Orthotropic elastic constants for polyimide film

The orthotropic constants of polyimide film have been characterized using the theory of elasticity of an anisotropic material. Experimental techniques coupled with the mechanics of orthotropic materials are used to determine all 9 independent orthotropic elastic constants (3 tensile moduli, 3 shear moduli, and 3 Poisson's ratios) and 3 coefficients of thermal expansion. Vibrational holographic interferom‐etry is used to determine the orthotropic axes of symmetry. For this polyimide film, the two principal axes coincided with the machine and transverse directions. It is also used to evaluate the 2 in‐plane Poisson's ratios by measuring residual stresses in 2‐D and 1‐D square membranes. Using other instruments such as a high pressure gas dilatometry apparatus, a tensile tester, a pressure‐volume‐temperature apparatus, a thermornechanical analyzer, and a torsion pendulum, the 7 other orthotropic constants and the 3 coefficients of thermal expansion are determined.     

Measurement of in‐plane elastic moduli of composites with a circular disk specimen and piezoelectric sensors

Many test specimen configurations and test methods have been used for measuring the in‐plane elastic constants of orthotropic composites. While the measurement of the Young's modulus is straightforward, the shear modulus determination is more difficult. Most of the experimental methods require more than one specimen for the measurement of all the in‐plane elastic constants. In the proposed method, a single test specimen in the form of a circular disk is sufficient. The Young's modulus and the shear modulus are measured with piezoelectric sensors that produce and detect dilatational and shear waves, respectively. The experimental techniques involved and the possible methods of interpreting the results are explained. The results obtained were compared with those determined for bar specimens of the same material, using piezoelectric sensors and strain gauges. The comparisons are encouraging. POLYM. COMPOS., 26:542–551, 2005. © 2005 Society of Plastics Engineers     

Elastic properties of adhesive polymers. I. Polymer films by means of electronic speckle pattern interferometry

The elastic modulus and Poisson's ratio of seven different polymers frequently used as wood adhesives and/or matrix polymers in wood‐ and natural‐fibre‐reinforced composites, respectively, were determined by means of tensile tests. Specimen deformation during testing was measured by means of a mechanical extensometer and an electronic speckle pattern interferometry system, respectively. The results from both methods show an excellent correlation for the elastic modulus. The elastic moduli of the studied polymers cover a wide range from 0.47 GPa for polyurethane to 6.3 GPa for melamine–urea–formaldehyde, whereas Poisson's ratios show less variability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3936–3939, 2007     

A comparative study of physical properties in Fe3O4 nanoparticles prepared by coprecipitation and citrate methods

Magnetite exhibits unique structural, electronic, and magnetic properties in extreme conditions that are of great research interest. In this work, the effects of preparation technique on X‐ray peak broadening, magnetic and elastic moduli properties of Fe₃O₄ nanoparticles prepared by coprecipitation (FcP‐NPs) and citrate (FC‐NPs) methods have been investigated. The structural characterization of the samples is evidence for a cubic structure with Fd‐3m space group. The Williamson‐Hall analysis was used to study crystallite sizes and lattice strain of the samples and also stress and energy density. In addition, the crystallite sizes are compared with the particle sizes and the magnetic core sizes obtained from TEM and VSM methods, respectively. In addition, the cation distribution obtained from calculated inversion parameter indicate that in the smaller particles, more amount of Fe²⁺ on the tetrahedral sites can be related to higher stress induced in the FcP‐NPs compared to the FC‐NPs. The saturation magnetization of the FcP‐NPs is almost two times bigger than the saturation magnetization of the FC‐NPs. It could be attributed to the decrease in the negative interaction on the octahedral site and also the magnetic moment on the tetrahedral site of the FcP‐NPs. The increase in force constants of the FC‐NPs determined by infrared spectra analysis compared to FcP‐NPs suggests the strengthening of their interatomic bonding. The values of shear and longitudinal wave velocities obtained from force constants have been used to determine the values of Young's modulus, rigidity modulus, bulk modulus, and Debye temperature. By comparison of the elastic results of FC‐NPs with the FcP‐NPs, we can observe that the elastic properties of the F‐NPs have been improved by synthesis method, while Poisson's ratio almost remains constant. In addition, using the values of the compliance s_ij obtained from elastic stiffness constants, the values of Young's modulus and Poisson's ratio along the oriented direction [hkl] have been calculated for the samples.     

