42 research outputs found
Unsaturated deformable porous media flow with phase transition
In the present paper, a continuum model is introduced for fluid flow in a
deformable porous medium, where the fluid may undergo phase transitions.
Typically, such problems arise in modeling liquid-solid phase transformations
in groundwater flows. The system of equations is derived here from the
conservation principles for mass, momentum, and energy and from the
Clausius-Duhem inequality for entropy. It couples the evolution of the
displacement in the matrix material, of the capillary pressure, of the absolute
temperature, and of the phase fraction. Mathematical results are proved under
the additional hypothesis that inertia effects and shear stresses can be
neglected. For the resulting highly nonlinear system of two PDEs, one ODE and
one ordinary differential inclusion with natural initial and boundary
conditions, existence of global in time solutions is proved by means of cut-off
techniques and suitable Moser-type estimates
Global existence of strong solutions to the one-dimensional full model for phase transitions in thermoviscoelastic materials
summary:This paper is devoted to the analysis of a one-dimensional model for phase transition phenomena in thermoviscoelastic materials. The corresponding parabolic-hyperbolic PDE system features a {\it strongly nonlinear} internal energy balance equation, governing the evolution of the absolute temperature , an evolution equation for the phase change parameter , including constraints on the phase variable, and a hyperbolic stress-strain relation for the displacement variable . The main novelty of the model is that the equations for and are coupled in such a way as to take into account the fact that the properties of the viscous and of the elastic parts influence the phase transition phenomenon in different ways. However, this brings about an elliptic degeneracy in the equation for which needs to be carefully handled. \endgraf First, we prove a global well-posedness result for the related initial-boundary value problem. Secondly, we address the long-time behavior of the solutions in a simplified situation. We prove that the -limit set of the solution trajectories is nonempty, connected and compact in a suitable topology, and that its elements solve the steady state system associated with the evolution problem
Global existence result for phase transformations with heat transfer in shape memory alloys
We consider three-dimensional models for rate-independent processes
describing materials undergoing phase transformations with heat transfer. The
problem is formulated within the framework of generalized standard solids by
the coupling of the momentum equilibrium equation and the flow rule with the
heat transfer equation. Under appropriate regularity assumptions on the initial
data, we prove the existence a global solution for this thermodynamically
consistent system, by using a fixed-point argument combined with global energy
estimates
Integrated research in constitutive modelling at elevated temperatures, part 1
Topics covered include: numerical integration techniques; thermodynamics and internal state variables; experimental lab development; comparison of models at room temperature; comparison of models at elevated temperature; and integrated software development
Laser-Assisted 3D Printing of Functional Graded Structures from Polymer Covered Nanocomposites: A Self-Review
As a method for conservation of nanoparticles with perspective properties, the three-dimensional (3D) printing is a promising technique for modeling, fabricating of functional graded structures (FGS) with nanoadditives and functional devices. The stabilization of nanoparticles in a polymeric matrix and additionally reinforced porous structure makes it possible to arrange a desired distribution of the nanoparticles in the polymer and thus to protect them from oxidation and corrosion and even to design not only the FGS but also micro/nanoelectromechanical systems (M/NEMS) devices. The synthesized nanocomposites with controlled porosity and large-specific surface may also find their application in implantation, catalysis, lab-on-chips, drug delivery systems, and 3D crystalline structures for hydrogen storage devices
CRYSTAL PLASTICITY MODELING FOR PREDICTING LOAD REVERSALS IN DUAL PHASE STEELS AND ALUMINIUM ALLOYS: APPLICATIONS TO PREDICTING SPRINGBACK BEHAVIOR
Numerical modeling of sheet metal forming is of growing interest for industry and academia. Metal forming operations often involve non-monotonic deformation paths with frequent unloading. This research explores the use of elasto-plastic self-consistent (EPSC) modeling in predicting the monotonic and load reversal deformation of aluminum alloys, and dual-phase steels. The EPSC model considers anisotropic elasticity, dislocation density-hardening, and intra granular slip system-level backstress fields in addition to accounting for inter granular stress fields; the detailed contribution of this helps in properly predicting the phenomena such as unloading non-linearity, the Bauschinger effect (BE), and changes in hardening rates during reversals. In this study the EPSC model is also linked with Finite element analysis software ABAQUS in predicting the spring back profiles in hat- shaped draw bending for various dualphase steels namely DP 780, DP 980, and DP 1180 which have various strengths based on the percentage of martensite and ferrite content
Unsaturated deformable porous media flow with phase transition
In the present paper, a continuum model is introduced for fluid flow in
a deformable porous medium, where the fluid may undergo phase transitions.
