摘要:

The formation of cavities during creep increases the creep rate as a result of the combined effects of the decrease in elastic modulus, which results in elastic creep, and the enhanced rate of the basic creep process caused by stress transfer. Analyses of these effects are presented for the special case of cavities in the form of cracks. The net rate of creep can be described by a total of four terms. Permanent crack‐opening displacement resulting from creep deformation of material adjacent to the cracks results in a permanent pore phase following unloadin

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1983.tb10026.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The kinetics of amorphous phase separation in BaO‐SiO2glasses was studied by small‐angle X‐ray scattering and positron annihilation. Results show that the annihilation of positrons depends primarily on the average composition of the glasses; it therefore does not depend on compositional fluctuations caused by phase separation and cannot be used to determine the kinetics of phase separation in gl

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1983.tb10027.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Static fatigue tests on metal‐coated silica fibers have shown subcritical crack growth with crack velocities ranging from ∼10−14to 10−17m.s−1. To induce subcritical crack growth, however, it is necessary that the test be performed at stress intensities, KI, of>0.8 KIC. Metal‐coated fibers provide a unique medium for studying static fatigue at these high stress levels because the metal coating protects the fiber from the external environment. Crack growth,for these tests demonstrates the sensitivity of crack velocity to OH−concentrations at t

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1983.tb10028.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Data are presented for the thermal diffusivity/conductivity of hot‐pressed mixtures of SiC and AlN. Results indicate that hot‐pressing at higher temperatures, which permits solid‐solution formation, results in significantly lower thermal diffusivity/conductivity than is obtained by hot‐pressing at lower temperatures, at which discrete phase

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1983.tb10029.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The optical absorption spectra of 22R2O.13Al2O3.65B2O3(mol%) glasses contain ing uranium indicate the presence of U6+, U5+, and U4+. The presence of U6+in the uranyl group is favored as alkali ion (R) is replaced in the direction Li

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1983.tb10030.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

(Ni,Zn)Fe2O4samples containing small amounts of Co were characterized in a transmission electron microscope to ascertain the micro structural changes accompanying low‐temperature oxidation of the samples. Although no new features resulting from oxidation were observed, prominent surjace reduction occurred in the thin foil specimens. Formation and growth of Ni particles on the ferrite surface are explained using the heats of formation of the oxides

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1983.tb10031.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Minimum strengths of proof‐tested optical fibers were investigated on the basis of the fracture mechanics concept. To confirm truncation of the minimum strength by the proof test, tensile tests were performed for long proofed fibers over a total length of 150 km. The results confirm that the proof test is useful in guaranteeing the minimum strengt

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1983.tb10032.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Elastic moduli of polycrystalline HfO2and ZrO2stabilized with 33 mol% Praseodymium oxide or terbium oxide were studied as functions of porosity and temperature. Thermal expansion was measured to 1200°C for each composition. The modulus‐vs‐porosity and thermal expansion curves were typical; however, modulus‐vs‐temperature relations were abnormally steep below 400°C, a phe nomenon observed previously for stabilized HfO2compositions. All compositions exhibited obvious stoichiometric changes resulting from oxidation‐reduction annealing, but only the Tb4O7‐stabilized ZrO2showed any significant effect of oxidation state on the modulus values; this effect was ve

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1983.tb10033.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The solid sodium electrolyte β″‐Al2O3(Li‐stabilized) was strengthened with additions of tetragonal ZrO2(15 vol%). The conductivity of this composite material, measured in an Na/Na cell, was 7.7 Ω· at 300°C. Average values of strength and the critical stress intensity factor were 350 MPa and 4.5 MPa·m1/2, respectively, for the sintered composit

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1983.tb10034.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Equations for the shear modulus of a two‐dimensional model with preferentially oriented microcracks were derived from a tentative equation for the shear modulus of a corresponding model with elliptical inclusions obtained from solutions of stress concentration factors. Exact agreement found with literature solutions based on energy und dislocation methods suggests that the elastic behavior of ceramic matrix composites and microcracked ceramics can be predicted from the same equatio

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1983.tb10035.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY