Showing papers on "Material properties published in 1991"

Modeling 1-3 composite piezoelectrics: thickness-mode oscillations

Abstract: A simple physical model of 1-3 composite piezoelectrics is advanced for the material properties that are relevant to thickness-mode oscillations. This model is valid when the lateral spatial scale of the composite is sufficiently fine that the composite can be treated as an effective homogeneous medium. Expressions for the composite's material parameters in terms of the volume fraction of piezoelectric ceramic and the properties of the constituent piezoelectric ceramic and passive polymer are derived. A number of examples illustrate the implications of using piezocomposites in medical ultrasonic imaging transducers. While most material properties of the composite roughly interpolate between their values for pure polymer and pure ceramic, the composite's thickness-mode electromechanical coupling can exceed that of the component ceramic. This enhanced electromechanical coupling stems from partially freeing the lateral clamping of the ceramic in the composite structure. Their higher coupling and lower acoustic impedance recommend composites for medical ultrasonic imaging transducers. The model also reveals that the composite's material properties cannot be optimized simultaneously; tradeoffs must be made. Of most significance is the tradeoff between the desired lower acoustic impedance and the undesired smaller electromechanical coupling that occurs as the volume fraction of piezoceramic is reduced. >

A thermodynamic assessment of the V-N system

Abstract: A thermodynamic analysis of phase equilibria in the V-N binary system has been carried out. The thermodynamic parameters for each phase were evaluated on the available experimental data, by using thermodynamic models for the Gibbs energy. Most of the experimental information was well reproduced by the present set of thermodynamic descriptions. However, some uncertainty still attaches to the nature of the γ(fcc) phase, and the need of further experimental investigations is emphasized.

A thermodynamic evaluation of the CR-N, FE-N, MO-N and CR-MO-N systems

Abstract: A thermodynamic evaluation of the Cr-N, Fe-N, Mo-N and Cr-Mo-N systems using a two sublattice model for the solid phases and a subregular solution model for the liquid is presented. A set of parameters describing the Gibbs energies of the various phases is given, and the calculated phase diagrams are presented and compared with various types of experimental data.

The Determination of Surface Plastic and Elastic Properties by Ultra Micro-indentation

Abstract: An ultra micro-indentation system for investigating the elastic and plastic properties of surface coatings and near-surface materials is described. The instrument produces minute indentations by the application of loads to geometrically accurate pointed or spherical diamond indenters. Material properties are derived from records of the load and depth of penetration. Depth of penetration is measured with a resolution less than 1 nm. The force at initial contact can be substantially less than 0,1 mN. The instrument has a wide range of research and quality control applications which include the determination of the depth distribution of hardness and elastic modulus of hard and soft materials – TiN, gold and polymer films and coatings, for example. It also has applications in the determination of the workhardening index, in fracture mechanics and in exploring the material properties of small areas of individual phases in polyphased materials.

傾斜機能材料平板におけるラム波伝播とその衝撃応答 : 第一報,解析手法

Abstract: The numerical methods which have been proposed by the present authors for Lamb waves in an anisotropic laminated plate and its transient responses are expanded for the wave propagation analysis of functionally gradient material (FGM) plates. The material properties of the plate change gradually in the thickness direction, and are anisotropic in the plane of the plate. The plate is divided into N plate elements. In the element, we assume that the material properties change linearly in the thickness direction, and that the displacement field is expressed by second-order polynomials. The principle of virtual work is used to develop approximate dynamic equilibrium equations. The dispersion relation and the mode shape of the Lamb waves are obtained by using the free boundary conditions. The energy velocities of the Lamb waves are formulated with the aid of the Rayleigh quotient. The method of Fourier transforms in conjunction with the modal analysis is used to determine the response of displacements. The formulation of the theory is described in this paper.

Chemical properties of asphalts and their relationships to pavement performance

Abstract: key words: adhesion aging asphalt chemical mode failure models fatigue cracking imermolecular metals moisture damage oxidation pavement performance permanent deformation polarity rutting thermal cracking virgin asphalt This manual represents the views of the author only, and is not necessarily reflective of the views of the National Research Council, the views of SHRP, or SHRP's sponsor. The results reported here are not necessarily in agreement with the results of other SHRP research activities. They are reported to stimulate review and discussion within the research community.

