Full Set Of Material Constants Research Articles

Ferroelectric, elastic, piezoelectric, and dielectric properties of Ba(Ti0.7Zr0.3)O3-x(Ba0.82Ca0.18)TiO3 Pb-free ceramics

We designed and synthesized a pseudo-binary Pb-free system, Ba(Ti0.7Zr0.3)O3-x(Ba0.82Ca0.18)TiO3, by combining a rhombohedral end (with only cubic to rhombohedral ferroelectric phase transition) and a tetragonal end (with only cubic to tetragonal ferroelectric phase transition). The established composition-temperature phase diagram is characterized by a tricritical point type morphotropic phase boundary (MPB), and the MPB composition has better ferroelectric, piezoelectric, and dielectric properties than the compositions deviating from MPB. Moreover, a full set of material constants (including elastic stiffness constants, elastic compliance constants, piezoelectric constants, dielectric constants, and electromechanical coupling factors) of the MPB composition are determined using a resonance method. The good piezoelectric performance of the MPB composition can be ascribed to the high dielectric constants, elastic softening, and large electromechanical coupling factor.

Validity evaluation of ScxAl1−xN material constants based on SAW characteristics

This paper is aimed at examining the validity of material constants reported for use in surface acoustic wave (SAW) device simulations. First, based on the full set of material constants calculated by first principle, bulk acoustic wave velocities are calculated for ScxAl1−xN and compared with published experimental results. Then, the effects of the ScxAl1−xN material constants with different Sc content on acoustic characteristics are calculated and the influence of shear vibrations on SAW characteristics are recognized. Then, a series of SAW devices are fabricated on ScxAl1−xN film/Si substrate structure with various Cu and ScAlN thicknesses hCu and hScAlN, respectively, and measured variations of phase velocity V and effective electromechanical coupling factor with these parameters are compared with the calculation. The fairly well-agreed results indicate a reliable set of ScxAl1−xN material constants for SAW device simulations.

Determination of full matrix material constants of [111]c poled Mn doped 0.24Pb(In1/2Nb1/2)O3-0.46Pb (Mg1/3Nb2/3)O3-0.30PbTiO3 single-domain single crystal using one sample

To date, there is no report in the literature regarding the full set of material constants of single crystals with 3m symmetries using less than 5 samples. Multiple samples make the data self-consistency difficult due to sample to sample variations, which is severe in ferroelectric materials because the poling depends strongly on the sample geometry. To eliminate errors caused by property variation from sample to sample, a combined ultrasonic and inverse impedance spectroscopy characterization method has been developed, which only needs one small sample to get all constants. The method has been used to determine full matrix material constants of [111]c poled Mn doped 0.24Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 single crystals. The validity of this method has been verified by comparing the results with those determined by the traditional resonance method using 5 different geometry samples, and the method was proved stable with input data variation within ±10%.

Material characterisation and finite element modelling of cyclic plasticity behaviour for 304 stainless steel using a crystal plasticity model

Low cycle fatigue tests were carried out for a 304 stainless steel at room temperature. A series of experimental characterisations, including SEM, TEM, and XRD were conducted for the 304 stainless steel to facilitate the understanding of the mechanical responses and microstructural behaviour of the material under cyclic loading including nanostructure, crystal structure and the fractured surface. The crystal plasticity finite element method (CPFEM) is a powerful tool for studying the microstructure influence on the cyclic plasticity behaviour. This method was incorporated into the commercially available software ABAQUS by coding a UMAT user subroutine. Based on the results of fatigue tests and material characterisation, the full set of material constants for the crystal plasticity model was determined. The CPFEM framework used in this paper can be used to predict the crack initiation sites based on the local accumulated plastic deformation and local plastic dissipation energy criterion, but with limitation in predicting the crack initiation caused by precipitates.