Determining the elastic properties of modified polystyrenes by sound velocity measurements

The effect of the binding of various polyfunctional groups to polystyrene's (PS's) aromatic ring on the elastic properties of the PS were investigated by an ultrasonic method. Various sets of samples were prepared by chemical modification of pure PSs having different molecular weights with SA, maleic anhydride, and phthalic anhydride. The ultrasonic wave velocities of modified PSs were measured with the pulse‐echo method at room temperature by a computer‐controlled analyzer and a digital oscilloscope. The values of the acoustic impedance, Poisson's ratio, and elasticity constants of the samples were calculated by the measured values of the densities and sound velocities. The longitudinal and shear wave velocities and the values of all elastic constants increased with chemical modification of the pure PS. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

First‐Principles Study of Elastic,Structural, Electronic,Thermodynamical, and Optical Properties of Yttria (Y2O3) Ceramic in Cubic Phase

Structural, elastic, optical, thermodynamical, and electronic properties of yttrium oxide compound in cubic phase have been studied using the full‐potential augmented plane waves (FP‐LAPW) within density functional theory (DFT) framework. Four different approximations were used for exchange‐correlation potentials terms, comprised Perdew–Burke–Ernzerhof generalized parameterization of gradient approximation (GGA‐PBE), Wu–Cohen (WC‐GGA), local‐density approximation (LDA), and new approximation modified Becke and Johnson (mBJ‐GGA). The structural properties such as equilibrium lattice parameter, bulk modulus and its pressure derivative have been obtained using optimization method. Moreover, Elastic constants, Young's modulus, shear modulus, Poisson's ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature, and Grüneisen parameters have been calculated. Obtained structural, elastic and other parameters are consistent with experimental data. Moreover pressure dependence of the elastic moduli was studied. From electronic calculations, it has been found that the band gap was 5.7 eV at Г point in the Brillouin zone using mBJ‐GGA approximation. Optical properties, such as the dielectric function, refractive index, extinction index, and optical band gap, were calculated for radiation up to 14 eV. In addition, the unique type of bonding in Y₂O₃ was discussed by three method including effective charge, B/G ratio, and charge density distribution.     

A method of determining the elastic properties of diamond-like carbon films

The elastic properties of diamond-like carbon (DLC) films were measured by a simple method using DLC bridges which are free from the mechanical constraints of the substrate. The DLC films were deposited on a Si wafer by radio frequency (RF) glow discharge at a deposition pressure of 1.33 Pa. Because of the high residual compressive stress of the film, the bridge exhibited a sinusoidal displacement on removing the substrate constraint. By measuring the amplitude with a known bridge length, we could determine the strain of the film which occurred by stress relaxation. Combined with independent stress measurement using the laser reflection method, this method allows the calculation of the biaxial elastic modulus, E/(1−ν), where E is the elastic modulus and ν is Poisson's ratio of the DLC film. The biaxial elastic modulus increased from 10 to 150 GPa with increasing negative bias voltage from 100 to 550 V. By comparing the biaxial elastic modulus with the plane–strain modulus, E/(1−ν²), measured by nano-indentation, we could further determine the elastic modulus and Poisson's ratio, independently. The elastic modulus, E, ranged from 16 to 133 GPa in this range of the negative bias voltage. However, large errors were incorporated in the calculation of Poisson's ratio due to the pile up of errors in the measurements of the elastic properties and the residual compressive stress.     

