The visioplasticity approach is developed to enable the complete stress history of any steady or non-steady, quasi-static or impact, plane strain plastic deformation process to be determined from a record of the deformation pattern. The velocity field is determined experimentally and for dynamic conditions high speed photographs are taken of a grid pattern marked on the end surface of the specimen. Digitization of the instantaneous grid node positions allows the velocity fields to be obtained at predetermined time intervals throughout
the transient deformation period. Hence, the strain-rate, equivalent strain rate, equivalent strain and finally stress fields can all be obtained.
A three dimensional surface fitting procedure, using fourth order polynomials, is used to smooth the scalar component
of the experimentally determined velocity field. The condition of continuity (Є [sub x]=- Є [sub y], for plane strain), is imposed on both surfaces thereby reducing the number of independent
parameters from 30 to 10. Besides smoothing the experimental points this procedure has the distinct advantage that the polynomials can be readily differentiated for determining
strain-rates and that deformation can be referred to a master reference grid that is fixed with respect to time.
Plane-strain upsetting tests, conducted at a speed of 0.02 ft/min give results that agree closely with the well documented 'friction hill' type of normal stress distribution for quasi-static rates of strain. However, with the specimen deformed at a speed of 15.7 ft/sec the normal stress distribution is radically different exhibiting a saddle type distribution. The effect of strain rate on the interface and body stresses will have significant bearing on a number of metal forming operations. / Applied Science, Faculty of / Mechanical Engineering, Department of / Unknown
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/21763 |
| Date | January 1978 |
| Creators | Dwivedi, Surendra Nath |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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