Search

Determining the properties of composite materials (knowing the properties of the component phases) is a primary objective in the design phase. Numerous methods have been developed to determine the elastic constants of a composite material. All these methods are laborious and require significant computing time. It is possible to make experimental measurements, but these too are expensive and time-consuming. In order to have a quick estimate of the value of the engineering constants of a new composite material (in our study a polymeric matrix reinforced with carbon fibers), this paper proposes a quick method for determining the homogenized material constants, using the finite element method (FEM). For this, the eigenfrequencies of a beam specimen manufactured by the studied composite material will be computed using FEM. The model will consider both phases of the composite, with the geometry and real size. The mechanical properties of the constituent's material phases are known. With the help of this model, the torsional, longitudinal and transverse vibrations of the beam are studied. Based on the eigenvalues obtained by this calculation, it now is possible to quickly estimate the values of homogenized material constants required in the design. An example for a fiber-reinforced polymer composite material is provided in the paper. [ABSTRACT FROM AUTHOR]

The excitation of surface acoustic waves (SAWs) on the surface of the ferroelectric film [barium strontium titanate (BST)] located on the dielectric substrate (silicon) was studied theoretically. We found that the most effective SAW excitation takes place when spontaneous polarization occurs in the film plane and the wave propagates along the direction adjacent to the direction of the spontaneous polarization vector. Based on a nonlinear model of phase transitions in solid BST solutions, the dependency of the material constants of piezo-effect equations on the misfit strain with a fixed concentration was obtained numerically. The effect of various misfit strains on SAW characteristics was studied for the film located on single-crystal silicon. It was shown that the effectiveness of SAW excitation increases as the misfit strain nears the boundary of phase transition. [ABSTRACT FROM AUTHOR]

Thermally coupled constitutive relations are generally used to determine material constants and elastic moduli (Young's modulus and shear modulus) of solid media. Conventional studies on this issue are mainly based on the linear temperature dependence of elastic moduli, whereas analytical difficulties are often encountered in theoretical studies on nonlinear temperature dependence, particularly at high temperatures. This study investigates the thermally coupled constitutive relations for elastic moduli and material constants using the assumption of axisymmetric fields, with applications to geologic materials (marble, limestone and granite). The Taylor power series of the Helmholtz free energy function within dimensionless temperatures could be used to develop the thermally coupled constitutive relations. The thermoelastic equivalent constitutive equations were formulated under the generalized Hooke's law. The material constants of solid rocks were determined by fitting experimental data using axisymmetric stress and strain fields at different temperatures, based on their thermomechanical properties. For these geologic materials, the resultant equivalent elastic moduli and deformations were in good agreement with those from the experimental measurements. Thermal stresses, internal moisture evaporation and internal rock compositions significantly affected the experimental results. This study provides a profound understanding of the thermally coupled constitutive relations that are associated with the thermomechanical properties of solid rocks exposed to high temperatures. [ABSTRACT FROM AUTHOR]

Lanthanum-gallium tantalate (LGT) is a member of the LGX crystal family (langasite, langanite, and langatate) known for high-quality factor and stability at higher temperatures. These characteristics enable filters and sensors for use in harsh environments. Accurate values for the second-order material constants are required for electromechanical modeling of such devices. A sufficient set of bulk acoustic wave (BAW) propagation velocities have been measured in cube-shaped samples to obtain the full set of second-order elastic and piezoelectric material constants along with the experimental uncertainties. The cross correlation method was used to accurately measure the time-of-flight (TOF) values between the first two back-wall echoes under a constant room-temperature environment. The calculated BAW velocities and extracted material constants show good agreement with earlier work. [ABSTRACT FROM AUTHOR]

The possibility of the development of MEMS devices based on the tunable ferroelectric film Ba 0.8Sr 0.2O3 properties under uniaxial deformation was studied theoretically. The thermodynamic model of the phase transitions for the film under uniaxial stress was constructed. The behavior of the material constants for the film in various phase states was investigated. The propagation properties of the surface acoustic wave (SAW) under the uniaxial stress were studied for the film located on the single-crystal silicon substrate. It was shown that the SAW resonance frequency changes within 3 MHz for the frequency of 274 MHz, and 9 MHz for the frequency of 512 MHz. [ABSTRACT FROM AUTHOR]

