2,442 research outputs found
Damage modelling in concrete subject to sulfate attack
In this paper, we consider the mechanical effect of the sulfate attack on concrete. The durability
analysis of concrete structures in contact to external sulfate solutions requires the definition of a proper
diffusion-reaction model, for the computation of the varying sulfate concentration and of the consequent
ettringite formation, coupled to a mechanical model for the prediction of swelling and material degradation. In
this work, we make use of a two-ions formulation of the reactive-diffusion problem and we propose a bi-phase
chemo-elastic damage model aimed to simulate the mechanical response of concrete and apt to be used in
structural analyses
A regularized damage model for structural analyses of concrete dams in the presence of alkali-silica reaction
Alkali-silica reaction is a chemical phenomenon that affects concrete structures built some decades ago and subject to a very wet environment, e.g. dams. The starting point of this work is a bi-phase damage model present in the literature. In general, finite element solutions with damage models for material having a softening behaviuor exhibit a sensitivity to the element size and do not converge to physically meaningful solutions as the mesh is refined. In literature, some regularization techniques have been proposed and the fracture energy one has been implemented in the bi-phase chemo-damage model. The limit of this approach is that the solution remains mesh-dependent, so if the mesh is refined the damage localizes in a band of width fixed by the element size. In this work the nonlocal formulation of this damage model has been developed, validated with simple examples and applied to an existing concrete gravity dam, subject to service loading and affected by the ASR. A comparison between fracture energy regularization approach and nonlocal formulation is performed
Cohesive crack approach to debonding analysis
Debonding of coatings from substrate due to coating compression occurs in many engineering applications. A
simplified analytical approach for the estimation of the ultimate coating compression leading to debonding is
developed in this paper, assuming an assigned out-of-plane defect of the coating. The formulation is based on the
solution of a beam on a Pasternak (two parameters) elastic foundation, and on the assumption of a Mode I
cohesive failure of the coating-substrate interface. The resulting formulas are simple and require the knowledge
of a limited number of parameters
Revisiting the Molecular Mechanism of Neurological Manifestations in Antiphospholipid Syndrome: Beyond Vascular Damage
Antiphospholipid syndrome (APS) is a multiorgan disease often affecting the central nervous system (CNS). Typically, neurological manifestations of APS include thrombosis of cerebral vessels leading to stroke and requiring prompt initiation of treatment with antiplatelet drugs or anticoagulant therapy. In these cases, alterations of the coagulation system at various levels caused by multiple effects of antiphospholipid antibodies (aPL) have been postulated to explain the vascular damage to the CNS in APS. However, several nonvascular neurological manifestations of APS have progressively emerged over the past years. Nonthrombotic, immune-mediated mechanisms altering physiological basal ganglia function have been recently suggested to play a central role in the pathogenesis of these manifestations that include, among others, movement disorders such as chorea and behavioral and cognitive alterations. Similar clinical manifestations have been described in other autoimmune CNS diseases such as anti-NMDAR and anti-VGCK encephalitis, suggesting that the spectrum of immune-mediated basal ganglia disorders is expanding, possibly sharing some pathophysiological mechanisms. In this review, we will focus on thrombotic and nonthrombotic neurological manifestations of APS with particular attention to immune-mediated actions of aPL on the vascular system and the basal ganglia
Two-scale asymptotic homogenization in a MEMS auxetic structure for over etch identification
The development and optimization of Micro electro-mechanical systems (MEMS) devices, due to their small size scale, require testing and precise characterization. As an example, over etch, which is the deviation between the designed masks and the effective dimensions of the suspended parts, strongly influences the performances of MEMS; therefore, to predict the correct functioning of the device its actual value must be carefully identified. In this work, we propose an efficient, time-saving tool to identify fabrication imperfections in MEMS devices. In particular, we replace the complex geometry of a MEMS mechanical filter with an equivalent homogeneous medium, whose linear-elastic effective properties are evaluated employing two-scale asymptotic homogenization and we identify the over etch by minimizing the relative error between experimental data and corresponding predictions obtained for different combinations of over etch
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