Structure, thermodynamic properties and cooling rate of glasses

Abstract: The concepts of the thermodynamics of irreversible processes are used in order to derive expressions describing the dependence of the structure and thermodynamic properties of glasses on cooling rate. The temperature dependence of the thermodynamic potential of a frozen-in system is calculated and estimates are made for the deviation from equilibrium in vitrified melts. The theoretical results thus obtained are compared with experimental evidence on the thermodynamic properties of typical glass-forming substances and for vitreous metallic alloys. In this way basic kinetic and thermodynamic properties of the vitrification process are determined.

Thermodynamics of superconducting phases in the Y-Ba-Cu-O system

Abstract: A thermodynamic phenomenological model is presented to describe thermodynamic properties, oxygen content and ordering in solid solutions from the family of phases Y2Ba4Cu6+nO14+n. All available thermodynamic and structural data on YBa2Cu3O6+z (123) are critically evaluated with the help of this model resulting in a self-consistent set of thermodynamic functions of the 123 tetragonal (t) and orthorhombic (o) phases. This can be used for T<100 K and for all compositions. The data phase diagram of the pseudobinary system YB2Cu3O6−YBa2Cu3O7 is calculated. The orthorhombic-to-tetragonal second-order phase transition curve terminates in a tricritical point where it bifurcates into two solvus lines that encircle the low-temperature two-phase (t+o) field. Thermodynamic properties of YBa2Cu4O8 (124), Y2Ba4Cu7O14+z (247) and some other phases from the homologous series Y2Ba4Cu6+nO14+n are estimated. The phase boundaries between the superconducting phases are calculated. They are plotted on an Ellingham and compared with data from the literature. The present thermodynamic data can be readily used for computing the conditions for thermodynamic stability of superconductors in various chemical environments.

Thermodynamic properties of the Fe-Mn-V-C system

Abstract: A thermodynamic description of the Fe-Mn-V-C system has been obtained by combining the consistent thermodynamic descriptions of lower-order systems by the use of thermodynamic models for the Gibbs energy of various phases. A number of calculated diagrams which are of interest to the high-strength low-alloy (HSLA) steels are presented. Though Mn increases the solubility of VC in the austenite, the effect is found to be very small.

傾斜機能圧電平板の波動伝播特性と応答解析 : 第1報, 解析手法

Abstract: The numerical methods which have been proposed by the present authors for investigating the characteristics of waves in a functionally gradient material (FGM) plate and its transient responses are expanded for functionally gradient piezoelectric material (FGPM) plates. The material properties of the plate change gradually in the thickness direction, and are anisotropic in the plane of the plate. The plate is divided into N plate elements. The variational principle is used to derive approximate governing equations. The dispersion relation and the mode shape of the waves are obtained by using mechanical ane electrical boundary conditions. The energy velocities of the waves are formulated with the aid of the Rayleigh quotient. The method of Fourier transforms in conjunction with modal analysis is used to determine the displacement and electrostatic potential responses excited by mechanical loads and/or interdigital electrodes. The formulation of the theory is described in this paper.

Steady Thermal Stresses in a plate of Functionally Gradient Material with Temperature-Dependent properties

Abstract: A functionally gradient material which decreases thermal stresses has been developed for structural components and/or mechanical elements in fields such as nuclear, aircraft and space engineering fields. Steady-state thermal stresses in a plate made of the functionally gradient material with temperature-dependent material properties are discussed. The main theme of this subject is how to distribute the components of the materials in the functionally gradient material to decrease thermal stress. The plate of an optimally functionally gradient material was determined to decrease the steady thermal stresses.