The data contained within this article relate to experimental data on mechanical behavior of an in-house cast hyperelastic Polydimethysiloxane (PDMS) based membrane (SilasticⓇ T-4, Dow Corning) for cell culture, which was used as a tool for applying tensile stress on cells and tissues. With the experimentally obtained material constants, tensile stress distribution over the membrane surface was numerically assessed using a finite element analysis (FEA). The membrane area having a uniform tensile stress distribution under different strain loading conditions of 1–20% was suggested for cell culture.

This work concerns mainly the finite element (FE) implementation of polyconvex incompressible hyperelastic models. A user material subroutine (UMAT) has been developed and can be utilized to define the aforementioned material behaviors in the FE system ABAQUS. The subroutine is written using a novel strategy in order to maximally simplify the relations for the analytical material Jacobian (MJ). The UMAT code is attached in the appendix. The developed subroutine allows to significantly decrease the time of computations and to avoid possible convergence difficulties. The structure of the code enables modifications which may lead to a rheological, damage or growth models, for instance. [ABSTRACT FROM AUTHOR]

To date, the complete sets of electromechanical-related coefficients of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals have been reported only at room temperature (RT). To meet the demands of practical applications, the full sets of elastic, piezoelectric, and dielectric constants of [001]-poled rhombohedral PIN-PMN-PT single crystals were measured as a function of temperature ranging from −10 °C to 70 °C by the resonance method. Variation trends of the material constants with temperature are discussed, and the corresponding mechanisms are analyzed. With increasing temperature, absolute values of the elastic compliance constants, the piezoelectric coefficients $d_{\mathrm {ij}}$ , and the dielectric permittivities $\varepsilon _{\mathrm {ij}}$ increase, but the piezoelectric voltage coefficients $g_{\mathrm {ij}}$ and the characteristic frequencies decrease. The electromechanical coupling factors $k_{\mathrm {ij}}$ are not sensitive to temperature, of which $k_{33}$ keeps 91% in the temperature range of −10 °C to 70 °C. Compared with other coefficients, the piezoelectric coefficients $d_{31}$ , $d_{33}$ , and $d_{15}$ , and the dielectric permittivities $\varepsilon _{11}^{T}$ , $\varepsilon _{33}^{T}$ , $\varepsilon _{11}^{S}$ , and $\varepsilon _{33}^{S}$ , show the largest enhancements with increasing temperature. For example, the piezoelectric coefficients $d_{31}$ and $d_{33}$ , and the dielectric permittivities $\varepsilon _{11}^{T}$ and $\varepsilon _{33}^{T}$ change from −560 pC/N, 1130 pC/N, 1050, and 3300 at −10 °C to −890 pC/N, 1700 pC/N, 2030, and 6140 at 70 °C, increasing by more than 50% from −10 °C to 70 °C. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Complete sets of elastic, dielectric, and piezoelectric properties of flux grown rhombohedral Pb(Zn1/3Nb2/3)O3–xPbTiO3 (PZN–PT; $x =0.0475$ , 0.055, and 0.065) single crystals poled along [001] crystal direction have been determined in the present work. Their phase transformation temperatures, coercive fields, and mechanical quality factors are also provided. The results show that [001]-poled rhombohedral PZN–PT single crystals exhibit superior longitudinal piezoelectric properties ($k_{33} \ge0.90$ , $d_{33} \approx 1580$ –2500 pC/N). While the piezoelectric properties increase with PT content, the $T_{\mathrm{ RT}}$ and hence temperature stability of the crystal degrade accordingly. These unique properties, together with the property matrices provided in this work, can be used advantageously to design high-performance piezoelectric devices of longitudinal activation/sensing mode to suit various application needs. [ABSTRACT FROM AUTHOR]

