At the outset, the effectiveness of published and in-house procedures for the engineering design and assessment of components operating under the conditions of interest was not reliably known. C-FAT provided the opportunity to evaluate the performance of a number of methodologies and to refine them, where necessary, to be more efficient in such circumstances. In this respect, significant developments were achieved in the optimisation of a range of simplified through to fully unified state-variable methods of predicting steady-state and evolutionary creep-fatigue deformation behaviour. Advances were also made in improving the accuracy of damage summation techniques, in particular for strain-fraction methods of calculating creep damage.
The key to these developments were the results from a series of complex-cycle conventional and large scale feature specimen tests which provided the necessary information to validate predictions made using the assessment methods examined. The elaboration of highly specialised testing techniques was necessary to apply the complex loading cycles defined by the industrial partners as being critical in engineering components. The achievements from this activity included (i) the design and manufacture of a tension-compression-internal pressure creep-fatigue testing machine, (ii) new and refined methods of conducting combined primary-secondary creep-fatigue loading on uniaxial testing machines, and (iii) a code of practice for the use of a high temperature local strain measuring sensor.
In order to determine the sensitivity of the assessment methods applied, it was necessary to generate and collage heat specific and alloy scatterband creep-fatigue property datasets. The data collations assembled for 1CrMoV casting and rotor steels, welded 9CrMoVNb piping and welded 18Cr11Ni plate were substantial and represented a major resource to the consortium. This uniaxial data along with the results of the feature specimen tests are contained in a custom built creep-fatigue knowledge based system. In addition to a multi-level database, the C-FAT KBS contains a document base and a dynamic worked example capability.
The project aims to develop and validate effective and economic methods of predicting deformation, crack initiation and early growth in components subject to complex cyclic/hold loading conditions at high temperatures. In particular, it will consider circumstances involving metallurgical and geometrical stress concentration such as weldments and blend radii, and fatigue cycles including creep due to both primary and secondary stress states and ratcheting; all being aspects of uncertainty in current engineering design and assessment codes concerned with creep-fatigue life prediction.
The proposed strategy is to assess, optimise and validate methodologies by using them to predict deformation, crack initiation and early growth behaviour in a number of critical feature type tests. These will employ characterised heats of three materials exhibiting very different cyclic and creep deformation/fracture characteristics and incorporate a range of complex loading features. In addition, the project will assess the sensitivity of the analyses to inter-laboratory and cast to cast variations in the material property input data. An integral part of the investigation will also be to evaluate the effectiveness of NDT inspection methods for detecting crack initiation and early growth from stress concentrations in components.
The data accumulated and the methodologies developed will be fully integrated into a knowledge based software system specifically devised to facilitate further exploration and the introduction of the predictive methods into codes of practice for engineering design and assessment.
Funding SchemeCSC - Cost-sharing contracts
WA3 6AT Warrington
PA4 8UW Renfrew
GL13 9PB Berkeley
4330 Mülheim An Der Ruhr