Experimental investigation on low-temperature fatigue crack propagation in offshore structural steel A131 under random sea ice loading

An apparatus of low-temperature controlling for fatigue experiments and its crack measuring system were developed and used for offshore structural steel A131 under conditions of both low temperature and random sea ice. The experimental procedures and data processing were described, and a universal random data processing software for FCP under spectrum loading was written. Many specific features of random ice-induced FCP which differed with constant amplitude FCP behaviours were proposed and temperature effect on ice-induced FCP was pointed out with an easily neglected aspect in designing for platforms in sea ice emphasized. In the end, differences of FCP behaviours between sea ice and ocean wave were presented.

Narrowing of band gap and low-temperature spin glass behavior of FeNi co-doped ZnO nanowires

This letter reports on the Raman, optical and magnetic properties of FeNi co-doped ZnO nanowires prepared via a soft chemical solution method. The microstructural investigations show that the NiFe co-dopants are substituted into wurtzite ZnO nanostructure without forming any secondary phase. The co-doped nanowires show a remarkable reduction of 34 nm (267.9 meV) in the optical band gap, while suppression in the deep-level defect transition in visible luminescence. Furthermore, these nanowires exhibit ferromagnetism and an interesting low-temperature spin glass behavior, which may arise due to the presence of disorder and strong interactions of frustrated spin moments of Ni and Fe co-dopants on the ZnO lattice sites. Copyright (C) EPLA, 2009

800nm Semiconductor Absorber with Low Temperature Method and Surface State Method Combined Absorber for Kerr Lens Modelocking of Ti∶Al2O3 Laser

A novel 800nm Bragg mirror type of semiconductor saturable absorption mirror with low temperature method and surface state method combined absorber is presented.With which passive Kerr lens mode locking of Ti∶Al2O3 laser pumped by argon ion laser is realized,which produces pulses as short as 40fs.The spectrum bandwidth is 56nm,which means that it can support the modelocking of 20fs.The pulse frequency is 97.5MHz;average output power is 300mW at the pump power of 4.45W.

Low-temperature molten salt synthesis and characterization of CoWO4 nano-particles

CoWO4 nano-particles were successfully synthesized at a low temperature of 270 degrees C by a molten salt method, and effects of such processing parameters as holding time and salt quantity on the crystallization and development Of CoWO4 crystallites were initially studied. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM). and photoluminescent spectra techniques (PL), respectively. Experimental results showed that the well-crystallized CoWO4 nano-particles with ca. 45 nm in diameter could be obtained at 270 degrees C for a holding time of 8 h with 6:1 mass ratio of the salt to CoWO4 precursor, and XRD analysis evidenced that the as-prepared sample was a pure monoclinic phase Of CoWO4 with wolframite structure. Their PL spectra revealed that the CoWO4 nano-particles displayed a very strong PL peak at 453 nm with the excitation wavelength of 230 nm, and PL properties of CoWO4 crystallites relied on their crystalline state, especially on their particle size. (C) 2009 Elsevier B.V. All rights reserved.

Ice induced low temperature fatigue crack propagation in offshore structural steel A131

To investigate the low temperature fatigue crack propagation behavior of offshore structural steel A131 under random ice loading, three ice failure modes that are commonly present in the Bohai Gulf are simulated according to the vibration stress responses induced by real ice loading. The test data are processed by a universal software FCPUSL developed on the basis of the theory of fatigue crack propagation and statistics. The fundamental parameter controlling the fatigue crack propagation induced by random ice loading is determined to be the amplitude root mean square stress intensity factor K-arm. The test results are presented on the crack propagation diagram where the crack growth rate da/dN is described as the function of K-arm. It is evident that the ice failure modes have great influence on the fatigue crack propagation behavior of the steel in ice-induced vibration. However, some of the experimental phenomena and test results are hard to be physically explained at present. The work in this paper is an initial attempt to investigate the cause of collapse of offshore structures due to ice loading.

Low Temperature Properties of PI/SiO_2 Nanocomposite Films

In this paper, the mechanical properties of PI/Si_O, nanocomposite hybrid films with different silica doping levels are experimentally studied at low temperature. Experimental results show that the coefficient of thermal expansion (CTE) of the PI/Si_O, nanocomposite hybrid films gradually reduces when the ambiance temperature is decreased. At the liquid nitrogen temperature (77 K), the CTE value is about five times less than that at room temperature (287 K). The measured CTEs of hybrid films greatly decrease when doped with inorganic silica, especially when the silica doping level is more than 1 wt.%. However, too high silica contents (more than 10 wt.%) can cause problem to disperse effectively and the specimens become quite opaque. Experimental results also show that the effects of the pre-applied stress levels can be neglected on the CTE testing. When the ambient temperature changes from 287 to 77 K, the measured average values of the films' ultimate tensile strength (UTS) and Young's modulus increase about 60 and 90%, respectively, while the breaking elongation decreases about 42%.

Low-temperature hydrothermal growth of oriented [0001] ZnO film

Well-aligned ZnO films have been successfully prepared by using low-temperature hydrothermal approach on (0001) sapphire substrates that were pre-coated with a ZnO nano-layer by dip-coating. The characterizations of scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicate that the ZnO films consist of hexagonal rods that grow along the c axis based on the sapphire substrates. It is found that the size of ZnO rods can be adjusted by an aqueous solution with some methenamine. (c) 2006 Elsevier B.V. All rights reserved.

Homoepitaxial growth of ZnO films via low-temperature liquid-phase epitaxy

Homoepitaxial ZnO films have been grown via liquid-phase epitaxy (LPE) on (000 1) oriented ZnO substrates. X-ray rocking curve revealed the high quality of the ZnO films with a FWHM of 40 arc sec. Films of thickness about 20 gm were gown in the temperature range 700-720 degrees C. The growth rate of ZnO films was estimated to be 0.3 mu m h(-1). Atomic force microscope analysis showed that the surface roughness of ZnO films was very low, which further confirmed the high crystallinity of ZnO films. (c) 2006 Elsevier B.V. All rights reserved.

Low temperature growth of c-axis oriented AlN films on gamma-LiAlO2 by radio frequency magnetron sputtering

Aluminum nitride (AlN) films were prepared on gamma-LiAlO2 substrates by radio frequency (rf) magnetron sputtering. The influence of substrate temperature (T-s) and nitrogen (N-2) concentration on film growth was investigated. The X-ray diffraction (XRD) results reveal that highly c-axis oriented AlN films can be obtained in the temperature range from room temperature (RT) to 300 degrees C. A smoother surface and a crystalline quality decrease with increasing N-2 concentration have been observed by XRD and atomic force microscopy (AFM) for the films deposited at lower substrate temperature. On the contrary, the degradation of the surface smoothness and the higher crystalline quality can be observed for the films deposited at a higher substrate temperature with N-2-rich ambient. The growth mechanism which leads to different crystalline quality of the films is discussed. (C) 2008 Elsevier B.V. All rights reserved.