Showing papers on "Young's modulus published in 1993"

A simple predictive model for spherical indentation

Abstract: A simple model is described with which the entire force versus penetration behavior of indentation with a sphere, during loading and unloading, may be simulated from knowledge of the four test material parameters, Young's modulus, Poisson's ratio, flow stress at the onset of full plastic flow and strain hardening index, and the elastic properties of the indenter. The underlying mechanisms are discussed and the predictions of the model are compared with data produced by an ultra low load, penetration measuring instrument.

The fracture resistance of all-ceramic crowns on supporting structures with different elastic moduli.

Abstract: This in vitro study evaluated the fracture resistance of all-ceramic crowns as a function of the elastic modulus of the supporting die. All-ceramic crowns were made for dies with three different elastic moduli and two different crown lengths. The occlusal surface was loaded in compression with a 12.7-mm steel ball. The fracture load increased markedly with the increase in elastic modulus. The largest increase was seen when only the occlusal surface of the crown was covered. The characteristic fracture load of the complete-crown restorations was more than double that of the occlusal-cover restorations in the dies with the lowest modulus of elasticity, while for the dies with the highest modulus of elasticity the difference in the characteristic fracture load for the two configurations was not significant.

Hardness and young's modulus determined by nanoindentation technique of filler particles of dental restorative materials compared with human enamel

Abstract: The recently developed nanoindentation technique was used to measure hardness and Young's modulus of small filler particles in resin composites and other dental restoratives. This technique eliminates the need to visualize indentations. Load and displacement are continuously monitored during a loading-unloading sequence, and hardness as well as Young's modulus are then calculated from the load-displacement curves taking into account the geometry of the indenter. Thirteen posterior composites, 3 dental ceramics for CAD/CAM restorations, 1 sintered porcelain, and 1 amalgam were investigated in this study. The results were compared to the hardness and Young's modulus determined by nanoindentation of human enamel. Of the dental materials tested, only five materials contain inorganic filler particles with a nanohardness not statistically different from that of enamel. The predominant fillers in all other materials, except amalgam and the prepolymerized resin fillers in Bell Firm PX, were found to be significantly harder. The dental restorative materials, except the alloy phase in amalgam, were composed of particles with a Young's modulus significantly lower than that of human enamel. The alloy phase in amalgam had a Young's modulus value comparable to that of enamel.

Dependence of ceramic fracture properties on porosity

Abstract: A connected-grain model developed earlier to study the modulus of elasticity as a power-law of density was extended to study the dependence of the flexural strength of polycrystalline ceramics on porosity. Relations were derived for specific surface fracture energy, fracture toughness and flexural strength as power laws of (1 −p), wherep is porosity. Model validity was confirmed with data on α-alumina, UO2, Si3N4, and the YBa2Cu3O7−δ superconductor.

Diamond/Al metal matrix composites formed by the pressureless metal infiltration process

Abstract: Diamond particles are unique fillers for metal matrix composites because of their extremely high modulus, high thermal conductivity, and low coefficient of thermal expansion. Diamond reinforced aluminum metal matrix composites were prepared using a pressureless metal infiltration process. The diamond particulates are coated with SiC prior to infiltration to prevent the formation of Al4C3, which is a product of the reaction between aluminum and diamond. The measured thermal conductivity of these initial diamond/Al metal matrix composites is as high as 259 W/m-K. The effects of coating thickness on the physical properties of the diamond/Al metal matrix composite, including Young's modulus, 4-point bend strength, coefficient of thermal expansion, and thermal conductivity, are presented.

A new method for tensile testing of thin films

Abstract: A new method for tensile testing of thin films is presented. The strain is measured directly on the unsupported thin film from the displacement of laser spots diffracted from a thin grating applied to its surface by photolithography. The diffraction grating is two-dimensional, allowing strain measurement both along and transverse to the tensile direction. In principle, Young’s modulus, Poisson’s ratio, and the yield stress of a thin film can be determined. Cu, Ag, and Ni thin films with strong ⟨111⟩ texture were tested. The measured Young moduli agreed with those measured on bulk crystals, but the measured Poisson ratios were consistently low, most likely due to slight transverse folding of the film that developed during the test. The yield stresses of the evaporated Cu and Ag thin films agreed well with an extrapolation of the Hall-Petch relation found for bulk materials. Ni thin films are known to deviate from a bulk Ni Hall–Petch relation for submicron grain sizes, and sputtered Ni films show much higher yield stresses than electrodeposited or vapor-deposited films of similar grain size. Our sputtered Ni films had higher yield stresses than other sputtered films from the literature.

