Factors Affecting Necking Elongation of Steel Sheets

Necking behaviour in tensile tests has been investigated for typical steel sheets. Local elongation in spontaneously necked region depends mainly upon the strain diffusibility of materials. Using specimens having artificial necking, a fomula describing this strain diffusibility has experimentally been deduced in relation to temperature and strain rate dependences of flow stress, and stress ratio. Furthermore, the relationship between necking elongation and macro-factors affecting it is formulated as follows, δn∝ΔP/P+0.22r/r+1where, δn : necking elongation, P: maximum load, ΔP : increment of maximum load with the change in tension speed from 10 mm/min to 100 mm/min, r: Lankford value in tensile direction.