1,721,515 research outputs found
Consistent derivation of the constitutive algorithm for plane stress isotropic plasticity. Part I: Theoretical formulation
No full textA derivation of the projected algorithm for general isotropic three-invariant plasticity models
under plane stress conditions is presented. It is obtained by consistently specializing the
3D formulation to the 2D subspace defined by the plane stress condition. Closed-form
intrinsic algorithm linearization and a novel expression of the consistent tangent tensor
are provided; these are also shown to directly emanate from the analogous quantities pertaining
to the fully 3D case. A detailed discussion of the proposed implementation along
with a representative set of numerical examples is provided in the second part of this paper
[Valoroso, N., Rosati, L., 2008. Consistent derivation of the constitutive algorithm for plane
stress isotropic plasticity. Part II: Computational issues. International Journal of Solids and
Structures, 46, 92–124.
Consistent derivation of the constitutive algorithm for plane stress isotropic plasticity. Part II: Computational issues
No full textThe implementation of the projected algorithm and of the consistent tangent tensor for general isotropic three-invariant elastoplastic models under plane stress conditions discussed in Part I of this paper [Valoroso, N., Rosati, L., 2008. Consistent derivation of the constitutive algorithm for plane stress isotropic plasticity. Part I: Theoretical formulation. International Journal of Solids and Structures, doi: 10.1016/j.ijsolstr.2008.08.012.] is addressed. The connections between the general three-dimensional case and the plane stress problem are analyzed in detail and an algorithmic treatment taking full advantage of the isotropic properties of the model is presented. In particular, intrinsic (matrix-free) expressions are provided for all steps of the stress computation scheme that allow one to carry out the numerical implementation in a way that is completely independent from the matrix representations. The numerical performances of the present solution scheme are evaluated through representative numerical examples
Graded damage solutions in one dimension
Full text linkA regularized damage model is considered named "Graded damage" in which the gradient enhancement has the form of an explicit bound for the spatial gradient of damage. The key features of the proposed approach are demonstrated by computing the analytical solution of two problems that are one-parameter dependent. The first one is the classical one-dimensional damageable rod under tensile load, for which the hardening function is determined based on the equivalence with a given cohesive relationship. The second application is a mode-I delamination problem for which the cohesive law for the interface is formulated starting from the graded damage concept, i.e. by prescribing the shape
of damage distribution within the cohesive process zone
Graded damage: a different view of the Thick Level Set approach
No full textIn this work we formulate a damage model by prescribing a free energy density and a dissipation potential to get the Graded damage model [2]. This is obtained by augmenting the potential energy via two scalar constraints: the first one prescribes the classical [0, 1] bounds for the damage variable whereas the second one provides the bounds for the spatial gradient of damage
A regularized interface model for simulating the response of adhesive joints
No full textA regularized interface damage model is presented grounded on the cohesive-zone concept. This is obtained using a gradient-based formulation, which is equivalent to the introduction of the laplacian of a scalar damage field into the threshold function of the corresponding local model. Unlike the classical cohesive-zone formulations, damage is driven by a non-local energy release rate and the size of the process zone is controlled by an independent model parameter. The capabilities of the proposed approach are shown via a mode-I fracture problem for an adhesive joint. Numerical results illustrate the effects of the gradient dependence against the usual cohesive zone implementation
Assemblaggi strutturali mediante incollaggio. Modellazione ed analisi del comportamento di interfaccia
No full textNegli ultimi due decenni la richiesta di strutture sempre più
efficienti e a ridotto impatto ambientale ha promosso significativamente
l’impiego dei compositi nell’Ingegneria Civile. Le
diverse realizzazioni consentono di trarre utili indicazioni sugli
aspetti da sviluppare al fine di un loro efficace utilizzo, primi
tra i quali emergono la necessità di implementare una raffinata
modellazione meccanica ed adeguati criteri di progettazione
strutturale, obiettivi raggiungibili solo a patto di garantire
la necessaria continuità tra la ricerca di base ed applicata,
lo sviluppo di metodologie di calcolo e criteri progettuali
e l’elaborazione di raccomandazioni tecniche e codici
normativi dedicat
Theoretical Aspects and Computational Issues in Plasticity and Viscoplasticity
No full textIn the present dissertation small deformation problems for elastoviscoplastic
materials are addressed, with special emphasis on the computational aspects.
Accordingly, in the presentation of the constitutive theories which will be dealt
with throughout this work, the discussion will be con ned to the mathematical
aspects of the theory which are relevant to the numerical solution of the nonlinear
boundary value problem arising in elasto- and elasto/visco- plasticity and to the
analysis of the related computational strategies
Characterization of a cohesive-zone model describing damage and de-cohesionat bonded interfaces. Sensitivity analysis and mode-I parameter identification
No full textThe identification of mode-I parameters of a cohesive-zone model for the analysis of adhesive joints is
presented. It is based on an experimental–numerical methodology whereby the optimal parameters
are obtained as the solution of a nonlinear programming problem. The data set for inverse analysis is provided
either by local kinematic data, by global static data, or a combination of the two. Parameter sensitivities
are computed via direct differentiation and identification exercises are discussed that show the
effectiveness of the procedure and its stability with respect to noise and time–space sampling
A cohesive zone model with rate-sensitivity for fast crack propagation
No full textThe subject of dynamic fracture has received increasing attention in recent years owing to its relevance in a variety
of industrial applications where crack initiation cannot be precluded. In this context design and verification of safe
crack arrest in structures is the primary risk management strategy against unwanted and possibly catastrophic events.
Tackling the problem of dynamic fracture via the classical cohesive-zone (CZ) approach requires a special care. This is
mainly due to the fact that in dynamic fracture additional dissipative mechanisms can manifest that, if not properly
accounted for, prevent from obtaining accurate numerical results. In particular, recent contributions have shown
that use of classical rate-independent CZ models to simulate dynamic fracture can produce unrealistic answers.
Conceptually this is not surprising since dynamic fracture phenomena typically occur over a quite short time scale,
whereby some form of rate-dependency at the crack tip region is expectable.
Basically, two different approaches have been used in the literature to account for this rate-dependency, that is either
by using the classical CZ model in conjunction with a rate-dependent constitution for the bulk material, either
introducing rate-sensitivity directly into the cohesive law. In the present work we introduce a basic form of rate-dependency
into the cohesive relationship initially developed in [Valoroso e Champaney, 2006] in a way to make it adjustable in run-time to
account for variations in the dissipation power with the velocity of the running crack. This requires in turn a suitable
modification of the traction-separation law in which one includes, though in a rather implicit form, also the dissipation
mechanisms that come into picture with kinetic energy
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