The setting of Acoustic Emission detecting parameters in running of steel structured
Acoustic Emission technology is still at the starting stage of monitoring in domestic bridge. To resolve the problem that Acoustic Emission detection parameters in scene are determined. Based on lead-breaking tests confirm threshold and time parameter. Studying on the characteristic of signal propagated and the attenuation laws of velocity and amplitude, it gets references for Acoustic emission technique in detection of the bridge.
Monitoring Damage of Arch Bridge Suspender Using Acoustic Emission Technique
Conventional non-destructive methods can't be dynamically monitored the suspenders'damage levels and types,so acoustic emission(AE) technique is proposed to monitor its activity.The validity signals are determined by the relationship with AE rise time and duration time.The ambient noise is eliminated using float threshold value and placing a guard sensor.The cement mortar and steel strand damage level is analyzed by AE parameter method and damage types are judged by waveform analyzing technique.Based on these methods,all the suspenders of Sichuan Ebian Dadu river arch bridge have been monitored using AE techniques.The monitoring results show that AE signal amplitude,energy and counts can visually display the suspenders'damage levels,the difference of waveform and frequency range express different damage type.The testing results are well coincide with the practical situation.
Across the structural re-entrant transition in BaFe2(PO4)2: influence of the two-dimensional ferromagnetism.
BaFe2(PO4)2 was recently prepared by hydrothermal synthesis and identified as the first two-dimensional (2D) Ising ferromagnetic oxide, in which honeycomb layers made up of edge-sharing FeO6 octahedra containing high-spin Fe(2+) ions (S = 2) are isolated by PO4 groups and Ba(2+) cations. BaFe2(PO4)2 has a trigonal R-3 structure at room temperature but adopts a triclinic P-1 structure below 140 K due to the Jahn-Teller (JT) instability arising from the (t2g)(4)(eg)(2) configuration. The triclinic crystal structure was refined to find significantly distorted Fe(2+)O6 octahedra in the honeycomb layers while the distortion amplitude QJT was estimated to 0.019 Å. The JT stabilization energy is estimated to be ∼7 meV per formula unit by DFT calculations. Below ∼70 K, very close to the ferromagnetic transition temperature Tc = 65.5 K, the structure of BaFe2(PO4)2 returns to a trigonal R-3 structure in the presence of significant ferromagnetic domains. This rare re-entrant structural transition is accompanied by a discontinuous change in the quadrupolar splitting of Fe(2+), as determined by Mössbauer spectroscopy. EPR measurements show the presence of magnetic domains well above Tc , as expected for a ferromagnetic 2D Ising system, and support that the magnetism of BaFe2(PO4)2 is uniaxial (g⊥ = 0).