The influence of martensite fraction on the wear mode and the energy dissipation by friction of dual phase (DP) steel tested under reciprocating sliding conditions was evaluated. The Ti-Nb micro alloyed steel was heat treated in a conventional furnace at temperatures between 780 and 880 ◦C (intercritical annealing temperature) for 3 min to obtain DP microstructures with volume fractions of martensite between 25 and 90%. Wear tests were carried out in both DP and as-received samples, using a reciprocating tribometer with ball-on-flat geometry, at two constant applied loads, 2.5 and 4 N. The wear damage of each sample was measured through volume loss and the dissipated energy during the test. The obtained results evidenced a significant influence of the contact load over the wear mode, because at low load the DP wear was reduced with increased hardness but just up to 75% of martensite. At high load, the sliding process promotes an oxide mixture in the ferritic microstructure that acts as a factor in wear reduction.
COBISS.SI-ID: 1027754
In this paper we focus on the preparation and mechanical properties of the nanosilica-reinforced, epoxy resin Epikote 828LVEL. Epoxy composites containing two sizes of spherical silica nanoparticles, 130 nm and 30 nm, were prepared at a fixed volume fraction (VP = 0.5%). To prevent agglomeration, the silica fillers were initially pre-treated with diglycidyl ether of bisphenol A (BADGE). Due to the low content of silica fillers, their inclusion in the matrix was confirmed by the increased roughness of a fracture surface compared to the smooth surface of the neat epoxy. Raman spectroscopy was employed to obtain additional information about the crack-propagation path. The mechanical properties, characterized by a three-point bending test, revealed a 10-20% increase in the composite's modulus of elasticity with 30-nm and 130-nm silica-filler inclusions. Elongation at break, on the other hand, decreased for 5-10% in both composites compared to neat epoxy, suggesting brittle fracture behavior in silica/epoxy composites. The fracture toughness results showed a 25-30% improved toughening for both composites compared to the pure epoxy. The composite's resistance to failure in terms of the impact energy was, however, strongly dependent on the size of the silica: we observed a 30% increase for the 130-nm, and a 60% increase for the 30-nm, silica/epoxy composites, compared to the pure epoxy.
COBISS.SI-ID: 5124634
Tungsten nanofibers are recognised as biologically potent. We study deviations in molecular composition between normal and digestive gland tissue of WOx nanofibers (nano-WOx) fed invertebrate Porcellio scaber (Iosopda, Crustacea) and revealed mechanisms of nano-WOx effect on digestive gland cells of a model organism in vivo. Fourier transform infrared (FTIR) imaging was performed on digestive gland epithelium of animals fed with WOx nanofibers and on controls. The FTIR analyses were supplemented by toxicity and cytotoxicity analyses as well as scanning electron microscopy (SEM) of the surface of the epithelium. The difference in the spectra of the WOx-treated and control cells showed up in the central region of the cells and were related to a changed protein to lipid ratio, lipid peroxidation and structural changes of nucleic acids. The conventional toxicity parameters failed to show toxic effects of nano-WOx, whereas the cytotoxicity biomarkers and SEM investigation of digestive gland epithelium indicated sporadic effects of nanofibers. In addition toxicological and cytological measurements did not, highlight severe effects on cell membrane stability and feeding behaviour of Porcellio scaber upon that the ingestion of nano-WOx. Therefore, the biochemical alterations evidenced by FTIR imaging have been explained as the result of cell protection mechanisms to unfavourable conditions and indication of non-homeostatic state, which can lead to toxic effects.
COBISS.SI-ID: 2855759