EPRI 2000 Session: Material Properties Measurement
Scaling of plastic and fracture properties of materials
V. P. Kisel, Institute of Solid State Physics, RAS
ABSTRACT
In spite of numerous recent studies on the plastic and frac ture behavior of different materials, there exists still uncertainty about the micromechanisms of deformation and their relationship with fracture modes. The remarkable finding of this work is the identical corre lation between the starting stresses of different stages of plastic flow and fracture at various scales of observations (internal friction, deformation photoluminescence and etch pit technique [1], macroscopic yield stress and the starting stresses for the first microcrack or macrocrack nucleations), in single/polycrystalline samples, disordered, composite or polymer, adhesive materials, metals and alloys, etc. The experimental data prove that this scaling is universal for the widest temperature, stress and stress rate ranges, for the materials with various volume fraction and state of impurities and composite fibers, precursor strain and thermal prehistory, etc. This universal scaling of stresses points to the c ontrolling role of the deformation stress and to the same mechanisms of plasticity in the strict chain of deformation stages: dislocation motion and multiplication, dislocation cross-slip, climb and full stop, the grain boundary origin and the first microcracks nucleation, then their coalescence into macrocracks (macrofracture) and the formation of fracture surfaces. Due to different properties of dislocation double cross-slip, climb and the Orowan bowing under various types of loadings (shock, impact, Instron or creep) the dislocation structure of plastic zones nearby the fibers, the corresponding fracture modes (so called "ductile", "brittle"/cleavage ones) and the structures of rupture surfaces differ to a great extent from each other. Literature data confirm the fundamental role of interfacial particle (fiber) - matrix stresses (which depend on their form and orientation, size and volume fraction, cohesion and cooling/heating rate, various binder phases and the coatings, temperature, etc. due to different elastic moduluses and thermal expansion mismatches [2]) in the deformation and fracture behavior of composites. The pore nucleation under deformation is often due to the jog-dragging and climb of dislocations emitted from the interface boundaries.
Publication Source: 2nd International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurized Components, May 24-26, 2000, New Orleans, Louisiana USA. Publisher: EPRI - [Homepage]
