Abstract
Fatigue (high- and gigacycle) crack initiation and its propagation in titanium alloys with coarse and fine grain structure are studied by fractography analysis of fracture surface. Fractured specimens were analyzed by interferometer microscope and electronic microscope to improve methods of monitoring of damage accumulation during fatigue test and verify the models for fatigue crack kinetics. Fatigue strength was estimated for high cycle fatigue (HCF) regime using the Luong method [1] by “in-situ” infrared scanning of the sample surface for the step-wise loading history for different grain size metals. Fine grain alloys demonstrated higher fatigue resistance for both HCF and gigacycle fatigue regimes. Fracture surface analysis for cylindrical samples was carried out using optical and electronic microscopy method. High resolution profilometry (interferometerprofiler New View 5010) data of fracture surface roughness allowed us to estimate scale invariance (the Hurst exponent) and to establish the existence of two characteristic areas of damage localization (different values of the Hurst exponent). Area 1 with diameter ~300 ?m has the pronounced roughness and is associated with damage localization hotspot. Area 2 shows less amplitude roughness, occupies the rest fracture surface and considered as the trace of the fatigue crack path corresponding to the Paris kinetics.
Highlights
H CF and VHCF are important fundamental and engineering problems for several areas o applications
Catastrophic events caused by failure of gas-turbine motors, high costs of fatigue life-time estimation for constructions and potential cost of development of new constructions initiated perspective conceptions in the area of high cycle fatigue (HCF) and VHCF based on the fundamental research in fatigue damage and reliability prediction
Traditional methods of testing do not provide an estimate of fatigue life in gigacycle loading conditions (109 cycles to failure) leading to the emergence of new techniques based on ultrasonic testing machines like [2] and studying the morphology of the fracture surfaces by modern methods of structural analysis
Summary
H CF and VHCF are important fundamental and engineering problems for several areas o applications. Traditional methods of testing do not provide an estimate of fatigue life in gigacycle loading conditions (109 cycles to failure) leading to the emergence of new techniques based on ultrasonic testing machines like [2] and studying the morphology of the fracture surfaces by modern methods of structural analysis.
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