Showing papers on "Young's modulus published in 2001"

Development and application of triglyceride‐based polymers and composites

Abstract: Triglyceride oils derived from plants have been used to synthesize several different monomers for use in structural applications. These monomers have been found to form polymers with a wide range of physical properties. They exhibit tensile moduli in the 1–2 GPa range and glass transition temperatures in the range 70–120 °C, depending on the particular monomer and the resin composition. Composite materials were manufactured utilizing these resins and produced a variety of durable and strong materials. At low glass fiber content (35 wt %), composites produced from acrylated epoxidized soybean oil by resin transfer molding displayed a tensile modulus of 5.2 GPa, a flexural modulus of 9 GPa, a tensile strength of 129 MPa, and flexural strength of 206 MPa. At higher fiber contents (50 wt %) composites produced from acrylated epoxidized soybean oil displayed tensile and compression moduli of 24.8 GPa each, and tensile and compressive strengths of 463.2 and 302.6 MPa, respectively. In addition to glass fibers, natural fibers such as flax and hemp were used. Hemp composites of 20% fiber content displayed a tensile strength of 35 MPa and a tensile modulus of 4.4 GPa. The flexural modulus was ∼2.6 GPa and the flexural strength was in the range 35.7–51.3 MPa, depending on the test conditions. The flax composite materials had tensile and flexural strengths in the ranges 20–30 and 45–65 MPa, respectively. The properties exhibited by both the natural- and synthetic fiber-reinforced composites can be combined through the production of “hybrid” composites. These materials combine the low cost of natural fibers with the high performance of synthetic fibers. Their properties lie between those displayed by the all-glass and all-natural composites. Characterization of the polymer properties also presents opportunities for improvement through genetic engineering technology. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 703–723, 2001

Structure and Thermomechanical Properties of Polyurethane Block Copolymers with Shape Memory Effect

Abstract: Shape memory polyurethane (PU) block copolymers composed of 4,4‘-methylenebis(phenylisocyanate), poly(tetramethylene glycol), and 1,4-butanediol as a chain extender were synthesized by a two-step process. FT-IR spectra showed that carbonyl peak appearing at 1700 cm-1 increased with higher hard segment content, whereas another carbonyl peak at 1730 cm-1 decreased. It suggests that hard segments get more aggregated to form domains in the PU block copolymer as hard segment content increases. Such domain formation has a significant influence on the mechanical and thermomechanical properties of PU, such as maximum stress, tensile modulus, and elongation at break. Especially, maximum stress, tensile modulus, and elongation at break increased significantly at 30 wt % of hard segment content, and the highest loss tangent was observed at the same composition. Heat of crystallization as measured by differential scanning calorimetry is also dependent on the hard segment content. Finally, 80−95% of shape recovery was...

Anisotropic and inhomogeneous tensile behavior of the human anulus fibrosus: experimental measurement and material model predictions.

Abstract: The anulus fibrosus (AF) of the intervertebral disc exhibits spatial variations in structure and composition that give rise to both anisotropy and inhomogeneity in its material behaviors in tension. In this study, the tensile moduli and Poisson's ratios were measured in samples of human AF along circumferential, axial, and radial directions at inner and outer sites. There was evidence of significant inhomogeneity in the linear-region circumferential tensile modulus (17.4+/-14.3 MPa versus 5.6+/-4.7 MPa, outer versus inner sites) and the Poisson's ratio v21 (0.67+/-0.22 versus 1.6+/-0.7, outer versus inner), but not in the axial modulus (0.8+/-0.9 MPa) or the Poisson's ratios V12 (1.8+/-1.4) or v13 (0.6+/-0.7). These properties were implemented in a linear an isotropic material model of the AF to determine a complete set of model properties and to predict material behaviors for the AF under idealized kinematic states. These predictions demonstrate that interactions between fiber populations in the multilamellae AF significantly contribute to the material behavior, suggesting that a model for th

