Extensions of nonlinear error propagation analysis for explicit pseudodynamic testing

Two important extensions of a technique to perform a nonlinear error propagation analysis for an explicit pseudodynamic algorithm （Chang, 2003） are presented. One extends the stability study from a given time step to a complete step-by-step integration procedure. It is analytically proven that ensuring stability conditions in each time step leads to a stable computation of the entire step-by-step integration procedure. The other extension shows that the nonlinear error propagation results, which are derived for a nonlinear single degree of freedom （SDOF） system, can be applied to a nonlinear multiple degree of freedom （MDOF） system. This application is dependent upon the determination of the natural frequencies of the system in each time step, since all the numerical properties and error propagation properties in the time step are closely related to these frequencies. The results are derived from the step degree of nonlinearity. An instantaneous degree of nonlinearity is introduced to replace the step degree of nonlinearity and is shown to be easier to use in practice. The extensions can be also applied to the results derived from a SDOF system based on the instantaneous degree of nonlinearity, and hence a time step might be appropriately chosen to perform a pseudodynamic test prior to testing.

APPLICATION OF SINTAP TO THE SAFETY ASSESSMENT OF X65 PIPELINE STEEL

The recently developed European flaw assessment procedure, structural integrity assessment procedure（SiNTAP） is applied to assessment for welded joints of the API 5L X65 pipeline steel with an assumed embedded flaw and surface flaw at the weld toe. As one of the basic input data, fracture toughness crack tip opening displacement （CTOD） tests are conducted at 0℃ and performed according to the requirements of the standard of BS7448. For the heat affected zone （HAZ） specimens, the microstructure observation is performed to insure that the tip of the crack is located in the coarse grain zone. The result explains the dispersity of the test values. In structural integrity assessment procedure-fracture assessment diagram（SINTAP FAD） method, the failure curves of welded joints at level 1 and 3 are derived from the tensile test results. The results of the assessment show that all assessment points are located within the failure lines of analysis level 1 and 3. So the welded joint of the pipeline is safe. This study laid the foundation of application of SINTAP to pipeline structure assessment.