Influence of brittle fracture on the crashworthiness of ship and offshore structures in Arctic conditions

Abstract

Structures operated in Arctic regions are exposed to low temperatures, which may be in the range of the ductile- brittle transition temperature (DBTT) of steel. This implies that the brittleness of the material in such condi- tions should be taken into account to assess the crash- worthiness of the structure at hand. This paper describes finite element simulations of the Charpy-V test for a wide range of low temperatures. To examine the energy absorption of the specimen under impact loading, simple failure criteria are implemented into nonlinear finite element simulations with ABAQUS/explicit using a user subroutine. Ductile failure is predicted by the shear failure criterion, which has been widely used for large-scale ship collision simu- lations. The RKR model, which was developed by Ritchie et al. (1973) based on fracture mechanics, is used for brittle fracture prediction. Fine solid elements corresponding to the grain size of the material are em- ployed in the expected failure area to satisfy the re- quirement of the RKR model. The energy absorption of the specimen at different low temperatures is investigat- ed both with and without consideration of brittle frac- ture and then compared with the DBTT curve from the Charpy-V tests. It is found that when the ductile and brittle fracture mechanisms are considered simultane- ously, the DBTT curve obtained by numerical simula- tion shows good agreement with the test results. The present procedure helps to identify the probability of the occurrence of brittle fracture in ship and offshore structures subjected to abnormal loads and accidental actions. It is concluded that brittle fracture should be taken into account in the estimation of the crashworthi- ness for structures operating in Arctic conditions. On the basis of the results of the present work, the authors intend to calibrate failure criteria adopted for large shell elements with respect to the occurrence of brittle frac- ture to allow the effect of low temperatures to be taken into account in simulations of large-scale structures subjected to collisions from ships or icebergs.