Full set of material constants of (Na0.5K0.5)NbO3–BaZrO3–(Bi0.5Li0.5)TiO3 lead-free piezoelectric ceramics at the morphotropic phase boundary

The perovskite solid solution system of (1−x−y)(Na0.5K0.5)NbO3–xBaZrO3–y(Bi0.5Li0.5)TiO3 (BZ/BLT/NKN) is a new family of lead-free piezoelectric material. Compositions near the morphotropic phase boundary (MPB) (x = 0.06, y = 0.02) have been reported to have good piezoelectric coefficients with the moderate Curie temperature. In this work, the full set of material constants for the MPB composition of BZ/BLT/NKN solid solution was characterized using the resonance method. ε33T, tanδ, d31, d33, d15, Qm and TC are 2496, 0.025, −159 pC/N, 321 pC/N, 602 pC/N, 44 and 256 °C, respectively. The piezoelectric properties are not only superior to those of other (Na,K)NbO3-based ceramics at room temperature, but also relatively stable against temperature up to 200 °C. These results show that BZ/BLT/NKN solid solution is a promising candidate for practical piezoelectric applications in actuating and sensing fields.

On the Determination of Material Creep Constants Using Miniature Creep Test Specimens

Full size creep test specimens, i.e., conventional uniaxial creep test specimen and Bridgman notch specimens are usually used to determine the full set of material constants for any creep model. However, in many situations, sufficient material is not available for theses specimens to be manufactured from it. Therefore, small creep test specimens have been introduced and used to determine (i) creep constants and (ii) the remaining life time for engineering components. Two commonly used small creep specimen types, i.e., the impression and the small ring creep tests, are used in this paper to determine the steady state creep constants. However, these specimen types are limited for use in determining the secondary creep properties, i.e., they are unable to determine the full set of material creep constants for creep damage models. In this paper the recently developed small two-bar creep test specimen and the newly developed small notched specimen test are described and used to determine a full set of material constants for Kachanov and Liu-Murakami creep damage models. The small notched specimen manufacturing, loading and testing procedures are described in this paper. P91 steel at 600 °C and (Bar-257) P91 steel at 650 °C have been used to compare the material constants obtained from the small two-bar and the small notched creep test specimens with those obtained from the conventional uniaxial creep test specimens and Bridgman notch specimens. The results show remarkably good agreement between the two sets of results.

Assessment of langatate material constants and temperature coefficients using SAW delay line measurements

This paper reports on the assessment of langatate (LGT) acoustic material constants and temperature coefficients by surface acoustic wave (SAW) delay line measurements up to 130 degrees C. Based upon a full set of material constants recently reported by the authors, 7 orientations in the LGT plane with Euler angles (90 degrees, 23 degrees, Psi) were identified for testing. Each of the 7 selected orientations exhibited calculated coupling coefficients (K(2)) between 0.2% and 0.75% and also showed a large range of predicted temperature coefficient of delay (TCD) values around room temperature. Additionally, methods for estimating the uncertainty in predicted SAW propagation properties were developed and applied to SAW phase velocity and temperature coefficient of delay calculations. Starting from a purchased LGT boule, the SAW wafers used in this work were aligned, cut, ground, and polished at University of Maine facilities, followed by device fabrication and testing. Using repeated measurements of 2 devices on separate wafers for each of the 7 orientations, the room temperature SAW phase velocities were extracted with a precision of 0.1% and found to be in agreement with the predicted values. The normalized frequency change and the temperature coefficient of delay for all 7 orientations agreed with predictions within the uncertainty of the measurement and the predictions over the entire 120 degrees C temperature range measured. Two orientations, with Euler angles (90 degrees, 23 degrees, 123 degrees) and (90 degrees, 23 degrees, 119 degrees), were found to have high predicted coupling for LGT (K(2) > 0.5%) and were shown experimentally to exhibit temperature compensation in the vicinity of room temperature, with turnover temperatures at 50 and 60 degrees C, respectively.

Complete set of material constants of Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal with morphotropic phase boundary composition

Using combined resonance and ultrasonic methods, a full set of material constants has been measured for morphotropic phase boundary (MPB) composition xPb(In(12)Nb(12))O(3)-(1-x-y)Pb(Mg(13)Nb(23))O(3)-yPbTiO(3) (PIN-PMN-PT) single crystals poled along [001](c). Compared with the MPB composition (1-x)Pb(Mg(13)Nb(23))O(3)-xPbTiO(3) (PMN-PT) single crystals, the PIN-PMN-PT single crystals have smaller anisotropy, higher Curie temperature (T(c) approximately 197 degrees C), and higher rhombohedral to tetragonal phase transition temperature (T(R-T) approximately 96 degrees C). The electromechanical properties obtained here are the best found so far for this ternary system with d(33) approximately 2742 pCN, d(31) approximately -1337 pCN, k(33) approximately 95%, and k(31) approximately 65%.

