| Popis: |
In situ TEM experiments of crack tips under deformation have been evaluated in detail for an Fe 2wt%Si polycrystalline sample under mode I loading. Number of dislocations emitted at increasing crack length and crack-tip opening displacement are recorded along with apparent dislocation free zones. Dislocation estimates from both slip-line densities and actual counts were utilized to determine values in reasonable agreement with observed crack-tip opening displacements. From this, it was possible to associate an applied mode I stress intensity, KI, from which equilibrium could be calculated. At stress intensities near 2, 4 and 8 MPa √m, the number of dislocations needed for shielding are in agreement with several analytical and numerical models. At the highest KI, this may be fortuitous as two {312} slip systems are calculated due to crack-tip, grain boundary interactions. Computer simulations of the dislocation configurations observed here and analytical solutions of the grain boundary interaction are discussed in detail in Part II of this three part series. |