Typically, such problems arise in modeling liquid-solid phase transformations
in groundwater flows. The system of equations is derived here from the
conservation principles for mass, momentum, and energy and from the
Clausius-Duhem inequality for entropy. It couples the evolution of the
displacement in the matrix material, of the capillary pressure, of the
absolute temperature, and of the phase fraction. Mathematical results are
proved under the additional hypothesis that inertia effects and shear
stresses can be neglected. For the resulting highly nonlinear system of two
PDEs, one ODE and one ordinary differential inclusion with natural initial
and boundary conditions, existence of global in time solutions is proved by
means of cut-off techniques and suitable Moser-type estimates
Composite Structural Materials
The development and application of filamentary composite materials, is considered. Such interest is based on the possibility of using relatively brittle materials with high modulus, high strength, but low density in composites with good durability and high tolerance to damage. Fiber reinforced composite materials of this kind offer substantially improved performance and potentially lower costs for aerospace hardware. Much progress has been made since the initial developments in the mid 1960's. There were only limited applied to the primary structure of operational vehicles, mainly as aircrafts
Thermomechanische Modellierung von Formgedächtnislegierung-basierten Mikroaktuatoren
Modeling finite deformation inelasticity often involves an incompressibility constraint on the inelastic stretches, which arises from physical considerations. Regularly, this constraint is fulfilled by use of the exponential map as a geometric integrator for the evolution equations. However, in this dissertation, a new geometric integrator for the unimodularity constraint is developed and analyzed. It builds on the work of Hurtado et al. from 2014, where this projection scheme was introduced for crystal plasticity. However, to make use of this projection scheme efficiently in a finite element context, additional numerical problems have to be overcome. The work at hand aims to contribute to this aim and extend existing works for shape memory alloys. It comprises of three publications of the author and his co-authors concentrating on the modeling of materials with an incompressibility constraint. The overall goal is to implement an efficient shape memory alloy model for the simulation of cooperative bistable shape memory nanoactuators.Die Modellierung von Inelastizität unter finiten Deformationen beinhaltet häufig eine Inkompressibilitätsbeschränkung für die inelastischen Dehnungen, welche sich aus physikalischen Überlegungen ergibt. In der Regel wird diese Bedingung durch die Verwendung der Exponentialabbildung als geometrischer Integrator für die Evolutionsgleichungen exakt erfüllt. In dieser Dissertation wird jedoch ein neuer geometrischer Integrator für die Unimodularitätsbeschränkung entwickelt und analysiert. Er baut auf der Arbeit von Hurtado et al. aus dem Jahr 2014 auf, wo dieses Projektionsschema für die Kristallplastizität eingeführt wurde. Um dieses Projektionsschema in einem Finite-Elemente-Kontext effizient nutzen zu können, müssen jedoch zusätzliche numerische Probleme überwunden werden.Die vorliegende Arbeit soll dazu beitragen und bestehende Arbeiten für Formgedächtnislegierungen erweitern. Sie ist ein Zusammenschluss von drei Publikationen des Autors und seiner Mitautoren, die sich auf die Modellierung von Materialien mit einer Inkompressibilitätsbeschränkung konzentrieren. Das übergeordnete Ziel ist es, ein effizientes Modell für Formgedächtnislegierungen zur Simulation von kooperativen bistabilen Formgedächtnis-Nanoaktuatoren zu implementieren
Fatigue Behavior of ULTIMET Alloy: Experiment and Theoretical Modeling
ULTIMET® alloy is a commercial Co-26Cr-9Ni (weight percent) superalloy, which possesses excellent resistance to both wear and corrosion. In order to extend the structural applications of this alloy and improve the fundamental understanding of the fatigue damage mechanisms, stress- and strain-controlled fatigue tests were performed at various temperatures and in different environments. The stress- and strain-life data were developed for the structural design and engineering applications of this material. Fractographic studies characterized the crack-initiation and propagation behavior of the alloy. Microstructure evolution during fatigue was revealed by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Specifically, it was found that the metastable face-centered-cubic structure of this alloy in the as-received condition could be transformed into a hexagonal-closepacked structure either under the action of plastic deformation at room temperature, or due to the aging and cyclic deformation at intermediate temperatures. This interesting observation constructed a sound basis for the alloy development. The dominant mechanisms, which control the fatigue behavior of UTLIETM alloy, were characterized