Some Physical Properties of High-Density Thorium Dioxide

The values for a number of physical properties are reported for a very high density form of thorium dioxide. When specimens of a mixture of 99½% ThO² and ½% CaO, by weight, were hydrostatically pressed at 30,000 lb. per sq. in. and heat-treated for 1 hour at 1800°C., they attained 99.0% of theoretical density. All the test specimens were extremely brittle. Physical-property values determined at room tempera- ture were the following: lattice constant; bulk and theoretical (X-ray) densities; compressive and impact strengths; Knoop hardness; modulus of rupture and Young's modulus, determined by a static method; Young's modulus and the shear modulus, determined by a dynamic method; Poisson's ratio and the bulk modulus, calculated from the dynamic-test data; and the velocity of sound through the material. The properties determined at elevated temperatures were the following : linear thermal expansion modulus of rupture and Young's modulus, determined by a static method; Young's modulus and the shear modulus, determined by a dynamic method; and Poisson's ratio, calculated from the elevated-temperature dynamic-test data. "Martin's diameter" grain counts were taken for the material both before and after heat-treatment.     

Elasticity and Internal Friction of Polycrystalline Yttrium Oxide

Young's modulus and internal friction of polycrystalline yttrium oxide were determined from room temperature to 1658°C by sonic techniques. A linear relation was found between volume fraction porosity and Young's modulus at room temperature. The effect of porosity on room temperature internal friction is also discussed. Young's modulus decreased linearly with increasing temperature to 1000° to 1100°C, where a slight anomaly was observed accompanied by an internal friction peak. The modulus was again linear from 100° to 13500°C. Above this temperature a rapid decrease in elastic modulus occurred with a rapid increase in internal friction.     

Mechanical properties of graphene oxides

The mechanical properties, including the Young's modulus and intrinsic strength, of graphene oxides are investigated by first-principles computations. Structural models of both ordered and amorphous graphene oxides are considered and compared. For the ordered graphene oxides, the Young's modulus is found to vary from 380 to 470 GPa as the coverage of oxygen groups changes, respectively. The corresponding variations in the Young's modulus of the amorphous graphene oxides with comparable coverage are smaller at 290-430 GPa. Similarly, the ordered graphene oxides also possess higher intrinsic strength compared with the amorphous ones. As coverage increases, both the Young's modulus and intrinsic strength decrease monotonically due to the breaking of the sp(2) carbon network and lowering of the energetic stability for the ordered and amorphous graphene oxides. In addition, the band gap of the graphene oxide becomes narrower under uniaxial tensile strain, providing an efficient way to tune the electronic properties of graphene oxide-based materials.     

Changes in Relation Between Refractive Index and Young's Modulus as the Result of Successive Heat Treatments

The relation between refractive index and elastic modulus is found to be a sensitive indicator of the nucleation and separation of submicroscopic phases in glass. In a study of the changes in properties with heat treatments of a wide variety of glasses containing SOa, B20s, and ZnO as major constituents, it was observed that large decreases in Young's moduli were not accompanied by decreases in refractive indices of the magnitude usually observed. The abnormal changes in properties resulted from a sequence of two heat treatments. The results indicate that during the first heat treatment an immiscible phase is nucleated which, on subsequent heat treatment at a higher temperature, develops into heterogeneous regions producing changes in the relation between the refractive index and the elastic modulus.     

Elastoplastic Finite Element Analysis and Strength Evaluation of Adhesive Butt Joints of Similar and Dissimilar Hollow Shafts Subjected to External Bending Moments

Stress distributions and deformation of adhesive butt joints are analyzed by an elastoplastic finite element method when the joints of similar and dissimilar shafts are subjected to external bending moments. The effects of the ratio of Young's modulus for the adherends to that for an adhesive and the effects of the adhesive thickness on the interface stress distribution are investigated. Joint strength is predicted by using the elastoplastic interface stress distributions. It is found that the singular stress at the edge of the interfaces increases with an increase of the ratio of Young's modulus. Measurement of strains in joints and experiments on joint strength were conducted. The numerical results are in fairly good agreement with the experimental results. It is observed that the joint strength for dissimilar shafts are smaller than those for similar shafts. A fracture of dissimilar adhesive up-bonded shafts occurred from the interface of the adherend with smaller Young's modulus. It is seen that joint strength increases as the adhesive thickness increases.     

THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS OF STRESS RESPONSE IN ADHESIVE BUTT JOINTS SUBJECTED TO IMPACT BENDING MOMENTS

The stress wave propagation and the stress distribution in adhesive butt joints of T-shaped similar adherends subjected to impact bending moments are calculated using a three-dimensional finite-element method (FEM). An impact bending moment is applied to a joint by dropping a weight. The FEM code employed is DYNA3D. The effects of the Young's modulus of adherends, the adhesive thickness, and the web length of T-shaped adherends on the stress wave propagation at the interfaces are examined. It is found that the highest stress occurs at the interfaces. In the case of T-shaped adherends, it is seen that the maximum principal stress at the interfaces increases as Young's modulus of the adherends increases. In the special case where the web length of T-shaped adherends equals the flange length, the maximum principal stress at the interfaces increases as Young's modulus of the adherends decreases. The maximum principal stress at the interfaces increases as the adherend thickness decreases. The characteristics of the T-shaped adhesive joints subjected to static bending moments are also examined by FEM and compared with those under impact bending moments. Furthermore, strain response of adhesive butt joints was measured using strain gauges. A fairly good agreement is observed between the numerical and the experimental results.     

Indentation Creep of Hydrated Soda–Lime Silicate Glass Determined by Nanoindentation

Time-dependent deformation behavior was investigated for soda–lime silicate glass with various water contents, using a nanoindentation technique. The complete indentation curve, loading and unloading part, is analyzed. It is shown that this deformation behavior may be represented in terms of a simple mechanical model analogous to a viscoelastic system. Values for Young's modulus were derived, a retardation spectrum was deduced, and apparent viscosity values were calculated. Structural rearrangements of the glass appear to be responsible for the observed changes of the viscoelastic properties. Water in the glass reduces Young's modulus and yield stress and thus promotes viscous flow.     

High-Temperature Young's Modulus of Alumina During Sintering

High-temperature Young's modulus of a partially sintered alumina ceramic has been studied dynamically during the sintering process. Comparative, room-temperature Young's modulus data were obtained for a suite of partially sintered alumina compacts with different porosities. The dynamic Young's modulus of a 1200°C partially sintered material was observed to decrease linearly with temperature, but then above 1200°C it increased sharply as sintering and densification of the alumina became dominant. The evolution of the Young's modulus due purely to sintering exhibited an exponential relationship with porosity in excellent agreement with room-temperature measurements of equivalent porous alumina ceramics.     

Role of Intergranular Damage-Induced Decrease in Young's Modulus in the Nonlinear Deformation and Fracture of an Alumina at Elevated Temperatures

The effect of the time-dependent decrease in Young's modulus due to damage accumulation by pore growth and intergranular cracking on the stress-strain behavior of a coarse-grained polycrystalline alumina deformed under conditions of displacement control at elevated temperatures was investigated. Considerable nonlinearity in stress-strain behavior, which increased with decreasing strain rate, was noted. At the higher strain rates, the failure stress was found to be independent of strain rate, thought to be due to a strain-rate-dependent fracture toughness due to the growth of microcracks at the tip of the failure-initiating macrocrack, which offsets the expected strain-rate sensitivity due to the growth of a single macrocrack only. Pore growth and intergranular cracking, accompanied by major reduction in Young's modulus by as much as a factor of 5, was most pronounced at the intermediate values of strain rate. This decrease in Young's modulus, under conditions of displacement-controlled loading, results in a decrease in stress, referred to as strain softening, which contributed to the observed nonlinear deformation. This conclusion was confirmed by a theoretical analysis, which showed that in addition to diffusional creep, time-dependent decreases in Young's modulus (elastic creep) by crack growth can make significant contributions to nonlinear deformation.     

