In Situ Digital Image Correlation Observations of Laser Forming

Abstract

In this study experimental and modelling methods are used to examine the microstructural and bending responses of laser-formed commercially pure titanium grade 2. The in situ bending angle response is measured for different processing parameters utilizing 3D digital image correlation. The microstructural changes are observed using electron backscatter diffraction. Finite element modelling is used to analyse the heat transfer and temperature field inside the material. It has been proven that the laser bending process is not only controlled by processing parameters such as laser power and laser beam scanning speed, but also by surface absorption. Grain size appears to have no influence on the final bending angle, however, sandblasted samples showed a considerably higher final bending angle. Experimental and simulation results suggest that the laser power has a larger influence on the final bending angle than that of the laser transverse speed. The microstructure of the laser heat-affected zone consists of small refined grains at the top layer followed by large elongated grains. Deformation mechanisms such as slip and twinning were observed in the heat-affected zone, where their distribution depends on particular processing parameters.

Application of DIC Method in the Analysis of Stress Concentration and Plastic Zone Development Problems

“…These methods and their advantages and disadvantages are described in the Introduction. Considering recent possibilities of the computers and high-speed cameras with high resolution, the DIC system seems to be convenient in the application of damage detection and growth [ 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 ]. With the use of the professional DIC system, it is possible to achieve good quantitative and qualitative calculation of displacements and strains fields over the investigated surface.…”

“…The detailed description of the different algorithms applied in DIC software and the basics of the DIC technique can be found in [ 51 ]. Generally, the DIC is used for detection and characterization of the surface damage [ 50 , 52 , 53 , 54 , 55 , 56 , 57 ], performance analyses of the structural objects [ 58 , 59 , 60 , 61 ], characterization of material properties [ 62 , 63 ], and damage detection under impact loadings [ 64 , 65 , 66 ]. The precision of the method depends on the camera resolution, quality of its optics, light intensity, and others.…”

Recent Advances in the Laser Forming Process: A Review

“…The rougher surface (such as sandblasted surfaces) and thicker coating layer increase the absorptivity of the laser beam and lead to higher bending angle [7]. Microstructural observation using electron backscatter diffraction (EBSD) technique shows that the grain size does not influence the final bending angle [8]. Cement and lime are two other coatings used in experiments, and the results show that the cement coating creates more deformation and bending than the lime coating [9,10].…”

“…Steel alloys are the most common materials in published research [13][14][15][16]. Aluminum alloys, titanium, and magnesium are other common materials [4,8,[17][18][19][20][21][22][23][24][25]. The main differences of different materials types are the melting temperature, mechanical properties variation by temperature, the heat conductivity of the material, and laser beam absorption.…”

“…The slip and twinning mechanisms also can be activated in the heat-affected zone according to the processing condition. The input heat in laser forming improves the micro-hardness of the heat-affected zone in the sheet [8,15]. By increasing the thermal gradient and heat flux from a specified limit, the grains can grow, and the hardness will decrease with an increase in the grain size [19].…”