Effect of second phase particle on fatigue crack growth behavior in microstructure controlled steels
A series of AK-constant fatigue crack growth tests in Paris regime were carried out to investigate the effect of second phase particle on fatigue crack growth behavior of microstructure controlled steels with uniformly distributed hard particles. Three kinds of materials were used in this study,...
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| 格式: | Thesis |
| 语言: | English |
| 出版: |
2010
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| 主题: | |
| 在线阅读: | http://eprints.uthm.edu.my/3667/1/24p%20MOHAMMAD%20SUKRI%20MUSTAPA.pdf |
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| 总结: | A series of AK-constant fatigue crack growth tests in Paris regime were carried out to
investigate the effect of second phase particle on fatigue crack growth behavior of
microstructure controlled steels with uniformly distributed hard particles. Three kinds of
materials were used in this study, ferrite matrix with pearlite particles (FP), ferrite matrix with
bainite particles (FB) and ferrite matrix with martensite particles (FM). The fatigue crack
growth tests by using a single edge cracked tension (SECT) type specimen was performed
inside a scanning electron microscope chamber equipped with a servo-hydraulic fatigue
machine. The results showed that the fatigue crack growth rates for all materials did not
coincide with each other, even when the crack growth curves were arranged by the effective
stress intensity factor range. From the in-situ observations, crack tip stress shielding
phenomena, such as interlocking, branching, etc. were found on the crack wake, which
enhanced fatigue crack growth resistance. In ferrite-pearlite (FP) steel, small size and small
spacing of hard particles seemed to induce small but frequent crack deflections, which
resulted in crack closure phenomena. On the other hand, large size of pearlite particle seemed
to induce stress shielding phenomena and then contribute to high crack growth resistance,
which was the main reason for higher fatigue crack growth resistance of the large size and
spacing of pearlite particle compared to the small size of pearlite particle. It was similar result
for the ferrite-bainite (FB) steel where the large size and large spacing of bainite particles
enhanced the fatigue crack growth resistance. The higher volume fraction of hard particle also
influenced the fatigue crack growth behavior. In this investigation, the result indicated the
higher volume fiaction of hard particle in the ferrite-bainite (FBI) steel has significantly
increased the fatigue crack growth resistance compared to the ferrite-bainite (FB2) with lower
volume fraction and ferrite-pearlite (FP) steels. The effect of hardness of second phase
particle was also investigated. The results revealed that the ferrite-martensite (FM) steel
showed significantly higher fatigue crack growth resistance compared to the ferrite-pearlite
(FP) and ferrite-bainite (FB) steels. From the in-situ observations, the crack tip stress
shielding phenomena, such as interlocking, branching, etc were found on the crack wake,
which enhanced fatigue crack growth resistance. In the FM steel, the deformation of plastic
constrained at the crack tip in ferrite region seemed to induce stress shielding phenomena and
then contribute to high crack growth resistance, which was the main reason for lower fatigue
crack growth rate of the FM steel with harden martensite particle compared to the FP and FB
steels with soften pearlite and bainite particles.
Keywords : Fatigue crack growth behavior, AK-constant fatigue crack growth tests, crack tip
stress shielding, interlocking, crack closure, ferrite-pearlite, ferrite-bainite, ferrite-martensite,
hardparticle, plastic zone size, plastic constrained deformation. |
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