A system for ultrasonic fatigue testing at temperatures as high as 700 C and at positive mean stresses has been developed. Its use is demonstrated by examining the fatigue behavior in the lifetime range of 10 to 10 cycles for the nickel-base superalloy Rene' 88 DT at 20 and 593 C for a load-ratio of 0.05. Crack initiation occurred from large grains and from inclusions, consistent with crack ini...

The effect of casting pores on the very high cycle fatigue (VHCF) behavior of a directionally solidified (DS) Ni-base superalloy DZ4 is investigated. Casting and hot isostatic pressing (HIP) specimens were subjected to very high cycle fatigue loading in an ambient atmosphere. The results demonstrated that the continuously descending S-N curves were exhibited for both the casting and HIP specime...

A study has been made of Hertzian contact damage in compressive shear stress field beneath the contact area. The observed microcrack density increases with grain size, porous and dense liquid-phase-sintered aluminas. Indentation stress–strain curves show increasing nonlinearity as the implying a threshold microstructural scale for crack initiation. In contrast, the micromechanisms controlling f...

The transducer-lens system is one major component in the performance of an acoustic microscope. The design criteria for the various types of applications of an acoustic microscope are different. For surface imaging applications, it is desired to have a small spot size and low sidelobe level. For materials characterization and subsurface imaging applications (sue~ as subsurface crack imaging), i...

Rolling contact fatigue failure is one of the main damages in railway wheels caused by cyclic rolling with rails. This internal defects such as nonmetallic inclusions or voids and may occur heavy haul freight car wheels. The subsurface crack propagation behaviors are evaluated twin-disc-type tests using test specimens artificial defects. Finite element analyses involving simulated also conducte...

Notches were machined in specimens of Inconel 718 by a broaching process, where differing broaching runs led to differing extents of sub-surface deformation and surface roughness. Fatigue tests were carried out at 600 ̊C with a trapezoidal loading waveform at 0.25Hz. The broaching process that led to the more severe sub-surface deformation (but lower surface roughness) showed the worst fatigue p...

Evaluation and non-destructive identification of stress-induced cracks or failures in metals is a vital problem in many sensitive environments, including transportation (steel railway tracks, bridges, car wheels, etc.), power plants (steam generator tubing, etc.) and aerospace transportation (landing gear, aircraft fuselages, etc.). There are many traditional non-destructive detection and evalu...

The ability of staining slurries containing silver and/or potassium compounds to enhance the mechanical properties of a leucite-reinforced glass ceramic (IPS Empress CAD) was investigated by measuring the Vickers hardness, median crack length, toughness, and compressive residual stress of specimens. A staining slurry containing potassium ions was found to increase the toughness of IPS specimens...

Validating simulated predictions of internal damage within armor ceramics is preferable to simply assessing a model s ability to predict penetration depth, especially if one hopes to perform subsequent ‘‘second strike’’ analyses. We present the results of a study in which crack networks are seeded by using a statistically perturbed strength, the median of which is inherited from a deterministic...