Evaluation of physical and dynamic mechanical properties of coconut husk ash (CHA) reinforced polyester composites

The evaluation of physical and dynamic mechanical analysis (DMA) properties was carried out using developed CHA Reinforced Polymer Composite. Sieve analysis of pretreated CHA was done to obtain 75 µm, 150 µm and 300 µm particles sizes. These particles were used at varying compositions of 5%, 10%, 15%, 20% and 25% as reinforcements for polyester composites. The catalyst and accelerator used were Methyl Ethyl Ketone Peroxide and Cobalt Naphthenate respectively. The densities of the evaluated composites made with 150 μm particles were found to be less dense with values ranging from 0.9792 g/cm3 to 1.2561 g/cm3 than those made with 75μm and 300μm. The results also show that the percentage water absorbed by samples increased, ranging from 0 to over 2000 E’/MPa for all percentage reinforcements of CHA, with an increase in the duration of immersion of the samples in distilled water. However, 25% reinforcement had better results for all particle sizes. There were obvious variations of storage modulus, loss modulus and mechanical loss factor with percentage weight of reinforcement, temperature and frequency. The composite with 15 % reinforcement displayed better results and can be used as a material for interior components in aerospace and automobile industries.

Embedded NiTi Wires for Improved Dynamic Thermomechanical Performance of Silicone Elastomers

The extraordinary properties of shape memory NiTi alloy are combined with the inherent viscoelastic behavior of a silicon elastomer. NiTi wires are incorporated in a silicon elastomer matrix. Benefits include features as electrical/thermal conductivity, reinforcement along with enhanced damping performance and flexibility. To gain more insight of this composite, a comprehensive dynamic thermomechanical analysis is performed and the temperature- as well as frequency-dependent storage modulus and the mechanical loss factor are obtained. The analyses are realized for the composite and single components. Moreover, the models to express the examined properties and their temperature along with the frequency dependencies are also presented.

Rheological Behaviors of Graphene Oxide/Polyacrylonitrile Spinning Solutions

The rheological behaviors of polyacrylonitrile (PAN) in NaSCN aqueous solutions containing different amount of Graphene oxide (GO) were investigated through both steady-state and dynamic rheological measurements. The parameters such as apparent viscosity (ηα), flow activation energy (Eη), structural viscosity index (Δη), storage modulus (G’), loss modulus (G’’) and mechanical loss factor (tanδ) were measured to illustrate the rheological behaviors of these solutions. The results showed that the apparent viscosity decreased with adding appropriate amount of GO, while the structural viscosity index, the flow activation energy and the mechanical loss factor of GO/PAN spinning solutions increased. Accordingly, a possible mechanism of GO effect on rheological behaviors of PAN solution was proposed in this work.

Assessment of Mechanical Parameters of PMMA Used in Human Body

Commercially available acrylic cement which has been popular in orthopaedics in the nineties of the recent century (SIMPLEX P, manufactured by HOWMEDICA LIMERICK) was used in the study. The choice of this material was caused by the fact that the average period of operation of cement prostheses in human body amounts to ca. 12 years and large percentage of prostheses implanted in this period is destabilized in the bone. The investigations focused on assessment of changes in strength parameters of PMMA used in human body over a period of 10 years and their effect on prosthesis loosening. In order to determine differences in strength parameters of the cement, directly after polymerization and after a particular period of use in human body, a series of tests were carried out, aimed at determination of the effect of aggressive environment inside human body and fatigue load which results from human motor activity on changes in strength parameters in PMMA. PMMA samples (30 days after polymerization, stored in saline solution) and the samples removed from human body due to aseptic loosening were used for comparison of strength. Due to a very complex character of operation and specific load, were tested in order to determine the dynamic properties by means of DMTA method, thus to determine the storage modulus E’ and the mechanical loss factor tgδ, responsible for dispersion of mechanical energy.

The acoustic transmission properties of anisotropic sandwich panels with perforations

A rectangular sandwich panel, consisting of two thin plane shells on either side of a cellular structure, has perforations in one of the bounding shells so that some or all of the cells may act as Helmholtz resonators. The compound panel is set in an otherwise rigid plane baffle and is irradiated by a plane wave travelling from the unperforated side of the system. An estimate is presented, in integral form, for the acoustic power transmitted through the panel, averaged with respect to time and with respect to all possible directions of incidence, in the limit of large values of ka and kb , where k is the acoustic wavenumber and a , b denote the plate dimensions. For operating frequencies below a certain critical coincidence value, the basic estimate is supplemented by an additional contribution from the resonantly driven but acoustically inefficient modes, which become significant at modest values of ka and kb if the mechanical loss factor ϵ is sufficiently small. There is good agreement between the numerical evaluation of the estimates and the available experimental data.