Fatigue Strength of HFMI-treated High-strength Steel Joints under Constant and Variable Amplitude Block Loading

AbstractLightweight-design of welded high-strength steel structures in cyclic service necessitates the use of post-treatment methods like the high frequency mechanical impact treatment (HFMI). Service loads during operation mostly consist of variable amplitudes, whereat recommendations are only available for the as-welded condition. Therefore, this paper deals with the effect of variable amplitude block loading on the fatigue strength of HFMI-treated T-joints. An evaluation of the real damage sum exhibits characteristic distinctions to constant amplitude test results in regard to the base material strength. The application of an equivalent stress range method by nominal and effective notch stress approach is finally presented

Lifetime evaluation of hot forged aerospace components by linking microstructural evolution and fatigue behaviour

AbstractThe present work aims at linking the local distribution of fatigue strength in a forged part to its manufacturing process. To this purpose, a predictive fatigue strength model for Inconel 718, also including the operating temperature, is derived from a reduced set of numerous microstructural parameters. The model is implemented, along with a microstructural evolution model from earlier work , into a finite element code in order to predict the local fatigue strength distribution in a component after being subjected to an arbitrary forging process

Local strain energy density approach to assess the fatigue strength of sharp and blunt V-notches in cast steel

In this work, the strain energy density approach (SED) is utilized to assess the fatigue strength of circumferential V-notched specimens covering axial loading and rotating bending. Subsequent calculations of the linear-elastic SED lead to a statistical proven accordance among about one-hundred experimental tests, thereby introducing extended H-function values for increased 15 Rc to values as well. Furthermore, low-cycle fatigue tests are conducted and utilized in an extensive elasto-plastic SED assessment. Thus, the scatter index of the evaluated equivalent strain energy density is reduced towards a ratio of about two. Concluding, the nite-volume-based energy approach provides an engineering-applicable fatigue assessment tool

Application studies for fatigue strength improvement of welded structures by high-frequency mechanical impact (HFMI) treatment

\ua9 2015 Elsevier Ltd.In 2013, a new guideline for the design of high-frequency mechanical impact (HFMI) treatment was drafted. The proposed design curves were made based on the fatigue data of axially-loaded welded joints which were manufactured from high-strength steels. All the S-N curves were shown to be conservative with respect to the existing fatigue data for laboratory-scale specimens of longitudinal, transverse, and butt welds. In reality, structures in civil, offshore, mechanical engineering and ship industries generally include large-scale and more complicated components rather than laboratory-scale specimens. Therefore, this paper firstly presents the validation of design proposals by considering fatigue data sets for large-scale welded structures. In total, 62 fatigue data points for bridge, crane and beam-like components are reported, in which the yield strength varies from 250 to 725 MPa, and stress ratio varies from -1 to 0.56. Validations are then extended also for cover plates by performing fatigue tests of 23 weld details both in as-welded and HFMI-treated cases for the use of crane industry. Both the extracted and obtained fatigue data are found to be in good agreement with the previously-proposed design guidelines for nominal and effective notch stress assessment