Search results for "plasticity"

The multiple slope discontinuity beam element for nonlinear analysis of RC framed structures

2018

The seismic nonlinear response of reinforced concrete structures permits to identify critical zones of an existing structure and to better plan its rehabilitation process. It is obtained by performing finite element analysis using numerical models classifiable into two categories: lumped plasticity models and distributed plasticity models. The present work is devoted to the implementation, in a finite element environment, of an elastoplastic Euler–Bernoulli beam element showing possible slope discontinuities at any position along the beam span, in the framework of a modified lumped plasticity. The differential equation of an Euler–Bernoulli beam element under static loads in presence of mul…

An energy residual-based approach to gradient effects within the mechanics of generalized continua

2012

AbstractGeneralized continua exhibiting gradient effects are addressed through a method grounded on the energy residual (ER)-based gradient theory by the first author and coworkers. A main tool of this theory is the Clausius-Duhem inequality cast in a form differing from the classical one only by a nonstandard extra term, the (nonlocality) ER, required to satisfy the insulation condition (its global value has to vanish or to take a known value). The ER carries in the nonlocality features of the mechanical problem through a strain-like rate field, being the specific nonlocality source, and a concomitant higher-order long-range stress (or microstress) field. The thermodynamic restrictions on …

From Structure to Behavior: Circuit Specificity of Stress-Induced Synaptic Plasticity in the Basolateral Amygdala Projection Neurons

2019

The build-up and relaxation of stresses in a glass-forming soft-sphere mixture under shear: A computer simulation study

2009

Molecular-dynamics computer simulations in conjunction with Lees-Edwards boundary conditions are used to investigate a glass-forming binary Yukawa fluid under shear. The transition from the elastic response to plastic flow is elucidated by studying the stress relaxation after switching off the shear. We find a slow stress relaxation starting from states in the elastic regime and a fast one starting from states in the plastic-flow regime. We show that these relaxation patterns are related to a different distribution of local microscopic stresses in both cases.

Equilibrium/steady-state concept in phytoplankton ecology

2003

This paper summarises the outcomes of the 13th Workshop of the International Association of Phytoplankton Taxonomy and Ecology (IAP). The authors mostly addressed their contributions on the following topics: the effect of trophic state on the attainment of a steady-state; the establishment of equilibria in deep and shallow lakes; the role of spatial heterogeneity, disturbance, and stress in the establishment of equilibrium assemblages; the mechanisms leading to the steady state; the frequency and longevity of equilibrium phases, and the role of morphological and physiological plasticity of phytoplankton in maintaining the (apparently) same populations under different environmental condition…

Metaplasticity of horizontal connections in the vicinity of focal laser lesions in rat visual cortex

2010

Focal cortical injuries are accompanied by a reorganization of the adjacent neuronal networks. An increased synaptic plasticity has been suggested to mediate, at least in part, this functional reorganization. Previous studies showed an increased long-term potentiation (LTP) at synapses formed by ascending fibres projecting onto layers 2/3 pyramidal cells following lesions in rat visual cortex. This could be important to establish new functional connections within a vertical cortical column. Importantly, horizontal intracortical connections constitute an optimal substrate to mediate the functional reorganization across different cortical columns. However, so far little is known about their p…

Presynaptic CB1 Receptors Regulate Synaptic Plasticity at Cerebellar Parallel Fiber Synapses

2011

Endocannabinoids are potent regulators of synaptic strength. They are generally thought to modify neurotransmitter release through retrograde activation of presynaptic type 1 cannabinoid receptors (CB1Rs). In the cerebellar cortex, CB1Rs regulate several forms of synaptic plasticity at synapses onto Purkinje cells, including presynaptically expressed short-term plasticity and, somewhat paradoxically, a postsynaptic form of long-term depression (LTD). Here we have generated mice in which CB1Rs were selectively eliminated from cerebellar granule cells, whose axons form parallel fibers. We find that in these mice, endocannabinoid-dependent short-term plasticity is eliminated at parallel fiber…

A unified approach to quasi-static shakedown problems for elastic-plastic solids with piecewise linear yield surface

1978

The paper concerns shakedown analysis of elastic-plastic bodies subjected to quasi-statically varying loads within a given domain. Using a perturbation method, a general inequality is given, from which, by simply specializing the perturbing terms, the generalized Melan theorem as well as bounds on various deformation parameters (such as displacements or plastic strain intensities) are derived. The solution of the «perturbed» shakedown problem in finite or holonimic terms permits the bound to be the most stringent and expressible in «local» terms instead of integral terms. A simple application concludes the paper.

Shakedown of Structures Subjected to Dynamic External Actions and Related Bounding Techniques

2002

The shakedown theory for dynamic external actions is expounded considering elastic-plastic internal-variable material models endowed with hardening saturation surface and assuming small displacements and strains as long with negligible effects of temperature variations on material data. Two sorts of dynamic shakedown theories are presented, i.e.: i) Unrestricted dynamic shakedown, in which the structure is subjected to (unknown) sequences of short-duration excitations belonging to a known excitation domain, with no-load no-motion time periods in between and for which a unified framework with quasi-static shakedown is presented; and ii) Restricted dynamic shakedown, in which the structure is…

Modeling of the Plastic Characteristics of AA6082 for the Friction Stir Welding Process

2015

Focus of this paper is to model the plastic forming behavior of AA6082, in order to develop the numerical FE analysis of the friction stir welding processes and the simulation of subsequent forming processes. During the friction stir welding process, the temperatures reached are until 500 °C and have a fundamental role for the correct performance of the process so the material data has to show a temperature dependency. Because of the tool rotation a strain rate sensitivity of the material has to be respected as well. In this context, the general material characteristics of AA6082 were first identified for different stress states. For the uniaxial state the standard PuD-Al used in the automo…