13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Fracture Based Testing and Modelling, and Component Life Assessment of Welds Kamran Nikbin Mechanical Engineering Department, Imperial College, London, SW7 2AZ, UK Corresponding author: k.nikbin@imperial.ac.uk Abstract Fracture mechanics based methodologies are an important area of research that benefit life assessment techniques in components operating at elevated temperatures. There are many factors which determine a successful methodology for remaining life assessment of engineering components. Important elements are good testing techniques, the development of appropriate and accurate correlating parameters to treat the results in a the unified and verifiable manner in order to produce ‘benchmark’ material crack growth properties and developing accurate modelling procedures for life assessment methods. This presentation considers the first two aspects and identifies future trends and improvements in the developments of standardisations in creep and creep/fatigue crack growth testing of weldments containing residual stress. The paper highlights the important points in these pre-standardisation collaborative efforts by presenting the methods of analyses and example of their application to feature type components. . Keywords Creep Damage; Damage Mechanics; Life Assessment; crack growth; fatigue 1. Introduction The power generation industry is striving to meet criteria for clean and sustainable energy production by increasing efficiency while simultaneously decreasing levels of chemical emissions and pollutants. The efficiency of conventional steam and gas turbine power plant can be significantly improved by increasing the operating temperature, leading to reduced fuel consumption and lower levels of harmful emissions. With the trend towards higher operating temperatures and the competing need to extend the life of existing power plant, more accurate and reliable experimental data for use in improved predictions of component lifetimes at elevated temperatures are needed. In recent years a number of European and International collaborative programmes [1-78] have developed the testing and analysis methodologies as well as a number of databases of laboratory crack growth data base on homogenous parent material. More recently work on crack growth of weldments has been initiated under the auspices of VAMAS TWA31 to address the problems relating to specimens containing welds. The main objective is to establish accurate and reliable testing methods and a unified procedure for assessing creep crack growth at elevated temperatures in industrial specimens, which contain defects. Determination of procedures for analysing the test data using fracture mechanics concepts is important and therefore the validated correlating parameters are made available in the Code of Practice (CoP) [1]. Validation of results against measurements on standard Compact Tension C(T) laboratory specimens using ASTM E1457 has been also been carried out as it indicates the effects of constraint on specimen geometry and size. There are a number of parameters such as K, linear elastic fracture mechanics, Q* based on the thermally activated process and Kcmat based on creep toughness properties that are included in the CoP [1]. However recommendations are only made
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