A shear transformation has previously been shown to account for the discontinuities or jumps in the crystallographic thermal expansion coefficients across the normal to superconducting transition temperature. The crys...
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A shear transformation has previously been shown to account for the discontinuities or jumps in the crystallographic thermal expansion coefficients across the normal to superconducting transition temperature. The crystallographic stress dependence of the superconducting transition temperature is shown here to also support a shear transformation;dT(c)/dtau = 4 K/GPa. The shear motion of the lattice restricts the elastic compliances involved in superconductivity to tetragonal symmetry while considering all nine elastic interactions with the orthorhombic super-conducting crystal. The shear transformation has isothermal elastic interactions with the lattice through the orthorhombic shear compliance changes of (DELTAs11 + DELTAs22 - 2DELTAs12). The onset of superconductivity restricts to a higher symmetry the shear motion of the orthorhombic lattice with DELTAs11 = DELTAs22 and DELTAs23 = DELTAs13 across the superconducting phase boundary. Crystallographic second order thermodynamics predicts that isothermally DELTAs11 = -DELTAs12 = 1.7 X 10(-15)/Pa. It is shown that the jumps in the elastic compliance matrix are unique functions of the thermal expansion matrix jumps and the heat capacity jumps for any second order phase transition.
Amorphous silicate grain boundary phases of varying chemistry and amounts were added to 3Y-TZP in order to determine their influence on the superplastic behavior between 1200-degrees and 1300-degrees-C and on the room...
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Amorphous silicate grain boundary phases of varying chemistry and amounts were added to 3Y-TZP in order to determine their influence on the superplastic behavior between 1200-degrees and 1300-degrees-C and on the room-temperature mechanical properties. Strain rate enhancement at high temperatures was observed in 3Y-TZP containing a glassy grain boundary phase, even with as little as 0.1 wt% glass. Strain rate enhancement was greatest in 3Y-TZP with 5 wt% glass, but the room-temperature hardness, elastic modulus, and fracture toughness were degraded. The addition of glassy grain boundary phases did not significantly affect the stress exponent of 3Y-TZP, but did lower the activation energy for superplastic How. Strain rate enhancement was highest in samples containing the grain boundary phase with the highest solubility for Y2O3 and ZrO2, but the strain rate did not scale inversely with the viscosity of the silicate phases. Grain boundary sliding accommodated by diffusional creep controlled by an interface reaction is proposed as the mechanism for superplastic deformation in 3Y-TZP with and without glassy grain boundary phases.
C 60 70 powder compact and C 60 70 infiltrated copper were prepared and some of their mechanical properties measured. Young's modulus of C 60 70 compact is lower than those of molecular dynamics calculation and CS...
Hot isostatic pressing (HIP) of powder mixtures (containing differently sized components) and of composite powders is analyzed. Recent progress, including development of a simple scheme for estimating radial distribut...
An experimental method was devised to increase the "packing density" of random spherical powder packings by agitation with an applied compressive force. Maximum random packing densities of both monosize and ...
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An experimental method was devised to increase the "packing density" of random spherical powder packings by agitation with an applied compressive force. Maximum random packing densities of both monosize and bimodal-size powder packings of various size ratios and volume fractions are compared to the as-received gas-atomized SS316L powder. Since the presence of a compressive load will tend to restrict the opening of interparticle passages through the powder pack, uniform mixing of the powders beforehand is important for achieving optimum packing. At the same time, however, macroscopic size segregation of mixer-mill-premixed powder packings was found not to be significant using this technique. Densities of optimized bimodal-size powder packings far exceed those of non-optimized packings and the as-received (continuously distributed) powder. This enhancement is also retained during subsequent hot isostatic pressing.
The stress and displacement fields of an edge dislocation near a semi-infinite or a finite interfacial crack are formulated by using the complex potential theory of Muskhelishvili's elasticity treatment of plane s...
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The stress and displacement fields of an edge dislocation near a semi-infinite or a finite interfacial crack are formulated by using the complex potential theory of Muskhelishvili's elasticity treatment of plane strain problems. The image forces exerted on the dislocation have an oscillatory character (with respect to the dislocation position) if the dislocation is originated elsewhere and moves to the vicinity of a finite interfacial crack. There is no such oscillation of image forces if the edge dislocation is emitted from the finite interfacial crack or if the crack is semi-infinite. The stress intensity factors produced by the edge dislocation also have an oscillatory character for both semi-infinite and finite interfacial cracks. They also depend on whether the dislocation is emitted from the crack or comes from elsewhere.
The discontinuities or jumps in the crystallographic thermal expansion coefficients across the superconducting to normal phase boundary have been reported to contain opposite signs and nearly equal magnitudes between ...
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The discontinuities or jumps in the crystallographic thermal expansion coefficients across the superconducting to normal phase boundary have been reported to contain opposite signs and nearly equal magnitudes between the a and b crystal axes. A shear transformation is shown to account for almost all of the thermal expansion jumps in a coordinate system that is rotated by pi/4 about the c axis. The heat capacity, the shear ther-mal expansion coefficient and the elastic compliance matrix jumps in this rotated coordinate are related using second order phase transformation thermodynamics for a solid. The lattice motion for the shear transformation involves a single coupled displacement. A shear stress that gives a pure shear strain displacement will change T(c) in this crystal. The thermal expansion jumps when restricted to contain no volume terms have been emphasized in this paper. This shear thermal expansion is found to interact with the lattice through the orthorhombic shear compliance Of (S11 + S22 - 2s12).
A chevron notch four-point bend geometry fracture specimen is presented which complements the chevron notched short rod and short bar geometry used in ASTM E1304, the newest standard for fracture toughness testing. Al...
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A chevron notch four-point bend geometry fracture specimen is presented which complements the chevron notched short rod and short bar geometry used in ASTM E1304, the newest standard for fracture toughness testing. Although the four-point bend samples require slightly more material, sample preparation is less involved. Therefore total testing costs are lower using this four-point bend geometry when testing materials with low to moderate toughness to yield strength ratios. To test the new four-point bend samples, a stand alone toughness tool has been developed which allows a fracture toughness measurement to be made in about 30 seconds. It is shown that the fracture toughness values, measured using this toughness tool, are identical to the values obtained when loading the samples in a servo hydraulic testing system using a four-point bend fixture in displacement control. The fracture toughness values obtained using either loading method agree with fracture toughness values obtained according to ASTM E399.
The photoelastic stress-freezing technique is applied to observe the stress distribution inside two spheres of different sizes compressed together elastically. After the stress is frozen in, thin slices of the materia...
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The photoelastic stress-freezing technique is applied to observe the stress distribution inside two spheres of different sizes compressed together elastically. After the stress is frozen in, thin slices of the material containing the symmetry axis are prepared for observation through a polariscope. The stress distribution is compared with both the finite element numerical analysis and the Hertz analytical theory which is limited to small deformations. Among the three, the agreement between the experimental results and the finite element analysis is the best. The deviation from the Hertz theory is less in the larger sphere contacting a smaller one than in the smaller sphere contacting a larger one.
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