Showing papers on "Material properties published in 2010"

The International Thermodynamic Equation Of Seawater 2010 (TEOS-10): Calculation and Use of Thermodynamic Properties

Abstract: This document outlines how the thermodynamic properties of seawater are evaluated using the International Thermodynamic Equation Of Seawater – 2010 (TEOS-10). This thermodynamic description of seawater is based on a Gibbs potential from which thermodynamic properties such as entropy, potential temperature, enthalpy and potential enthalpy are calculated directly. When determined from the Gibbs function, these quantities are fully consistent with each other. Entropy and enthalpy are required for an accurate description of the advection and diffusion of heat in the ocean interior and for quantifying the ocean’s role in exchanging heat with the atmosphere and with ice. The Gibbs function is a function of Absolute Salinity, temperature and pressure. In contrast to Practical Salinity, Absolute Salinity is an SI variable and it incorporates the small spatial variations of the composition of seawater in the global ocean. Absolute Salinity is the appropriate salinity variable for the accurate calculation of horizontal density gradients in the ocean. Absolute Salinity is also the appropriate salinity variable for the calculation of freshwater fluxes and for calculations involving the exchange of freshwater with the atmosphere and with ice.

Phase Equilibria and Thermodynamic Properties in the Fe-Cr System

Abstract: Phase equilibria and thermodynamic properties in the Fe-Cr system have been reviewed comprehensively based on experimental information and available computer simulations in different scales. The ev ...

Use of a Ni60Ti shape memory alloy for active jet engine chevron application: I. Thermomechanical characterization

Abstract: A shape memory alloy (SMA) with a composition of Ni60Ti40 (wt%) was chosen for the fabrication of active beam elements intended for use as cyclic actuators and incorporated into a morphing aerospace structure. The active structure is a variable-geometry chevron (VGC) designed to reduce jet engine noise in the take-off flight regime while maintaining efficiency in the cruise regime. This two-part work addresses the training, characterization and derived material properties of the new nickel-rich composition, the assessment of the actuation properties of the active beam actuator and the accurate analysis of the VGC and its subcomponents using a model calibrated from the material characterization. The characterization performed in part I of this work was intended to provide quantitative information used to predict the response of SMA beam actuators of the same composition and with the same heat treatment history. Material in the form of plates was received and ASTM standard tensile testing coupons were fabricated and tested. To fully characterize the material response as an actuator, various thermomechanical experiments were performed. Properties such as actuation strain and transformation temperatures as a function of applied stress were of primary interest. Results from differential scanning calorimetry, monotonic tensile loading and constant stress thermal loading for the as-received, untrained material are first presented. These show lower transformation temperatures, higher elastic stiffnesses (60–90 GPa) and lower recoverable transformation strains (≈1.5%) when compared to equiatomic NiTi (Nitinol). Stabilization (training) cycles were applied to the tensile specimens and characterization tests were repeated for the stable (trained) material. The effects of specimen training included the saturation of cyclically generated irrecoverable plastic strains and a broadening of the thermal transformation hysteresis. A set of final derived material properties for this stable material is provided. Finally, the actuation response of a structural beam component composed of the same material given the same thermomechanical processing conditions was assessed by applying a constant bias load and a variable bias load as thermal actuation cycles were imposed.

Numerical Analysis of Lateral Inertial Confinement Effects on Impact Test of Concrete Compressive Material Properties

Abstract: Dynamic material properties, in particular the dynamic strength, of concrete material are usually obtained by conducting laboratory tests such as drop-weight test and Split Hopkinson Pressure Bar (SHPB) test. It is commonly agreed that a few parameters associated with stress wave propagation will affect the test results, including the lateral and axial inertial effect, end friction confinement and stress wave reflection and refraction. Many different measures have been proposed to eliminate or limit the influences of these effects in dynamic tests of material properties. However, owing to the nature of dynamic loadings, especially those with high loading rates, it is very unlikely to completely eliminate these influences in physical testing. Moreover, it is also very difficult to quantify these influences from the laboratory testing data. In the present study, a refined mesoscale concrete material model is developed to simulate impact tests and to study the influences of lateral inertial confinement on co...

Material and interaction properties of selected grains and oilseeds for modeling discrete particles

Abstract: Experimental investigations of grain flow can be expensive and time consuming, but computer simulations can reduce the large effort required to evaluate the flow of grain in handling operations. Published data on material and interaction properties of selected grains and oilseeds relevant to discrete element method (DEM) modeling were reviewed. Material properties include grain kernel shape, size, and distribution; Poisson's ratio; shear modulus; and density. Interaction properties consist of coefficients of restitution, static friction, and rolling friction. Soybeans were selected as the test material for DEM simulations to validate the model fundamentals using material and interaction properties. Single- and multi-sphere soybean particle shapes, comprised of one to four overlapping spheres, were compared based on DEM simulations of bulk properties (bulk density and bulk angle of repose) and computation time. A single-sphere particle model best simulated soybean kernels in the bulk property tests. The best particle model had a particle coefficient of restitution of 0.6, particle coefficient of static friction of 0.45 for soybean-soybean contact (0.30 for soybean-steel interaction), particle coefficient of rolling friction of 0.05, normal particle size distribution with standard deviation factor of 0.4, and particle shear modulus of 1.04 MPa.

