Karl Edgar Hagedorn

Measurements of stretched zone width (SZW)—A round robin program of european group on fracture

Abstract In fracture mechanics tests on metallic materials, blunting of the crack tip always leads to the formation of a stretched zone ahead of the crack tip, prior to actual physical crack growth. A round robin program of the European Group on Fracture Task Group ‘Micromechanism of Fracture’ has shown some problems which seem to arise, when trying to determine the stretched zone width (SZW). The comparison of SZW-values determined from scanning electron micrograph with those coming directly from the scanning screen will be discussed.

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.