Papers by Keyword: Fatigue Life Evaluation

Abstract: The availability of reliable fatigue data is of continuous and often urgent need. The paper to be presented therefore intends to show how the potential of non-destructive testing methods, digitisation in metrology as well as signal processing can be combined in order to achieve a significant gain in information concerning the fatigue behaviour combined with a reduction of required experimental effort and cost. The new SteBLife approach is an enhanced short-time calculation method developed at the Chair of Non-Destructive Testing and Quality Assurance at Saarland University, which takes into account that a material’s elastic-plastic reaction and hence relationship is non-linear. With respect to a test strategy, the number of fatigue experiments required to determine a material’s complete S-N-curve can be limited to three to five tests only (SteBLife_mtc, mtc: multiple tests, trend curve and SteBLife_msb, msb: multiple tests, scatter bands) in cases that mean values and/or complete scatter bands of S-N-curves are required. If a trend S-N-curve is sufficient, the effort can be reduced to one single test only (SteBLife_stc, stc: single test, trend curve) with a special step-shaped specimen. This leads to a significant improvement in efficiency when compared to the conventional way an S-N-curve is determined where a minimum of 15 fatigue tests is required. Within the work to be presented the SteBLife method is demonstrated for normalized SAE 1045 (C45E) steel.

Abstract: Operating characteristics of small and medium tonnage lattice boom crane which withstand fatigue loads was analyzed in this paper. It showed that the lattice boom crane utilization level is in the overlap zone of low cycle fatigue and high cycle fatigue. There may be some plastic deformation in the structure. So the total damage calculated by the Palmgren-Miner rule had a large scatter. Typical operating conditions was analyzed that K-type welded joints of the boom is under axial load and in-plane bending loads. Several critical areas of K-type welded joints were determined by ANSYS finite element calculation software where the stress amplitude was larger on the single side of the lattice boom. A new stress spectrum acquisition method based on the “measured+statistics+compare+simulation” integrated strategy of crane K-type welded joints was proposed. Based on a simplified Huffman non-linear cumulative damage theory, fatigue life of crane K-type welded Joints were calculated based on the strain parameters. They were compared with Palmgren-Miner rule and together with fracture mechanics method. Results showed that although they were all conservative compared with test results, the new method can be applied easily in for engineering applications because it only need amplitude constant amplitude fatigue strain-life data.

Abstract: This paper aims to evaluate the fatigue life of an existing railway riveted steel bridge. Based on the measured train load information, the current load spectrum of the bridge is obtained, and the stress histories and stress spectrum of main members of the bridge are achieved using FE model and rain-flow counting method. The fatigue life of the bridge using traditional method is evaluated. At the same time, the finite element (FE) model of riveted component is established and the stress intensity factor of crack tip is calculated. The fatigue crack is simulated on the basis of linear elastic fracture mechanics (LEFM), and the fatigue life of the main members is also evaluated based on the damage tolerance analysis method. The evaluated results of fatigue life show that the fatigue remaining life of the bridge is very long due to the lower live load stress level.

Abstract: While the demand on electric power is consistently increasing, public concerns and regulations for the construction of new nuclear power plants are getting restrict, and also operating nuclear power plants are gradually ageing. For this reason, the interest on lifetime extension for operating nuclear power plants by applying lifetime management system is increasing. The 40-year design life concept was originally introduced on the basis of economic and safety considerations. In other words, it was not determined by technological evaluations. Also, the transient design data which were applied for fatigue damage evaluation were overly conservative in comparison with actual transient data. Therefore, the accumulation of fatigue damage may result in a big difference between the actual data and the design data. The lifetime of nuclear power plants is mostly dependent on the fatigue life of a reactor pressure vessel, and thus, the exact evaluation of fatigue life on a reactor pressure vessel is a crucial factor in determining the extension of operating life. The purpose of this paper is to introduce a real-time fatigue monitoring system for an operating reactor pressure vessel which can be used for the lifetime extension. In order to satisfy the objectives, a web-based transient acquisition system was developed, thereby, real-time thermal-hydraulic data were reserved for 18 operating reactor pressure vessels. A series of finite element analyses was carried out to obtain the stress data due to actual transient. The fatigue life evaluation has been performed based on the stress analysis results and, finally, a web-based fatigue life evaluation system was introduced by combining analysis results and on-line monitoring system. Comparison of the stress analysis results between operating transients and design transients showed a considerable amount of benefits in terms of fatigue life. Therefore, it is anticipated that the developed web-based system can be utilized as an efficient tool for fatigue life estimation of reactor pressure vessel.

Abstract: In general, the fatigue life of major nuclear components has been evaluated based on design codes conservatively. However, sometimes, more exact fatigue life evaluation is required for continued operation beyond the endorsed life. The purpose of this paper is to carry out 3-D stress and fatigue analyses reflecting full geometry as well as actual operating data. The actual operating data acquired through a monitoring system were filtered and assessed. Then, temperature and stress transfer Green’s functions were developed and applied to critical locations of reactor pressure vessel. The finite element analyses results for representative design transients were verified through comparison to reference solution and showed that the conservatism of current 2-D evaluation. Therefore, it is anticipated that the proposed scheme adopting Green’s function and real operating histories can be utilized for remaining life time evaluation of major components.

Abstract: The interest of the fatigue life for rubber components was increasing according to the extension of warranty period of the automotive components. In this study, the fatigue lifetime prediction methodology of the vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue tests. Finite element analysis of 3D dumbbell specimen and rubber component was performed based on a hyper-elastic material model determined from the mechanical tests. The Green-Lagrange strain at the critical location determined from the finite element analysis was used for evaluating the fatigue damage parameter of the natural rubber. Fatigue tests were performed using the 3D dumbbell specimens and rubber component with different levels of maximum strain and various load. Fatigue life curves can be effectively represented by a following single function using the maximum Green-Lagrange strain. Fatigue lives of the natural rubber are predicted by using the fatigue damage parameters at the critical location. Predicted fatigue lives of the rubber component for automobile vehicle agreed fairly with the experimental fatigue lives.

Abstract: In this paper, a knowledge-based information system for the plant operation of steel making company has been proposed. The system, which is named as K-VRS(Knowledge-based Virtual Reality System), provides a connection between ERP plant maintenance module and knowledge-based engineering methodologies, and thus, enables network-based highly effective plant maintenance process. The developed system is expected to play a great role for more efficient and safer plant maintenance.