Investigation of creep behaviour under load during indentation experiments and its influence on hardness and modulus results

Abstract: To improve the accuracy and comparability of hardness and modulus results from nanoindentation experiments an evaluation of the creep behaviour is required. Creep depends on the material and normally diminishes to very low values within some seconds. Nevertheless, it influences the maximum depth and the upper part of the unloading curve in a way that measurement errors of more than 20% may occur. In this work, a detailed analysis of the creep behaviour for different film and substrate materials is done. In addition, the influence of loading time and hold period at maximum load on the hardness and modulus results is investigated. The results show that especially for materials with low hardness-to-modulus ratio (mostly metals), the modulus results are not reliable if the hold period is chosen too low. Hold periods are proposed in dependence on the material type that should be kept for high accuracy measurements.

The Young's modulus of a microcrystalline cellulose

Abstract: This research is concerned with an investigation into the determination of the micromechanical properties of particulate form of cellulose; namel microcr stalline cellulose Using the technique of Raman spectroscop the shift in the 1095cm−1 Raman band, characteristic of cellulose, with strain is monitored and compared to the deformation of natural cellulose fibres (flax and hemp) From the values of the shift rate of the 1095cm−1 band for flax and hemp and the experimentally-determined value for microcrystalline cellulose the value for the Young's modulus of microcrystalline cellulose was estimated to be 25±4GPa It has been shown that this value is consistent with the measured degree of crystallinity of microcrystalline cellulose Theoretical modelling has also enabled the Young's modulus for compacted microcrystalline cellulose to be determined for fibres in either 2-D in-plane and 3-D arrangements These values have been show to be consistent with recent direct measurements of the modulus of compacted material

Influence of porosity on Young's modulus and Poisson's ratio in alumina ceramics

Abstract: This work presents a study on the influence of the porosity level on Young's modulus and Poisson's ratio of sintered alumina. A non-destructive technique using ultrasonic waves was used to determine the different parameters. Longitudinal and transverse wave velocities are measured by reflection method respectively at two frequencies: 10 and 5 MHz. The elastic modulus and Poisson's ratio were calculated from the measured ultrasonic velocities. The porosity dependence of the Poisson's ratio constitutes an originality as this ratio is considered as constant in many papers. Moreover, the authors take into account the pore shape modification during the densification in Young's modulus and Poisson's ratio calculations.

A New Coupled Approach of Residual Stiffness and Strength for Fatigue of Fibre-reinforced Composites

Abstract: During the last decades, fibre-reinforced composites have been established as competitive materials for naval, automotive and aerospace industry. However, the fatigue behaviour of fibre-reinforced composites is so diverse and complex that present knowledge is far from complete. Two commonly used approaches to model fatigue damage are the residual stiffness and the residual strength approach. In this paper, the change in the modulus of elasticity due to fatigue damage is studied for uni-axial bending. The proposed modelling approach is new in two ways: (i) the damage growth rate – a measure for stiffness loss – is expressed by two separate terms representing the initiation and propagation phase of damage respectively, (ii) a static failure criterion is modified to represent the decreasing reserve to ultimate static strength. In that way this coupled approach of residual stiffness and strength is capable of simulating the three stages of stiffness degradation: initial decline, gradual reduction and final failure, as well as the stress redistribution due to the loss of stiffness in the damaged zones. The model has been applied to displacement-controlled bending fatigue experiments of plain woven glass/epoxy specimens.

Temperature dependence of the elastic moduli of the nickel-base superalloy CMSX-4 and its isolated phases

Abstract: Elastic constants of anisotropic cubic materials were determined by acoustic resonance measurements at temperatures ranging from RT to 1300 K. The temperature dependence of Young's modulus E , shear modulus G , and Poisson's ratio ν of superalloy CMSX-4 and its isolated γ ′ and matrix phases were measured and compared with room temperature ultrasonic speed measurements. The orientation dependence of the engineering constants E , G and ν was determined. A comparison to models in literature predicting γ ′ morphology changes during creep is presented and agreement is found with the experimental data measured in this work.

