Narrow Results

In this paper, the formation energies and elastic constants of $\alpha$-Al₂O₃, MgO and AlN in both rock salt (cubic) and wurtzite (hexagonal) structures were investigated by first principles calculations. The results show that the formation energy being −17.8, −6.3, −3.06 and −3.46 eV/formula unit for $\alpha$-Al₂O₃, MgO, AlN (rock salt) and AlN (wurtzite). It suggests that in the ground state, $\alpha$-Al₂O₃ is relatively more stable than MgO and AlN. The elastic properties for a polycrystalline in the ground state were calculated with the obtained elastic constants, the elastic properties reveal the rock salt structure AlN is the hardest particles among all the inclusions, and all of these inclusions are classified as brittle materials, which is detrimental to the ductile nature of aluminum matrix. The calculated anisotropy index shows that the AlN (wurtzite) and $\alpha$-Al₂O₃ have a lower degree of anisotropy compared with MgO and AlN (rock salt). The calculated results are in good agreement with the values of experimental and other works.

This work is focused to investigate the effect of various discontinuities like cracks, inclusions and voids for an orthotropic plate, to evaluate the normalized mixed-mode stress intensity factors (NMMSIFs) by implementing the extended finite element method (XFEM) under uniaxial tensile loading though considering the various numerical examples. The NMMSIFs are investigated with the interaction of crack, single- and multi-inclusions/voids for an orthotropic plate. The effect of NMMSIFs is analyzed for an orthotropic plate with several orthotropy axis orientations by changing the position of single- and multi-inclusions/voids while aligned, above and away with respect to an edge crack of the plate and for the both side inclusions/voids aligned the center crack. It is also investigated for the effect of various shapes of inclusions/voids for an edge crack orthotropic plate under uniaxial tensile loading using XFEM.

The global reduction of CO₂ emission generated by cars is a major challenge of the 21st century. The lightweighting of automotive structures is mandatory to achieve the ambitious environmental targets. The use of high strength steels in the car design, and especially, Press Hardened Steels (PHS) with tensile strength higher than 1000MPa, is one the most cost-efficient way to help the car makers to keep excellent crash behavior on mass saving body-in-white structures. The 2nd generation of PHS recently developed at ArcelorMittal is being deployed worldwide with Usibor^®2000 and Ductibor^®1000. These new grades demonstrate that CMnB metallurgies, commonly used in hot stamping, must be optimized to offer steel solutions with suitable properties for anti-intrusion and energy absorption parts. As a key metallurgical feature of these martensitic steels, a good control of inclusions and precipitations is necessary to improve the crash ductility. Among different factors influencing the bending properties of the martensitic microstructure, the present paper focuses on the effect of cleanliness of advanced steels for press hardening. The characteristics of the particles formed in the earlier stage of the steelmaking production are linked to the final In-Use Properties of the PHS. The type of particles and its geometry, such as cubic TiN, spherical complex oxides or disk-like manganese sulfides plays a different role in the crack initiation and crack propagation mechanisms. A high density of large inclusions is to be avoided as they act as local heterogeneities in the microstructure which can be detrimental to achieve a good crash performance. Particles close to the surface are even more damaging than particles localized in mid thickness. As an indirect effect, grain size refinement induced by precipitation of micro-alloying elements (Ti, Nb, V) also contributes to the achievement of a fine martensite which is essential to obtain a PHS grade with superior crash ductility. All these aspects have been integrated in the metallurgical design of Usibor^®2000 and Ductibor^®1000 and contribute to the remarkable and robust performances of these new PHS products.