Papers by Keyword: Low Cycle Fatigue

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Authors: Xian Min Chen, Qin Sun, Di Guan, Feng Ping Yang
Abstract: A damage evolution model is presented for fatigue life prediction of metallic structures. This model is formulated based on damage mechanics and the irreversible thermodynamics framework developed by LEMAITRE and CHABOCHE. Using this model, the fatigue lifetime can be predicted both in the high cycle fatigue (HCF) regime and the low cycle fatigue (LCF) regime. Based on the energy theory and material fatigue test data, the plastic strain threshold for damage initiation was modified for HCF and LCF respectively. The damage evolution parameters were determined according to the fatigue test results of standard specimens. A damage mechanics-finite element full-couple method was adopted to simulate the process of fatigue damage evolution. The numerical simulation of fatigue lives were compared with the fatigue tests of 2A12-T4 open-hole plates and good agreement was obtained.
Authors: Qin Dong, Ping Yang, Jun Lin Deng, Hong Wang
Abstract: A low-cycle fatigue damage model for stiffened plates has been derived based on the theory of damage mechanics. The fatigue damage variable equation of the stiffened plate under cyclic loading was introduced into the accumulative plastic strain equation. Then by means of integral transformation, the evolution equation of axial plastic strain was derived under low cyclic loading condition. The analysis results by the presented model compare well with those by the finite element method.
Authors: C.K. Seal, M.A. Hodgson, W. George Ferguson
Abstract: During the mid 1990s earthquakes in Northridge, California, and Kobe, Japan, illustrated a lack of understanding of the behaviour of structural steels exposed to seismic loads. Under this type of load regime, structural steel members are subjected to fully plastic load cycles and unexpectedly brittle failures resulted. This paper presents a simple, yet powerful, method for predicting the accumulation of damage in a steel element, based on its toughness. In addition the damage parameter chosen provides an accurate prediction of when failure of the element can be expected to occur. The damage accumulation model developed allows for the deconvolution of complex load histories, such as could be expected to occur during a seismic event, in a systematic, stepwise manner. This approach is ideally suited to automation and could readily be implemented into a finite element model.
Authors: S. Gao, Ewald Werner
Abstract: The forging die material, a high strength steel designated W513 is considered in this paper. A fatigue damage model, based on thermodynamics and continuum damage mechanics, is constructed in which both the previous damage and the loading sequence are considered. The unknown material parameters in the model are identified from low cycle fatigue tests. Damage evolution under multi-level fatigue loading is investigated. The results show that the fatigue life is closely related to the loading sequence. The fatigue life of the materials with low fatigue loading first followed by high fatigue loading is longer than that for the reversed loading sequence.
Authors: Michael Katcher, Dwaine L. Klarstrom
Abstract: HAYNES® 230® and 617 alloys are competing for use on Generation IV, high temperature gas cooled reactor components because of good high temperature creep strength in the temperature range between 760°C and 982°C and resistance to oxidation in the gas cooled reactor environment. A review of the metallurgy affecting the properties in each alloy will be discussed. Grain size and carbide precipitation developed during fabrication effect short term and long term ductility, fatigue, and creep. For example, 230 alloy has a finer grained structure which promotes fatigue strength with a slight sacrifice in creep strength. The 617 alloy has a coarser grain structure which provides slightly higher creep resistance while sacrificing some fatigue strength. Thermal aging also introduces gamma prime precipitation to the 617 alloy as well as grain boundary carbides, and this, in addition to grain boundary oxidation, reduces the low cycle fatigue strength of 617 alloy compared to 230 alloy. Independent studies have shown that 230 alloy possesses higher resistance to thermal fatigue than 617 alloy. However, welds of both base metals with similar weld composition have about the same thermal fatigue life. Cooling rates from solution annealing temperatures during processing effect the ductility and creep strength of these alloys with the highest cooling rates preferred for retention of ductility and creep strength. The reason; slow cooling rates promote carbide precipitation in the grain boundaries which reduces ductility and creep strength.
