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- Miroshnikova, N., et al.
(författare)
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Study of the interaction mechanisms between different materials and pulses from CO2- and Nd:YAG-lasers using digital speckle photography
- 2004
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5506, s. 42-50
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Tidskriftsartikel (refereegranskat)abstract
- Pulsed irradiation from CO2- and Nd:YAG lasers focused on the front side of different plates produces nearly instantaneous surface changes on the rear side of the plate. The responses of the materials depend on physical parameters such as pulse energy and duration, photon energy, the absorption and mechanical characteristics of the target material. The equipment built up for visualization of these phenomena consists of a cw. He-Ne laser, a digital CCD camera and a fast computer. The analysis is done using Digital Speckle Photography (DSP). Using focused and defocused laser speckle patterns, DSP enables measurement of in-plane strain fields, Brownian motion and residual micro-structural changes in the material caused by a laser pulse. Results are obtained at the frame rate of the digital camera and allow the creation of animated real-time or "movie" sequences. Results from CO2- and Nd:YAG pulse interaction on Al2O3 ceramics and steel plates will be presented. The Brownian motion during the relaxation phase is more or less localized to the impacted area for both materials and both wavelengths but the relaxation times differ significantly. Steel also exhibits some residual material changes and doesn't recover completely while Al2O3 returns to its initial state some time after the impact
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| 6. |
- Yalukova, O., et al.
(författare)
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Investigation of interaction mechanisms in laser drilling of thermoplastic and thermoset polymers using different wavelengths
- 2006
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Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 66:10, s. 1289-1296
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Tidskriftsartikel (refereegranskat)abstract
- In this paper a comparison of the percussion drilled holes in fiber reinforced polymer and non-reinforced thermoplastic sheets using three wavelengths, 1064, 532 and 266 nm is presented. At near infrared and visible wavelengths, 1064 and 532 nm, most of the bulk thermoplastic and thermoset polymers are partially transparent. The degree of transparency is dependent upon the degree of crystallinity. The most amorphous thermoplastics, such as PMMA have the highest transparency. In comparison, the fibre reinforced thermosets - graphite fibre reinforced epoxy - have low transparency. If the IR or visible laser beam is strongly focused, it can cause thermally induced degradation and sometimes burning and other damages (cracking, boiling, etc.) around the focused laser spot and the interaction zone. By using the fourth harmonics ultraviolet light (266 nm) of a diode-pumped and AOQ-switched Nd:YAG-laser with pulse duration of about 100 ns, the hole drilling process was significantly improved and the risk for thermal damage has been significantly reduced for both materials. Around the irradiated spot or drilled holes the material is influenced. This was investigated by both scanning electron microscopy and optical microscopy. There was clear evidence of a change in the interaction mechanism if UV light with high enough photon energy was used. By using UV light, bond breaking rather than thermal material removal occurred, i.e., a change from thermal to photo-chemical dissociation or photo-ablation becomes the dominant interaction mechanism.
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| 7. |
- Yalukova, O., et al.
(författare)
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Investigation of laser percussion hole drilling by use of speckle correlation
- 2005
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 44:30, s. 6338-44
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Tidskriftsartikel (refereegranskat)abstract
- In this paper speckle correlation is introduced as a tool to investigate the heat-influenced area during material processing with laser light. Two materials were investigated, a pure silver sheet and a sheet of SiC-diamond composite. The processing laser used in the experiments was a diode-pumped acousto-optical Q-switched Nd:YAG laser that allowed percussion hole drilling to be performed using green light through a second-harmonic crystal. The measurements were performed using a continuous-wave He-Ne laser and a digital camera. The experimental results show that the heat-influenced area is ~5000 times larger than the actual hole being drilled and that it reaches a steady-state condition toward the end of the processing cycle
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