Abstract

Metal cutting or machining is a process in which a thin layer or metal, the chip, is
removed by a wedge-shaped tool from a large body. Metal cutting processes are
present in big industries (automotive, aerospace, home appliance, etc.) that
manufacture big products, but also high tech industries where small piece but
high precision is needed. The importance of machining is such that, it is the
most common manufacturing processes for producing parts and obtaining
specified geometrical dimensions and surface finish, its cost represent 15% of
the value of all manufactured products in all industrialized countries.
Cutting is a complex physical phenomena in which friction, adiabatic shear
bands, excessive heating, large strains and high rate strains are present. Tool
geometry, rake angle and cutting speed play an important role in chip
morphology, cutting forces, energy consumption and tool wear.
The study of metal cutting is difficult from an experimental point of view,
because of the high speed at which it takes place under industrial machining
conditions (experiments are difficult to carry out), the small scale of the
phenomena which are to be observed, the continuous development of tool and
workpiece materials and the continuous development of tool geometries, among
others reasons.
Simulation of machining processes in which the workpiece material is highly
deformed on metal cutting is a major challenge of the finite element method
(FEM). The principal problem in using a conventional FE model with
langrangian mesh is mesh distortion in the high deformation. Traditional
Langrangian approaches such as FEM cannot resolve the large deformations
very well. Element distortion has been always matter of concern which limited
the analysis to incipient chip formation in some studies. Instead, FEM with an
Eulerian formulation require the knowledge of the chip geometry in advance,
which, undoubtedly, restricts the range of cutting conditions capable of being
analyzed. Furthermore serrated and discontinuous chip formation cannot be
simulated.

The main objective of this work is precisely to contribute to solve some of the
problems described above through the extension of the Particle Finite
Element Method (PFEM) to thermo-mechanical problems in solid mechanics
which involve large strains and rotations, multiple contacts and generation of
new surfaces, with the main focus in the numerical simulation of metal cutting
process. In this work, we exploit the particle and lagrangian nature of PFEM and
the advantages of finite element discretization to simulate the different chip
shapes (continuous and serrated) that appear when cutting materials like steel
and titanium at different cutting speeds. The new ingredients of PFEM are
focused on the insertion and remotion of particles, the use of constrained
Delaunay triangulation and a novel transfer operator of the internal variables.

The remotion and insertion of particles circumvents the difficulties associated to
element distortion, allowing the separation of chip and workpiece without using
a physical or geometrical criterion. The constrained Delaunay improves mass
conservation and the chip shape through the simulation, and the transfer allows
us to minimize the error due to numerical diffusion.

Abstract

Living biological tissues are complex structures that have the capacity of evolving
in response to external loads and environmental stimuli. The adequate modelling
of soft biological tissue behaviour is a key issue in successfully reproducing
biomechanical problems through computational analysis.
This study presents a general constitutive formulation capable of representing
the behaviour of these tissues through finite element simulation. It is based on
phenomenological models that, used in combination with the generalized mixing
theory, can numerically reproduce a wide range of material behaviours.
First, the passive behaviour of tissues is characterized by means of hyperelastic
and finite-strain damage models. A generalized damage model is proposed,
providing a flexible and versatile formulation that can reproduce a wide range of
tissue behaviour. It can be particularized to any hyperelastic model and requires
identifying only two material parameters. Then, the use of these constitutive
models with generalized mixing theory in a nite strain framework is described
and tools to account for the anisotropic behaviour of tissues are put forth.
The active behaviour of tissues is characterized through constitutive models
capable of reproducing the growth and remodelling phenomena. These are built
on the hyperelastic and damage formulations described above and, thus, represent
the active extension of the passive tissue behaviour. A growth model considering
biological availability is used and extended to include directional growth. In addition,
a novel constitutive model for homeostatic-driven turnover remodelling is
presented and discussed. This model captures the stiffness recovery that occurs
in healing tissues, understood as a recovery or reversal of damage in the tissue,
which is driven by both mechanical and biochemical stimuli.
Finally, the issue of correctly identifying the material parameters for computational
modelling is addressed. An inverse method using optimization techniques
is developed to facilitate the identification of these parameters.

Abstract

This work is about the development of a general algorithm for the numerical solution of flow equations: the Navier-Stokes set. This set of differential equations models the time dependent behavior of fluids. It is formed by continuity, linear momentum and an energy transport equations. The algorithm here described is a general one since it can handle equally a great variety of problems, ranging from incompressible to compressible flows, viscous to inviscid, stationary and transient, all of them phisically modeled by the same set of differential equations.

In the present work, a quest for a general algorithm is described, following one of many possible ways to tackle the problem. In general, this is done extending methods either from compressible to incompressible flows or from incompressible to compressible ones.

Abstract

In this paper some results of a wide experimental program are presented and compared with some finite element solution of sheet metal forming problems using a viscous shell formulation.

Abstract

Generally, the effects of suction in fine sands can be evidenced by a stiffening of the material, as the capillary front advances in the granular skeleton. In geotechnical retention structures this effect can be translated in an increasing of earth pressure, which is not normally considered in geotechnical designs. This study analyzes the capillary effects by implementing a physical modelling in centrifuge and a numerical simulation, using different constitutive models that involve suction within the analysis. The modelling is based on a structure of retention in sheetpiles built on a real scale. Some factors that affect both physical and numerical modelling were taken into account and should be considered in the analysis of the results obtained and, in the comparisons, carried out by both methodologies. As a point of interest, numerical modelling showed less dispersion in the results obtained than physical modelling, these and other aspects are analyzed in the document