Correlation between work hardening and stress relaxation in polycrystalline nickel

Stress-relaxation rate s at a constant strain in A-grade nickel polycrystal s has been reported to depend in a peculiar manner on the initial stress le vel sigma(0) at which relaxation is allowed to start. For large grains (D > 75 mu m), s varies with sigma(0) linearly over the entire stress strain cu rve. For small grains (D < 75 mu m), s-sigma(0) curve undergoes a change in its slope at a critical value of plastic strain epsilon, which decreases a s grain size increases. The observation referred to are found to correlate well with the work-hardening behaviour of the nickel polycrystals.