Aktuella disputationer
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Här visas endast kommande disputationer som är publicerade i DiVA.
Faezeh Javadzadeh Kalahroudi
Materialteknik
Institutionen för ingenjörsvetenskap och fysik (from 2013)
Licentiatavhandling, sammanläggning
Datum: 2024-04-12
Tid: 09:00
Plats: Sjöströmsalen, 1B305, Karlstads universitet, Karlstad
Abstrakt
Near-net shape manufacturing using powder metallurgy (PM) and hot isostatic pressing (HIP) can serve as an efficient manufacturing process to produce high-performance alloys. Among the variety of engineering alloys, Nickel-based superalloys and tool steels stand out as well-known high-performance alloys, widely employed across diverse industries. PM-HIP technology can successfully address conventional manufacturing challenges associated with highly alloyed materials, such as segregation during the casting process or cracks during hot working processes of Ni-based superalloys, and carbide segregation and the formation of large and irregularly shaped carbides in wrought and hot rolled tool steels. However, the presence of precipitates on prior particle boundaries in Ni-based superalloys, and metallurgical defects like non-metallic inclusions in both alloys, may affect the fatigue performance of these PM-HIPed products.
The present study aims to assess two PM-HIPed alloys, namely Inconel 625 and high-nitrogen tool steel, with a comprehensive examination of their microstructure and fatigue properties. The objectives include examining the microstructural features introduced by the PM-HIP process and understanding how they influence fatigue failure mechanisms in these alloys.
Surendra Nepal
Matematik
Institutionen för matematik och datavetenskap (from 2013)
Doktorsavhandling, sammanläggning
Datum: 2024-04-16
Tid: 13:15
Plats: Eva Eriksson lecture hall, 21A342, Karlstad
Abstrakt
Understanding the transport of diffusants into rubber plays an important role in forecasting the material's durability. In this regard, we study different models, conduct numerical analysis, and present simulation results that predict the evolution of diffusant penetration fronts. We employ a moving-boundary approach to model this phenomenon, utilizing a numerical scheme based on the Galerkin finite element method combined with the backward time discretization, to approximate the diffusant profile and the position of the penetration front. Both semi-discrete and fully discrete approximations are analyzed, demonstrating good agreement between numerical and theoretical convergence rates. Numerically approximated diffusants penetration front recovers well the experimental data. We introduce a random walk algorithm as an alternative tool to the finite element method, showing comparable results to the finite element approximation. In a multi-dimensional scenario, we consider a strongly coupled elliptic-parabolic two-scale system with nonlinear dispersion, describing the particle transport in a porous medium. We present two numerical schemes and compare them based on computational time and approximation errors. A precomputing strategy significantly improves computational efficiency.
Vishnu Raveendran
Matematik
Institutionen för matematik och datavetenskap (from 2013)
Scaling effects and homogenization of reaction-diffusion problems with nonlinear drift
Doktorsavhandling, sammanläggning
Datum: 2024-04-18
Tid: 13:15
Plats: Sjöström lecture hall, 1B309, Karlstads universitet, Karlstad
Abstrakt
We study the homogenization of reaction-diffusion problems with nonlinear drift. The microscopic model is derived as the hydrodynamic limit of a totally asymmetric simple exclusion process of interacting particles. We first look into a situation when the interacting particles cross a thin composite layer. To understand the effective transmission condition, we perform the homogenization and dimension reduction of the model with variable scalings. One physically interesting scaling that we look at separately is when the drift is large. In this case, we consider the overall process taking place in an unbounded porous media. We first upscale the model using the asymptotic expansions with drift. Then, using two-scale convergence with drift, we rigorously derive the homogenization limit for a similar microscopic problem with a nonlinear boundary condition. Additionally, we show the strong convergence of the corrector function. In the large drift case, the resulting upscaled model is a nonlinear reaction-dispersion equation strongly coupled with a system of nonlinear elliptic cell problems. We study the solvability of a similar strongly coupled two-scale system with nonlinear dispersion by constructing an iterative scheme. Finally, we illustrate the behavior of the solution using the iterative scheme.