This paper presents a numerical procedure for the analysis of complex laminate structures. The procedure is based on the application of reduced stiffness of complex laminate. Introduction of reduced stiffness of composite facilitates both linear and nonlinear numerical integration, i.e. the tangential stiffness matrix is translated in the classical plate theory problem. The formulated numerical procedure was implemented in the program system KOMIPS. Special subroutine REDKRUT that calculates reduced stiffness of the laminate was written, and its application in numerical verification of experiments conducted on chairs was presented in (Nestorovic, 2010). At the end of this work, for 3D stress and strain analysis of veneer composites, recommendations were given for experimental determination of all nine independent material constants Ex, Ey, Ez, vxy, vxz, Gxy, Gxz, Gyz, fi ve of which were determined in the previous paper of the author (Nestorović, 2010).

Copyright of Materials & Technologies / Materiali in Tehnologije is the property of Institute of Metals & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to investigate the tensile deformation behavior of ultra-high-strength-steel BR1500HS, a series of isothermal tensile experiments were carried out in a temperature range of 1023˜1123 K and a strain rate range of 0.01˜10 s−1 on a Gleeble-3500 thermo-mechanical simulator. The results indicate that the flow stress initially increases to a peak value and then decreases gradually to a steady state. Based on the analysis of the effect of strain, temperature and strain rate on flow stress, dynamic recrystallization (DRX) type softening characteristics of the stress-strain curve with single peak were identified. The flow stress level decreases with increasing temperature and decreasing strain rate. By regression analysis for Arrhenius type equation, the hot deformation activation energy Q and material constants (n, α, β and A) were calculated. Further, the Arrhenius-type constitutive equation of flow stress was developed by considering the effect of strain on the variable coefficients (including activation energy Q, material constants n, α, and A). The validity of the developed constitutive equation incorporating the influence of strain was evaluated through comparing the experimental and predicted data. Furthermore, the predictability of the developed model was also evaluated using two standard statistical parameters, correlation coefficient (R) and average absolute relative error (AARE). And R-value and AARE-value for the model are 0.997 and 4.06% respectively, which indicates that the developed model can precisely estimate the flow behavior for BR1500HS alloy throughout the entire temperature and strain rate range.

Highlights • The circular Couette flow of Herschel–Bulkley fluids is analysed. • The conditions under which the rates of strain share a common point are specified. • The errors when using apparent instead of true shear rates are highlighted. • The errors in the calculated material parameters are discussed. • The findings of the present work are demonstrated on experimental data. Abstract We analyse the circular Couette flow of Herschel–Bulkley fluids to investigate the validity of the assumption that the rate of strain distributions across the gap share a common point. It is demonstrated that this is true only with fully-yielded Bingham -plastic flow. In other cases, e.g., in partially-yielded Bingham-plastic flow or fully-yielded Herschel–Bulkley flow, the common point for the fully-yielded Bingham case provides a good approximation for determining material constants only if the gap is sufficiently small. We also revisit the important issue of determining material properties of viscoplastic fluids by using "true values" for the rate of strain and demonstrate that the material properties can be very different from those obtained using "apparent' values for the rate of strain. [ABSTRACT FROM AUTHOR]

In order to investigate the compressive deformation behavior of 3Cr20Ni10W2 alloy, a series of isothermal upsetting experiments were carried out in the temperature range of 1203-1403 K and strain rate range of 0.01-10 s-1 on a Gleeble-1500 thermo-mechanical simulator. The results indicate that the flow stress initially increases to a peak value and then decreases gradually to a steady state. The characteristics of the curves are determined by the interaction of work hardening (WH), dynamic recovery (DRV) and dynamic recrystallization (DRX). The flow stress decreases with increasing temperature and decreasing strain rate. The relationship between microstructure and processing parameters is discussed to give an insight into the hot deformation behavior of 3Cr20Ni10W2 alloy. Then, by regression analysis for constitutive equation, material constants (n, α, β, A and Q) were calculated for the peak stress. Further, the constitutive equation along the flow curve was developed by utilizing an eighth order polynomial of strain for variable coefficients (including n, α, A and Q). The validity of the developed constitutive equation incorporating the influence of strain was verified through comparing the experimental and predicted data by using standard statistical parameters such as correlation coefficient (R) and average absolute relative error (AARE) that are 0.995 and 4.08% respectively.

