Forming limit and fracture mode of microscale laser dynamic forming

Abstract

The microscale laser dynamic forming (LDF) process is a high strain rate micro-fabrication technique which uses a pulse laser to generate high pressure by vaporizing and ionizing an ablative coating, and thus produce complex 3D microstructures in thin foils. One of the most important features of this technique is ultra high strain rate (typically 106-7s−1), which is theoretically favorable for increasing formability. However, due to the lack of measurement techniques in micro-scale and submicro-scale, the formability of work pieces in LDF is hardly studied. In this article, experiments were carried out on aluminum foils to study the forming limits and fracture of thin films in LDF. The deformation depth was measured by an optical profilometer, and the formed feature was observed using focused ion beam (FIB) and scanning electron microscope (SEM). Meanwhile, a finite element model based on a modified Johnson-Cook constitutive model and Johnson-Cook failure model was developed to simulate the mechanical and fracture behavior of materials in LDF. Experimental results were used to verify the model. The verified model was used to predict forming limit diagram of aluminum foil in LDF. The forming limit diagrams show significant increase of formability compare with other metal forming processes.The microscale laser dynamic forming (LDF) process is a high strain rate micro-fabrication technique which uses a pulse laser to generate high pressure by vaporizing and ionizing an ablative coating, and thus produce complex 3D microstructures in thin foils. One of the most important features of this technique is ultra high strain rate (typically 106-7s−1), which is theoretically favorable for increasing formability. However, due to the lack of measurement techniques in micro-scale and submicro-scale, the formability of work pieces in LDF is hardly studied. In this article, experiments were carried out on aluminum foils to study the forming limits and fracture of thin films in LDF. The deformation depth was measured by an optical profilometer, and the formed feature was observed using focused ion beam (FIB) and scanning electron microscope (SEM). Meanwhile, a finite element model based on a modified Johnson-Cook constitutive model and Johnson-Cook failure model was developed to simulate the mechanical and...