Auxetic polypropylene films

Auxetic materials are those exhibiting negative Poisson's ratio (ν) behavior. Polymeric auxetic extruded products in the form of cylinders and fibers have previously been reported. This article reports the successful production of auxetic polypropylene films (～0.15‐mm thick) using a melt extrusion process. Video extensometry and tensile testing techniques have been used to measure the in‐plane Poisson's ratios and Young's moduli of the auxetic film, both on an Instron tensile testing machine and a Deben microtensile testing machine. The film is elastically anisotropic with the Poisson's ratio and Young's modulus along the extrusion (x) direction being ν_xy = ?1.12 ± 0.06 and E_x = 0.34 ± 0.01GPa, respectively, while the Poisson's ratio and Young's modulus in the transverse (y) direction to the extrusion direction are ν_yx = ?0.77 ± 0.01 and E_y = 0.20 ± 0.01GPa, respectively. POLYM. ENG. SCI., 45:517–528, 2005. © 2005 Society of Plastics Engineers     

The Uniaxial Tensile Response of Porous and Microcracked Ceramic Materials

The uniaxial tensile stress–strain behavior of three porous ceramic materials was determined at ambient conditions. Test specimens in the form of thin beams were obtained from the walls of diesel particulate filter honeycombs and tested using a microtesting system. A digital image correlation technique was used to obtain full‐field 2D in‐plane surface displacement maps during tensile loading, and in turn, the 2D strains obtained from displacement fields were used to determine the Secant modulus, Young's modulus, and initial Poisson's ratio of the three porous ceramic materials. Successive unloading–reloading experiments were performed at different levels of stress to decouple the linear elastic, anelastic, and inelastic response in these materials. It was found that the stress–strain response of these materials was nonlinear and that the degree of nonlinearity is related to the initial microcrack density and evolution of damage in the material.     

Theoretical and experimental studies of anisotropic shrinkage in injection moldings of various polyesters

A novel approach to predict anisotropic shrinkage of slow crystallizing polymers in injection moldings was proposed, using the flow‐induced crystallization, frozen‐in molecular orientation, elastic recovery, and PVT equation of state. In the present study, three different polyesters, polyethylene terephthalate, polybutylene terephthalate, and polyethylene‐2,6‐naphthalate (PEN), are used. The anisotropic thermal expansion and compressibility affected by the frozen‐in orientation function and the elastic recovery that was not frozen during moldings were introduced to obtain the in‐plane anisotropic shrinkages. The frozen‐in orientation function was calculated from the amorphous contribution based on the frozen‐in and intrinsic amorphous birefringence and crystalline contribution based on the crystalline orientation function determined from the elastic recovery and intrinsic crystalline birefringence. To model the elastic recovery and frozen‐in stresses related to birefringence during molding process, a nonlinear viscoelastic constitutive equation was used with the temperature‐dependent viscosity and relaxation time. Occurrence of the flow‐induced crystallization was introduced through the elevation of melting temperature affected by entropy production during flow of the viscoelastic melt. Kinetics of the crystallization was modeled using Nakamura and Hoffman‐Lauritzen equations with the rate constant affected by the elevated melting temperature. Numerous injection molding runs were carried out by varying the packing time, packing pressure, flow rate, melt and mold temperature, and anisotropic shrinkage of moldings were measured. The experimental results were compared with the simulated data and found in a fair agreement. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3526–3544, 2006     

Theoretical and experimental studies of anisotropic shrinkage in injection moldings of semicrystalline polymers

A novel approach to predict anisotropic shrinkage of semicrystalline polymers in injection moldings was proposed using flow‐induced crystallization, frozen‐in molecular orientation, elastic recovery, and PVT equation of state. The anisotropic thermal expansion and compressibility affected by the frozen‐in orientation function and the elastic recovery that was not frozen during moldings were introduced to obtain the in‐plane anisotropic shrinkages. The frozen‐in orientation function was calculated from amorphous and crystalline contributions. The amorphous contribution was based on the frozen‐in and intrinsic amorphous birefringence, whereas the crystalline contribution was based on the crystalline orientation function, which was determined from the elastic recovery and intrinsic crystalline birefringence. To model the elastic recovery and frozen‐in stresses related to birefringence during molding process, a nonlinear viscoelastic constitutive equation was used with temperature‐ and crystallinity‐dependent viscosity and relaxation time. Occurrence of the flow‐induced crystallization was introduced through the elevation of melting temperature affected by entropy production during flow of the viscoelastic melt. Kinetics of the crystallization was modeled using Nakamura and Hoffman‐Lauritzen equations with the rate constant affected by the elevated melting temperature. Numerous injection molding runs on polypropylene of various molecular weights were carried out by varying the packing time, flow rate, melt temperature, and mold temperature. The anisotropic shrinkage of the moldings was measured. Comparison of the experimental and simulated results indicated a good predictive capability of the proposed approach. POLYM. ENG. SCI., 46:712–728, 2006. © 2006 Society of Plastics Engineers     

