Tham khảo tài liệu 'laser welding part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 174 Laser Welding stresses are caused by external loads applied during process and discontinuity of materials on the interface Inoue and Koguchi 1997 . In our case the most important external load is represented by pressure strength Fpres used to ensure an adjustment between Laser platform and lens holder. Relaxation of accumulated stresses in the sub-assembly 1 can occur and could be accelerated by defects induced in the welded zone Inoue and Koguchi 1997 Hariprasad Sastry and Jerina . Rapid solidification processing in HAZ leads to a metastable phase formation solid solution or dispersion strengthened alloys and intermetallics and the whole physical phenomenon is at the origin of defects formation located in welded joints Hariprasad Sastry and Jerina Cheng and Wang 1996 . It has demonstrated that metallic alloys creep fatigue is related to defects rate located in welded joints considered as a metallic alloy zones Asayama 2000 . In particular a model based on molecular dynamics calculations developed by . Vazquez has discussed on isotropic and anisotropic relaxation phenomenon from simulations of lattice relaxation of metallic alloys considering the sudden appearance of vacancy or an interstitial site in the crystal Dominguez-Vazquez 1998 . This microscopic relaxation model allows highlighting macroscopic effective displacement of system responsible of relaxation phase. Experimental measurements using in particular an optical method have been also conducted to observe strains stresses and fractures of welded joints at the mesoscale level Panin and al. 1998 . This study has characterized in bulk material the accumulated stresses located in HAZ and their evolution after Laser welding process. So our interpretation of gradual optical power drift between the subassembly 1 and the pigtail can be explained by relaxation phenomenon and time evolution can be directly related to the number and the location of defects into the welded joints but also in the structure. .
