Experimental and numerical studies of micro-scale laser bending
Abstract
Laser bending or laser forming is a newly developed, flexible technique that modifies the curvature of sheet materials by thermal residual stresses instead of external forces. This thesis project investigates high precision deformation of stainless steel and ceramic specimens with the use of a pulsed or continuous wave (CW) laser beam as the energy source. Experiments are conducted to study the bending behavior of ceramics and stainless steel due to laser irradiation. The amount of bending angle from each laser scan is correlated with various laser and processing parameters. A 2-D plane strain model and a fully 3-D model of the laser bending process are developed based on thermo-elasticity-plasticity. Numerical simulations are carried out to estimate the laser-induced temperature field, the residual stress field, and the amount of bending of the specimen. Experimental measurements and computational results are in good agreement. In pulsed laser bending, when melting and evaporation occur, the temperature and stress fields are extremely complex to compute. A numerical model is developed to compute the transient temperature and phase changes induced by pulsed laser irradiation. The enthalpy-based model tracks both the solid/liquid and liquid/vapor interfaces with the interfacial kinetic relations considered. The results agree with previous experimental work on the mechanism of material removal due to high power laser irradiation. The decrease of material's mechanical strength due to material removal by pulsed laser ablation is also investigated by tension tests on steel specimens and three-point bending tests on ceramic specimens. Experimental results show that the breaking strength of the steel specimen is not sensitive to the laser-ablated groove, while the bend strength of the ceramic specimen decreases drastically with the increasing groove depth. While the experimental studies and numerical simulations are of significance in understanding the deformation behavior of the laser bending process, more theoretical investigations on this process are needed to fully understand the complex physical phenomena involved.
Degree
Ph.D.
Advisors
Xu, Purdue University.
Subject Area
Mechanical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.