is found showing strong dependences on contents of NCB, the absorption–damping performance.

Low‐velocity impact behavior of a carbon/bismaleimide composite proposed for supersonic flight simulation after hygrothermal cycling

The combined high temperature oxidation, humidity exposure, thermal cycling, and a low temperature period were simultaneously performed on a carbon fiber‐reinforced bismaleimide (C/BMI) composite to simulate the supersonic hygrothermal flight‐cycles on long durability of the C/BMI applied in supersonic aircraft. After a hygrothermal cycling for 300 times, the drop‐weight impact test and ultrasonic analysis were carried out to evaluate low‐velocity impact damage behavior of the composite caused by foreign objects during service. The fiber/matrix interface degradation caused by hygrothermal cycling was demonstrated through a parameter proposed by Sarasua (parameter b), which is shown to reflect the level of the interfacial bond by estimating the contribution of the interphase on the damping properties of composites through the dynamic thermomechanical analysis (DMA) test. A secondary increase of delamination area initiated from one long edge was detected for the first time in the hygrothermal cycled C/BMI composite impacted by energy higher than 20 J. After experiencing 300 combined ageing cycles, the damage model of C/BMI composite impacted by more than 20 J changes from the pine tree model to gyro model because of free‐edge delamination, resulting in a serious potential risk to the application of C/BMI composite laminates in aeronautics. POLYM. COMPOS., 40:E1588–E1599, 2019. © 2018 Society of Plastics Engineers

Study on Damping Properties of Fe<sub>12</sub>O<sub>19</sub>Sr/NBR Composite

Magnetic damping composite was prepared by mechanical blending method. As acrylonitrile butadiene rubber was matrix, strontium ferrite magnetic powder was function phase. The vibrating sample magnetometer (VSM) test shows that the magnetic properties of the magnetic rubber composite are related with the content of the magnetic powder and unrelated with rubber matrix. The dynamic mechanical analysis (DMA) and TA method compare show that the damping properties of the composite are improved with adding the strontium ferrite magnetic particle, but the damping properties of composite are best after magnetizing the sample, but the damping properties of the composites decreased with increasing the content of the magnetic powder. The damping properties of the composites at the test frequency 30HZ and 50HZ are higher than 1HZ.

Dynamic Characteristics of Carbon Nanotube Reinforced Epoxy Resin Composite Materials

Carbon nanotubes (CNTs) were modified by alkali, and carbon nanotubes epoxy composites samples were prepared by the hot pressing method. Dynamic characteristics of the composites were studied by experiments. The results suggest that carbon nanotubes can hardly enhance the first natural frequency of epoxy composite, but the change of second and third order natural frequencies are obvious compared with the first one. Damping properties of the composites are improved, and with the mass ratio of CNTs increasing, the first three order damping properties of composites are all increased initially followed by the decrease. The results also indicate that flexural elastic modulus of the composites is enhanced, the first and the second order dynamic elastic modulus is greater than it but the third order is opposite. The first three order dynamic modulus of elasticity moments of CNTs composites whose mass fraction is two percent are all high.

Vibration damping characteristics of short hemp fibre thermoplastic composites

In this project, free vibration testing and dynamic mechanical analysis methods were used to study the damping properties of noil hemp fibre-reinforced polypropylene composites with varying fibre contents (0 to 60 wt%) and compatibilizers (maleic anhydride-grafted polypropylene and maleic anhydride-grafted polyethylene octane) under applied frequencies of 1 to 200 Hz. The storage modulus of the composites was increased by the increase in hemp fibre content. However, the maximum damping ratio was obtained from the composite with 30 wt% noil hemp fibre. The addition of coupling agents reduced the damping capacity of all composites. However, 30 wt% noil hemp fibre-reinforced polypropylene coupled with 2.5 wt% anhydride-grafted poly ethylene octane revealed the highest damping ratio among coupled composites. Damping properties of the composites were relatively constant over the frequency range, except at frequencies which the material–instrument system began to resonate and peaks were observed in the curves.

An Experimental Evaluation of Micromechanical Approaches for Damping Characterization of Polymer Matrix Composites

There are two main approaches for prediction of the mechanical properties of composite materials; macro-mechanical and micro-mechanical approaches. At the micromechanical level, analytical, experimental, and semi-empirical methods have been developed to predict the stiffness of composite materials. In this study, these methods have been reviewed and modified to predict the damping properties of composites. In order to validate these theories, experimental techniques using a universal testing machine were performed to extract the specific damping capacity (SDC). The results show that the presented experimental technique can be employed successfully to measure the damping and stiffness properties of composites. In addition, it is concluded that semi-empirical approaches that consider the experimental correlation factors are closer to reality than purely analytical micromechanical methods. This study shows that the analytical micromechanical approaches are not suitable to predict the damping properties because of different mechanisms of energy dissipation that have not been discussed in this article.

Evaluation of damping and elastic properties of composites and composite structures by the resonance technique

This paper describes the resonance technique for determining the stiffness and damping properties of a composite or composite structure. Pultruded GRP composites and optical fibre cables (multi-component structures) were investigated. The resonance frequencies (natural frequencies) of a material, or a system, are a function of its elastic properties, dimensions and mass. This concept is used to determine the stiffness of a vibrated material by the resonance technique, which applies only very low stresses through the application of acoustic energy. This makes it applicable to measure the stiffness of multi-element cables. The damping properties, in terms of Q−1 (internal friction) were determined by both a free exponential decay curve and half-peak bandwidth methods. The influence of specimen length and measurement set-up was investigated. The applicability and accuracy of the resonance technique for a composite structure were discussed. The measured elasticity of optical cables was found to be in good agreement with the derived theoretical value.