Results for "Thermodynamics" : Scipedia

Collection of Energy Science & Engineering

Energy harvesting for assistive and mobile applications

Abstract

Technology advances have enabled modification of the size and shape of the electronic components to the microscale, with commensurate scaling down of their power requirements to milliwatts and microwatt range. Consequently, many complex electronic systems and devices such as wearable [...]

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Research Reports of the International Centre for Numerical Methods in Engineering (CIMNE)

On isotropic scalar damage models for the numerical analysis of concrete structures

Abstract

Within the framework of Continuum Damage Mechanics some isotropic scalar damage models for concrete are revisited, with emphasis on a recent one proposed by the authors. This scalar damage model is based on the assumption that a stress split is required to capture unilateral behaviour [...]

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Enfoque UTE - Scientific Engineering Journal

Dried muña leaves (minthostachys mollis): Modeling, kinetics and thermodynamic properties

Abstract

The muña leaf is consumed as an infusion, it has pharmacological properties and is used to relieve digestive and respiratory symptoms. Therefore, drying is important for preservation and storage until use or processing. The objective of this research was to evaluate the influence [...]

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Papers Repository of the International Centre for Numerical Methods in Engineering (CIMNE)

A novel positive/negative projection in energy norm for the damage modeling of quasi-brittle solids

Abstract

The asymmetric tensile/compressive material behavior and microcracks closure-reopening (MCR) effects exhibited by quasi-brittle solids are of significant importance to the nonlinear responses of engineering structures under cyclic loading, e.g., earthquake excitations. Based on our previous work (Cervera et al., 1995; Faria et al., 1998; Wu et al., 2006) this work addresses a novel thermodynamically consistent unilateral damage model for concrete. In particular, the positive/negative projection (PNP) of the effective stress tensor and the additive bi-scalar damage constitutive relation are maintained owing to the conceptual simplicity and computational efficiency. It is found that the classical PNP widely adopted in the literature is not optimal for this damage model, since the resulting stiffness is not always of major symmetry. Consequently, a well-defined free energy potential does not exist in general cases and the model cannot be cast into the framework of thermodynamics with internal variables. Furthermore, the damage induced anisotropy cannot be captured, exhibiting excessive lateral deformationsunder uniaxial tension. To overcome the above issues, a novel PNP, variationally interpreted as the closest point projection of the effective stress in energy norm, is proposed with closed-form solution. With the novel PNP, the secant stiffness tensorof the proposed unilateral damage model always possesses major symmetry and exhibits orthotropic behavior under uniaxial tension and mixed tension/compression. The corresponding thermodynamics framework is then given, resulting in an energy release rate based rounded-Rankine type damage criterion appropriate for tensile failure in quasi-brittle solids. Several numerical examples of single-point verifications and benchmark tests are presented. It is demonstrated that the proposed model is capable of characterizing localized failureof concrete under proportional and non-proportional static loading, as well as the MCR effects under seismic cyclic loading.

Abstract

The asymmetric tensile/compressive material behavior and microcracks closure-reopening (MCR) effects exhibited by quasi-brittle solids [...]

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Collection of closed articles in transport research

Key findings and recommendations from the IMPACTS project

Abstract

The IMPACTS project investigated how impurities affect the design and operation of CO2 transport and storage processes. Experimental work and modelling have advanced the state of the art in the areas of how impurities in CO2 affect thermo-physical properties, fluid flow, corrosion, [...]

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Presentations and videos to 16th International Conference on Computational Plasticity (COMPLAS 2021).

New formulation of metallic materials constitutive models by an energy approach

Abstract

In a classical way the Cauchy stress tensor is expressed in function of instantaneous internal variables as the strain, the strain rate and the temperature. If good predictions of the response of materials are obtained under quasi-static loadings, inaccurate estimations are finding for some severe dynamic conditions where high plastic strain, high strain rate or temperature gradients and microstructures changes occur during the plastic flow. To describe the metals work hardening under specific loadings, the traditional laws reduce the influence of the material deformation history only through the cumulated plastic strain defined from the time integral of the generalized strain rate. From a thermodynamic point of view the material stress is rather related to the dissipated plastic strain energy responsible for any change in the material thermomechanical state. This work propose then a new formalism to define a material constitutive equation from an equivalent stress expressed as a function of the dissipated plastic deformation energy. This new approach takes into account the microstructure changes which govern a lot of the physical mechanisms responsible for plastic flows: work-hardening, dynamic softening and phase transformation. This formulation remains valid for large paths of material deformation and for all the spectrum of loading conditions: from static, transient until rapid dynamic ones. Variational energetic approaches were first mentioned by R. HILL [1] indicating that the work-hardening phenomenon depends on the plastic strain energy. Recently a new formalism introduced by M. YOSHINO et al. [2] define for a first time a named reference stress as a function of plastic strain energy. From a thermodynamics point of view a reliable energy approach must be based on the principle that any system finds its time evolution by minimizing the losses energies and minimising the generated entropy [3]. One of the main objectives of this work is to find in an energetic framework the proposed general constitutive laws [4] defining the equivalent stress as a mixture between a hardening and a saturation term via the material fraction undergoing dynamic softening (recovery, recrystallization or phase transformation) described by an Avrami law expressed in terms of plastic strain. Firstly will be finding the energetic form of the usual hardening formulations proving the equivalency between the new formulation and the traditional ones. The obtained new constitutive model will be discussed comparing to a numerical implementation on the incremental elastic-plastic Prandtl-Reuss equations resolution. References: [1] R. Hill, The Mathematical theory of plasticity, Oxford, The Clarendon Press, (1950). [2] M. Yoshino et T. Shirakashi, Flow-stress equation including effects of strain-rate and temperature history, Int. J. Mech. Sci., 39 (12) :1345-1362 (1997). [3] A. Bejan, Advanced Engineering Thermodynamics, 2nd ed. Wiley, New York, (1997). [4] A. Gavrus, Constitutive equation for description of metallic materials behavior during static and dynamic loadings taking into account important gradients of plastic deformation, Key Engineering Materials, 504-506:697–702 (2012).

Abstract

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Presentations and videos to 16th International Conference on Computational Plasticity (COMPLAS 2021).

Numerical investigation of load sequence effect and energy dissipation in concrete due to compressive fatigue loading using the new microplane fatigue model MS1

Abstract

Modeling the fatigue behavior of concrete is a challenging task that has attracted the interest of researchers during the last decades. A new formulation of a microplane fatigue model denoted as MS1 introduced by the authors is employed. It aims to capture the basic inelastic mechanisms [...]

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XV International Conference on Durability of Building Materials and Components (DBMC 2020)

Thermodynamic Processes in Nanostructured Thermocoatings

Abstract

In the 21st century, global climate change and the high level of fossil energy consumption have introduced changes affecting all sectors of the economy, including the building industry. This process has prompted EU members to create strict regulations in building energetics. It has [...]

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