Mean Strain Effect on the Cyclic Stress-Strain Behavior of Steel Structure Materials Q235
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Abstract:
The low cycle fatigue (LCF) behavior of Q235 steel under mean strain control has been investigated. A serious of the strain controlled cyclic loading experiments with several combinations of strain amplitudes and mean strains have been performed. Significant cyclic hardening and mean stress relaxation were observed in all cases. Fractography by scanning electron microscopy (SEM) was used to determine the LCF failure mechanisms and fatigue crack propagation modes of the Q235 steel.Keywords:
Fractography
Cyclic stress
Low-cycle fatigue
Strain (injury)
Hardening (computing)
Strain hardening exponent
Stress–strain curve
Stress relaxation
Fractography
Low-cycle fatigue
Strain (injury)
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Abstract Two‐level cumulative low‐cycle fatigue lives of AISI 316 stainless steel notched specimens with different biaxial loading mode sequences were experimentally analyzed in this paper. Forty‐eight cases were conducted in the experimental program by considering the loading level sequence effect, the biaxiality of two levels and the cycle ratios. Results show that interlock effect caused by the characteristic fracture surfaces of the different biaxial states is beneficial to the cumulative fatigue lives. On the other hand, the tensile loading of the second level will accelerate the opening of cracks and decrease fatigue strength. Miner's rule predicts most fatigue lives within 30% error bands, and the loading level sequence effect was not found in this research involving complex fracture modes. Fractography of specimens in the cumulative fatigue tests is reported and discussed in this paper.
Fractography
Low-cycle fatigue
Interlock
Sequence (biology)
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A scanning electron microscopy study is reported of the nature and morphology of fracture surfaces in pyrocarbons commonly used for the manufacture of mechanical heart-valve prostheses. Specifically, silicon-alloyed low-temperature-isotropic (LTI)-pyrolytic carbon is examined, both as a coating on graphite and as a monolithic material, following overload, stress corrosion (static fatigue), and cyclic fatigue failures in a simulated physiological environment of 37 degrees C Ringer's solution. It is found that, in contrast to most metallic materials yet in keeping with many ceramics, there are no distinct fracture morphologies in pyro-carbons which are characteristic of a specific mode of loading; fracture surfaces appear to be identical for both catastrophic and subcritical crack growth under either sustained or cyclic loading. We conclude that caution should be used in assigning the likely cause of failure of pyrolytic carbon heart-valve components using fractographic examination.
Fractography
Pyrolytic carbon
Cyclic stress
Corrosion Fatigue
Carbon fibers
Carbon steel
Structural material
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Low-cycle fatigue
Cyclic stress
Lüders band
Strain (injury)
Fatigue limit
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Cyclic fatigue under rotary bending tests were conducted on partially stabilized zirconia (PSZ) from NGK and Nilsen, and silicon nitride from NGK and Norton. Fractography was performed on the failed specimens to determine the fracture structure and morphology. The results showed that the cyclic fatigue fracture was the same as the fracture structure previously observed in bending tests. The cyclic fatigue data indicated that structural ceramic could function in fatigue stress levels at a higher percentage of their average fast fracture strength than the fifty percent of ultimate strength used for wrought steels.
Fractography
Cyclic stress
Fatigue limit
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Cyclic stress
Lüders band
Low-cycle fatigue
Strain (injury)
Fatigue limit
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The low cycle fatigue (LCF) behavior of Q235 steel under mean strain control has been investigated. A serious of the strain controlled cyclic loading experiments with several combinations of strain amplitudes and mean strains have been performed. Significant cyclic hardening and mean stress relaxation were observed in all cases. Fractography by scanning electron microscopy (SEM) was used to determine the LCF failure mechanisms and fatigue crack propagation modes of the Q235 steel.
Fractography
Cyclic stress
Low-cycle fatigue
Strain (injury)
Hardening (computing)
Strain hardening exponent
Stress–strain curve
Stress relaxation
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Low-cycle fatigue
Cyclic stress
Strain (injury)
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Influence of Dynamic strain aging (DSA) under low cycle fatigue (LCF) and high cycle fatigue (HCF) loading was investigated by conducting LCF and HCF tests on specimens over a wide range of temperature from 573 to 973 K. DSA was found to be highly pronounced in the temperature range of 823–873 K. DSA was seen to have contrasting implications under LCF and HCF deformation. The cyclic hardening owing to DSA caused an increase in the cyclic stress response under LCF, leading to decrease in cyclic life. On the other hand, the DSA-induced strengthening suppressed the crack initiation phase under HCF where the applied stress remains fixed, leading to an increase in the cyclic life.
Low-cycle fatigue
Cyclic stress
Hardening (computing)
Strain (injury)
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