Motivation. The low temperature fracture behaviour is one of the main concerns regarding steels and weldments for Arctic applications. In Arctic Materials I project, properties of steel and weldments at low temperature (mainly at -60°C) were investigated, and the first generation guideline was proposed. Deterministic design criteria for C-Mn steels were defined as well. However, there is a need to extend the criteria to include quantification of safety levels. Thus, development of knowledge-based quantitative models for brittle fracture will be of the highest importance with regards to laying down the basis for robust guideline requirements. This will include investigations on the impact of geometry constraint, materials mismatch and temperature on fracture toughness level and scatter. In addition to the general models for brittle fracture, there is a need to address specific topics, e.g., wider temperature range from -60°C to -15°C, quantification the effect of residual stresses, low-temperature fatigue behaviour, crack arrest and tensile properties. The way of treatment of residual stresses is extremely important to increase the utility of materials. It is believed that the current fracture assessment procedure is too conservative. Therefore, the investigation of the impact of residual stresses will have huge impact on materials utilization and required fracture toughness. Fatigue properties were not tested in AM I, and the temperature effect on crack growth rate and fatigue should be examined. Finally, as disclosed in AM I, the crack arrest properties seem to be important.
Objectives
To develop knowledge-based quantitative models for brittle fracture and establish a basis for the Guideline
To assess the effect of residual stresses on crack driving force and initiation of brittle fracture
To develop a revised approach to incorporate the effect of residual stresses into integrity assessment procedure
Develop experimental methods that enable quantifying crack arrest properties (e.g. combination of instrumented Charpy and AE methods)
To assess the effect of temperature on crack arrest properties in steel
To develop quantitative models describing the effect of temperature on crack arrest toughness
Evaluate the need and ability for implementing the crack arrest barrier concept in the Arctic Materials guideline
To evaluate the effect of low temperatures on tensile properties
To provide a basis for definition of procedure for tensile testing at lower temperatures
To devise revised models for correction of tensile properties based on room temperature testing.
To investigate the importance of lower temperatures on fatigue
To define if special requirements regarding low temperature fatigue is needed
Work description. The following tasks are included:
