Mesh Morphing Methods for Virtual Prototyping and Mechanical Component Optimization

In this thesis, the coupling of mathematical geometry and its discretization (mesh) is performed using a method that fills the gap between simulation and design. Different modelling strategies are studied, tested and developed to bridge commercial CAD with a new methodology able to perform more accurate simulations without loosing the connection with the geometrical features. The aim of the thesis is to enhance the capabilities of Finite Element Methods (FEM) with the properties of Non-Uniform Radial Basis Functions (NURBS) inherited from CAD models in the design phase leading to a perfect representation of the model's boundary. The parametric space definition of the basis functions is borrowed from standard IGA (Isogeometric Analysis) and the possibility of process CAD models without the need for trivariate NURBS from NEFEM (NURBS Enhanced Finite Element Method). This particular combination yields to a bilinear Lagrangian basis and a new mapping between Cartesian and Parametric spaces for quadrilaterals. Using this new formulation it is possible to track the changes of the geometry and reduce the simulation's error up to 25-50% because of the perfect shape representation when compared to an equivalent FEM system. The problems presented are defined in a 2D space and solved using Matlab. NURBS are the key point to perform parametric morphing and simple optimizations while FEM remains the best way to perform simulations. This new method prevents to remodel B-Rep (Boundary Representation) parts after some simple modification due to the analysis and improves the geometry accuracy of the discretization. The geometrical file is directly imported from commercial software and processed by the method. Accuracy, convergence and seamless integration with commercial CAD packages are demonstrated applied to problems of arbitrary 2D geometry. The main problems treated are thermal analysis and solid mechanics where the better results are achieved

3D-printing of porous structures for reproduction of a femoral bone

Background: 3D-printing has shown potential in several medical advances because of its ability to create patient-specific surgical models and instruments. In fact, this technology makes it possible to acquire and study physical models that accurately reproduce patient-specific anatomy. The challenge is to apply 3D-printing to reproduce the porous structure of a bone tissue, consisting of compact bone, spongy bone and bone marrow. Methods: An interesting approach is presented here for reproducing the structure of a bone tissue of a femur by 3D-printing porous structure. Through the process of CT segmentation, the distribution of bone density was analysed. In 3D-printing, the bone density was compared with the density of infill. Results: The zone of compact bone, the zone of spongy bone and the zone of bone marrow can be recognized in the 3D printed model by a porous density additive manufacturing method. Conclusions: The application of 3D-printing to reproduce a porous structure, such as that of a bone, makes it possible to obtain physical anatomical models that likely represent the internal structure of a bone tissue. This process is low cost and easily reproduced

Production readiness assessment of low cost, multi-material, polymeric 3D printed moulds

Fused Deposition Modelling (FDM) technology allows to choose a large variety of materials and it is widely used by companies and individuals nowadays. The cost effectiveness of rapid prototyping is achievable via FDM, that makes this technology useful for research and innovation. The application of 3D printing to aid production is the most common approach. Moreover, the use of 3D printing in prototypes result in a waste of material since no reuse is considered. In the following manuscript, this technology is applied to mould fabrication by achieving a low surface roughness at a modest cost compared to conventional manufacturing methods. Moreover, the possibility to use a combination of thermoplastic materials is analysed by examination of the CAD model optimized for Additive Manufacturing (AM) from scratch and was verified using metrology tools. Several moulds were finally built and applied to the specific case study of carbon fibre laminated components. This manuscript aims to analyse the manufacturing process by comparing the mould surface geometry before and after the smoothing process. The achieved tolerance between the produced moulds is ±0.05 mm that ensures the repeatability of the process from an industrial point of view; whilst the deviation between CAD and mould is ±0.2 mm. To combine an accurate FDM process together with chemical smoothing proved to be a powerful strategy to produce high quality components that can be inserted in the production process by means of traditional manufacturing techniques. This will aid to reduce the cost of standard manufacturing for low production batches and prototypes of carbon fibre composites

Virtual Surgical Planning, 3D-Printing and Customized Bone Allograft for Acute Correction of Severe Genu Varum in Children

Complex deformities of lower limbs are frequent in children with genetic or metabolic skeletal disorders. Early correction is frequently required, but it is technically difficult and burdened by complications and recurrence. Herein, we described the case of a 7-year-old girl affected by severe bilateral genu varum due to spondyloepiphyseal dysplasia. The patient was treated by patient-specific osteotomies and customized structural wedge allograft using Virtual Surgical Planning (VSP) and 3D-printed patient-specific instrumentation (PSI). The entire process was performed through an in-hospital 3D-printing Point-of-Care (POC). VSP and 3D-printing applied to pediatric orthopedic surgery may allow personalization of corrective osteotomies and customization of structural allografts by using low-cost in-hospital POC. However, optimal and definitive alignment is rarely achieved in such severe deformities in growing skeleton through a single operation