Ultrasonic properties of epoxy resin/marble waste powder composites

Non‐destructive techniques are suitable alternatives for characterization of composites. The aim of this study is to analyze the composites of epoxy resin (ER)/marble waste powder (MWP) by ultrasonic method. The effects of marble powder, coagulant type, and dosage on the ultrasonic properties of ER/MWP composites were investigated. The ultrasonic wave velocities of composites were measured with the pulse–echo method at room temperature by a flaw detector. The values of the acoustic impedance, Poisson's ratio, and elastic constants of the samples were calculated by the measured values of the densities and both longitudinal and shear ultrasonic wave velocities. According to the results, the ER/MWP composite using sepiolite coagulant in dosages of 4 g/500 mL has showed the highest values of elastic constants. POLYM. COMPOS. 36:584–590, 2015. © 2014 Society of Plastics Engineers     

Elastic characterization of CVD diamond by static and dynamic measurements

The present paper describes two different nondestructive approaches for the direct identification of the elastic constants of thin square isotropic plates. First a static method is presented, by which the identification of the Young's modulus and Poisson's ratio is carried out by the full field measurement of the out-of-plane displacements detected on the upper surface of the plate in two biaxial bending tests. Then a dynamic method is illustrated, by which the elastic constants are determined from two different natural frequency of a free vibrating plate. Both techniques, previously verified on a carbon steel specimen, have been applied to a CVD diamond specimen; a comparison between the two approach is reported and the influence of the measurement errors is also discussed.     

Impact of titanium and silica/titanium fumed oxide nanofillers on the elastic properties and thermal decomposition of a polyester resin

The impact of nanoparticles of titanium (rutile) and silica–titanium fumed oxide (STO) on both the acoustic properties and thermal decomposition of a styrene‐crosslinked unsaturated polyester resin were studied with the methods of ultrasonic probing and thermal decomposition mass spectrometry at filler loadings ranging from 0.5 to 5.0%. It was shown that the elastic modulus, Poisson's ratio, and thermal resistivity in the titanium‐filled nanocomposites increased at small loadings of about 0.5%, whereas in the STO‐filled nanoparticles, the decreases in the parameters at loadings of up to 1.5% was replaced by some increases at higher loadings of up to 5.0%. Distinctions in the concentration dependences of the elastic parameters and the thermal decomposition intensity for both fillers could be explained by the features of the polymer–particle interactions because of the differences in both the number of active sites located on the particle's surface and the polymer structure within interface regions. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42010.     

Characterisation of mechanical properties of thin polymer films using a bi-axial tension based on blow-up test

Abstract

Blow-up tests were carried out to evaluate mechanical properties of the thin Nylon film used as bagging films. A new method for calculating bi-axial stress and strain of the thin film in blow-up tests was developed based on the theory of membrane with large strain solutions. The bi-axial tensile elastic modulus, Poisson's ratio, yield strength, fracture stress and bi-axial stress–strain relationship of the thin Nylon film were obtained. Meanwhile, uni-axial tensile tests were conducted and the results were compared with those from blow-up tests. For the Richmond HS-8171 thin Nylon film studied, the bi-axial tensile elastic modulus was slightly more than 2 times greater than the uni-axial tensile elastic modulus. The yield strength was the same for both bi-axial and uni-axial tension. The bi-axial fracture stress was about one-third greater than the uni-axial one, while the bi-axial failure strain was about two-thirds greater than the uni-axial counterpart.     