Authors: George C. Kaschner, Jeffrey C. Gibeling
Abstract: Strain rate jump tests were performed during low cycle fatigue using plastic strain rate as the real time computed control variable. Test materials included OFE polycrystalline copper, AA7075-T6 aluminum, and 304 stainless steel. The evolution of dislocation interactions was observed by evaluating the activation area and true stress as a function of cumulative plastic strain. Activation area values for each of the three materials were evaluated from an initial state to saturation. All three materials exhibit a deviation from Cottrell-Stokes law during cyclic deformation. Tests performed on each of the three materials at saturation reveal a dependence of activation area on plastic strain amplitude for copper and aluminum but no such relationship for stainless steel. These results reflect a contrast between wavy slip for pure copper and 7075 aluminum versus planar slip for 304 stainless steel tested at room temperature. Dislocation motion in copper transitions from forest dislocation cutting [1-6] to increasing contributions of cross slip. Dislocation motion in 7075 aluminum and 304 stainless steel is controlled by obstacles that are characteristically more thermal than forest dislocations: obstacles in 7075-T6 aluminum are identified as solutes from re-dissolved particles; obstacles in 304 stainless steel are also solutes.
Authors: Kyung Su Kim, Byung Ok Kim, Young Kwan Kim, Chang Hwan Lee, Sung Won Lee
Abstract: Recently, most of fatigue cracks in ship structures are reported within a few years after delivery. This type of fatigue characteristics cannot be explained adequately by the S-N curve based on high cycle fatigue. Calculation results under critical loading conditions reveal that stress magnitude higher than three times the yield stress occurs at some critical locations. It shows the fatigue cracks are related to low cycle fatigue. But the existing recommended design procedures in maritime industry do not properly cover low cycle fatigue problems. This work represents the first step in an effort to develop a design code that addresses low cycle fatigue problems. Low cycle fatigue test for uniform round specimen made of base/weld metal and for cruciform welded joint are carried out under constant amplitude alternating load, controlled by strain. Strain-cycle curves for the base metal and weld joints show good agreement with published data as well as some code recommended design curves.
Authors: Takehiko Takahashi, Susumu Hioki, Ikuo Shohji, Osamu Kamiya
Abstract: The low-cycle fatigue behavior and the relationship between the surface features in the low-cycle fatigue testing and the fatigue life of Sn-3.5Ag and Sn-0.7Cu lead-free solders were investigated at strain rate of 0.1%/s at room temperature, 80 and 120oC. In addition, the fatigue life was estimated by using the surface deformation of the solders, and image processing. And also, it was compared with Coffin-Manson type of fatigue behavior. The fatigue life of Sn-3.5Ag solder was superior to that of Sn-0.7Cu solder at temperatures, 80 and 120oC. The fatigue life determined by surface deformation indicated a close behavior to Coffin-Manson type fatigue behavior in those solders. Therefore the low-cycle fatigue life of solders could be estimated by the surface deformation.
Authors: Jae Hoon Kim, Duck Hoi Kim, Young Shin Lee, Young Jin Choi, Hyun Soo Kim, Won Shik Park
Abstract: Low cycle fatigue tests are performed on the Inconel 617 super alloy that be used for structural material of hot gas casing for gas turbine. The relations between strain energy density and number of cycles to failure are examined in order to predict the low cycle fatigue life of Inconel 617 super alloy. The lives predicted by strain energy methods are found to coincide with experimental data and results obtained from the Coffin-Manson method. And, the cyclic behavior of the Inconel 617 super alloy is characterized by cyclic hardening with increasing number of cycles.
Authors: Andriy Vyshnevskyy, Shehzad Khan, Joern Mosler
Abstract: One of the important considerations in the design of components is the estimation of cyclic lifetime and analysis of the critical regions of a construction. The local approach of lifetime estimation using continuum damage mechanics (CDM) has shown a great potential in predicting material failure not only for monotonic, but also for fully reversed loadings. In this paper, the CDM model of Desmorat-Lemaitre [1] was investigated regarding the prediction of cyclic lifetime. A series of experiments on tension specimens with different geometries were performed. The latter were used for the determination of model parameters as well as for the validation of the predictive capability of the model.
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