The biomechanical properties of the female pelvic floor tissues, such as muscles, fascia or ligaments are relevant when explaining pelvic disorders, since these may result from changes in the properties of those tissues. The aim of this study is to understand the influence of pelvic organ prolapse (POP) on the passive biomechanical properties of the pelvic floor muscles. For this purpose, magnetic resonance images at Valsalva maneuver were used, and an inverse finite element analysis technique was applied. The numerical models of the pubovisceralis muscle and pelvic bones were built from axial magnetic resonance images acquired at rest. The numerical simulation was based on the finite element method (FEM), by which the material constants were determined for three different constitutive models (Neo-Hookean, Mooney-Rivlin and Yeoh). The ratio between the values of the material constants for women with and without prolapse was approximately 43% for the parameter in the Neo-Hookean constitutive model, 57% and 24% for and in the Mooney-Rivlin constitutive model, and 35%, 21% and 14% for , and in the Yeoh constitutive model. For the three constitutive models, the mean values of the material properties related with stiffness were higher for the muscles of women with POP. These increases in stiffness are in line with other experimental works involving vaginal tissue, which showing that the elasticity module is significantly higher in the prolapsed tissue when compared with normal tissue. The present work presents a noninvasive methodology based on the application of the FEM, which allows the establishment of a relationship between the stiffness of the pelvic floor muscles of women with POP and without this pathology. [ABSTRACT FROM AUTHOR]

Resonant ultrasound spectroscopy (RUS) was used to determine the temperature dependence of full matrix material constants of PZT-8 piezoceramics from room temperature to 100 °C. Property variations from sample to samples can be eliminated by using only one sample, so that data self-consistency can be guaranteed. The RUS measurement system error was estimated to be lower than 2.35%. The obtained full matrix material constants at different temperatures all have excellent self-consistency, which can help accurately predict device performance at high temperatures using finite element simulations. [ABSTRACT FROM AUTHOR]

Pelvic disorders can be associated with changes in the biomechanical properties in the muscle, ligaments and/or connective tissue form fascia and ligaments. In this sense, the study of their mechanical behavior is important to understand the structure and function of these biological soft tissues. The aim of this study was to establish the biomechanical properties of the pelvic floor muscles of continent and incontinent women, using an inverse finite element analysis (FEA). The numerical models, including the pubovisceral muscle and pelvic bones were built from magnetic resonance (MR) images acquired at rest. The numerical simulation of Valsalva maneuver was based on the finite element method and the material constants were determined for different constitutive models (Neo-Hookean, Mooney-Rivlin and Yeoh) using an iterative process. The material constants (MPa) for Neo-Hookean (c1) were 0.039 ± 0.022 and 0.024 ± 0.004 for continentvs.incontinent women. For Mooney-Rivlin (c1) the values obtained were 0.026 ± 0.010vs.0.016 ± 0.003, and for Yeoh (c1) the values obtained were 0.031 ± 0.023vs.0.016 ± 0.002, (p < 0.05). Muscle displacements obtained in the numerical simulations of Valsalva maneuver were compared with the muscle displacements obtained through additional dynamic MRI. Incontinent women presented a higher antero-posterior displacement than the continent women. The results were also similar between MRI and numerical simulations (40.27%vs.42.17% for Neo-Hookean, 39.87% for Mooney-Rivlin and 41.61% for Yeoh). Using an inverse FEA coupled with MR images allowed to obtain thein vivobiomechanical properties of the pelvic floor muscles, leading to a relationship between them for the continent and incontinent women in a non-invasive manner. [ABSTRACT FROM AUTHOR]