Mechanical Properties of Woodceramics: A Porous Carbon Material

The mechanical properties of woodceramics, which are new porous carbon materials utilizing the natural structure of wood, were investigated. The effects of burning temperature and amount of impregnated phenol resin on Young's modulus, compressive strength and fracture toughness were measured. The fracture morphology was then observed, and simplified mechanical models of the woodceramics were discussed to explain the mechanical properties. The fracture was initiated at the cell walls that were located in vertical direction against the applied stress. The effect of impregnated phenol resin on the Young's modulus and the compressive strength was reasonably explained by a wall-bending model.     

Young's Modulus of Various Refractory Materials as a Function of Temperature

Young's modulus as a function of temperature was determined by a dynamic method for single-crystal sapphire and ruby and for polycrystalline aluminum oxide, magnesium oxide, thorium oxide, mullite, spinel, stabilized zirconium oxide, silicon carbide, and nickel-bonded titanium carbide. For the single crystals, Young's modulus was found to decrease linearly with increasing temperature from 100°C. to the highest temperature of measurement. For all the polycrystalline materials, except silicon carbide, stabilized zirconium oxide, and spinel, Young's modulus was found to decrease approximately linearly with increasing temperature until some temperature range characteristic of the material was reached in which Young's modulus decreased very rapidly and in a nonlinear manner with increasing temperature. This rapid decrease at high temperature is attributed to grain-boundary slip. Stabilized zirconium oxide and spinel were found to have the same rapid decrease in Young's modulus at high temperature, but they also had a decidedly nonlinear temperature dependence at low temperature.     

The effect of glass transition on the desired and undesired agglomeration of amorphous food powders

In the food manufacturing and pharmaceutical industry several agglomeration technologies are applied: fluidised bed agglomeration, steam jet agglomeration, agglomeration during drying and pressure agglomeration like extrusion, roller compaction or tabletting. In addition, caking or sticking of amorphous substances, which is a kind of undesired agglomeration, is frequently observed.Any desired or undesired agglomeration of amorphous substances is dependent on the mechanical properties of the entire particle or the particle surface. Changes in the mechanical properties of the material are linked to changes in moisture and temperature and can be predicted by applying the glass transition concept. Using this concept it is possible to estimate the viscosity and the Young's modulus for a given amorphous substance while knowing their glass transition temperature in dependence on the water content.Knowing the viscosity and the Young's modulus and applying equations derived from the sintering technology or the theory of viscoelasticity it is possible to define suitable conditions for most of the agglomeration processes mentioned above.     

Mechanical Properties of Chemically Strengthened Glasses at High Temperatures

Young's modulus, shear modulus, and modulus of rapture for two chemically strengthened glasses were determined at high temperatures. The Young's modulus and shear modulus decreased with increasing temperature, with a sharp inflection slightly above room temperature. The region of inflection indicated an internal friction peak. For comparison Young's modulus and shear modulus were determined as a function of temperature on a thermally tempered soda-lime-silica glass and on a semitempered borosilicate glass. Curves of these moduli, in contrast to those for the chemically strengthened glasses, did not reveal regions of inflection. The modulus of rupture is not affected by short exposure to heat up to 260°C., but decreases appreciably when exposed to temperatures above 204°C for 200 hr or more. Deflection measurements at room temperature showed that the two chemically strengthened glasses had about five times as much delayed elasticity as did thermally tempered soda-lime-silica glass.     

Some Physical Properties of Thoria Reinforced by Metal Fibers

Values are presented for several physical properties of thoria reinforced by metal fibers. Properties determined at room temperature include compressive strength, modulus of rupture, and Young's modulus (dynamic method); those determined at elevated temperatures include modulus of rupture, Young's modulus, thermal conductivity, thermal expansion, and oxidation resistance. The widespread presence of fine cracks in reinforced thoria results in significantly lower strengths compared with thoria alone. The thermal conductivity of reinforced thoria is slightly greater than that of thoria at room temperature and the difference becomes more pronounced at elevated temperatures.     

Elasticity and Anelasticity of Uranium Oxides at Room Temperature: II, Hyperstoichiometric Oxides

The Young's modulus and internal friction of hyperstoichiometric uranium oxide at room temperature were determined by a sonic technique. Young's modulus decreased, whereas internal friction increased, with increasing O/U ratios. These effects are attributed to the precipitation of U₄O₉. A complete microstructural characterization is needed.     

