Fatigue strength of thermal cut steel edges at sub-zero temperatures

Abstract

Openings in the outer shell of ship structures are typically thermal cut. Thermal cut steel edges have an increased risk for fatigue failure due to their local geometry. Additionally the temperature also effects the fatigue strength of thermal cut edges. Since fatigue crack growth testing of base material had shown that the crack growth can be accelerated at low temperatures the effect of low temperatures on thermal cut edges is of particular interest for the fatigue assessment of cruise ships and large yachts, which operates in seasonal freezing temperatures. However the current guidelines for the fatigue assessment of ship structures do not take the effect of low temperatures on the fatigue performance of thermal cut steel edges into account. In order to investigate whether low temperatures have an influence on the fatigue strength of thermal cut steel edges, fatigue tests of plasma cut specimens at -20°C, -50°C and at room temperature are conducted. The results are then statistically evaluated with linear regression and the maximum likelihood method. Thereby it is found that the fatigue strength increase significantly at the tested sub-zero temperatures compared with room temperature. Accordingly no increased risk to fatigue failure of thermal cut steel edges at sub-zero temperatures were found in this thesis.