Title page for ETD etd-06082009-170819

Type of Document Master's Thesis
Author Laurent, Michel P.
URN etd-06082009-170819
Title A continuum surface layer effect in polycrystalline aggregates
Degree Master of Science
Department Engineering Mechanics
Advisory Committee
Advisor Name Title
No Advisors Found
  • Aluminum alloys
Date of Defense 1994-08-05
Availability restricted

Uniaxial tension tests on uniform cross section specimens of Ti-6Al-4V and aluminum 7475-T651 show that the stress in the direction of load application determined by x-ray diffraction and the nominal applied stress display the expected linear correspondence up to a maximum stress somewhat below the bulk yield paint. Above this stress, the xray stress is noticeably less than expected. Upon unloading, there is a substantial acquired compressive residual stress. Because the x-ray diffraction measurements provided average stress values in a surface layer of only a few grain diameters, these results suggest that the surface layer of the metal is yielding at a lower stress than the bulk. This anomalous behavior is duplicated qualitatively with a continuum model of an aggregate of soft and hard square grains obeying the Von Mises yield criterion. The effect is purely mechanical. No material effects, such as lower yield point or dislocation density for the surface grains, are invoked. The continuum effect decreases rapidly with depth, becoming negligible for depths exceeding 2-3 grain or domain diameters. Further work is required to refine the model for real systems and to assess the importance of material effects acting in conjunction with the continuum effect.

  Filename       Size       Approximate Download Time (Hours:Minutes:Seconds) 
 28.8 Modem   56K Modem   ISDN (64 Kb)   ISDN (128 Kb)   Higher-speed Access 
[VT] LD5655.V855_1994.L387.pdf 53.48 Mb 04:07:35 02:07:20 01:51:25 00:55:42 00:04:45
[BTD] next to an author's name indicates that all files or directories associated with their ETD are accessible from the Virginia Tech campus network only.

Browse All Available ETDs by ( Author | Department )

dla home
etds imagebase journals news ereserve special collections
virgnia tech home contact dla university libraries

If you have questions or technical problems, please Contact DLA.