Cyclic deformation and fracture of metal-matrix composites: Monofilamentary specimens with mono- and multi-crystalline matrices.

Format:

Book

Thesis/Dissertation

Author/Creator:

Zhang, Jieping.

Contributor:

University of Pennsylvania.

Language:

English

Subjects (All):

Materials science.

Metallurgy.

Mechanical engineering.

0548.

0743.

0794.

Local Subjects:

0548.

0743.

0794.

Physical Description:

306 pages

Contained In:

Dissertation Abstracts International 58-03B.

System Details:

Mode of access: World Wide Web.

text file

Summary:

Studies on cyclic response and fatigue fracture have been conducted on tungsten monofilament-reinforced mono- and multi-crystalline copper composites. The back stress of the composites was found so high and so much larger than the friction stress that there was a pronounced Bauschinger effect. The high cyclic stress in the composites was predominantly due to the back stress which resulted from the interaction between the fiber and dislocations.

The effect of the fiber on strain localization has been investigated using interferometry. Local strain and volume fraction of the Persistent Slip Bands (PSBs) in the composite appeared no different from these in monolithic copper single crystals. However, the distribution of the PSBs was observed to be more uniform, and the total number of the PSBs is substantially higher than that in monolithic crystals. The PSBs appeared mostly in the form of micro-PSBs or macro-PSBs with very limited width. Instead of expanding existing PSBs, new PSBs were more likely to nucleate at new locations during cyclic deformation. The volume fraction and width of the PSBs were observed to increase during saturation, which indicates that some of the PSBs may become aged and new PSBs may form in order to continue to carry the plastic strain.

Fatigue fracture mechanism was governed by the magnitude of the applied strain. At a low or intermediate strain, matrix cracking dominated the fatigue fracture, while at a high strain fiber breaking controlled the process. The enhanced fatigue life of the monocrystalline composite at a low or intermediate strain can be attributed to two factors: (1) delaying formation of a fatal crack because of the uniform distribution of the PSBs; (2) maintaining the stage I crack for most of the fatigue life.

Finally, a model was established to link the cyclic stress-strain response of the mono- and multi-crystalline composites to the behavior of monolithic single crystals and fibers. The results calculated by the model showed very good agreement with the experimental data.

Notes:

Source: Dissertation Abstracts International, Volume: 58-03, Section: B, page: 1479.

Thesis (Ph.D.)--University of Pennsylvania, 1997.

Local Notes:

School code: 0175.

ISBN:

9780591362961

Access Restriction:

Restricted for use by site license.