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.

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This work aims in studying the mechanical behaviour of concrete, reinforced with steel fibres of different geometry and volume fraction. Experiments include compression tests and four‐point bending tests. Slump and air content tests were performed on fresh concrete. The flexural toughness, flexural strength and residual strength factors of the beam specimens were evaluated in accordance with ASTM C1609/C1609M‐05 standard. Improvement in the mechanical properties, in particular the toughness, was observed with the increase of the volume fraction of steel‐fibres in the concrete. The fibre geometry was found to be a key factor affecting the mechanical performance of the material.

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A novel two-step approach for preparing carbon nanotube (CNT) systems, exhibiting an extraordinary combination of functional properties, is presented. It is based upon nanocomposite films consisting of metal (Me = Ni, Fe, Mo, Sn) nanoparticles embedded into diamond-like carbon (DLC). The main concept behind this approach is that DLC inhibits the growth of Me, resulting in the formation of small nanospheres instead of layers or extended grains. In the second step, DLC:Me substrates were used as catalyst templates for the growth of CNTs by the thermal chemical vapor deposition (T-CVD) process. X-ray photoelectron spectroscopy (XPS) has shown that at the T-CVD temperature of 700 °C DLC is completely graphitized and NiC is formed, making DLC:Ni a very effective catalyst for CNT growth. The catalyst layers and the CNT systems have been characterized with a wide range of analytical techniques such as Auger electron spectroscopy and X-ray photoelectron spectroscopy (AES/XPS), X-ray diffraction, reflectivity and scattering, Raman spectroscopy, scanning electron microscopy, atomic force microscopy, and optical and electrical testing. The produced CNTs are of excellent quality, without needing any further purification, durable, firmly attached to the substrate, and of varying morphology depending on the density of catalyst nanoparticles. The produced CNTs exhibit exceptional properties, such as super-hydrophobic surfaces (contact angle up to 165°) and exceptionally low optical reflection (reflectivity <10(-4)) in the entirety of the visible range. The combination of the functional properties makes these CNT systems promising candidates for solar thermal harvesting, as it is demonstrated by solar simulation experiments.

The change in ultrasonic nonlinear property of a titanium alloy subjected to cyclic loading has been studied, with an objective to develop a new characterization methodology for quantifying the level of damage in the material undergoing fatigue. In order to determine the degree of nonlinearity, the ultrasonic second harmonic generation technique has been used. The second harmonic signal was monitored during the fatigue process, and a substantial increase in the second harmonic amplitude (180% increase in nonlinear factor) was observed. This indicates that the second harmonic signal is very sensitive to the microstructural changes in the material caused by fatigue.