The hot deformation behaviors of Cr5 steel were investigated. The hot compression tests were conducted in the temperature range of 900150 °C under strain rates of 0.01, 0.1 and 1 s. The constitutive equation and material constants ( Q, n, α ln A) are obtained according to the hyperbolic sine function and Zener-Hollomon parameter. Besides, dynamic recrystallization (DRX) grain size model and critical strain model are acquired. The processing maps with the strain of 0.1, 0.3 and 0.5 are obtained on the basis of dynamic materials model. It has been observed that DRX occurs at high temperature and low strain rate. According to the processing map, the safety region exists in the temperature range of 920150 °C with strain rate of 0.01−0.20 s. [ABSTRACT FROM AUTHOR]

In order to perform the numerical simulations of forging response and establish the processing parameters for as-extruded 7075 aluminum alloy, the compressive deformation behavior of as-extruded 7075 aluminum alloy were investigated at the temperatures of 573 K, 623 K, 673 K and 723 K and the strain rates of 0.01 s-1, 0.1 s-1, 1 s-1 and 10 s-1 on a Gleeble1500 thermo-mechanical simulator. Based on the analysis of the effect of strain, temperature and strain rate on flow stress, dynamic recrystallization (DRX) type softening characteristics of the stress-strain curve with single peak were identified. The traditional Arrhenius type model is in favor of the prediction for the flow stress at a fixed strain, and can not satisfy the need of the numerical simulations of various hot forming processes due to the lack of the effect of strain on flow stress. Lin et al. improved Arrhenius type model with a series of variable coefficients as functions of true strain (including activation energy of deformation Q, material constants n and a, and structure factor A) to predict the flow stress during the hot compression. The application has been demonstrated in this work for as-extruded 7075 aluminum alloy. The comparisons between the predicted and experimental results show that, for the worst case, the error in the flow stress estimate is 5.63%, and the max mean error is 3.6%. The developed model provides fast, accurate and consistent results, making it superior to the conventional Arrhenius type model. In further it can be used in computer code to model the forging response of 7075 aluminum alloy mechanical part members under the prevailing loading conditions.

Experimental determination of the elastic constants of orthotropic composite materials and their bearing capacity (strength) for furniture intended for sitting, and numerical verification of the experiment results by analysing with the final elements, was performed on the basis of the theory of elasticity of orthotropic and anisotropic composite materials. The requisite and sufficient material constants were determined in the experiments: moduli of elasticity and Poisson’s coefficients (longitudinal and tangential) and skate modulus for plain stress. These constants, calculated by 3D measurements of deformation, are sufficient for determining the constitutive matrix of the lamina, and for reducing stiffness of the composite irrespective of the thickness of the layers, fibre orientation and choice of material. Experiments were conducted for the stiffness, shear and flexing of uniformly and complexly layered beech veneer sheets, while for new materials experiments for stiffness and shear in a uniform orientation were sufficient. Analysis of stiffness and deformations were conducted layer by layer, as well as by reduced volume stiffness for multilayered orthotropic shells of chair systems by a method of final elements by application of a composite final element, where combined reduced membrane matrices and flexing matrices are used. Numerical verification of the experiments, including systems of furniture intended for sitting – chairs – was conducted using the KOMIPS software system, which contains in its library a composite final element of the sheet. Experiments with chairs were performed with the aim of determining the stiffness of such systems, and they were confirmed by analytical results and measurement of the real movements on selected models. The results of research provide the design, re-design, construction and determination of the dimensions of not just chairs, but also of any other girder or surface systembased on laminates.

A CaTiO3-doped (K,Na)NbO3 (KNN-CT) film is a lead-free piezoelectric film that is expected to substitute Pb(Zr,Ti)O3 (PZT) film in piezoelectric micro electro mechanical systems (MEMS). However, the full set of the material constants (elastic constants, piezoelectric constants and dielectric constants) of the KNN-CT film have not been reported yet. In this study, all the material constants of a sputter-deposited blanket KNN-CT film were investigated by the resonance responses of MEMS-based piezoelectric resonators and the phase velocities of leaky Lamb waves on a self-suspended membrane. The phase velocities measured by a line-focus-beam ultrasonic material characterization (LFB-UMC) system at different frequencies were fitted with theoretical ones, which were calculated from the material constants, including fitting parameters. A genetic algorithm was used to find the best-fitting parameters. All the material constants were then calculated. Although some problems arising from the film quality and the nature of deliquescence are observed, all the material constants were obtained exhibiting accuracy within 16 m/s in the phase velocity of leaky Lamb wave.

