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Posts Tagged ‘LASER beams’

A numerical study of the temperature gradient mechanism in laser forming using different laser beam geometries

Laser forming has attracted considerable attention as a viable technique to form sheet metal by thermal residual stresses. Many numerical and experimental investigations of laser forming processes were carried out to understand the mechanisms and the effects of various parameters on the characteristics of the formed parts. The objective of this work is to investigate the effect of different beam geometries on laser bending process of metal sheets, which is dominated by temperature gradient mechanism (TGM). In this paper a comprehensive thermal and structural finite element analysis is conducted to investigate the effect that these laser beam geometries have on the process and the final product characteristics. To achieve this, the temperature distribution, deformation, plastic strains and stresses produced by different beam geometries are compared numerically. The findings suggest that beam geometry could be an important controlling parameter for bending angle, edge effect and bend radius. [ABSTRACT FROM AUTHOR]

July 8, 2012 Tags: BENDING, DEFORMATIONS (Mechanics), FINITE element method, LASER beams, NUMERICAL analysis, STRAINS & stresses, TEMPERATURE distribution
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Laser-induced surface modification of a cu-based powder metallurgy friction material

A Cu-based powder metallurgy friction material was modified by CO2 laser radiation to improve its combination properties. The microstructures were characterized by means of X-ray diffraction (XRD), electro-probe microanalyser, a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The properties were characterized using a microhardness tester, a Brinell hardness tester and a wear tester. It was found that the material with and without laser treatment was mainly composed of α-Cu and graphite. But after the laser surface modification the grain size of the Cu had decreased by 35%, the average square root value of second strain was increased by 39% and the apparent value of dislocation density was increased by 97%. The α-Cu was refined to form a amorphousnanocrystal microstructure. The microhardness of the α-Cu was increased by 14%. The apparent hardness of the laser treated material was increased 12.7%, while the wear resistance was increased by 45% and the friction coefficient was increased by 1% as compared with the untreated material. [ABSTRACT FROM AUTHOR]

May 22, 2012 Tags: COPPER powder, FRICTION materials, LASER beams, POWDER metallurgy, SCANNING electron microscopy, TRANSMISSION electron microscopy, X-rays -- Diffraction
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Influence of laser beam brightness during surface treatment of a zro2 engineering ceramic

A comparative study between fibre and Nd:YAG (neodymium, yttrium, aluminium, garnet) laser surface treatment on a cold isostatic pressed (CIP) ZrO2 engineering ceramic was conducted to investigate the individual differences of laser brightness (radiance) produced by the two laser sources. The effects of brightness exhibited by the two lasers were investigated in respect to the change in the hardness, dimensional size of the laser irradiated zones and the microstructure of the ZrO2 engineering ceramic. The results showed that the hardness of the ZrO2 engineering ceramic was reduced by 36% for the Nd:YAG laser in comparison to the as-received surface. However, only 4% reduction in the surface hardness was found from employing the fibre laser surface treatment which was not significant as much as the results of the Nd:YAG laser irradiation. The change in hardness occurred due to softening of the laser irradiated surface of the ZrO2 with a changed composition which was softer than the laser unaffected surface. The dimensional size of the fibre laser irradiated track was also found to produce broader surface profiles in comparison to that of the Nd:YAG laser. The fibre laser irradiated surface track was 32% larger in width and 51.5% longer in depth of penetration in comparison to that of the Nd:YAG laser. Change in microstructure of the ZrO2 engineering ceramic irradiated by both lasers was found as opposed to the ground and polished untreated surface. The fibre laser affected the grain mor- phology to a greater extent in comparison to that of the Nd:YAG laser irradiation. The physical and micro-structural effects from applying the two laser types to the ZrO2 engineering ceramic differed as deep penetration and broader laser irradiated track as well as larger grains were produced by the fibre laser, despite using identical laser processing parameters such as spot size, power density, traverse speed, gas flow rate, wavelength and the Gaussian beam profile. This occurred due to the high brightness exhibited by the fibre laser irradiation which generated larger power per unit area which in turn induced into the ZrO2 engineering ceramic and resulted to producing high processing temperature, larger fibre laser-ceramic-interaction zone and melt-pool at the laser-ZrO2 interface in comparison to that of the Nd:YAG laser which intrinsically resulted to a change in physical attributes of the ceramic. [ABSTRACT FROM AUTHOR]

May 21, 2012 Tags: ALUMINUM, BRIGHTNESS temperature, COMPARATIVE studies, HARDNESS, LASER beams, YTTRIUM, ZIRCONIUM compounds
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Analyzing forest canopies with ground-based laser scanning: a comparison with hemispherical photography

Abstract: We tested ground-based high resolution laser scanning as a tool for analyzing the complex canopy structure of temperate broad-leaved forests. The canopies of 35 groups of trees were analyzed by laser scans from various positions inside a mixed stand to generate three-dimensional (3D) point clouds of the axes and leaves. The scan data was used to produce hemispheric views of the canopy at various locations that were compared to synchronously taken hemispherical photographs of the same part of the canopy. We conclude that terrestrial laser scanning (TLS) in mature forests can overcome several of the methodological problems inherent to conventional canopy analysis with optical methods and thus may soon offer a promising tool for functional research in complex forest canopies. Certain limitations of the TLS approach, mostly caused by hardware limitations that will probably soon be overcome, are encountered. [Copyright &y& Elsevier]

