Abstract Solvent stress cracking studies have been carried out in o-xylene and other solvents on polyetherimide-based materials including neat resin, woven fabric composites, and adhesively bonded systems. The results show crack growth in solvents at very low G(I) levels as compared with tests in air. The composite and adhesively bonded systems have sufficiently high residual thermal stresses to drive an array of intersecting matrix/adhesive cracks even without mechanical loading. The matrix/adhesive residual stress-driven crack patterns retard main delamination crack growth relative to that in the neat resin, and raise the applied threshold G(I) level for main crack growth by about a factor of 10. Stress-corrosion cracking in a commercially available, hot isostatically pressed (HIPed), yttria-fluxed, silicon nitride was the prevalent mode of failure in specimens creep-ruptured at 1,370 C. High-temperature diffusional processes associated with oxygen were responsible for the creation of an advancing stress-corrosion front that had formed at the specimen surface and advanced radially inward. The volume of material in the wake of the stress-corrosion front possessed a high concentration of lenticular cavities at two-grain boundaries, a high concentration of multigrain junction cavities, and large amorphous ``pockets`` in other multigrain junctions that were abnormally rich in oxygen and yttrium.
Protel for windows 10. The combination of tensile stress and the high concentration of cavities in the near-surface volume of the material resulted in microcrack coalescence or the formation of a planar, stress-corrosion crack. The concurrent growth of the stress-corrosion front and crack during the tensile creep-rupture tests ultimately led to stress-induced failure.
Aug 1, 2018 - We thus observe that viscoelastic effects are important for parallel fractures. Very close to the tip (l ≪ R), the shape merges to a lenticular form . The cracks in the y−zplane and the x−zplane are called a.
Santee Cooper (South Carolina Public Service Authority) experienced twenty-three tube failures in a high pressure feedwater heater that was in service less than three years. The tube failures were located at baffles adjacent to both exists of the dual flow desuperheater. Metallurgical analysis of the failed tubes indicated that stress corrosion cracking of the 304N stainless steel was the primary failure mode (Rudin, 1994; Shifler, 1994). Denoiser serial number cracked tongue. The investigation to determine the factors leading to the onset of stress corrosion cracking included analysis of heater acceptance tests, the heater manufacturer`s proposal and manufacturing procedures, operational data, eddy current reports, metallurgical reports, and a heater design review for vibration and wet wall potential (formation of condensation on the outside diameter (OD) of the tube prior to the desuperheater exit). Ceramic matrix composites are being developed to operate at elevated temperatures and in oxidizing environments. Considerable improvements are being made in the creep resistance of SiC fibers and hence in the high-temperature properties of SiCf/SiC composites; however, more needs to be known about the stability of these materials in oxidizing environments before they will be widely accepted. Experimental weight change (1,2) and crack growth data (3,4) supports the conclusion that O2 enhanced crack growth of SiCf/SiC occurs by more than one mechanism depending on the experimental conditions.