Probabilistic Simulation of Multi-Scale Composite Behavior

A methodology is developed to computationally assess the non-deterministic composite response at all composite scales (from micro to structural) due to the uncertainties in the constituent (fiber and matrix) properties, in the fabrication process and in structural variables (primitive variables). The methodology is computationally efficient for simulating the probability distributions of composite behavior, such as material properties, laminate and structural responses. Bi-products of the methodology are probabilistic sensitivities of the composite primitive variables. The methodology has been implemented into the computer codes PICAN (Probabilistic Integrated Composite ANalyzer) and IPACS (Integrated Probabilistic Assessment of Composite Structures). The accuracy and efficiency of this methodology are demonstrated by simulating the uncertainties in composite typical laminates and comparing the results with the Monte Carlo simulation method. Available experimental data of composite laminate behavior at all scales fall within the scatters predicted by PICAN. Multi-scaling is extended to simulate probabilistic thermo-mechanical fatigue and to simulate the probabilistic design of a composite redome in order to illustrate its versatility. Results show that probabilistic fatigue can be simulated for different temperature amplitudes and for different cyclic stress magnitudes. Results also show that laminate configurations can be selected to increase the redome reliability by several orders of magnitude without increasing the laminate thickness--a unique feature of structural composites. The old reference denotes that nothing fundamental has been done since that time

Effects of temperature on columnar microstructure and recrystallization of TiO2 film produced by ion-assisted deposition

Titanium oxide thin films were deposited by electron-beam evaporation with ion-beam-assisted deposition. The effect of the substrate temperature and annealing temperature on the columnar microstructure and recrystallization of titanium oxide was studied. The values of the refractive index varied from 2.26 to 2.4, indicating that the different substrate temperatures affected the film density. X-ray diffraction revealed that all films were amorphous as deposited. At annealing temperatures from 100 degrees C to 300 degrees C, only the anatase phase was formed. As the substrate temperature increased from 150 degrees C to 200 degrees C to 250 degrees C, the recrystallization temperature fell from 300 degrees C through 250 degrees C to 200 degrees C. Changing the substrate temperature resulted in the formation of various types of columnar microstructure, as determined by scanning-electron microscopy. Different columnar structures resulted in different surface morphologies, as measured by atomic-force microscopy. (c) 2006 Optical Society of America

Characterization of AlN thin films prepared by unbalanced magnetron sputtering

Aluminum nitride (AIN) thin films were deposited on silicon wafers and glass substrates by an unbalanced magnetron (UBM) sputtering system equipped with a pulse dc power supply. Microstructure and chemistry of the AIN-coated specimens were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The optical transmission properties of the AIN-coated glass were investigated using an ultraviolet/visible (UV/VIS) spectrophotometer. It was found that the thin films are polycrystalline and have a hexagonal wurtzite structure with (002) preferred orientation, as revealed by XRD and TEM. AFM analysis indicates that the surface of the thin films is smooth, with an average roughness R-a = 6.464 nm, which is suitable for application in surface acoustic wave devices. XPS analysis gives the chemical composition of the coatings as well as the bonding states of the elements. In addition, the AIN thin films are transparent in the visible region with an average transmittance of 60%. (C) 2004 The Electrochemical Society

Microstructural evolution of AIN coatings synthesized by unbalanced magnetron sputtering

Polycrystalline aluminum nitride (AlN) thin films with wurtzite structure were deposited on silicon substrate by an unbalanced magnetron sputtering system equipped with a pulse dc power supply. Microstructure and chemistry of the AIN-coated substrates under different deposition time were characterized by x-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), energy-dispersive spectroscopy (EDS), and electron energy loss spectroscopy (EELS). XRD results show that the thin films exhibit enhanced (002) preferred orientation. It was obtained from FE-SEM and TEM results that the AIN films have a columnar structure, and that the size of the columns increases with the distance from the substrate and the deposition time. Furthermore, AFM analysis indicates that the surface roughness of the coatings increases with the deposition time. In addition, EDS and EELS analyses give the chemical composition of the coating and the Al-N bonding state present in the coating. (c) 2065 American Vacuum Society

Microstructural evolution in the oxidized chromium nitride coatings prepared by unbalanced magnetron sputtering

Chromium nitride thin films were deposited by unbalanced magnetron (UBM) sputtering on AISI 304 stainless steel. The oxidation behavior of the nitride-coated steel at elevated temperatures ranging from 300 to 800 degreesC in air for 60 min was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. It was observed that the surface morphology and the color of the specimens oxidized below 500 degreesC remains similar to the as-deposited specimen, and the coating surface was fully covered by a granular oxide layer at 800 degreesC. Unlike the arc ion-plated chromium nitride coatings, the UBM-prepared coatings contain a small amount of beta-Cr(2)N in the as-deposited specimen besides the CrN phase. Pronounced phase decomposition from CrN into beta-Cr(2)N occurred at temperature above 500 degreesC and the phase transformation was completed at 800 degreesC. Oxidation of the nitrides to form a Cr(2)O(3) oxide layer was observed in the specimen oxidized above 500 degreesC, and the grain size of both the nitrides and the oxide increases with the oxidation temperature. (C) 2003 The Electrochemical Society

Effects of ion assistance and substrate temperature on optical characteristics and microstructure of MgF2 films formed by electron-beam evaporation

Magnesium fluoride thin films were prepared by electron-beam evaporation and ion-assisted deposition (IAD). The effects of ion, assistance and substrate temperature during deposition on the optical properties and microstructure were studied. The grain size, the crystallinity and the surface roughness of MgF2 films deposited without ion assistance all decreased with substrate temperature. MgF2 films deposited with IAD exhibited small grains, rough surfaces, fluorine deficiencies and large optical losses in the 200-500 nm wavelength range when bombarded with argon ions