Transient thermal stress analysis of an edge crack in a functionally graded material

Abstract: An edge crack in a strip of a functionally graded material (FGM) is studied under transient thermal loading conditions. The FGM is assumed having constant Young's modulus and Poisson's ratio, but the thermal properties of the material vary along the thickness direction of the strip. Thus the material is elastically homogeneous but thermally nonhomogeneous. This kind of FGMs include some ceramic/ceramic FGMs such as TiC/SiC, MoSi2/Al2O3 and MoSi2/SiC, and also some ceramic/metal FGMs such as zirconia/nickel and zirconia/steel. A multi-layered material model is used to solve the temperature field. By using the Laplace transform and an asymptotic analysis, an analytical first order temperature solution for short times is obtained. Thermal stress intensity factors (TSIFs) are calculated for a TiC/SiC FGM with various volume fraction profiles of the constituent materials. It is found that the TSIF could be reduced if the thermally shocked cracked edge of the FGM strip is pure TiC, whereas the TSIF is increased if the thermally shocked edge is pure SiC.

Comparison of photo-activation versus chemical or dual-curing of resin-based luting cements regarding flexural strength, modulus and surface hardness.

Abstract: This study investigated the efficiency of chemical activation of dual-cure resin-based luting cements as compared with light- and dual-curing. Curing was performed by (i) mixing base and catalyst without subsequent irradiation (chemical curing=CC), (ii) mixing base and catalyst with direct irradiation (dual-cure=DC) or with (iii) irradiation through 2.5 mm of leucite-reinforced glass-ceramics (IPS Empress, Ivoclar) (dual-cure through porcelain=DCtP), (iv) using only the base paste with direct irradiation (light-curing=LC) or with (v) irradiation through porcelain (light-curing through porcelain=LCtP). Specimens of four fine-hybrid DC resin composites and one self-cure hybrid resin composite (only CC) were prepared and tested after 24 h for flexural strength, modulus of elasticity (ISO 4049) and surface hardness (Vickers). For all materials and parameters, dual-curing produced higher values than LC, even when irradiation was performed through porcelain. Following self-curing without photo-activation, flexural strength was 68.9-85.9%, the modulus 59.2-94.5% and Vickers hardness 86.1-101.4% of the corresponding values obtained by dual-curing with direct irradiation. Light-curing through porcelain as compared with direct irradiation reduced the values for most parameters and materials. In contrast, dual-curing maintained flexural strength for all, the modulus for three and the hardness for one of the materials. The mechanical properties of the self-curing resin cement ranged between those of the DC materials.

Linear elastic properties of 2D and 3D models of porous materials made from elongated objects

Abstract: Porous materials are formed in nature and by man by many different processes. The nature of the pore space, which is usually the space left over as the solid backbone forms, is often controlled by the morphology of the solid backbone. In particular, sometimes the backbone is made from the random deposition of elongated crystals, which makes analytical techniques particularly difficult to apply. This paper discusses simple two- and three-dimensional porous models in which the solid backbone is formed by different random arrangements of elongated solid objects (bars/crystals). We use a general purpose elastic finite element routine designed for use on images of random porous composite materials to study the linear elastic properties of these models. Both Young's modulus and Poisson's ratio depend on the porosity and the morphology of the pore space, as well as on the properties of the individual solid phases. The models are random digital image models, so that the effects of statistical fluctuation, finite size effect and digital resolution error must be carefully quantified. It is shown how to average the numerical results over random crystal orientation properly. The relations between two and three dimensions are also explored, as most microstructural information comes from two-dimensional images, while most real materials and experiments are three dimensional.

