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Volume 26, Issue 11
Displaying 1-11 of 11 articles from this issue
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Shuntaro WATANABE1998 Volume 26 Issue 11 Pages 781
Published: November 15, 1998
Released on J-STAGE: August 25, 2010
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Akira MATSUNAWA1998 Volume 26 Issue 11 Pages 782
Published: November 15, 1998
Released on J-STAGE: August 25, 2010
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Akira MATSUNAWA, Seiji KATAYAMA1998 Volume 26 Issue 11 Pages 783-787
Published: November 15, 1998
Released on J-STAGE: August 25, 2010
JOURNAL FREE ACCESSIn laser welding, a deep cavity, or a so-called keyhole or beam hole, is formed in the weld pool by the intense recoil pressure of metal evaporation. The keyhole formation is advantageous, on the one hand, because a deep and narrow weld is obtained in laser welding. On the other hand, a hole formed in the liquid pool is by nature very unstable. In high-power keyhole laser welding, quite a large number of characteristic porosities are observed in the weld metal, and this tendency is enhanced at higher power. However, the porosity-formation mechanism has not been clarified at all. The authors have, therefore, conducted a direct observation of keyhole behavior as well as allied phenomena by various optical and X-ray methods. This paper describes methods for observing keyhole dynamics in laser welding with high temporal and spatial resolution as well as observed keyhole behaviors and allied phenomena, mechanisms of porosity formation, and relevant suppression methods.View full abstractDownload PDF (1560K) -
Takashi YABE1998 Volume 26 Issue 11 Pages 788-792
Published: November 15, 1998
Released on J-STAGE: August 25, 2010
JOURNAL FREE ACCESSWe have succeeded for the first time in simulating the dynamic phase transition from metal to liquid and vapor. This success is due to the CIP (Cubic-Interporated Pseudoparticle/Propagation) method that can treat solid, liquid and gases together and can trace a sharp interface with almost one grid. We review various activities related to laser-induced evaporation and welding processes, and clarify the formation mechanism of debris during evaporation and keyhole in deep-penetration welding.View full abstractDownload PDF (2505K) -
Yuji SANO, Masaki YODA, Naruhiko MUKAI, Minoru OBATA1998 Volume 26 Issue 11 Pages 793-799
Published: November 15, 1998
Released on J-STAGE: August 25, 2010
JOURNAL FREE ACCESSThis paper describes recent advances in the observation and modeling of laser peening phenomenon. Laser peening changes the stress field in metallic materials from tensile to compressive by the impulsive effect of laser-induced plasma. The plasma, generated by the irradiation of the second harmonic of a Nd: YAG laser on an SUS304 test piece, was directly observed by imaging the plasma luminescence. Comparing the observed image to the plasma expansion velocity calculated using an analytical model, we calibrated the time evolution of the calculated plasma pressure. The propagation of a shock wave induced by laser irradiation and the dynamic response of the material was simulated by an elasto-plastic analysis with a finite element program using the plasma pressure as an external load. The calculated residual stress was compared to the results of corresponding laser peening experiments.View full abstractDownload PDF (1386K) -
Etsuji OHMURA, Isamu MIYAMOTO1998 Volume 26 Issue 11 Pages 800-805
Published: November 15, 1998
Released on J-STAGE: August 25, 2010
JOURNAL FREE ACCESSSome results of a molecular dynamics simulation of the atomic behavior of metals and silicon during laser ablation are introduced. Many small voids are at first generated in the liquid phase. They then become larger and larger, and adjacent voids combine with each other, developing into a larger void. Finally, the surface begins to bulge out, forming into relatively large lumps. In metals undergoing laser irradiation of relatively high power density, the molten metal, whose kinetic energy is too low for evaporation to occur, becomes spherical due to the surface tension and is deposited around the hole. On the other hand, in the case of relatively low power density, fusing atoms flow out from the molten pool and deposit around the hole. In silicon, some of the vaporizing atoms are deposited around the hole, which is smaller in diameter than that in metals under the same irradiating conditions. The surface of the generated wall of silicon is rough compared to that of metal.View full abstractDownload PDF (1469K) -
Mitsugu HANABUSA, Masayuki OKOSHI1998 Volume 26 Issue 11 Pages 806-811
Published: November 15, 1998
Released on J-STAGE: August 25, 2010
JOURNAL FREE ACCESSWe compared excimer lasers, a free electron laser, and synchrotron radiation as photon sources in laser ablation for the production of carbon films, such as dimond-like carbon films, using graphite and frozen hydrocarbon targets.View full abstractDownload PDF (1671K) -
Hiroshi YAMASHITA, Masahito KATTO, Shunshiro OHNISHI, Yutaka KURIOKA, ...1998 Volume 26 Issue 11 Pages 812-815
Published: November 15, 1998
Released on J-STAGE: August 25, 2010
JOURNAL FREE ACCESSAn Imaging Plate (IP) has been developed as an image storing medium for use in medical X-ray diagnosis. We confirmed the IP to be a good medium not only for X-ray radiation but also for vacuum ultraviolet (VUV) and ultraviolet (UV) radiation. We found that the photo-stimulated luminescence (PSL) intensity showed a linear response to UV photon numbers in the range of 104.5, and that showed saturation as the irradiated photon number increased. The sensitivity curve of the IP showed a peak at the wavelength of 200 nm and decreased at longer wavelengths. When the wavelength of the irradiated UV radiation was longer than 320 nm, the PSL intensity was too low to detect with our system. This means that the cut-off wavelength of the sensitivity was measured as 310 nm.View full abstractDownload PDF (668K) -
Yoshihisa UCHIDA, Jun YAMADA, Shigeo WATANABE, Yoshiyuki UCHIDA1998 Volume 26 Issue 11 Pages 816-820
Published: November 15, 1998
Released on J-STAGE: August 25, 2010
JOURNAL FREE ACCESSFunctionally graded materials (FGMs), which possess dual characteristics of two materials, are expected to be useful materials in industry. An excimer laser is one of the powerful processing tool that can be used to reprocess FGMs. To obtain the best possible quality in laser processing, it is necessary to understand the details of the ablation plasma in laser processing. The XeCl excimer laser with a maximum pulse energy of 500 mJ was used. The ablation plasma was observed by a high-speed streak camera. Kaolin-magnetite FGMs were produced by a newly developed layer-accretion method using vacuum filtration followed by consolidation and sintering. The temporal and spatial profiles of the ablation plasma plumes were measured. It was found that the properties of the ablation plasma plumes depended on the kaolin-magnetite content of the FGMs.View full abstractDownload PDF (806K) -
Masahiro UEDA, Toshihiko YAMAGUCHI, Jing CHEN, Katsuhiko ASADA, Keiji ...1998 Volume 26 Issue 11 Pages 821-822
Published: November 15, 1998
Released on J-STAGE: August 25, 2010
JOURNAL FREE ACCESSAn optical method has been proposed for detecting torsion in a power transmission shaft in rcaltime. The method detects both light signals reflected on two mirrors attached to both sides of a rotating shaft and the time difference between them simultaneolisly. The system consists of a sensor head consisting of two semiconductor lasers, two mirrors, and two silicon photodiodes, and includes a data processing system composed of a comparator, high frequency oscillator, logic circuit, and counter. In principle, the method has no error factors.View full abstractDownload PDF (234K) -
Ultra-Short High-Intensity LasersShuji SAKABE, Sadao NAKAI1998 Volume 26 Issue 11 Pages 823-827
Published: November 15, 1998
Released on J-STAGE: August 25, 2010
JOURNAL FREE ACCESSDownload PDF (1610K)
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