University of Architecture, Civil Engineering and Geodesy

About: University of Architecture, Civil Engineering and Geodesy is a education organization based out in Sofia, Bulgaria. It is known for research contribution in the topics: Finite element method & Beam (structure). The organization has 3808 authors who have published 3822 publications receiving 30736 citations. The organization is also known as: Sofia Polytechnic.

An analytical solution to the stain energy release rate of a crack in functionally graded nonlinear elastic beams

Abstract: An analytical approach was developed for studying the delamination fracture behaviour of functionally graded beam configurations with considering the material non-linearity. It was assumed that the mechanical response of functionally graded beams can be described by a non-linear stress-strain curve that is not symmetric for tension and compression (different stress-strain relations were used for tension and compression). The material is functionally graded along the beam height. Fracture behaviour was analyzed in terms of the strain energy release rate. A delamination crack located arbitrarily along the beam height was considered. The strain energy release rate was expressed in a function of the bending moments and axial forces in the cross-sections ahead and behind the crack front. The approach developed was applied to analyze the strain energy release rate in the functionally graded Double Cantilever Beam (DCB) configuration with material non-linearity. The strain energy release rate derived was compared with fracture analysis by the J -integral for verification. The effects of material properties and crack location on the fracture in the DCB were evaluated. It was shown that the approach developed is very useful for studying the fracture in functionally graded beam structures that exhibit material non-linearity.

Magnetoelectric coupling and spin reorientation in BiFeO3

Abstract: We have studied the electric properties of multiferroic BiFeO3 (BFO) using the transverse Ising model in terms of pseudo-spin variables S with S= 7/2 and the Green's function method. Mechanisms of magnetoelectric (ME) couplings and electric field-induced spin-reorientation (SR) transition in BFO (71∘ in-plane and 109∘ out-of-plane switching) are examined. It is established that the spontaneous polarization Ps is responsible for the origin of an incommensurate non-collinear magnetic phase below TN. The relevance of two types of ME mechanisms is shown: the first one is quadratic with respect to the magnetic spins and the ferroelectric variables, whereas a second one defines a ME interaction which is induced from the appearance of a spontaneous polarization in BFO, called antisymmetric ME interaction. When an external magnetic field is applied they compete against each other and as a result the spontaneous polarization Ps is renormalized. The extraordinary polarization below TN is numerically calculated and its dependency on the easy-axis anisotropy K and the external magnetic field is examined. The type of magnetic SR transition under the influence of the electric field is determined. The critical values of E for different switching processes are numerically calculated.

Mechanical and Nondestructive Testing to Verify the Effectiveness of Composite Strengthening on Historical Cast Iron Bridge in Venice, Italy

Abstract: The oldest cast iron arch bridge built in 1852 in Venice exhibits serious deterioration due to corrosion and cracking of its members. The Municipality accepted a proposal to strengthen it with Aramid fiber reinforced polymers (AFRP) materials. The AFRP materials application aims to arrest cracks and reduce the structure’s vulnerability to impact by boats. Tests have already been performed on structural cast iron beams taken from similar cast iron bridges dismantled. Results from four point bending tests showed an increase in strength and a different fracture mode depending on FRP application. Charpy tests showed an increased fracture energy in specimens strengthened with FRP and primer. Utilization of bidirectional and triaxial fabrics was discussed. However this paper is particularly focused on nondestructive testing following the FRP application. Nondestructive testing has been planned both for laboratory test specimens and for a long term monitoring program. Artificial defects, embedded during manufact...

Effect of creep aging forming on the fatigue crack growth of an AA2524 alloy

Abstract: Effects of creep aging forming on the microstructural evolution, conventional mechanical properties and fatigue crack propagation (FCP) behavior for 2524 aluminum alloy were studied by tensile and hardness testing, the FCP behavior testing and transmission electron microscopy (TEM) observation. The results show that in the low stress intensity range, the characteristics of precipitates have a significant effect on fatigue performance of the creep-aged aluminum alloy, and the mainly precipitated S″ phases in the alloy creep-aged for 4 h is beneficial to the reversibility of coplanar slip and dislocation slip, and the alloy presents better FCP resistance and relatively lower FCP rate, while the FCP rate increases with increasing aging time. In the Paris regime, effects of microstructure on the FCP rate are no longer obvious, and the FCP rates are almost consistent. Meanwhile, the presence of creep stress significantly accelerates the aging precipitation process. In terms of yield strength σ0.2, hardness and FCP resistance, the 9 h artificial aged alloy is analogous to the 4 h creep aged alloy. The peak strength of the alloy creep-aged for 24 h is the highest, but the fatigue crack growth resistance degraded obviously. It is not comprehensive to determine the optimal process of creep aging only in accordance with the peak strength.

UV and visible light photodegradation effect on Fe–CNT/TiO2 composite catalysts

Abstract: Using multi-walled carbon nanotube (CNT) as an one-dimensional support, we have succeeded in uniformly anchoring of TiO2 and Fe nanoparticles at its surface. The as-prepared Fe–CNT/TiO2 composite photocatalysts have been investigated by degrading methylene blue (MB) under UV and differently intensified visible light irradiation. The ability of CNT to store and shuttle electrons, and Fe nanoparticles demonstrate its capability to serve as a yield and transfer electrons on demand to separate h + /e − pairs. Moreover, the MB photodegradation increase with an increase of visible light intensity can be ascribed to the enhancement MB cationic radical. In addition, chemical oxygen demand (COD) of piggery waste and reduction efficiency of Cr (IV) was done at regular intervals, which gave a good idea about mineralization of wastewater.