Interferometry of actuated microcantilevers to determine material properties and test structure nonidealities in MEMS

Abstract: By integrating interferometric deflection data from electrostatically actuated microcantilevers with a numerical finite difference model, we have developed a step-by-step procedure to determine values of Young's modulus while simultaneously quantifying nonidealities. The central concept in the methodology is that nonidealities affect the long-range deflections of the beams, which can be determined to near nanometer accuracy. Beam take-off angle, curvature and support post compliance are systematically determined. Young's modulus is then the only unknown parameter, and is directly found. We find an average value of Young's modulus for polycrystalline silicon of 164.3 GPa and a standard deviation of 3.2 GPa (/spl plusmn/2%), reflecting data from three different support post designs. Systematic errors were assessed and may alter the average value by /spl plusmn/5%. An independent estimate from grain orientation measurements yielded 163.4-164.4 GPa (the Voigt and Reuss bounds), in agreement with the step-by-step procedure. Other features of the test procedure include that it is rapid, nondestructive, verifiable and requires only a small area on the test chip.

Thickness dependent dielectric strength of a low-permittivity dielectric film

Abstract: The dielectric strength of a promising interlevel low relative permittivity dielectric is investigated for various film thicknesses and temperatures by using I-V measurements with metal-insulator-semiconductor (MIS) structures. It is found that the dielectric breakdown mechanism also depends on thickness. For relatively thick films (thickness >500 nm), the dielectric breakdown is electromechanical in origin, i.e. the dielectric strength is proportional to the square root of Young's modulus of the films. By scanning electron microscopy (SEM) observation, a microcrack in thicker films may contribute to a lower value of Young's modulus, which may confirm that the electromechanical breakdown is the dominant mechanism for dielectric breakdown of thicker films. In addition, the thickness dependent dielectric strength can be described by the well-known inverse power-law relation by using different exponents to describe different thickness ranges, However for thinner films, i.e., <500 nm, the experimentally observed relationships among the dielectric strength, Young's modulus, and film thickness cannot be explained by the existing models.

Effect of a rippling mode on resonances of carbon nanotubes

Abstract: A recent study determined the Young's modulus of carbon nanotubes by measuring resonance frequency and using the modulus-frequency relation resulting from the linear vibration theory. It leads to the report that the Young's modulus decreases sharply, from about 1 to 0.1 TPa with the diameter D increasing from 8 to 40 nanometers, and the investigators attributed this decrease to the emergence of an unusual bending mode during the measurement that corresponds to rippling on the inner arc of the bent nanotubes. The nonlinear analysis presented in this paper that captures the rippling mode suggests that the effective Young's modulus can indeed decrease substantially with increasing diameter, and that the results from the classical linear theory may be invalid in such measurements.

Microstructure and tensile properties of in situ (TiB+TiC)/Ti6242 (TiB:TiC=1:1) composites prepared by common casting technique

Abstract: In the present work, (TiBw+TiCp)/Ti6242 composites with TiB:TiC=1:1 were produced by common casting and hot-forging technology utilizing the SHS reactions between titanium and B4C, C powder. The microstructures of composites were examined using optical microscopy (OM) and transmission electron microscopy (TEM). The X-ray diffraction (XRD) was used to identify the phases that were present in the composites. There are three phases — TiB, TiC and titanium matrix alloy. TiB grows in short-fiber shape, whereas TiC grows in dendritic, equiaxed or near-equiaxed shape. TiB whiskers were made to align the longitudinal direction and TiC dendritic was broken up after hot-forging. The reinforcements are distributed uniformly in matrix alloy. The interfaces between reinforcements and titanium matrix alloy are very clean. The tensile strength (yield strength and ultimate tensile strength) and the Young's modulus improve with the addition of TiB whiskers and TiC particles although some reduction in ductility is observed. (TiBw+TiCp)/Ti6242 composites with TiB:TiC=4:1 will fracture on a lower level of applied stain due to deformation restraint of TiB whiskers on titanium matrix alloy. The (TiBw+TiCp)/Ti6242 composites with TiB:TiC=1:1 show higher tensile strength and ductility. The addition of graphite not only improves the tensile strength and the Young's modulus but also increases the ductility. The improved Young's moduli and increased tensile strengths of the composites are explained using shear lag and rule-of mixtures theories. The Young's moduli of the composites were found in good agreement with that calculated from Tsai–Halpin equation applied for discontinuous-reinforced composites.

