Infrared thermography study of the fatigue crack propagation

The work is devoted to the experimental study of heat dissipation process caused by fatigue crack propagation. To investigate a spatial and time temperature evolution at the crack tip set of experiments was carried out using specimens with pre-grown centered fatigue crack. An original mathematical algorithm for experimental data treatment was developed to obtain a power of heat source caused by plastic deformation at crack tip. The algorithm includes spatial-time filtration and relative motion compensation procedures. Based on the results of mathematical data treatment, we proposed a way to estimate the values of J-integral and stress intensity factor for cracks with pronounced the plastic zone

Scaling Invariance of Fatigue Crack Growth in Gigacycle Loading Regime

The role of the collective behavior of defect ensembles at the crack tip and the laws of fatigue crack propagation in R4 high strength steel have been studied under conditions of symmetric tension–compression gigacycle loading at 20 kHz. At every stage of the fatigue crack growth, replicas from the sample side surface were taken and studied by the method of three dimensional relief profilometry (using NewView interferometer profilometer) so as to study the scaling invariant laws of defect related structure evolution.This study was supported in part by the Russian Foundation for Basic Research, Project nos. 08-01-00699, 09-01-92005-NNS_a, and 09-01-92441-KE-

A study of the stored energy in titanium under deformation and failure using infrared data

The work is devoted to the experimental study of heat dissipation caused by plastic deformationand failure processes taking place in a titanium alloy Ti-4.2Al-1.6Mn. To investigate the spatial and timeevolution of temperature, a set of experiments has been carried out on plane titanium smooth specimens andspecimens with pre-grown centered fatigue cracks. The original mathematical algorithm for experimental dataprocessing has been applied to obtain the rate of heat dissipation generated by plastic deformation and storedenergy. It is shown that the stored energy is accumulated in titanium specimens undergoing fatigue tests, and atthe time of damage to fracture transition it is equal to zero

Infrared thermography study of the fatigue crack propagation

The work is devoted to the experimental study of heat dissipation process caused by fatigue crack propagation. To investigate a spatial and time temperature evolution at the crack tip set of experiments was carried out using specimens with pre-grown centered fatigue crack. An original mathematical algorithm for experimental data treatment was developed to obtain a power of heat source caused by plastic deformation at crack tip. The algorithm includes spatial-time filtration and relative motion compensation procedures. Based on the results of mathematical data treatment, we proposed a way to estimate the values of J-integral and stress intensity factor for cracks with pronounced the plastic zone

Scaling invariance of fatigue crack growth in gigacycle loading regime

The role of the collective behavior of defect ensembles at the crack tip and the laws of fatigue crack propagation in R4 high-strength steel have been studied under conditions of symmetric tension-compression gigacycle loading at 20 kHz. At every stage of the fatigue crack growth, replicas from the sample side surface were taken and studied by the method of three-dimensional relief profilometry (using NewView interferometer profilometer) so as to study the scaling-invariant laws of defect-related structure evolution.This study was supported in part by the Russian Foundation for Basic Research, Project nos. 08-01-00699, 09-01-92005-NNS_a, and 09-01-92441-KE_a

Scaling invariance of fatigue crack growth in gigacycle loading regime

The role of the collective behavior of defect ensembles at the crack tip and the laws of fatigue crack propagation in R4 high-strength steel have been studied under conditions of symmetric tension-compression gigacycle loading at 20 kHz. At every stage of the fatigue crack growth, replicas from the sample side surface were taken and studied by the method of three-dimensional relief profilometry (using NewView interferometer profilometer) so as to study the scaling-invariant laws of defect-related structure evolution.This study was supported in part by the Russian Foundation for Basic Research, Project nos. 08-01-00699, 09-01-92005-NNS_a, and 09-01-92441-KE_a

Experimental investigation of crack initiation and propagation in high- and gigacycle fatigue in titanium alloys by study of morphology of fracture

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

Experimental and Theoretical Study of Multiscale Damage-Failure Transition in Very High Cycle Fatigue

Multiscale mechanisms of failure of metals (Armco iron, titanium, aluminum) are studied for high cycle and very high cycle fatigue. By correlating with the results of structural studies, a theoretical approach is developed to describe fatigue crack kinetics in damaged material under high cycle and very high cycle fatigue loading conditions. Stages of crack nucleation and propagation are analyzed using the profilometry data from the fracture surface. The scale invariance of fracture surface roughness is established, which allows an explanation of the self-similar nature of fatigue crack kinetics under high cycle and very high cycle fatigue. Variation of elastic-plastic properties of Armco iron under very high cycle fatigue is studied using an acoustic resonance method. It is found that the material density decreases during fatigue damage accumulation, with the minimum of the material density in the bulk of the specimen