Advances of SiC-based MOS capacitor hydrogen sensors for harsh environment applications

Abstract: SiC-based hydrogen sensors have attracted much attention due to applications in harsh environments. In this paper, harsh environment is defined. Characteristics of SiC-based hydrogen sensors for harsh environment applications are reviewed. Various types of SiC-based field effect hydrogen sensor in terms of their respective history, structure, advantages and disadvantages have been discussed. SiC-based MOS capacitor hydrogen sensor will be conferred in detail. The reasons for selecting SiC in fabricating MOS capacitor hydrogen sensor for harsh environment applications are elucidated. Different hydrogen sensing mechanisms depend on the temperatures and the conditions of catalytic metal layer are highlighted. MOS capacitor SiC-based sensors fabricated by previous research groups are listed. Each catalytic electrodes and oxide layers selected have their significant properties. Examples of nanostructured materials that have been used in forming oxide layer are illustrated. The future challenges in terms of material (metal electrodes and oxide layers) properties and surface properties of materials are described. It is concluded that MOS capacitor SiC-based hydrogen sensors promote green technology.

Material characterization and residual stresses simulation during the manufacturing process of epoxy matrix composites

Abstract: A thermal, rheological and mechanical material characterization of an aeronautic epoxy resin from commercial prepreg is reported in this article. The kinetic of the crosslinking reaction of the resin is characterized and modeled. The specific heat, the glass transition temperature, the thermal expansion coefficients, the chemical shrinkage coefficients and the thermo-mechanical properties have been investigated as a function of temperature and degree of cure. Dynamic mechanical measurements are used to determine the gel point. Finally, the residual stresses developed during the curing process are calculated using a finite element simulation, taking into account the material properties evolutions according to proposed models. The results highlight the importance of the characterization accuracy and the associated models.

Multi-axial strain transfer from laminated CFRP composites to embedded Bragg sensor: I. Parametric study

Abstract: Embedded optical fibre sensors are considered in numerous applications for structural health monitoring purposes. However, since the optical fibre and the host material in which it is embedded, will have different material properties, strain in both materials will not be equal when load is applied. Therefore, the multi-axial strain transfer from the host material to the embedded sensor (optical fibre) has to be considered in detail. In the first part of this paper the strain transfer will be determined using finite element modelling of a circular isotropic glass fibre embedded first in an isotropic host and second in an anisotropic composite material. The strain transfer or relation depends on the mechanical properties of the host material and the sensor (Young's modulus and Poisson's ratio), on the lay-up of the composite material (uni-directional lay-up/cross-ply lay-up) and the position of the sensor in a certain layer. In the second part of the paper the developed strain transfer model will be evaluated for one specific lay-up and sensor type.

Thermodynamic model of hardness: Particular case of boron-rich solids

Abstract: A number of successful theoretical models of hardness have been developed recently. A thermodynamic model of hardness, which supposes the intrinsic character of correlation between hardness and thermodynamic properties of solids, allows one to predict hardness of known or even hypothetical solids from the data on Gibbs energy of atomization of the elements, which implicitly determine the energy density per chemical bonding. The only structural data needed is the coordination number of the atoms in a lattice. Using this approach, the hardness of known and hypothetical polymorphs of pure boron and a number of boron-rich solids has been calculated. The thermodynamic interpretation of the bonding energy allows one to predict the hardness as a function of thermodynamic parameters. In particular, the excellent agreement between experimental and calculated values has been observed not only for the room-temperature values of the Vickers hardness of stoichiometric compounds, but also for its temperature and concentration dependencies.

Thermodynamic properties of cementite (Fe3C)

Abstract: Cementite ( Fe 3 C ) is one of the most common phases in steel. In spite of its importance, thermodynamic investigations, either experimental or theoretical, of cementite are infrequent. In the present work, the thermodynamic properties of cementite are reevaluated and Gibbs energy functions valid from 0 K upwards presented. At high temperature (1000 K and above), the Gibbs energy is practically unchanged compared to previous evaluations. The energy of formation at 0 K was also calculated using density functional theory. This energy of formation (+8 kJ/mol at 0 K) is in reasonable agreement with the present thermodynamic evaluation (+23.5 kJ/mol at 0 K and +27.0 kJ/mol at 298.15 K) and with a solution calorimetric measurement of the enthalpy of formation (+18.8 kJ/mol at 298.15 K). In addition, the heat capacity was calculated theoretically using ab initio data combined with statistical concepts such as the quasiharmonic approximation. The theoretical calculation agrees equally well as the present evaluation with experimental data, but suggests a different weighting of the experimental data. In order to use it directly in the thermodynamic evaluation further modifications in the Fe–C system, primarily of the fcc phase, would be required in order to reproduce phase equilibrium data with sufficient accuracy.