Two-point bending is a useful method for investigating the mechanical properties of optical fiber and has several advantages when compared to the traditional tensile test. However, the strength of the fiber is usually...
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Two-point bending is a useful method for investigating the mechanical properties of optical fiber and has several advantages when compared to the traditional tensile test. However, the strength of the fiber is usually determined at constant faceplate velocity rather than at constant strain rate as in the uniaxial tensile test, and previous work casts doubt on the comparability of fatigue results obtained using different loading modes and hence on the reliability of the bending technique. This paper presents dynamic fatigue results using a two-point bend apparatus that can be programmed to operate in constant velocity, constant strain rate, and constant stress rate loading modes. These results, obtained for both bare and polymer-coated fused silica optical fiber, show no significant differences in the calculated fatigue parameters for the three loading modes and clearly indicate the reliability of the two-point bend method at constant faceplate velocity. The results, however, show that the obtained value of the stress corrosion susceptibility parameter, n, is dependent on the quantity used to define it, i.e., stress or strain to failure, because of the nonlinear elastic behavior of silica.
The room‐temperature strength distributions of a sintered and a hot‐pressed Si3N4were examined in the as‐machined condition, after oxidation at 1370°C and after oxidation under load at 1370°C. The strengt...
The room‐temperature strength distributions of a sintered and a hot‐pressed Si3N4were examined in the as‐machined condition, after oxidation at 1370°C and after oxidation under load at 1370°C. The strength‐controlling flaw populations were highly transient in nature. Both the duration of oxidation and the magnitude of the applied load were observed to effect changes in strength. This dynamic situation is related to both strengthening and weakening processes, which at times may occur simultaneously in the same strength dis
In transmission electron microscopy examinations of cast Al matrix-SiC particulate composites, it was noted that a coating of Al4C3 had been formed in contact with some SiC particles. The observed epitaxial orientatio...
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In transmission electron microscopy examinations of cast Al matrix-SiC particulate composites, it was noted that a coating of Al4C3 had been formed in contact with some SiC particles. The observed epitaxial orientation relationships at the SiC/Al4C3 interface and between the carbides and interfacial Al formed by Al4C3 decomposition are described. The lattice matching between SiC, Al4C3, and reprecipitated Al particles may result in strong bonding and thus permit crack propagation across such interfaces, contributing to the detrimental effects on fracture and fatigue associated with the presence of Al4C3 in aluminum-silicon carbide composites,
The effects of 60 Co gamma radiation on the strength-related mechanical properties of a borosilicate glass were examined. Although the glass darkened considerably, only a very slight densification was observed after i...
The effects of 60 Co gamma radiation on the strength-related mechanical properties of a borosilicate glass were examined. Although the glass darkened considerably, only a very slight densification was observed after irradiation to levels of 10 8 rads. The strength distributions were not appreciably changed by the irradiation, nor was the calculated slow crack growth parameter, or N value. Neither did radiation affect the elastic modulus or the fracture toughness of the glass. Gamma radiation does not affect the strength below 10 8 rads.
Silicon-oxynitride glasses were prepared in the NaSiON, NaSiON, and the NaBSiON systems by conventional melting techniques. Increasing amounts of nitrogen were substituted for oxygen to a two weigh...
Silicon-oxynitride glasses were prepared in the NaSiON, NaSiON, and the NaBSiON systems by conventional melting techniques. Increasing amounts of nitrogen were substituted for oxygen to a two weight percent level of nitrogen. The Young's elastic moduli, Vicker's microhardnesses, and the fracture toughnesses were measured and observed to increase linearly with nitrogen content in each of these systems. These results are consistent with the incorporation of nitrogen into the glass structure in three-fold coordination with silicon.
Acoustic emission analysis showed that the failure of some low density aluminous cement bonded perlite composites cannot be explained adequately using the classical Griffith type approach in which it is assumed that f...
Acoustic emission analysis showed that the failure of some low density aluminous cement bonded perlite composites cannot be explained adequately using the classical Griffith type approach in which it is assumed that failure is caused by the catastrophic propagation of the most severe flaw. It was found that the general concept of cumulative weakening could be applied to the failure of these composites. A change in failure mode from that of cumulative weakening to Griffith type fracture occurred when the bulk density of the composite was greater than about 1.6 lb/bd ft and/or the cement content of the material was greater than approximately 30%. In addition, microscopic examination showed a change in fracture surface morphology from primarily interparticle failure at low density or low cement contents to primarily transparticle failure at high density or high cement content. L'analyse d'émission acoustique montre qu'on ne peut pas suffisamment expliquer la fracture de certains composites en perlite, liés par du ciment alumineux de densité basse, en utilisant une approche de type traditionnel comme celle de Griffith; celle-ci affirme que la fracture est causée par la propagation destructive de la plus sévère craquelure. On a prouvé qu'on peut appliquer le concept de l'affaiblissement cumulatif à la fracture de ces composites. La fracture type “affaiblissement cumulatif” est remplacé par fracture type Griffith lorsque la masse volumique est plus grande que 1.6 lb/bd ft et/ou le contenu en ciment des matériaux est approximativement plus grande que 30%. En outre, un changement apparait dans la morphologie de la fracture en surface selon la densité et le contenu en ciment: Fracture surtout intraparticulaire pour un ciment de basse densité et en faible quantité et plutôt transparticulaire pour un ciment de haute densité et en grande quantité.
The η-phase compound (Ti,Cu,Al)6O previously reported at the Al2O3-Ag-Cu-Ti interface on the basis of selected-area electron diffraction has been confirmed by convergent-beam electron diffraction (CBED), and the pres...
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The η-phase compound (Ti,Cu,Al)6O previously reported at the Al2O3-Ag-Cu-Ti interface on the basis of selected-area electron diffraction has been confirmed by convergent-beam electron diffraction (CBED), and the presence of oxygen has been verified. The fine structure in the central disk of the [111] zone axis CBED pattern is compared to that from the similar (Ti,Cu,Al)6N compound and to simulated patterns for M6X, M23X6, and M22Si7 compounds. The details of the higher-order Laue zone lines allow one to discern between the various phases with a single CBED pattern. For this work, a commercial brazing alloy with nominal composition 63 wt% Ag, 35 wt% Cu, and 2 wt% Ti was utilized.
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.
The resistance of several polycrystalline TiB2materials to penetration by liquid aluminum at 970°C was investigated, and their microstructures were characterized. The grain‐boundary properties of individual dibo...
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The resistance of several polycrystalline TiB2materials to penetration by liquid aluminum at 970°C was investigated, and their microstructures were characterized. The grain‐boundary properties of individual diborides rather than the intrinsic properties of TiB2are thought to control stress corrosion susceptibility in liquid metal environmen
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