Papers by Keyword: Low Cycle Fatigue

Abstract: The low cycle fatigue behaviour of TA29 titanium alloy blisk forging at 300°C, 400°C, 500°C, 600°C were studied. The cyclic stress response, the stress-strain behaviour, the fatigue life and the fractograph were observed and analyzed. Through the double logarithm linear regression, the Coffin-Manson model parameters of TA29 titanium alloy at different temperatures were obtained. The results showed that the fatigue life decreases as the strain amplitude increases. Also, the testing temperature has a significant effect on the low cycle fatigue properties of TA29 titanium alloy. At the same level of the strain amplitude, the fatigue life and the peak value of cyclic stress decrease, while the plastic strain component in total strain amplitude increases with the increase of testing temperature. On the basis of the fractograph of fatigue specimens, the initiation of crack is mainly on the surface of the specimen. Fatigue striations can be seen clearly at fatigue crack propagation area. The fatigue striations in stable fatigue crack propagation area were broadened, and the propagation area was reduced and the final rupture area was increased with the increase of testing temperature.

Abstract: Design of Turbo machinery is complex and efficiency is directly related to material performance, material selection is of prime importance. Temperature limitations are the most crucial limiting factors to gas turbine efficiencies. This paper presents the life of GTD 111 applied to gas turbine blade based on LCF and TMF test results. The LCF tests were conducted under various strain ranges based on gas turbine operating conditions. In addition, IP (in-phase) and OP (out of-phase) TMF tests were conducted under various strain ranges. The paper will focus light on above issues and each plays an important role within the Gas Turbine Material literature and ultimately influences on planning and development practices. It is expected that this comprehensive contribution will be very beneficial to everyone involved or interested in Gas Turbines.

Abstract: This work presents results of fatigue tests of P91 steel specimens under constant-amplitude and programmed loading in temperature T=600°C. Two strain levels, applied in different order, were used for programmed loading. The loading program level changes were introduced for different levels of damage. The tests provided the basis for analysis of strain energy ΔW_pl in the function of the number of load cycles under constant-amplitude and programmed loading. It has been found that that the form of a loading program has an influence on the life and value of energy cumulated in the specimen until crack initiation. Verification of Palmgren Miner hypothesis revealed that its effectiveness depends on the loading program and temperature.

Abstract: When a material is subjected to a cyclic loading at high values of stress or strain, both thermal and damage develop together with cyclic plastic strain. These processes are often accompanied by damage deactivation characterized by actual state of micro-cracks, which are generally active under tension and passive under compression. In classical formulation damage deactivation occurs instantly when loading changes sign and consequently leads to non-smooth path separating both load ranges. The real materials, however, do not exhibit such bilinear paths. Therefore, the more realistic model based on continuous damage deactivation is proposed, in which micro-cracks close gradually, see Cegielski and Ganczarski [2, 3, 4], Hansen and Schreyer [5]. Simultaneously, thermo-mechanical coupling may play essential role in processes of cyclic plasticity hence present formulation comprises an additional heat transfer equation.

Abstract: The low-cycle fatigue (LCF) behavior specially the fracture initiation mechanism in a cast hybrid metal matrix composite (MMC) was investigated in this research. Conventional three point bending fatigue test was carried out on a rectangular bar smooth specimen. Factographic analysis was conducted to observe the fracture initiation site. Experimental results showed that microcracks in LCF initiated at the particle–matrix interface which was located in the hybrid clustering region. Due to continued fatigue cycling, the interface debonding occurred, created additional secondary microcracks and the microcrack coalesced with other nearby microcracks caused the final fracture.

Abstract: This research discussed on the determination of the appropriate fatigue damage parameter to predict the fatigue life when material subjected to the biaxial loading condition with the consideration of the energy dissipated. Servo-hydraulic machine is used for the constant amplitude cyclic testing on smooth solid mild steel. The results showed that in the low cycle fatigue, the total strain energy density can represent the accumulative of fatigue damage and characterize on the damage parameters. The relationship has been proposed which the data satisfactorily correlated for the R² is 0.8656. In addition, the hysteresis loop represent the area under the graph was the energy stored in the material during the loading and unloading condition. Hence the circumstances showed the deformation process governing the nucleation and propagation of fatigue cracks associated with the energy dissipated.

Abstract: In this paper, cycles jumping scheme integration is used to numerically integrate fully coupled constitutive equations in order to predict the low cycle fatigue life under cyclic loading. This procedure avoids the calculation of the full loading cycles (some millions of loading cycles) while considering the transient stages due to the hardening (at the beginning) and the high damage-induced softening during the last tens of loading cycles. The model parameters have been identified using the results obtained from a 316L steel cylindrical specimen subject to symmetric tension-compression loading path. The effects of the specimen size as well as the mesh size on the fatigue life prediction are investigated.

Abstract: Strain controlled uniaxial low cycle fatigue (LCF) tests of P92 steel were conducted at strain amplitudes of 0.4%, 0.6% and 0.8% in fully reversed manner with strain rate of 1.0×10^-3s^-1 at high temperature of 650 °C. Cyclic softening behavior was studied and time-independent cyclic plasticity model was used to represent the cyclic mechanical behavior of this steel. Material parameters were determined step by step at higher strain amplitude of 0.8%, experimental data with lower strain amplitude were used to validate the extrapolation of the model. Comparison of the simulated and experimental results shows that the proposed model can give a reasonable prediction of stress-strain hysteresis loop for P92 steel at high temperature.

Abstract: Jacketed polypropylene reaction kettle is the key equipment of polypropylene reaction setting. Cracks and leakage occurred in the kettle wall near the lower thermometer pipe branch, which is a widespread phenomenon in this refinery. The results showed that the cracks were caused by low cycle fatigue. High edge stress concentration resulted from incorrect design of the jacket structure is responsible for the fatigue cracks. An improved measurement which is available and simple was introduced.

Abstract: Strain-controlled low cycle fatigue (LCF) and creep-fatigue interaction (CFI) tests of K447A are conducted at 760oC in order to investigate the effects of different dwell times and strain ratios on the fatigue behavior and life. For the cases of stain ratio R_ε=-1 with balanced hold time, the tensile and compressive mean stresses will generate. For the case of stain ratio R_ε=-1 with compressive holding 60s, the tensile mean stress will produce. For the case of stain ratio R_ε=-1 with tensile holding 60s, the compressive mean stress will produce. For the cases of stain ratio R_ε=0.1 and R_ε=-1with no hold time, the tensile mean stress will produce. The cyclic damage accumulation (CDA) method and modified CDA method were employed to predict the fatigue life for K447A, respectively. The fatigue life predicted by CDA method is within the scatter band of 18.2X. The fatigue life predicted by the modified CDA method agrees very well with the experimental life and the predicted life is well within the scatter band of 3.1X, which means that the modified CDA method is able to consider the influences of dwell time and strain ratio on the fatigue life of K447A.