Effect Of Orientation And Loading Rate On The Toughness Transition CurveOf A Ship Steel

Abstract

Toughness measurements are needed to assess the risk of brittle fracture in warship hulls under operational conditions. This demands laboratory testing at minimum service temperatures and loading rates equivalent to hull impact events. However plate thickness is insufficient to permit valid Kjc determinations at the required strength and toughness levels. The master curve approach specified in ASTM Standard El921 provides an alternative means of quantifying the cleavage fracture resistance in the brittle-to-ductile transition temperature regime. Limited replicate testing yields a reference temperature T<,. It also defines a material-specific fracture toughness master curve, and a lower bound failure probability, which can be applied to material selection and structural integrity analyses. The determination of TO and master curves for a 400 MPa yield strength steel plate is described. Variations in specimen orientation and test loading rate have been investigated, and comparisons are made between the reference temperature results and those from other standardized fracture tests, ft is concluded that the master curve approach is a useful way of quantifying hull toughness for warship fracture control.