The paper deals with observation and description of the influence of strain rate on true stress - true strain. It compares various material models that consist strain rate for deep drawing sheets in order to work out the most accurate material models. The more accurate input to the simulation program, give the more exact output. These simulation programs introduce higher accuracy into development and production of the pressed material and reduce production costs. Computer simulation using the software programs (e.g. PAM-STAMP, ABAQUS – Explicit, DYNA 3D etc.) also presents replacement of financially expensive experiment, utilization of potential properties of materials and error detection in the production process. [ABSTRACT FROM AUTHOR]

The dynamic recrystallization behavior of high strength steel during hot deformation was investigated. The hot compression test was conducted in the temperature range of 950-1150 °C under strain rates of 0.1, 1 and 5 s. It is observed that dynamic recrystallization (DRX) is the main flow softening mechanism and the flow stress increases with decreasing temperature and increasing strain rate. The relationship between material constants ( Q, n, α and ln A) and strain is identified by the sixth order polynomial fit. The constitutive model is developed to predict the flow stress of the material incorporating the strain softening effect and verified. Moreover, the critical characteristics of DRX are extracted from the stress-strain curves under different deformation conditions by linear regression. The dynamic recrystallization volume fraction decreases with increasing strain rate at a constant temperature or decreasing deformation temperature under a constant strain rate. The kinetics of DRX increases with increasing deformation temperature or strain rate. [ABSTRACT FROM AUTHOR]

The constants of the Johnson-Cook and Zerilli-Armstrong material models are determined using an inverse Taylor test. In this technique, the target (specimen) and the projectile (striker) swap their positions as usually considered in the conventional Taylor test. This type of test configuration eliminates the difficulties that are normally associated with in situ heating up the specimen. The experiments are conducted at ambient and elevated temperatures under high impact velocities. The constants of the models correspond to the case when the difference between the experimental and numerical mushroomed profiles of the specimen after impact is optimized. The results indicate that Z-A model is superior to J-C model in prediction of the copper alloy deformation in the inverse Taylor test. The reason is believed to the fact that the effects of strain, strain rate, and temperature are coupled in Z-A model, but have separate effects in J-C model. [ABSTRACT FROM AUTHOR]

The mechanical characteristics of the female pelvic floor are relevant when explaining pelvic dysfunction. The decreased elasticity of the tissue often causes inability to maintain urethral position, also leading to vaginal and rectal descend when coughing or defecating as a response to an increase in the internal abdominal pressure. These conditions can be associated with changes in the mechanical properties of the supportive structures-namely, the pelvic floor muscles-including impairment. In this work, we used an inverse finite element analysis to calculate the material constants for the passive mechanical behavior of the pelvic floor muscles. The numerical model of the pelvic floor muscles and bones was built from magnetic resonance axial images acquired at rest. Muscle deformation, simulating the Valsalva maneuver with a pressure of 4 KPa, was compared with the muscle displacement obtained through additional dynamic magnetic resonance imaging. The difference in displacement was of 0.15 mm in the antero-posterior direction and 3.69 mm in the supero-inferior direction, equating to a percentage error of 7.0% and 16.9%, respectively. We obtained the shortest difference in the displacements using an iterative process that reached the material constants for the Mooney-Rivlin constitutive model (c10=11.8 KPa and c20=5.53 E-02 KPa). For each iteration, the orthogonal distance between each node from the group of nodes which defined the puborectal muscle in the numerical model versus dynamic magnetic resonance imaging was computed. With the methodology used in this work, it was possible to obtain in vivo biomechanical properties of the pelvic floor muscles for a specific subject using input information acquired non-invasively. [ABSTRACT FROM AUTHOR]

Copyright of Wood Industry / Drvna Industrija is the property of Drvna Industrija and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)