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Laser Power Density (laser + power_density)

Distribution by Scientific Domains
Polymers and Materials Science66%

Selected Abstracts

The effect of laser power density on the fatigue life of laser-shock-peened 7050 aluminium alloy

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2007
Q. LIU
ABSTRACT Laser shock peening (LSP) is an innovative surface treatment method that can result in significant improvement in the fatigue life of many metallic components. The process produces very little or no surface profile modification while producing a considerably deeper compressive residual stress layer than traditional shot peening operations. The work discussed here was designed to: (a) quantify the fatigue life improvement achieved by LSP in a typical high strength aircraft aluminium alloy and (b) identify any technological risks associated with its use. It is shown that when LSP conditions are optimal for the material and specimen configuration, a ,three to four times increase in fatigue life over the as-machined specimens could be achieved for a representative fighter aircraft loading spectrum when applied at a representative load level. However, if the process parameters are not optimal for the material investigated here, fatigue lives of LSP treated specimens may be reduced instead of increased due to the occurrence of internal cracking. This paper details the effect of laser power density on fatigue life of 7050-T7451 aluminium alloy by experimental and numerical analysis. [source]

Laser shock peening on fatigue crack growth behaviour of aluminium alloy

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2004
Y. TAN
ABSTRACT The effect of laser shock peening (LPS) in the fatigue crack growth behaviour of a 2024-T3 aluminium alloy with various notch geometries was investigated. LPS was performed under a ,confined ablation mode' using an Nd: glass laser at a laser power density of 5 GW cm,2. A black paint coating layer and water layer was used as a sacrificial and plasma confinement layer, respectively. The shock wave propagates into the material, causing the surface layer to deform plastically, and thereby, develop a residual compressive stress at the surface. The residual compressive stress as a function of depth was measured by X-ray diffraction technique. The fatigue crack initiation life and fatigue crack growth rates of an Al alloy with different preexisting notch configurations were characterized and compared with those of the unpeened material. The results clearly show that LSP is an effective surface treatment technique for suppressing the fatigue crack growth of Al alloys with various preexisting notch configurations. [source]

Bifunctional Gd2O3/C Nanoshells for MR Imaging and NIR Therapeutic Applications

ADVANCED FUNCTIONAL MATERIALS, Issue 2 2009
Chih-Chia Huang
Abstract This paper reports dual function Gd2O3/C nanoshells for application in MR contrast images and NIR-triggered killing cancer cells. The nanoshells are prepared using biological gelatin particles as core templates through a two-step thermal treatment. The surfaces of the nanoshells can be readily modified by poly(styrene-alt-maleic acid) (PSMA) polymer to improve their water-dispersible properties and increase their biocompatibility. The Gd2O3/C nanoshells show brightened images of kidney cortex and liver in mice, whereas the Gd2O3/C@PSMA nanoshells show a darkened liver signal. The biodistribution is measured as a function of time and shows that the nanoshells circulate in the vessels and are cleared out gradually from organs. The graphite carbon coated on the Gd2O3 nanoshells displays absorbance in the near-IR (NIR) region. A large extinction coefficient is obtained, indicating the potential of the nanoshells as photothermal agents. The Gd2O3/C@PSMA nanoshells conjugated with anti-epithermal growth factor receptor antibodies are used for targeting and destroying A549 lung cancer cells by means of NIR-triggered killing capability. Both laser power density and material dose dependence are investigated to evaluate photothermolysis in cancer cells. [source]

Micro-fabrication and monitoring of three-dimensional microstructures based on laser-induced thermoplastic formation

MICROSCOPY RESEARCH AND TECHNIQUE, Issue 10 2009
Leyan Wang
Abstract This article reports a novel laser-induced micro-fabrication method and its monitoring system for three-dimensional (3D) microstructures. The mechanism of the method is that a small zone of thermoplastic material melted by laser heating grows in liquid surrounding environment, solidifying into a convex microstructure, such as micro-dot or micro-pillar. A laser diode (808 nm) with maximum power output of 130 mW is used as power source, and a kind of paraffin mixed with stearic acid and paint serves as the thermoplastic material for 3D microstructure formation experiments. A light microscope system consisting of a charge-coupled device (CCD) and a computer is utilized to realize real-time observation of the micro-fabricating process. The distribution of local temperature rise on material surface created by laser irradiation is simulated. The effects of liquid environment on microstructure formation have been theoretically analyzed and experimentally studied. Experiments are further carried out to investigate the relationship between laser spot and fabricated microstructures. The results indicate that the widths of micro-dots or micro-pillars are mostly determined by the size of focal spot, and their heights increase with the enlargement of laser power density. With this method, a micro-dot array of Chinese characters meaning "China" has been successfully fabricated through computer programming. This method has the advantages of implementing direct, mask-less, real-time and inexpensive 3D microstructure fabrication. Therefore, it would be widely applied in the fields of micro/nano-technology for practical fabrication of different kinds of 3D microstructures. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc. [source]

Imaging of uranium on rat brain sections using laser ablation inductively coupled plasma mass spectrometry: a new tool for the study of critical substructures affined to heavy metals in tissues

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2008
J. Sabine Becker
The specific toxicity of trace metals and compounds largely depends on their bioavailability in different organs or compartments of the organism considered. Imaging mass spectrometry (IMS) using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) with a spatial resolution in the 100,µm range was developed and employed to study heavy metal distribution in brain tissues for toxicological screening. Rat brain post-mortem tissues were stained in an aqueous solution of either uranium or neodymium (metal concentration 100,µg,g,1) for 3,h. The incubation of heavy metal in thin slices of brain tissue is followed by an imaging mass spectrometric LA-ICP-MS technique. Stained rat brain tissue (thickness 30,µm) were scanned with a focused laser beam (wavelength 266,nm, diameter of laser crater 100,µm and laser power density 3,×,109,W,cm,2). The ion intensities of 235U+, 238U+, 145Nd+ and 146Nd+ were measured by LA-ICP-MS within the ablated area. For quantification purposes, matrix-matched laboratory standards were prepared by dosing each analyte to the pieces of homogenized brain tissue. Imaging LA-ICP-MS allows structures of interest to be identified and the relevant dose range to be estimated. Copyright © 2008 John Wiley & Sons, Ltd. [source]