Experimental analyses of the poly(vinyl chloride) foams' mechanical anisotropic behavior

Assessing a full set of mechanical properties is a rather complicate task in the case of foams, especially if material models must be calibrated with these results. Many issues, for example anisotropy and heterogeneity, influence the mechanical behavior. This article shows through experimental analyses how the microstructure affects different experimental setups and it also quantifies the degree of anisotropy of a poly(vinyl chloride) foam. Monotonic and cyclic experimental tests were carried out using standard compression specimens and non‐standard tensile specimens. Results are complemented and compared with the aid of a digital image correlation technique and scanning electron microscopy analyses. Mechanical properties (e.g., elastic and plastic Poisson's ratios) are evaluated for compression and tensile tests, for two different material directions (normal and in‐plane). The material is found to be transversely isotropic. Differences in the results of the mechanical properties can be as high as 100%, or even more depending on the technique used and the loading direction. Also, the experimental analyses show how the material's microstructure behavior, like the evolution of the herein identified “yield fronts” and a “spring back” phenomenon, can influence the phenomenological response and the failure mechanisms as well as the hardening curves. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Variations in mechanical properties of an epoxy adhesive on exposure to warm moisture

The detrimental effects of a humid environment on the mechanical properties of adhesives have been investigated for many years. However, from early studies to recent contributions most of the interest has been focused on the reduction of strength related to plasticity associated with moisture uptake, interfacial weakening, etc. Much less attention has been paid to variations of elastic constants, which influence both the stiffness of the joint and the distribution of stresses. The goal of this study was to measure the effects of a humid and warm environment on tensile strength, Young's modulus and Poisson's ratio of a two-component epoxy adhesive, Henkel Hysol 3425. The measurements have been carried out on bulk specimens of dogbone shape, instrumented with two-grid (axial/transverse) strain gauge rosettes and tested in tension. The conditions of exposure, generated in a climatic cabinet, were 100% relative humidity and 50?°C. To relate the exposure time to the moisture uptake, the weight of the specimens was monitored. It has been noticed that most of the water uptake occurs in the first week of exposure; however, at progressively slower rate, the phenomenon is noticeable almost until the fourth week and then saturation is achieved. Over the same period, the mechanical properties decay as moisture uptake continues; at the end, the loss in strength is about 75% whilst for the elastic moduli the loss is approximately 20%. No clear evidence is found about the Poisson's ratio, which exhibits a non-monotonic behaviour: stable in the early weeks, then increasing and decreasing of a few per cent. In accord with previous works, the behaviour of the mechanical properties seems to be governed by the amount of moisture uptake.     

Intrinsic Mechanical Properties of 20 MAX‐Phase Compounds

The intrinsic mechanical properties of 20 MAX‐phase compounds are calculated using an ab initio method based on density functional theory. A stress versus strain approach is used to obtain the elastic coefficients and thereby obtain the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio based on the Voigt–Reuss–Hill (VRH) approximation for polycrystals. The results are in good agreement with available experimental data. It is shown that there is an inverse correlation between Poisson's ratio and the Pugh ratio of shear modulus to bulk modulus in MAX phases. Our calculations also indicate that two MAX compounds, Ti₂AsC and Ti₂PC, show much higher ductility than the other compounds. It is concluded that the MAX‐phase compounds have a wide range of mechanical properties ranging from very ductile to brittle with the “A” in the MAX phase being the most important controlling element. The measured Vickers hardness in MAX compounds has no apparent correlation with any of the calculated mechanical parameters or their combinations.     

Study on the Viscoelastic Poisson‘s Ratio of Solid Propellants Using Digital Image Correlation Method

Digital image correlation methods were used for further studies of the viscoelastic Poisson's ratio of solid propellants. The Poisson's ratio and the Young's relaxation modulus of solid propellants were separately determined in a single stress relaxation test. In addition, the effects of temperature, longitudinal strain, preload and storage time on the Poisson's ratio of solid propellants were discussed. The Poisson's ratio master curve and the Young's relaxation modulus master curve were constructed based on the time‐temperature equivalence principle. The obtained results showed that the Poisson's ratio of solid propellants is a monotone non‐decreasing function of time, the instantaneous Poisson's ratio increased from 0.3899 to 0.4858 and the time of the equilibrium Poisson's ratio occurred late when the temperature was varied from −30 °C to 70 °C. The Poisson's ratio increased with temperature and longitudinal strain, decreased with preload and storage time, while the amplitude Poisson's ratio increased with preload, decreases with longitudinal strain and storage time. The time of the equilibrium Poisson's ratio occurred in advance with the increase of longitudinal strain, preload and storage time.