Carbon fibre compressive strength and its dependence on structure and morphology

Abstract: The axial compressive strength of carbon fibres varies with the fibre tensile modulus and precursor material. While the development of tensile modulus and strength in carbon fibres has been the subject of numerous investigations, increasing attention is now being paid to the fibre and the composite compressive strength. In the present investigation, pitch- and PAN-based carbon fibres with wide-ranging moduli and compressive strengths were chosen for a study of fibre structure and morphology. A rayon-based carbon fibre was also included in this study. Structural parameters (L c, La(0), L a(90), orientation parameter Z, and the spacing between graphitic planes d(00, 2)) were determined from wide angle X-ray spectroscopy (WAXS). Fibre morphology was characterized using high-resolution scanning electron microscopy (HRSEM) of fractured fibre cross-sections. The mechanical properties of the fibres, including compressive strength, the structural parameters from WAXS, and the morphology determined from HRSEM are reported. The influence of structure and morphology on the fibre compressive strength is discussed. This study suggests that the width of the graphitic sheets, the crystallite size perpendicular to the fibre axis (L c and L a(0)), and crystal anisotropy play significant roles in accounting for the large differences in compressive strengths of various carbon fibres.

Mechanical properties of sisal fibre at elevated temperatures

Abstract: Sisal fibres extracted from the leaves of Agava sisalana plants 3, 5, 7 and 9 years old were tested at different temperatures for tensile strength, elongation, toughness and modulus. The tensile strength, modulus and toughness values of sisal fibre decreased with increase in temperature. The effect of plant age on tensile strength, tensile modulus and toughness of sisal fibre became very much less at 100 °C as compared to 30 °C. Fractured fibres were observed by using a scanning electron microscope. The ends of fibres fractured at elevated temperature showed a failure similar to that of inorganic fibres. Elongation values at all temperatures increased with age. Elongated capillaries were observed in fibres fractured at 80 and 100 °C, due to the removal of moisture and volatiles originally present in the fibres. The fibrils are clearly observed in the form of hollow cylinders. Fractured surfaces are composed of brittle as well as ductile phases. The ductile portion increased with the increase of temperature.

Creep and shrinkage revisited

Abstract: Modern construction techniques and the changes they have engendered in the construction process, toghether with the increasing use of finite element programs, warrant a review of the validity of current creep and shrinkage provisions. Based upon a survey of published experimental data, equations were developed to calculate the modulus of elasticity, shrinkage, and creep coefficient in terms of developed concrete strength. The time function used was the product of a Ross-type relationship for size effects and logarithmic time. The proposed equations, together with those recommended by ACI 209-82 and the CEB 1990 Model Code, are compared with the published data.

Notch Ductile-to-Brittle Transition Due to Localized Inelastic Band

Abstract: Holes are often drilled in a panel for cooling or fastening. For a panel made of a monolithic ceramic, such a hole concentrates stress, reducing load-carrying capacity of the panel by a factor of 3. By contrast, for a ductile alloy panel, plastic flow relieves stress concentration so that the small hole does not reduce load-carrying capacity. A panel made of ceramic-matrix composite behaves in the middle: matrix cracks permit unbroken fibers to slide against friction, leading to inelastic deformation which partially relieves stress concentration. Load-carrying capacity is studied in this paper as an outcome of the competition between stress concentration due to the notch, and stress relaxation due to inelastic deformation. The inelastic deformation is assumed to be localized as a planar band normal to the applied load, extending like a bridged crack. The basic model is large-scale bridging. A material length, δ0 E/σ0 , scales the size of the inelastic band, where σ0 is the unnotched strength, δ0 the inelastic stretch at the onset of rupture, and E Young’s modulus. Load-carrying capacity is shown to depend on notch size a, measured in units of δ0 E/σ0 . Calculations presented here define the regime of notch ductile-to-brittle transition, where ceramic-matrix composites with typical notch sizes would lie. Both sharp notches and circular holes are considered. The shape of the bridging law, as well as matrix toughness, is shown to be unimportant to load-carrying capacity.

Neutral axis location in bending and Young's modulus of different layers of arterial wall.

Abstract: With few exceptions, experimental results on the blood vessel elasticity have been analyzed with the blood vessel wall treated as a homogeneous material, probably because the experiments have been ...

Model for the prediction of the mechanical behaviour of nanocrystalline materials

Abstract: A model is proposed in the present paper to account for the mechanical behaviour of nanocrystalline materials. In this model, the distribution of the grain size in nanocrystals is simulated with a logarithmic normal distribution, and one dislocation per grain is assumed. The plastic yielding for nanocrystalline materials is considered to be controlled by the stress required to attain dislocation loops (the Frank-Read source) in a set of larger grains with their critical semicircle configuration. The dislocations in the rest of the smaller grains are considered to be in the subcritical configuration, which produces a reversible deformation and only contributes to an inelastic deformation. The model presents a very good agreement with the σyvs. Dav−1/2 relationships for five nanocrystalline materials; of these, three metals exhibit a negative Hall-Petch slope and two a positive Hall-Petch slope. The model also predicts a decrease in Young's modulus with diminishing grain size, which is in agreement with experimental results for nanocrystalline copper and palladium.

