Papers by Keyword: Fatigue Evaluation

Abstract: The traditional Low Cycle Fatigue (LCF) evaluation method is based on elastic analysis with Neuber’s rule which is usually considered to be over conservative. However, the effective strain range at the steady cycle should be calculated by detailed cycle-by-cycle analysis for the alternative elastic-plastic method in ASME VIII-2, which is obviously time-consuming. A Direct Steady Cycle Analysis (DSCA) method within the Linear Matching Method (LMM) framework is proposed to assess the fatigue life accurately and efficiently for components with arbitrary geometries and cyclic loads. Temperature-dependent stress-strain relationships considering the strain hardening described by the Ramberg-Osgood (RO) formula are discussed and compared with those results obtained by the Elastic-Perfectly Plastic (EPP) model. Additionally, a Reversed Plasticity Domain Method (RPDM) based on the shakedown and ratchet limit analysis method and the DSCA approach within the LMM framework (LMM DSCA) is recommended to design cyclic load levels of LCF experiments with predefined fatigue life ranges.

Abstract: Finite element model updating is a well-known technique to better characterize the real behaviour of civil engineering structures. The updated numerical model can be used to perform a more accurate structural assessment. Herein, its effectiveness is validated through the fatigue assessment of a lively footbridge considering two different numerical models: (i) a preliminary finite element (FE) model and (ii) an updated version of the preliminary model based on the modal parameters of the footbridge identified experimentally. For this purpose, the Malecon footbridge (Murcia, Spain) has been considered. This footbridge, a cable-stayed structure, is prone to vibrate in vertical direction under continuous walking pedestrian flows so fatigue damage might be expected on its supporting cables. A detailed FE model of the footbridge has been performed and subsequently updated based on the experimental modal parameters of the structure. The behaviour of the pedestrian flows was characterized by field observations. Finally, a comparison is performed between the fatigue damage of some cables of the footbridge considering the two mentioned FE models. The safe life method was used to assess such damage. As result, a maximum relative difference around 52 % was obtained between the two numerical models.

Abstract: The fatigue life of autofrettaged thick-walled cylinders with a radial cross-bore is investigated by applying inelastic finite element analysis with cyclic pressure loading. A non-linear kinematic hardening model considering bauschinger effect is used for determining cyclic plastic strain ranges in fatigue evaluations. A macro is written in ANSYS to calculate the equivalent alternating stress intensity, based on the ASME Boiler and Pressure Vessel Code. For a specific cyclic load level, a distinct optimum autofrettage pressure is identified by plotting autofrettage pressure against the equivalent alternating stress intensity and the number of cycles from design fatigue data. The optimum autofrettage pressure was found in the range of 80.5%-92.5% of limit pressure. The hydrotest had little influence on the fatigue life when the thick-walled cylinder was autofrettaged with an optimum autofrettage pressure.

Abstract: As the capacity and thermal parameters of turbine generator become larger and higher, the strength design plays increasingly important part in manufacturing process while the traditional strength check method based on the nominal stress which is modified by the stress concentration factor has many disadvantages. The paper proposed Finite Element Analysis (FEA) to analyze the local stress which is more accurate and convenient to seek the dangerous failure point. The possible running conditions which maybe encountered in field are needed to be adequately considered in design process. Two phase short circuit which is the unavoidable condition in the unit’s running porcess plays significant impact on the shafts strength life and the unit’s life-cycle. The paper analyzes the fatigue evaluation of two phase short circuit to enhance the design reasonability as a typical case study. Using FEA and fatigue evaluation methods, more details of the shafts structures and the running processes are taken into accounts which make the dseign process more reliable.

Abstract: Fatigue strength of welded structures can be estimated by obtaining local notch stress concentration under the service loading. On the bases of considering influence of weld geometry details and micro-support notch effect at weld toe, the local notch stress fields of welded structure of large-scale electromotor rotor were simulated by global-local analysis in finite element method (FEM) to evaluate the fatigue strength. The fatigue notch factors of different weld shapes were also determined. For longitudinal fillet weld of shaft-ribs welded structure under moment of torsion, as well as sealing weld in axis head faces of ribs under gravity, the simulation results show that at weld toe the fatigue notch factor of concave fillet weld is the lowest, the one of flat fillet weld is second lowest, and the one of convex fillet weld is the highest.

Abstract: The suspension bridge has more flexibility and repetitive vehicles produce stress cycles in members. Then fatigue of the member is accumulated with the daily traffic loadings. In order to evaluate the working condition of the Tsing Ma Bridge, the online monitoring health system has been installed in long suspension bridge. The location of the strain sensor is not exactly at the critical member locations. The hot spot stress analysis for critical members is necessary for accurate fatigue evaluation of the bridge. The global finite element analysis of the Tsing Ma Bridge under traffic loading is performed to determine the critical fatigue member locations. A detailed local finite element analysis for the welded connections is performed to determine the hot spot stress of critical fatigue location. As a case for study, the calculated stress concentration factor is combined with the nominal representative stress block cycle to obtain the representative hot spot stress range cycle block under traffic loading from online health monitoring system. The comparison result shows that the nominal stress approach cannot consider the most critical stress of the fatigue damage location and the hot spot stress approach is more appropriate for fatigue evaluation.

Abstract: This study was aimed at evaluating the durability of the car body for rubber-tired light rail vehicles according to Korean-standardized specifications for light rail vehicles (size, strength, structure, weight, etc.). The strengths of the car body were analyzed under two weight conditions (tare weight and maximum passenger weight) by using the finite element method. Based on the results of the analysis, dynamic stresses were measured by using strain gauges, including rosette gauges, while the train was running on the test track. Various experimental results have verified the durability and safety of the car body.