Ahmet Gökay Öztürk 030050143 (9th week)

Dispersion Strengthening

In the case of dispersion strengthening (hardening), the fine strengthening particles are a discontinuous second phase without atomic continuity with the matrix. The behavior of such particles is shown schematically in Figure 12.1.7a as a function of increasing aging time or aging temperature (fixed time) which result in larger, more widely spaced dispersed-phase particles. Under stress, dislocations must move around (bypass) such particles, so that yield strength decreases with increased aging. Long aging imes may be used to decrease yield strength (“soften”) of the metal for fabrication. A short aging time, would be used for maximum strength. The dispersed phase can also provide some enhancement of ductility. A dispersion-strengthened metal for which the dispersed phase is stable at elevated temperatures can provide both high-temperature strength and creep resistance (subsection on high-temperature effects).
Surface diffusion treatments usually produce dispersion hardening.
(Frank Kreith, CRC Press Mechanical Engineering Handbook 1999, sec.12 pg.10)



Pitting

Pitting is a very localized attack that results in holes, or voids, on a metal surface.
Although not restricted to active-passive metals, pitting is commonly related to
these. With active-passive metals, pieces of dirt, scale, or other solid particles may
rest on the bottom of a pipe or tank where velocities are not sufficient to move
them. These particles form crevices, resulting in a localized attack similar to crevice
corrosion.
(Joseph E. Shigley, Charles R. Mischke, STANDARD HANDBOOK OF MACHINE DESIGN, sec. 44.3.4)



Resonance

Resonance: A critical aspect of forced vibrations; it occurs when the forcing frequency equals the
system’s natural frequency. In this condition the amplitude of the displacements becomes infinite in theory, or dangerously large in practice when the damping is small. Near-resonance conditions may also be undesirable.
(Frank Kreith, CRC Press Mechanical Engineering Handbook 1999, sec.1 pg.128)



BSFC

Brake specific fuel consumption (bsfc) is a measure
of the effectiveness of an engine’s ability to
convert the chemical energy in the fuel into useful
work. Brake specific fuel consumption is calculated
as shown, for example
bsfc = (mass of fuel consumed per hour)/(brake power)
(Allan Bonnick, Automotive Science and Mathematics, pg. 166)