ABSTRACT

The crack propagation characteristics of steel A537. under constant load, were studied at 238K.273K and 303K. using fracture mechanics. The fatigue crack propagation in steel A537 at the above testing temperatures was in accordance with Paris law. As the temperature decreased, the fatigue crack growth rate decreased for most region of the crack propagion and the Paris exponent n greatly increased. This caused a much higher acceleration of growth rates at lower temperatures. The curves of the propagation diagram at different temperatures tend to converge with the increase of stress intensity factor range ∆K and intersect at a certain high ∆K level. Thus. after the intersection, the crack growth rate at lower temperatures was inversely higher than that at room temperature. The crack growth rates are represented by the Yokobori formula. The fracture surfaces were observed under a scanning electron microscope. showing that the fracture of steel A537 at all the testing temperatures took the form of microvoid coalescence. which characterizes ductile fracture.

INTRODUCTION

In cold climates, structures such as bridges, towers and buildings may be subjected to temperatures that fall as low as 220K. The materials used in constructing these structures are low-carbon structural steels, rather than steels designed for low temperatures. Because of reduced fracture toughness of such low-carbon structural steels. fatigue cracks are quickly propagated and become unstable at low temperatures(1). Therefore. to prevent unstable fractures. reliable data on the fatigue crack growth rates of such steels at low temperatures is required for safely designing and determing the inspection period of these structures. This proposal was for Bohai Oil Company. one of the largest offshore oil companies in China. Bohai's winter temperatures fall to 248K and the Bohai Sea stays frozen for almost three months of the year.

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