Modelling of Interfacial Problems at Various Length Scales in Polycrystalline Materials

The goal of this research project was to develop a modelling technique making it possible to simulate grain boundaries and inclusion-matrix material interfaces using numerical techniques. This is particularly of interest when investigating the effects of grain boundary sliding and decohesion of the material interfaces under hot deformation conditions. This can then be used to predict damage nucleation and growth at the grain boundaries applicable to both creep type damage and plasticity induced damage. A novel scheme was developed based on the Controlled Voronoi Poisson’s Tessellation technique (CVPT) to generate statistically equivalent microstructures based on the physical parameters of the microstructure in free cutting steel under hot forming conditions. The generated microstructure was then used to study the effect of different parameters on the global response of the material. Furthermore, this model was utilised to calibrate the crystal plasticity material model using the experimental data available for high strain rate deformation of free cutting steel at elevated temperatures. A micro-scale Representative Volume Element (RVE) was developed in which the grain boundaries and material interfaces have been represented by cohesive elements. The RVE consisting of an MnS inclusion surrounded by four austenitic grains was used to study the effect of inclusion orientation, grain orientations and the relative strength of grain boundaries and the matrix/inclusion interfaces on overall failure of the RVE. Furthermore, in the endeavour of finding the right modelling technique an extension to the conventional finite element method called XFEM proved to be capable of modelling strong and weak discontinuities independent of the FE mesh. The crystal plasticity material model was implemented in the open-source FE package OOFEM and was used to simulate interface decohesion and grain boundary motion using the XFEM technique

An Investigation into Different Power Consumption Parameters of Rushton Turbines: A Computational Survey

In the present work, the mixing process of shear thinning liquids in a six-blade Rushton turbine is studied. A finite volume based computational fluid dynamics (CFD) simulation has been carried out and the three-dimensional turbulent flow is numerically analyzed by using the Shear Stress Transport k-ω (k-ω SST) model. Shear thinning liquids were investigated and shear thinning behaviour was modelled by the Ostwald-de Waele law. The used stirred vessel has a cylindrical shape with a flat bottom and the liquid height was kept equal to the vessel diameter. Effects of the power law index and the angle of attack of the blade on power consumption have been investigated. The results show that decreasing the angle of attack from 90° to 45° not only results in an increase in the flow rate down to the bottom of the vessel, resulting in a better mixture qualification, but also reduces the power consumption of the stirring process. To verify the simulation, axial, radial and tangential velocity components were compared with other experimental data and satisfactory agreement was found

Analysis and Simulation of the Effect of Knee Structure on the Condylar Forces

The varus deformity of the femur and the tibia leads to an increase in the medial condylar force, which may result in osteoarthritis in the medial condyle, if left untreated. Through Medial Open Wedge Osteotomy for these patients, it is possible to realign the load bearing surfaces of the knee joint which can lead to the tightening of some of the ligaments between the femur and the tibia on the medial side, and it can generate an excessive force on the medial condyle. The correction angle of osteotomy determines how much force is removed from the medial condyle, due to the realignment of the joint, and how much force is exerted due to the tightening of the Medial Collateral Ligament. If the post-surgical force exerted on the medial condyle is greater than the force was before surgery, it can cause even further damage in the medial condyle. OpenSim was utilized to simulate patients with varus deformity as well as calculating the Condylar forces during the gait cycle. The objective of this research is to find the critical correction angle in varus-aligned knee joints for specific patient; the threshold of the correction angle at which the medial condylar force increases after surgery, due to ligament tightening. Medial condylar force of the knee and tension in the Lateral Collateral Ligament (LCL) and Popliteofibular Ligament (PFL) in a specific subject show that a scenario with a 76 degree Medial Proximal Tibial Angle (MPTA) corresponding to 14 degrees of deformity is a critical point beyond which the surgeon must perform an MCL release. Without releasing of MCL during High Tibial Osteotomy (HTO), increased tension in this ligament make greater force in medial condyle after the surgery

Novel modified triply periodic minimal surfaces (MTPMS) developed using genetic algorithm

The desirable properties of natural porous materials have inspired humans to design cellular materials with remarkable properties such as high energy absorption, acoustic and thermal insulation, and high specific strength structures. Triply Periodic Minimal Surface (TPMS) structures are particularly important among the architected materials. In this research, we have developed a novel approach based on a genetic algorithm for geometry modification of TPMS structures. The approach is exploited to enhance the effective thermal and mechanical properties of TPMS structures, namely Primitive, IWP, Gyroid, and GPrime. New modified TMPS structures (MTPMS) have much higher Young's modulus and thermal conductivity than their base structures, and some of them have properties very close to the upper Hashin-Shtrikman bounds. Unlike previous studies conducted to improve the properties of TPMS structures, MTPMS can be expressed by simple equations. Although MTPMS are not generally considered minimal surfaces, they nonetheless possess the desirable geometric qualities of TPMS structures, such as being smooth and splitting space into two non-intersecting and continuous domains, etc

Management of tibial nonunion and osteoarthritis using a 3D-printed titanium cone: A case report

The use of customized 3D-printed structures has been gaining popularity in non-union management, as it allows for bypassing the defect while promoting osseointegration. Additionally, porous titanium implants minimize stress shielding due to their stiffness and elastic modulus being closer to that of bone. The interconnected channels increase the surface area and provide space for cell adhesion and proliferation. This study presents the case of a 62-year-old female patient with concomitant knee osteoarthritis recalcitrant aseptic atrophic nonunion in the tibial proximal metaphysis. Due to the small distance between the nonunion site and the joint line, nonunion treatment had to be included in the treatment plan, as it would result in a lack of mechanical stability of the tibial component, and techniques such as plating were not an option. A customized 3D-printed porous titanium cone was used to bypass the fracture site and support the stem used with the CCK prosthesis, allowing for simultaneous nonunion and osteoarthritis management