Shear lag analysis of strength of dual phase steels

Considering the similarities between structural distribution and deformation behaviour of martensite–ferrite dual phase steels with composite materials reinforced by short, discontinuous fibres, a new expression for the tensile strength of these steels was suggested using shear lag analysis, i.e. σbDP=1K(β23+0⋅65)σbMVM+σbF(1−VM) where σbDP, σbM, and σbF are the tensile strengths of the steel, the martensite, and the ferrite phases respectively, β is the aspect ratio of martensite islands, K is the strength ratio of martensite to ferrite σbM/σbF, V M is the volume fraction of martensite, and (1 – V M) is the volume fraction of ferrite. The experimentally measured strengths of a variety of dual phase steels are shown to be in good agreement with those calculated using this equation. Problems concerning the load transfer from ferrite to martensite and the degree of utilization of martensite strength are discussed.