March 1, 2012 Tags: CLOUDS, COMPARATIVE studies, FOREST canopies, FORESTS & forestry -- Research, HEMISPHERICAL photography, LASER beams, LEAVES
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Numerical simulation of process dynamics during laser beam drilling with short pulses

In the last years, laser beam drilling became increasingly important for many technical applications as it allows the contactless production of high quality drill holes. So far, mainly short laser pulses are of industrial relevance, as they offer a good compromise between precision and efficiency and combine high ablation efficiency with low thermal damage of the workpiece. Laser beam drilling in this pulse length range is still a highly thermal process. There are two ablation mechanisms: evaporation and melt expulsion. In order to achieve high quality processing results, a basic process understanding is absolutely necessary. Yet, process observations in laser beam drilling suffer from both the short time scales and the restricted accessibility of the interaction zone. Numerical simulations offer the possibility to acquire additional knowledge of the process as they allow a direct look into the drill hole during the ablation process. In this contribution, a numerical finite volume multi-phase simulation model for laser beam drilling with short laser pulses shall be presented. The model is applied for a basic study of the ablation process with μs and ns laser pulses. The obtained results show good qualitative correspondence with experimental data. [ABSTRACT FROM AUTHOR]

March 1, 2012 Tags: COMPUTER simulation, DRILLING & boring, FINITE volume method, LASER ablation, LASER beams, MOLECULAR dynamics, PHASE transformations (Statistical physics)
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Optical transmission and reflection of aluminum film irradiated by nanosecond laser beam and experimental studying of phase-explosion

In this paper we present evidence for a phase explosion during the laser-induced ablation process by studying the optical reflectivity of the ablated plume. The ablation was produced by irradiating thin film aluminum coated on a quartz substrate with a single pulse laser beam in ambient air. The laser pulse was provided by the second harmonic of a Q-switched Nd:YAG laser with ∼10 ns pulse duration. The transmission of a low power He-Ne laser beam through the hot ablated material plume and its reflection (from the front surface, and rear surface of aluminum film) were also monitored during the duration of the ablation event. The results show that the front surface reflectivity is enhanced at an early time of ablation which is described as strong evidence for the creation of a phase explosion in this process. [ABSTRACT FROM AUTHOR]

March 1, 2012 Tags: ALUMINUM films, EXPLOSIONS, LASER ablation, LASER beams, METALS -- Surfaces, PHASE transformations (Statistical physics), QUARTZ, REFLECTION (Optics)
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Structural, optical and electrical properties of cubic aln films deposited by laser molecular beam epitaxy

Cubic AlN films were successfully deposited on TiN buffered Si (100) substrates by a laser molecular beam epitaxy (LMBE) technique, and their crystal structure and optical and electrical properties were studied. The results indicate that cubic AlN films show the NaCl-type structure with a (200) preferred orientation, and the lattice parameter is determined to be 0.4027 nm. The Fourier transform infrared (FTIR) pattern of the cubic AlN film displays sharp absorption peaks at 668 cm and 951 cm, corresponding to the transverse and longitudinal optical vibration modes. Ellipsometric measurements evidence a refractive index of 1.66-1.71 and an extinction coefficient of about zero for the cubic AlN film in the visible range. Capacitance-voltage ( C- V) traces of the metal-insulator-semiconductor (MIS) device exhibit that the cubic AlN film has a dielectric constant of 8.1, and hysteresis in the C- V traces indicates a significant number of charge traps in the film. [ABSTRACT FROM AUTHOR]

March 1, 2012 Tags: ALUMINUM nitride, FOURIER transform infrared spectroscopy, LASER beams, METAL insulator semiconductors, METALS -- Electric properties, METALS -- Optical properties, MOLECULAR beam epitaxy, MOLECULAR structure, PERMITTIVITY, THIN films
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Laser-assisted atom probe tomography investigation of magnetic fept nanoclusters: first experiments

Abstract: FePt nanoclusters dispersed in a Cr matrix have been investigated by laser-assisted atom probe tomography. The results were analysed according to simulated evaporation experiments. Three–dimensional (3D) reconstructions reveal the presence of nanoclusters roughly spherical in shape, with a size in good agreement with previous transmission electron microscopy observations. Some clusters appear to be broken up after the evaporation process due to the fact that the Cr matrix has a lower evaporation field than Fe and Pt. It is thus shown that the observed FePt nanoclusters are chemically homogeneous. They contain Fe and Pt in equiatomic proportions, with no core–shell structure observed. [Copyright &y& Elsevier]

March 1, 2012 Tags: BINARY systems (Metallurgy), IRON alloys, LASER beams, METAL clusters, METALS -- Magnetic properties, NANOSTRUCTURED materials, PLATINUM alloys, TOMOGRAPHY
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