Creep-fatigue Interaction Tests Research Articles

Low cycle fatigue behaviour of Inconel® alloy 783

Low cycle fatigue (LCF) tests were performed on Inconel® Alloy 783 at a strain rate of 3×10−3s−1 and a strain amplitude of ±0.6%. The tests were conducted in the temperature range, 573 to 923 K besides room temperature. Further, influence of strain amplitude on LCF behaviour was studied at a constant temperature of 923 K using strain amplitudes in the range, ±0.3 to ±0.8%. Creep-fatigue interaction tests were conducted at a strain amplitude of ±0.4%, at 923 K. The material generally showed a stable stress response followed by a region of continuous softening upto failure. Also, the alloy was seen to exhibit dynamic strain ageing (DSA) in the temperature range, 573 to 723 K as evidenced by the observed peaks in the half-life stress in the above temperature range. Dynamic strain ageing was seen to offset the softening exhibited by the alloy outside the above temperature range. Fractography/EDS analysis of the failed samples showed numerous brittle Nb-rich precipitates that were seen to influence crack propagation. A continuous reduction in the LCF life was noticed with increase in the test temperature. The observed material behaviour has been correlated with the damage mechanisms through microstructural observations.

Finite element-based life prediction for high-temperature cyclic loading of a large superplastic forming die

The thermomechanical, time-dependent, elastic-plastic creep behaviour of a representative tool in a high-temperature superplastic forming press has been simulated using a sequential finite element-based heat transfer and mechanical stress analysis approach. The heating and cooling aspects of the heat transfer model have been previously validated against laboratory measurements. This paper focuses on the prediction of die life based on this model. The determination and modelling of the high-temperature mechanical properties of the materials and die are described for both so-called (a) major cycles, relating to die heat-up and cool-down from and to ambient temperature, and (b) minor cycles, relating to die heat-up and cool-down associated with part removal and blank insertion. A creep-fatigue life prediction method using non-linear damage summation is developed and applied to the die-life problem. Isothermal fatigue and creep-fatigue interaction tests at 700 and 900 °C on 40%Ni-20%Cr die material XN40F are carried out to estimate the required strain-life relationships.

Life Estimation Method Based on Creep-fatigue Interaction

A series of creep-fatigue interaction tests were conducted in order to evaluate a criterion for failure taking into account the detrimental effect caused by the time dependent process. From the test data on commonly used high temperature materials for gas turbine and diesel engine in air, hydrogen gas and corrosive ash, we proposed a life estimation method under the combined creep-fatigue loadings. This method based on linear cummulative creep damage expressed by the equivalent hold time is stress dependent and independent of loading modes. We confirm by this method that the correlation between experimental data or available data in literatures and estimation is quite good for several types of loadings. Our experiments need no complicate testing to obtaining the material constants but require only the conventional simple low cycle fatigue tests with the effects of hole time considered at peak strain or stress and creep rupture tests.

Life estimation method based on creep-fatigue interaction. (Example of hot parts materials of gas turbine and diesel engine)

A program of creep-fatigue interaction tests was conducted in order to evaluate a criterion for failure taking into account the detrimental effect causing by the time dependent process. From the test data on commonly used high temperature materials for gas turbine and diesel engine in air, hydrogen gas and corrosive ash, we proposed the life estimation method under the combined creep-fatigue loadings. This method based on liner cummulative creep damage expressed by the equivalent hold time is stress dependent having nothing to do with loading patterns. We confirm from this method the correlation between experimental data or available data in literatures and estimation is quite good for a several type of loadings. Our experiments are unnecessary the complicate testing for obtaining the material constants but only require the conventional simple low cycle fatigue tests with the effects of hold time inserted at peak strain or stress and creep rupture tests.