Fabrication of polymeric microchannels with focused and defocused CO2 lasers

 The control of energy distribution or energy intensity inside a laser spot using a defocusing method enables the formation of high-quality microchannels of multiple cross-sections in polycarbonate. Moreover, a thermal mathematical model of the process was developed to aid understanding of the process and to allow channel topology prediction.

Modelling of laser beam spot-weld using 2-D hybrid crack finite elements

Laser beam spot-welding is widely applied to join sheet metals for automotive components especially for thinsheet components in automotive industries. The spot welds in such metallic structures contribute a lot to the integrated strength and fatigue life for the whole structures and they are responsible for their damage or collapse in some loading cases. In this paper, the 2-D hybrid special finite elements each containing an edge crack are employed to study the fracture behaviors of laser beam spot-welds. Hence the calculation accuracy in the vicinity of crack tips is ensured, and a better description of stress singularity with only one hybrid element surrounding one crack is provided. The numerical modeling for laser beam spot-welds subjected to three typical modes ofloadings including tension-lap, shear-lap and angle-clip can be greatly simplified with the applications of such elements. Three specimens under lap-shear, lap-tension and angle clip are devised and analyzed respectively, and main fracture parameters such as stress intensity factors and the initial direction of crack growth are obtained through tinite element analyses. The computed results ti'om numerical examples demonstrate the validity and versatility of the proposed modeling.