Dynamic properties of viscoelastic composites

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A study of Carbon Fibre /Epoxy Interface using Remote Laser Raman Microscopy

PhdThe micromechanics of reinforcement of model carbon fibre / epoxy composites has been investigated using the technique of Remote Laser Raman Microscopy. The technique allows in situ axial stress monitoring in highly crystalline fibres, such as carbon. For this purpose a remote fibre -optic probe was designed and tested. Tailor - made optics have been introduced at both input and output positions of each fibre - optic to provide laser collimation and maximum efficiency. The probe design takes advantage of the pinhole nature of the optical fibre to achieve depth discrimination. A full characterisation of the high modulusM 40 fibres using conventional testing and Raman Spectroscopy preceded the study of the stress transfer. The study was performed as a function of fibre sizing, coupon geometry and elevated temperature. Model composites were subjected to incremental tensile loading, while the stress in the fibre was monitored at each level of applied strain. The stress transfer regime was studied in the elastic domain using the short fibre coupon test and shear lag approach was employed to model the stress transfer efficiency of the interface through the use of the shear-lag parameter/ The study of the long fibre coupon test led to the identification of interfacial failure mechanisms which were also investigated by Scanning Electron Microscopy (SEM). Finally, the stress build-up in the fibre in the presence of energy dissipation mechanisms was modelled,and the stress-transfer efficiency was assessed at different levels of applied composite strain.European Commission BRITE - EURAM project BREU/CT91-9503

Acoustic emission behavior of steel fibre reinforced concrete under bending

The present paper describes the acoustic emission (AE) behavior of concrete under four-point bending. Steel fibres of varying content were used as reinforcement in concrete slabs and their influence on the fracture process and the acoustic activity was investigated. The total acoustic emission (AE) activity was found to be directly proportional to the fibre content. Analysis revealed that particular AE parameters change monotonically with the progress of damage and can be used for the characterization of the failure process

Quality assessment and damage detection in nanomodified adhesively-bonded composite joints using inkjet-printed interdigital sensors

In this work, the development of a planar interdigital capacitive sensor, directly onto the surface of a composite, for determining the initial quality of curing of bonded composite joints and assessing their long-term durability is presented. The sensor consisted of an interlocking comb-shaped array of silver electrodes and used to monitor the progress of cure of an adhesive resin and the subsequent damage state of the bond line in adhesively-bonded composite joints using impedance spectroscopy. The obtained results from the mechanical characterization indicated that the developed sensor did not affect the quality of the bondline while the added weight of the sensor is negligible. The curing process of the adhesive epoxy was successfully monitored while the ability of the sensor to assess the developed damage created by the mechanical loading was confirmed using transient infrared thermography

Thermoelectric energy harvesting from single-walled carbon nanotube alkali-activated nanocomposites produced from industrial waste materials

A waste-originated one-part alkali-activated nanocomposite is introduced herein as a novel thermoelectric material. For this purpose, single-walled carbon nanotubes (SWCNTs) were utilized as nanoinclusions to create an electrically conductive network within the investigated alkali-activated construction material. Thermoelectric and microstructure characteristics of SWCNT-alkali-activated nanocomposites were assessed after 28 days. Nanocomposites with 1.0 wt.% SWCNTs exhibited a multifunctional behavior, a combination of structural load-bearing, electrical conductivity, and thermoelectric response. These nanocomposites (1.0 wt.%) achieved the highest thermoelectric performance in terms of power factor (PF), compared to the lower SWCNTs’ incorporations, namely 0.1 and 0.5 wt.%. The measured electrical conductivity (σ) and Seebeck coefficient (S) were 1660 S·m−1 and 15.8 µV·K−1, respectively, which led to a power factor of 0.414 µW·m−1·K−2 . Consequently, they have been utilized as the building block of a thermoelectric generator (TEG) device, which demon-strated a maximum power output (Pout ) of 0.695 µW, with a power density (PD) of 372 nW·m−2, upon exposure to a temperature gradient of 60 K. The presented SWCNT-alkali-activated nanocomposites could establish the pathway towards waste thermal energy harvesting and future sustainable civil engineering structures