Single wall penetration equations

Abstract: Five single plate penetration equations are compared for accuracy and effectiveness. These five equations are two well-known equations (Fish-Summers and Schmidt-Holsapple), two equations developed by the Apollo project (Rockwell and Johnson Space Center (JSC), and one recently revised from JSC (Cour-Palais). They were derived from test results, with velocities ranging up to 8 km/s. Microsoft Excel software was used to construct a spreadsheet to calculate the diameters and masses of projectiles for various velocities, varying the material properties of both projectile and target for the five single plate penetration equations. The results were plotted on diameter versus velocity graphs for ballistic and spallation limits using Cricket Graph software, for velocities ranging from 2 to 15 km/s defined for the orbital debris. First, these equations were compared to each other, then each equation was compared with various aluminum projectile densities. Finally, these equations were compared with test results performed at JSC for the Marshall Space Flight Center. These equations predict a wide variety of projectile diameters at a given velocity. Thus, it is very difficult to choose the 'right' prediction equation. The thickness of a single plate could have a large variation by choosing a different penetration equation. Even though all five equations are empirically developed with various materials, especially for aluminum alloys, one cannot be confident in the shield design with the predictions obtained by the penetration equations without verifying by tests.

Means and method for ultrasonic measurement of material properties

Abstract: The system for field measurement of texture, stress and related material properties such as formability parameters using ultrasonic velocity measurements through crystalline plate or sheet. Electromagnetic acoustic transducers are utilized to generate, transmit, and receive ultrasonic bursts through the plate at different angular orientations with respect to the plane of the plate. Two of the transducers are driven in series when generating the ultrasonic bursts. Time measurements between transmission and reception of the bursts are precisely derived and converted into velocities. Information regarding stress, texture, and other related material properties such as formability parameters can be derived from these velocity measurements. The system is adjustable to be used for both ferrous and nonferrous crystalline plate. Alteration of the types of ultrasonic waves utilized, and the methods of generating the waves allows different properties such as texture and stress to be derived.

Finite Element Analysis of Mixed-Mode Fracture of Bolted Composite Joints

Abstract: The presence of a flaw or crack near a bolt-loaded hole can significantly reduce the strength of a mechanical joint Stress intensity factors of mixed-mode cracks emanating from a bolt-loaded hole in a loaded finite composite are evaluated here using the finite element method Both a horizontal crack adjacent to the bolt and a vertical crack beneath the bolt of a mechanical joint are studied Linear elastic fracture mechanics is used, and the bolt is assumed to be rigid The contact stresses are evaluated rather than assumed Effects of friction, both clearance, geometric nonlinearity between the bolt and the composite, variations in geometry (end distance, crack length, and edge distance), and material properties are accommodated The magnitudes of the stress intensity factors are found to be highly influenced by variations in the material properties, crack length, and in-plane geometry

Determining material properties in anisotropic plates using Rayleigh's method

Abstract: Material parameters of anisotropic plates are determined. Rectangular anisotropic plates are tuned by changing the quotient between the length of the sides, so that the second and third modes of vibration, for free-free boundary conditions, degenerate into the well-known cross-shaped and ring-shaped modes, respectively. The first three modes of vibrations for these plates are determined by optical methods. The propagation of bending waves, generated by the impact of a ballistic pendulum on the plates, has also been optically studied. It is found that bending waves generated in the middle of the tuned plates will reach the boundaries of the plates simultaneously. This gives a relationship between main material parameters. Using this relation and Rayleigh's method for the first three modes of vibrations, the main material parameters for the plates, that is, the effective two Young's moduli, the shear modulus, and the Poisson's ratio, are determined.

Physically based dispersion curve feature analysis in the NDE of composites

Abstract: The oblique incidence of longitudinal waves onto a structure generates different wave modes, each one having unique physical characteristics and hence a different degree of sensitivity to the state of the material. The primary focus, thus far, has been to generate acoustical models and to confirm their integrity. In this paper, an attempt is being made to use the mechanics of plate waves with specific emphasis on solving the anomaly estimation problem for composite materials and to device inspection guidelines using a feature based analysis. Theoretical models for anomalies such as porosity, fiber volume fraction, fiber orientation defects, and hybrid ply layup effects, are all built into an effective material stiffness constants model. The results are then coupled to a generalized plate wave dispersion algorithm. Thus material properties with different anomaly content could be generated and their corresponding plate wave dispersion diagrams computed. Several new features from these dispersion curves were defined and shown to correlate quantitatively with anomaly content. The analytical studies were further supplemented with strong experimental observations, thus defining several new viable features. The promising features could improve anomaly presence prediction because they show an increased the sensitivity to subtle variations in material degradation.

