Showing papers on "Fractography published in 1968"

Comparison of Transmission Electron Microscopy and Scanning Electron Microscopy of Fracture Surfaces

Abstract: Based on the above considerations, the scanning electron microscope has unique capabilities for the study of fracture surfaces and should extensively replace the replication fractography currently used with the TEM. The most attractive advantages of the SEM are (a) direct examination, (b) no sample preparation, (c) accommodation of large size samples, (d) satisfactory resolution, (e) range of magnification from 20X to 100,000X, (f) very large depth of focus, and (g) capability to examine a specimen in a number of orientations. Despite the absence of diffraction in the SEM (which appears to be the only disadvantage of this process, at present), it is obvious that, for fractography purposes, scanning electron microscopy has an equally important or a greater role to play than TEM fractography in the coming years.

Plasma sprayed metal matrix fiber reinforced composites.

Abstract: : High strength, high modulus boron reinforced metal matrix composites were fabricated by plasma spraying. A new fabrication technique which includes the plasma spraying of monolayer fiber reinforced tapes and the subsequent diffusion bonding of these tapes was found to be an excellent method to insure reproducible properties in the composites. Boron fibers coated with silicon carbide were found to have superior resistance to degradation at elevated temperatures compared to that of boron. The elastic and strength properties of the composites were characterized for unidirectional composites. Strengths of up to 189,000 psi in tension and 297,000 psi in compression were measured for composites with 50% volume fraction BORSIC fiber in aluminum. Other properties measured include fatigue strength, creep, stress rupture, impact resistance, and high temperature strength. Analytical mechanics, fractography, metallographic examination and nondestructive testing were used to better understand the properties of the composite structures. (Author)

Structural modes of fracture.

Abstract: Structural modes of fracture, analyzing brittle, ductile, fatigue and stress corrosion fractures using fractography

Subcritical Flaw Growth in 9Ni-4Co-0,25C Steel - A Fatigue and Fractographic Investigation and Its Relationship to Plane Strain Fracture Toughness

Abstract: : Fatigue crack propagation and plane strain fracture toughness (K(sub Ic)) studies were conducted on a 9Ni-4Co-0.25C steel which had been quenched and tempered to a yield strength of 180 ksi. Fatigue specimens were cycled to failure in a room air environment under several combinations of cyclic and tensile mean loads. It was observed that fatigue crack propagation became unstable at a critical level of stress-intensity which led to rapid failure. This critical stress-intensity level in fatigue was consistently below the stress-intensity value for crack instability predicted by conventional rising load K(sub Ic) tests. Electron fractography studies were conducted on the fatigue surfaces. A gradual change in fracture surface appearance with cyclic stress-intensity level was found to occur. Fatigue striations predominated at low cyclic stress-intensity levels, changing to dimpled rupture at high cyclic stress-intensity levels. No abrupt change in fracture surface appearance was observed to coincide with the critical stress-intensity level in fatigue. It is concluded from this study that, although K(sub Ic) provides a lower-bound estimate of stress-intensity for terminal fracture in monotonic loading, subcritical flaw growth by fatigue in some high-strength materials may define a more conservative estimate of structural material performance.