Elastic Moduli and Internal Friction of Low Carbon and Stainless Steels as a Function of Temperature

Abstract: Elastic (Young, shear and bulk moduli, Poisson's ratio and Lame parameter), longitudinal and transverse internal friction values for low carbon steel and stainless steel were simultaneously measured over a temperature range 300-1500 K, by an ultrasonic pulse sing-around method. These elastic moduli decrease and Poisson's ratio increases with increasing temperature, suggesting activation of shear mode in a high temperature region. Longitudinal and transverse internal frictions are sensitive to recrystalization, and to α(ferritic)/γ(austenitic) phase transition and solution of precipitated carbide phases into the austenitic matrix, respectively. A relaxation peak with an apparent activation energy of 0.97 eV was observed at around 610 K for the carbon steel.

Unique metallic glass formability and ultra-high tensile strength in AlNiFeGd alloys

Abstract: The metallic glass formability of aluminum-rich AlNiFeGd alloys has been systematically investigated. The critical cooling rate required to form an amorphous state in this system is generally low, and comparable to that of some of the best metallic glass formers, such as PdCuSi. Amorphous ribbons up to 0.25 mm thick can easily be produced by the single-roller melt-spinning technique. Tensile strengths as high as 1280 MPa and Young's modulus of 75 GPa have been obtained. Bulk amorphous alloys with good mechanical properties are optimized in Al 85 Ni 6 Fe 3 Gd 6 . DSC and DTA studies reveal that the glass formability is unique for Al-based alloys because the reduced glass temperature T rg for AlNiFeGd can be as low as 0.44. This is much lower than conventional theory would suggest for easy glass forming systems. A mechanism for the unusual glass formability is suggested.

Composite orthopedic implant

Abstract: A beam (10) adapted for implantation within a bone is able to support bending and torsional loading forces applied thereto. The beam (10) has a stiffness defined by a modulus elasticity, which stiffness varies along the length of the beam to match the corresponding stiffness of the cortical bone adjacent the beam after implantation within the bone. The beam is made from an elongated core (14) formed of chopped carbon fibers embedded in a thermoplastic polymer matrix. Encasing the core (14) is a sheath (16) formed of carbon reinforced filament fibers embedded in the thermoplastic polymer which is wound in spiral formation around the core (14) and molded thereto. The winding angle and the sheath (16) thickness along the beam may be varied to vary the modulus of elasticity to match that of the cortical bone adjacent thereto.

Silicon carbide platelet/alumina composites: II. Mechanical properties

Abstract: The mechanical properties, i.e., Young's modulus, fracture toughness, and flexural strength, of SiC-platelet/Al[sub 2]O[sub 3] composites with two different platelet sizes were studied. Both Young's modulus and the fracture toughness of composites using small platelets (12 [mu]m) increased with increasing SiC volume fraction. Maximum values for toughness and Young's modulus of 7.1 MPa [center dot] M[sup 1/2] and 421 GPa were obtained for composites containing 30 vol% platelets. Composites fabricated using larger platelets (24 [mu]m), however, showed spontaneous microcracking at SiC volume fractions of [>=] 0.15. The presence of microcracks decreased Young's modulus and the fracture toughness substantially. Two types of radial microcracks were identified by optical microscopy and found to be consistent with a residual stress analysis. Anisotropy in fracture toughness was identified with a crack length identification technique. Cracks propagating in a plane parallel to platelet faces experienced the least resistance, which was the lowest toughness plane in platelet composites with preferred orientation. Enhanced fracture toughness was found in the plane parallel to the hot-pressing direction, but no anisotropy in toughness was observed in this plane. The flexural strength of alumina showed a decrease from 610 to 480 MPa for a 30 vol% composite and was attributed tomore » the presence of the platelets.« less

Effect of drawing on structure and properties of a liquid crystalline polymer and polycarbonate in - situ composite

