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Underwater Explosion (UNDEX) due to terrorism or accidental incident affects the people and structures causing irreparable loss of life and damage to survivability of the structure. These blast loading due to the explosion is challenging both the civilian and military structures. In order to minimize the effect on the structure, we need to understand the mechanics and the response of the structure submitted to blast loading. After a review of existing methods to simulate the response of a steel and composite structure submitted to dynamic pressure waves, the focus will be on the analysis of naval steel and composite structures when they are submitted to the primary shock wave generated from the underwater explosions. Finite element numerical simulations will be carried out to simulate the dynamic response of a non-stiffened immersed cylindrical shell submitted to such pressure loading. The pressure loading on the structure as a kinetic energy, which is transmitted by the shock wave is calculated from the explosion parameters by using analytical formulation. The assessment of the dynamic response and the fluid structure interaction was performed with explicit finite element solver LS-DYNA. Sensitivity analyses of the response to different parameters like shock factor, treatment of the fluid domain, Anisotropy of material will also be performed

LS-DYNA, Steel Cylinder, Composite Structure, Finite element analysis, fluid structure interaction, UNDEX. --- Ingénierie, informatique & technologie > Ingénierie civile

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Craniomaxillofacial surgery is the field of medical sciences that reconstructs the faces of patients who have had, for example, a car accident or bone cancer. This type of surgery mainly consists of the implantation of a graft to allow the rehabilitation and restoration of the shape and the function of the injured bone region. The current treatments, such as autografts, allografts or alloplastic grafts, present some disadvantages that can have severe consequences for the patient. Cerhum, a company focused on ceramic 3D printing, proposes an implant that overcomes some of these disadvantages: a 3D printed bioceramic bone graft. The ceramic used, which is mainly composed of hydroxyapatite, allows excellent biocompatibility. In addition to its supporting role, the microstructure must have a geometry that guides and stimulates bone regeneration in the implant. 

The main aim of this research work is to study in silico the influence of different microstructures on the mechanical support performance of the implant. In order to fulfil their role as a guide and stimulus for the bone regeneration process, the microstructures must exhibit several geometrical characteristics, such as a pronounced tortuosity. The different architectures selected are Orthogonal unit cells, TPMS (Triply Periodic Minimal Surface) unit cells (Primitive, Gyroid and Diamond) and Isometric TPMS unit cells (Isometric Gyroid and Isometric Diamond). These microstructures are numerically modelled in scaffolds with four cell repetitions in all three directions. For a given architecture, several scaffolds are built with different porosity percentages. Finite Element (FE) analysis in compression, under the assumption of a quasi-static state, are performed on these models. From this FE analysis, Young's moduli in compression of the different structures are compared. 

The two main characteristics affecting the elastic mechanical performance of a structure are its architecture and its porosity rate. Young's modulus decreases when the porosity rate increases. The results of this research work suggest that, in the 35-85\% porosity range, Diamond cells present a higher elastic modulus than Orthogonal and other TPMS structures. However, Gyroid scaffolds have Young's moduli in the same order as the bone, unlike Primitive and Diamond. Regarding structures made of Isometric TPMS cells, Diamond and Isometric Diamond have similar Young's moduli in compression. While Isometric Gyroid cells offer higher elastic strength than Gyroid cells. 

The second part of this research work focuses on scaffolds made of Primitive, Gyroid and Diamond cells including a porosity gradient within the structure. Indeed, as in natural bone, the implant shell is made of a compact structure, i.e. with low porosity, while the interior is spongy, i.e. with higher porosity. The region linking them present a porosity gradient. This study suggests that inserting a porosity gradient weakens the structures. Moreover, regarding the Young's modulus, the sensitivity to porosity gradient is less significant for Gyroid cells than Diamond and Primitive cells.

In conclusion, microstructures made of Gyroid cells are the more interesting. Their Young's moduli are matching the native bone one which leads to better implant osseointegration. Their high mechanical resistance remains when explored to porosity gradients.

Graft --- Implant --- Bioceramics --- Microstructure --- Triply Periodic Minimal Surface (TPMS) --- Porosity gradient --- Scaffold --- In silico study --- Young's modulus --- Modelling --- Compression simulation --- Finite element analysis --- Ingénierie, informatique & technologie > Multidisciplinaire, généralités & autres