40,891 research outputs found
A study of volumetric contact modelling approaches in rigid tyre simulation for planetary rover application
© Inderscience Enterprises Ltd. The original source of publication is available at InderScience. Petersen, W., & McPhee, J. (2014). A study of volumetric contact modelling approaches in rigid tyre simulation for planetary rover application. International Journal of Vehicle Design, 64(2â4), 262â279. https://doi.org/10.1504/IJVD.2014.058489For planetary rover applications, a volumetric contact modelling approach is used to capture the dynamics of the rigid tyre/soil interface. The volumetric contact model allows for determining closed-form expressions for the tyre contact forces. These volumetric force representations contain information about the shape of the contact geometry so that the analytical expressions result in fast simulations. Three different volumetric rigid tyre models are developed and evaluated from a plasticity point of view. The performance of each tyre is tested and compared with respect to the resistance force caused by the ongoing compaction of the soil and the resultant plastic deformation. The quantity used to model the plastic deformation of the soil is represented by the soil rebound. Moreover, each tyre model is compared against experimental data to evaluate its validity
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A p-adaptive scheme for overcoming volumetric locking during isochoric plastic deformation
A p-adaptive scheme is developed in order to overcome volumetric locking in low order finite elements. A special adaptive scheme is used which is based on the partition of unity concept. This allows higher order polynomial terms to be added locally to the underlying finite element interpolations basis through the addition of extra degrees of freedom at existing nodes. During the adaptive process, no new nodes are added to the mesh. Volumetric locking is overcome by introducing higher order polynomial terms in regions where plastic flow occurs. The model is able to overcome volumetric locking for plane strain, axisymmetric and three-dimensional problems
Hydrostatic compression on polypropylene foam
Models currently used to simulate the impact behaviour of polymeric foam at high strain rates use data from mechanical tests. Uniaxial compression is the most common mechanical test used, but the results from this test alone are insufficient to characterise the foam response to three-dimensional stress states. A new experimental apparatus for the study of the foam behaviour under a state of hydrostatic stress is presented. A flywheel was modified to carry out compression tests at high strain rates, and a hydrostatic chamber designed to obtain the variation of stress with volumetric strain, as a function of density and deformation rate. High speed images of the sample deformation under pressure were analysed by image processing. Hydrostatic compression tests were carried out, on polypropylene foams, both quasi statically and at high strain rates. The stressâvolumetric strain response of the foam was determined for samples of foam of density from 35 to 120 kg/m3, loaded at two strain rates. The foam response under hydrostatic compression shows a non-linear elastic stage, followed by a plastic plateau and densification. These were characterised by a compressibility modulus (the slope of the initial stage), a yield stress and a tangent modulus. The foam was transversely isotropic under hydrostatic compression
An elastoplastic framework for granular materials becoming cohesive through mechanical densification. Part I - small strain formulation
Mechanical densification of granular bodies is a process in which a loose
material becomes increasingly cohesive as the applied pressure increases. A
constitutive description of this process faces the formidable problem that
granular and dense materials have completely different mechanical behaviours
(nonlinear elastic properties, yield limit, plastic flow and hardening laws),
which must both be, in a sense, included in the formulation. A treatment of
this problem is provided here, so that a new phenomenological, elastoplastic
constitutive model is formulated, calibrated by experimental data, implemented
and tested, that is capable of describing the transition between granular and
fully dense states of a given material. The formulation involves a novel use of
elastoplastic coupling to describe the dependence of cohesion and elastic
properties on the plastic strain. The treatment falls within small strain
theory, which is thought to be appropriate in several situations; however, a
generalization of the model to large strain is provided in Part II of this
paper.Comment: 42 pages, 27 figure
Thermo-micro-mechanical simulation of bulk metal forming processes
The newly proposed microstructural constitutive model for polycrystal
viscoplasticity in cold and warm regimes (Motaman and Prahl, 2019), is
implemented as a microstructural solver via user-defined material subroutine in
a finite element (FE) software. Addition of the microstructural solver to the
default thermal and mechanical solvers of a standard FE package enabled coupled
thermo-micro-mechanical or thermal-microstructural-mechanical (TMM) simulation
of cold and warm bulk metal forming processes. The microstructural solver,
which incrementally calculates the evolution of microstructural state variables
(MSVs) and their correlation to the thermal and mechanical variables, is
implemented based on the constitutive theory of isotropic
hypoelasto-viscoplastic (HEVP) finite (large) strain/deformation. The numerical
integration and algorithmic procedure of the FE implementation are explained in
detail. Then, the viability of this approach is shown for (TMM-) FE simulation
of an industrial multistep warm forging
Fluid-driven deformation of a soft granular material
Compressing a porous, fluid-filled material will drive the interstitial fluid
out of the pore space, as when squeezing water out of a kitchen sponge.
Inversely, injecting fluid into a porous material can deform the solid
structure, as when fracturing a shale for natural gas recovery. These
poromechanical interactions play an important role in geological and biological
systems across a wide range of scales, from the propagation of magma through
the Earth's mantle to the transport of fluid through living cells and tissues.
The theory of poroelasticity has been largely successful in modeling
poromechanical behavior in relatively simple systems, but this continuum theory
is fundamentally limited by our understanding of the pore-scale interactions
between the fluid and the solid, and these problems are notoriously difficult
to study in a laboratory setting. Here, we present a high-resolution
measurement of injection-driven poromechanical deformation in a system with
granular microsctructure: We inject fluid into a dense, confined monolayer of
soft particles and use particle tracking to reveal the dynamics of the
multi-scale deformation field. We find that a continuum model based on
poroelasticity theory captures certain macroscopic features of the deformation,
but the particle-scale deformation field exhibits dramatic departures from
smooth, continuum behavior. We observe particle-scale rearrangement and
hysteresis, as well as petal-like mesoscale structures that are connected to
material failure through spiral shear banding
Effects of finite strains in fully coupled 3D geomechanical simulations
Numerical modeling of geomechanical phenomena and geo-engineering problems often involves complex issues related to several
variables and corresponding coupling effects. Under certain circumstances, both soil and rock may experience a nonlinear material response
caused by, for example, plastic, viscous, or damage behavior or even a nonlinear geometric response due to large deformations or displacements of the solid. Furthermore, the presence of one or more fluids (water, oil, gas, etc.) within the skeleton must be taken into account when evaluating the interaction between the different phases of the continuum body. A multiphase three-dimensional (3D) coupled model of finite strains, suitable for dealing with solid-displacement and fluid-diffusion problems, is described for assumed elastoplastic behavior of the solid phase. Particularly, a 3D mixed finite element was implemented to fulfill stability requirements of the adopted formulation, and a permeability tensor dependent on deformation is introduced. A consolidation scenario induced by silo filling was investigated, and the effects of the adoption of finite strains are discusse
A porous crystal plasticity constitutive model for ductile deformation and failure in porous single crystals
The author thankfully acknowledges the financial support of EPSRC funding (EP/ L021714/1).Peer reviewedPostprin
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