Abstract: Fibers (strands) with various draw ratios were spun from the liquid crystalline state of a pure aromatic liquid crystalline copoly(ester amide) and the melts of its blend with polycarbonate. Scanning electron microscopy (SEMI, wide angle X-ray scattering (WAXS), and differential scanning calorimetry (DSC) were employed to investigate the structure and properties of the resulting fibers. Mechanical properties of the fibers were also evaluated. It was found that both the crystallite size and heat of fusion of the liquid crystalline polymer (LCP) increase steadily with draw ratio. However, the crystal-nematic transition temperature of the LCP is virtually unaffected by drawing. Moreover, heat of fusion of LCP is much smaller than that of isotropic condensation polymers despite the presence of very sharp dmraction peaks in WAXS measurements. These results are ascribed to the (semi)rigid rod nature of the LCP chains and the persistence of an ordered structure in the LCP melt, i.e., entropy effect. It was further observed that tensile modulus and tensile strength along fiber axis rise with draw ratio for the composite fibers. The elastic modulus of the composite fibers were found to be as high as 19 GPa and tensile strength reached 146 MPa with draw ratios below 40 and an LCP content of 30 wt%. Compared with the thermoplastic matrix, the elastic modulus and tensile strength of the in-situ composite have increased by 7.3 times and 1.4 times, respectively, with the addition of only 30 wt% LCP. This improvement in mechanical properties is attributed to fibrillation of the LCP phase in the blend and the increasing orientation of the LCP chains along the fiber axis during drawing.

Effective properties of composite materials containing voids

Abstract: Recent results of theoretical and practical importance prove that the two-dimensional (in-plane) effective (average) Young’s modulus for an isotropic elastic material containing voids is independent of the Poisson’s ratio of the matrix material. This result is true regardless of the shape and morphology of the voids so long as isotropy is maintained. The present work uses this proof to obtain explicit analytical forms for the effective Young’s modulus property, forms which simplify greatly because of this characteristic. In some cases, the optimal morphology for the voids can be identified, giving the shapes of the voids, at fixed volume, that maximize the effective Young’s modulus in the two-dimensional situation. Recognizing that two-dimensional isotropy is a subset of three-dimensional transversely isotropic media, it is shown in this more general case that three of the five properties are independent of Poisson’s ratio, leaving only two that depend upon it. For three-dimensionally isotropic composite media containing voids, it is shown that a somewhat comparable situation exists whereby the three-dimensional Young’s modulus is insensitive to variations in Poisson’s ratio, v m , over the range 0 ≤ v m ≤ ½, although the same is not true for negative values of v m . This further extends the practical usefulness of the two-dimensional result to three-dimensional conditions for realistic values of v m .

Numerical Modeling of Yield Zones in Weak Rock

Abstract: Publisher Summary This chapter discusses numerical modeling of yield zones in weak rock. Weakened or partly fractured materials can be modeled by a linear elastic material with a low modulus of elasticity. The major difficulty in the numerical modeling of geological materials is in the determination of the input parameters. Results of laboratory tests for such parameters as the modulus of elasticity and Mohr–Coulomb or Hoek–Brown failure properties are not always relevant to the rock in situ. Equivalent elastic properties of a weakened or yielded rock can be related, via the deformation theory of plasticity, to failure and postfailure properties such as pre-and postfailure cohesion and angle of friction of the rock. A major advantage of the deformation theory is ease of computation. The formulation is done in such a way that an iterative procedure can be set up with a linear elastic finite element program. In the incremental theories, the boundary tractions are reduced in increments until the material adjacent to the opening yields.

Tensile properties of aluminum/alumina multi-layered thin films

Abstract: Thin, free standing aluminum and alumina films were produced by physical vapor deposition and tensile properties were measured. Young’s modulus of the aluminum was microstructure insensitive, but the plastic behavior was very structure sensitive. The natural surface oxide of the aluminum had no apparent affect on the measured value ofYoung’s modulus. The alumina films showed true brittle behavior, but Young’s modulus was lower than bulk. Impurities residing at the grain boundaries were observed in the aluminum films using transverse Auger electron spectroscopy (AES). The films were well characterized using AES, transmission electron microscopy, Rutherford backscattering spectroscopy, and secondary electron microscopy. Well characterized, thin three-layered aluminum/alumina compositionally modulated films were produced by alternate depositions and tensile properties were measured. Young’s modulus was found to be less than a weighted thickness average of Young’s modulus of the individual constituents. Otherwise, the mechanical measurements yielded typical bulk behavior.

On the Effective Young's Modulus of Elasticity for Porous Materials: Microstructure Modelling and Comparison Between Calculated and Experimental Values

Abstract: A model equation for the prediction of Young's modulus of elasticity of porous materials has been proposed on the basis of an earlier theoretical work on two-phased composite materials. The derivation assumes a definite microstructural spheroidal model and the effective Young's modulus can be given as a function of the volume fraction of closed porosity and the microstructural parameters: shape (axial ratio of the spheroidal pores) and orientation. The theoretical predictions for different pore geometries have been compared with experimental data on porous metals, ceramics and glasses. Good agreement between theory and experiment was found. The microstructural parameters involved in the equation can be obtained from real microstructural data via quantitative microstructural analysis and stereology, no fitting is involved. This fact makes the proposed equation substantial also for practical applications. * The present article is the second part of a comprehensive study under the same title« The first part has already been published and is quoted in ref, [2].