Mechanical and Structural Properties of Phosphate Glasses

Abstract: Mechanical and structural properties of sodium (NAFP) and zinc (ZAFP) iron–aluminum–phosphate bulk glass and fibers have been investigated. Young's modulus of the fibers was measured by a three-point bending method while the strength was measured by a two-point bending method. In general, the tensile strength of the ZAFP fibers (4.2–7.2 GPa) was higher than the tensile strength of the NAFP fibers (2.8–4.2 GPa). After exposing the fibers to air for 10 days, the strength decreased by 15–34%. The structure of bulk glass as well as fibers, studied by Mossbauer and IR spectroscopy, was very similar for all the compositions studied.

Hybrid effects on tensile properties of hybrid short-glass-fiber-and short-carbon-fiber-reinforced polypropylene composites

Abstract: Hybrid composites of polypropylene reinforced with short glass fibers and short carbon fibers were prepared using extrusion compounding and injection molding techniques The tensile properties of these composites were investigated taking into account the effect of the hybridization by these two types of short fibers It was noted that the tensile strength and modulus of the hybrid composites increase while the failure strain of the hybrid composites decreases with increasing the relative carbon fiber volume fraction in the mixture The hybrid effects for the tensile strength and modulus were studied by the rule of hybrid mixtures (RoHM) using the tensile strength and modulus of single-fiber composites, respectively It was observed that the strength shows a positive deviation from that predicted by the RoHM and hence exhibits a positive hybrid effect However, the values of the tensile modulus are close to those predicted by the RoHM and thus the modulus shows no existence of a hybrid effect Moreover, the failure strains of the hybrid composites were found to be higher than the failure strain of the single carbon fiber-reinforced composite, indicating that a positive hybrid effect exists Explanations for the hybrid effects on the tensile strength and failure strain were finally presented

Microsample tensile testing of LIGA nickel for MEMS applications

Abstract: Electro-deposited LIGA Ni components are being considered for use in a number of microelectromechanical systems (MEMS) and applications. The metrology of these components and their non-equilibrium microstructures play an important role in determining the mechanical response of these structures. Microsample testing has proven to be a reliable way of measuring the elastic and plastic tensile properties of these 100–200 μm thick films. Measured values of the in-plane Young's modulus (180±24 GPa) are significantly lower than the modulus for bulk coarse grained Ni (207 GPa), but can be explained and modeled in terms of the crystallographic texture in the as-deposited films. Variations in strength associated with post-processing heat treatments are highlighted and explained in terms of microstructural coarsening. The effect that coarsening and the related drop in strength have on the performance of LIGA Ni spring-like structures is discussed, and the need for further high temperature testing is highlighted.

Thermal, Mechanical and Electrical Properties of Pd-Based Thin-Film Metallic Glass

Abstract: As a kind of amorphous alloy, metallic glasses are suitable materials for micromachines because their size effect is considered to be absent. However, neither the fabrication process nor the physical properties of thin-film metallic glasses (TFMGs) have yet been examined. In this paper, Pd-based (Pd76Cu7Si17, atomic composition) TFMG was first fabricated by an RF-magnetron sputtering method. The existence of a supercooled liquid region (SCLR) and the thermal stability with respect to crystallization were measured by a differential scanning calorimeter (DSC). The existence of the SCLR was reconfirmed by a thermomechanical analyzer (TMA). The hardness of Pd-TFMG was measured by a mechanical testing machine for micro-sized specimens (MMT2000), while the Young's modulus was measured by a MMT2000 in the bending mode as well as by a TMA in the tensile mode. The resistivity of Pd-TFMG was tested by the four-point probe method. Finally, the influences of deposition conditions were discussed and the physical properties of TFMG were compared with those of Pd-based bulk metallic glass.