Evaluation of the Structural Integrity of Laser Formed Steel Sheets for Possible Load Bearing Applications
S.A. Akinlabi and M. Shukla
This paper reports on the evaluation of the structural integrity of laser formed steel sheets for possible load carrying applications. The tensile tests conducted revealed 46.000% elongation while the yield strength of the laser formed components were enhanced with about 18.00%. Furthermore, elongated grain structures were observed in the micrographs of the three components formed at the maximum parameter setting. It was revealed that this elongation varied indirectly to the applied line energy. The measured grain sizes further showed that the components formed at the optimized maximum process parameter window were characterized by smaller grain structures with about 60.00% of the grain sizes of the parent material. A progressive increase in the Vickers microhardness of about 40.000% was also observed in the three laser formed components in comparison to the parent material. The analysis of the residual stresses conducted in this study revealed that the changes in the residual stresses are a function of the process condition to which the samples were subjected. In the case of the parent material, the residual stresses across the three measured points were compressive. Similarly, the observed differences in the tensile stresses between the three samples formed at the different parameters can be attributed to the effect of the flow stress, the temperature and the cooling rate. The consistently high value of the stress at a particular point designated as Point 2 can be attributed to the highest temperature recorded at this point, because this is the point where the whole process cycle ends having a high energy density. Looking closely at the stress values captured at the three points, theoretically Point 2 is believed to be the point of maximum deformation; hence, the maximum strain results. At low scan velocity and low temperature, the flow stress associated is high. Therefore, the stress is higher than those at higher velocity. But on the other hand, at high temperatures, the associated flow stress becomes low. It can be summarized that the material characterization and the evaluations conducted on the formed samples revealed the inherent structural integrities.
Keywords: Nd:YAG laser, mild steel, laser forming, structural integrity, microstructure, residual stress