Analysis of the temperature dependence of the fracture stress of sharp notched bending specimens of a structural steel with respect to intermediate transitions

Abstract

The flow and fracture stresses, σ y g and σ f g (δ = crack tip displacement), of sharply notched bending specimens of a structural steel U St 37-1 are measured in the temperature range from full scale to small scale yielding. The best adaption of the experimental results for σ f g is obtained by a curve which exhibits an intermediate transition, i.e. which follows in a temperature range between an upper, T tM 1 and a lower, T tl 1 , transition temperature to the curve σ y g(T) for the flow stress with a constant δ = δ 1 . This transition corresponds to that of the slip to the twin nucleated fracture. Two analyses [3,5] according to the local fracture stress, σ f ∗ , concept show that the amount and the temperature dependence of σ f ∗ are somewhat different for both methods, but that both exhibit an increase of σ f ∗ in the transition range. It is concluded that each transition in the nucleation mode of the fracture is connected with such a transition in the fracture stress. It may, however, become indistinct or even be covered by the scatter of the experimental points.