Characterization of Hard Piezoelectric Lead-Free Ceramics

K4CuNb8O23 doped K(0.45)Na(0.55)NbO3(KNNKCN) ferroelectric ceramics were found to exhibit asymmetrical polarization hysteresis loops, related to the development of an internal bias field. The internal bias field is believed to be the result of defect dipoles of acceptor ions and oxygen vacancies, which lead to piezoelectric "hardening" effect, by stabilizing and pinning of the domain wall motion. The dielectric loss for the hard lead-free piezoelectric ceramic was found to be 0.6%, with mechanical quality factors Q on the order of >1500. Furthermore, the piezoelectric properties were found to decrease and the coercive field increased, when compared with the undoped material, exhibiting a typical characteristic of "hard" behavior. The temperature usage range was limited by the polymorphic phase transition temperature, being 188 degrees C. The full set of material constants was determined for the KNN-KCN materials. Compared with conventional hard PZT ceramics, the lead-free possessed lower dielectric and piezoelectric properties; however, comparable values of mechanical Q, dielectric loss, and coercive fields were obtained, making acceptor modified KNN based lead-free piezoelectric material promising for high-power applications, where leadfree materials are desirable.

Characterization of Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 ferroelectric crystal with enhanced phase transition temperatures

The full set of material constants for relaxor-based ternary single crystals Pb(In(12)Nb(12))O(3)-Pb(Mg(13)Nb(23))O(3)-PbTiO(3) (PIN-PMN-PT) were determined and compared to binary Pb(Mg(13)Nb(23))O(3)-PbTiO(3) (PMNT) crystals. The Curie temperature for rhombohedral compositions of PIN-PMN-PT was found to be in the range of 160-200 degrees C with ferroelectric rhombohedral to tetragonal phase transition on the order of 120-130 degrees C, more than 30 degrees C higher than that found for PMNT. The piezoelectric coefficients (d(33)) were in the range of 1100-1500 pCN, with electromechanical coupling factors (k(33)) about 89%-92% comparable to PMNT crystals. The coercive field of the ternary crystal was found to be 5.5 kVcm, double the value of the binary counterparts. The dielectric behavior under varying dc bias exhibited a similar trend as observed in PMNT with a much broader usage temperature range. Together with its enhanced field induced phase transition level, the ternary PIN-PMN-PT crystals are promising candidates for high temperature and high drive transducer applications.

Characterization of lead free (K 0.5Na 0.5)NbO 3–LiSbO 3 piezoceramic

(K 0.5Na 0.5)NbO 3 (KNN) based lead free ceramics have been fabricated by a solid state reaction. In this work, LiSbO 3 (LS) modified KNN based ceramics were sintered at atmospheric pressure and high density (>96% theoretical) was obtained. The detailed elastic, dielectric, piezoelectric and electromechanical properties were characterized by using the resonance technique combined with the ultrasonic method. The full set of material constants for the obtained polycrystalline ceramics were determined and compared to the pure hot pressed KNN counterpart. KNN-LS polycrystalline ceramic was found to have higher elastic compliance, dielectric permittivity and piezoelectric strain coefficients, but lower mechanical quality factor, when compared to pure KNN, exhibiting a “softening” behavior. However, a high coercive field (∼17 kV/cm) was found for the LS modified KNN material. The properties as a function of temperature were determined in the range of −50–250 ∘C, showing a polymorphic phase transition near room temperature, giving rise to improved piezoelectric behavior.

Identification of constants of a viscoplastic constitutive model for a single crystal alloy

In this paper uniaxial experiments conducted at 1033 K with specimens from the cubic face centered, nickel base single crystal alloy SRR99 are described. Specimens with 〈001〉-orientation and orientations deviating considerably form 〈001〉 have been used. We describe the results of tension tests with constant strain rate, relaxation tests and creep tests. From these tests the full set of material constants for a constitutive model by Choi and Krempl [1] is identified. We compare the experimental data with simulations by the model using the identified constants. The correspondence between simulations and experimental data is satisfactory until good depending on the type of the experiment. Finally, we describe a comparison between experimental data and simulations where the experiments have not been used for constant identification. The correspondence is very satisfactory. Therefore, we conclude that the model of Choi and Krempl is applicable on practical problems in the temperature range covered by our experiments.