In Situ X-ray Diffraction and Young's Modulus Measurement during Heat Treatment of High-Alumina Cement Castables

In situ Young's modulus measurements and synchrotron radiation-energy dispersive diffraction have been used to study changes in high-alumina castables subjected to heat treatment from room temperature to 1600°C. Particular attention was paid to the hydrate "conversion" process and the effects of high temperature.     

Temperature Dependence of Anelastic Deformation in Polycrystalline Silicon Nitride

The influence of grain-boundary sliding on the evaluation of the apparent Young's modulus and plastic-deformation (flow) stress was investigated by bending tests for two types of silicon nitrides sintered with Y₂O₃-based additives The apparent Young's moduli measured at high temperatures are consistent with those predicated from a theory based on polycrystalline anelasticity due to grain-boundary sliding. The temperature dependence of the critical bending stress for the onset of plastic deformation shows viscoplastic properties of the interglanular glass. The ductile-to-brittle transition of fracture is discussed by the bending strengths normalized by the measured Young's modulus.     

Dynamic Young's modulus of open-porosity titanium measured by the electromagnetic acoustic resonance method

As biological implants, porous titanium with adjustable mechanical properties can solve the stress-shielding effect. In this paper, porous titanium was prepared by the powder metallurgy method, where urea powders as the second phase were removed by heat treatment. Pore morphology (such as pore size and character) was controlled by the character of urea powders. The dynamic Young's moduli of such porous titanium with different morphology was measured by the electromagnetic acoustic resonance method. From the semi-log plots of Young's modulus versus the porosity, it was found that with increased porosity this modulus firstly decreases linearly, then decreases rapidly and goes to zero at certain porosity. However, the Young's modulus was independent of pore size. The relationship between Young's modulus and the porosity was explained by a parallel model based on the Minimum Solid Area method. The value of linear slop `b' and the percolation limit `P_C' were used for predicting the trend of Young's modulus varied with the porosity and pore size. So porous titanium with appropriate Young's modulus can be chosen as a candidate for bone substitutes.     

Mullite/Alumina Particulate Composites by Infiltration Processing: III, Mechanical Properties

The effect of incorporating mullite into alumina by an infiltration process on the mechanical properties was investigated. Data for Young's modulus, strength, and fracture toughness for various composite compositions were compared with those for the unreinforced matrix (alumina). Measurements of Young's modulus by a resonance technique showed that the addition of mullite decreased Young's modulus. Up to 14 vol%, these changes were close to those expected, but above this mullite content, the decrease was more dramatic and indicated specimen damage during processing. The addition of mullite led, in some cases, to increases of more than 60% in both the strength (biaxial flexure) and indentation fracture toughness. These increases have been attributed to the method of introducing mullite and the resulting residual compressive surface stresses. The strength of the indented composite bodies deviated from the ideal behavior, indicating the probability of R -curve behavior in these materials.     

Low-Temperature Oxidation, Hydrothermal Corrosion, and Their Effects on Properties of SiC (Tyranno) Fibers

The effects of oxidation in air and corrosion in high-temperature, high-pressure water on the mechanical properties of three commercially available amorphous Si-Ti-C-O (Tyranno) fibers with different oxygen contents (12%–18%) and diameters (8–11 μm) were investigated. The fibers were exposed to isothermal treatments at elevated temperatures and subsequently tested at room temperature. Structural changes in the fibers after oxidation and corrosion were also studied in order to understand better the degradation mechanisms of the fibers. Oxidation resulted in the formation of vitreous silica films and decreases of strength and Young's modulus of the fibers. Hydrothermal corrosion under 100 MPa water pressure started above 300°C and resulted in the formation of a carbon layer on the surface of the fibers. Dissolution of silica in water during the treatment was observed. Corrosion at temperatures above 400°C led to the formation of relatively thick carbon films which delaminated easily. It caused a decrease of strength and Young's modulus of the fibers. The hydrothermal method can be used for producing carbon coatings with thickness up to 2 μm on the surface of silicon carbide fibers. The degrading of the mechanical properties after oxidation and corrosion was controlled by the thickness of the oxide or carbon layer. Based on this fact, it is possible to predict changes in the mechanical properties from the oxidation data.