Thermodynamic properties of 1,1,1,2-tetrafluoroethane (R134a) in the critical region

Abstract: A theoretically based simplified crossover model, which is capable of representing the thermodynamic properties of fluids in a large range of temperatures and densities around the critical point, is presented. The model is used to predict the thermodynamic properties of R134a in the critical region from a limited amount of available experimental information. Values for various thermodynamic properties of R134a at densities from 2 to 8 mol·L−1 and at temperatures from 365 to 450 K are presented.

A Thermodynamic Analysis of the Mn-V And Fe-Mn-V Systems

Abstract: The phase diagram and thermodynamic properties of the Mn-V and Fe-Mn-V systems are analysed by the use of thermodynamic models. Though experimental information is very limited, reasonable descriptions of the systems are obtained based on some estimation.

A thermodynamic study on the V-C and FE-V systems

Abstract: The thermodynamic data for all the phases in the V-C and Fe-V systems were optimized from experimental thermodynamic and phase equilibrium data. The calculated phase diagrams of the V-C and Fe-V systems and the Gibbs free energies of formation for the V2C and VC carbides were in good agreement with corresponding experimental data. All the thermodynamic data used in calculation of phase diagrams are presented.

Thermodynamic behavior of fluids in the supercritical region

Abstract: A procedure for constructing a thermodynamic free energy of fluids is discussed which incorporates a crossover from singular thermodynamic behavior at the critical point to regular thermodynamic behavior far away from the critical point. The, procedure is based on an approximate solution of the renormalization-group theory of critical phenomena and yields an accurate representation of the thermodynamic properties of fluids in a large range of temperatures and densities around the critical point.

Predictive Approach to Thermodynamic Properties of the Metastable Cr3C Carbide

Abstract: In thermodynamic modeling of phase diagrams it is often necessary to deal with the properties of metastable compounds, which are not known from experiments. As an illustrative example, we choose the Cr3C(oP16) carbide, which is involved in the modeling of the Me3C(oP16) (“cementite”) structure of the Fe-Cr-C system but is metastable in the Cr-C system. We discuss in detail the estimation of its thermodynamic properties, relying on regularities in bonding properties of 3d-transition metal carbides, and an account of the vibrational entropy through the so-called “entropy Debye temperature.” Our predictions are compared with values derived in thermodynamic modeling of the Fe-Cr-C phase diagram. Relying on the present results, we perform calculations of metastable phase equilibria in the Cr-C system and use them in analyzing information about Cr3C from splat-quenching experiments.

Structural Properties of a Pultruded E-Glass Fibre-Reinforced Polymeric I-Beam

Abstract: This paper reports experimental data from a number of short term laboratory test studies. The data have been used to establish and evaluate the structural properties of a small commercial pultruded E-glass/vinylester I-beam (102 by 51 by 6-4 mm). Material properties for the flange and web material were measured in tension and compression. The coupon test methods for strength and elastic modulus properties were simplified from the recommendations in standard test methods without serious loss of performance. Three-point bend tests on full sections of the I-beam demonstrated that conventional linear elastic theory formulae may be used to predict the beam deflections and critical loading for lateral-torsional buckling, provided the moduli in the formulae are those of the section. Experimental data from test studies have been used to show the measured tensile strength of the flange material may provide a good estimate for the resistance of the beam in three-point bending, providing no other failure mechanism has a lower load.

Thermodynamic properties of propane

Abstract: Experimental data on the thermodynamic properties of propane method of constructing a single equation of state and calculating tables of thermodynamic properties equations of state and tables of thermodynamic functions of propane basic numerical values and principal constants thermodynamic properties of propane on the boiling and condensation curves.