13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- fatigue regime were investigated. Test samples were prepared from sheet with thickness 3 mm. Geometry of specimens shown in Figure 1. In order to study thermal effects at the crack tip, specimen was pre-weakened by holes (Fig. 1a).At the initial stage of the experiment with the increased load was created fatigue crack with size of about 10 mm. Initiation of the cracks was carried out at an average load of 215 MPa, load amplitude 238 MPa and loading frequency 20 Hz. Then load was decreased for slow down crack propagation rate and for detailed study of heat generation processes in the crack tip. Mechanical testing were carried out at 100 KN servo-hydraulic machine Bi-00-100. Analysis of the results of quasi-static testing of investigated material determine following mechanical properties of the material: Young's modulus of 64 GPa σ0.2 = 683 MPa σв = 790 MPa. a) b) Fig. 1. Geometry a) and structure b) of the Ti4AlMn samples to study the thermal effects in the crack tip. During investigation the process of thermoelasticity, samples was loaded in the elastic range at frequencies 0.5, 1, 5, 10, 20 Hz and different amplitudes ranging from 100 to 350 MPa with the coefficient of asymmetry of the cycle, R = 0. To determine the strain during the experiment used an axial extensometer - Bi-06-304 with an accuracy of ± 1,5 mm. The temperature field study was carried out by infrared camera FLIR SC 5000. Recording of the temperature field was carried out at frequencies from 350 to 950 Hz and a minimum spatial resolution from 2·10-4 m. For the calibration of camera used standard calibration table. During the experiment grips and specimen was shielded from external heat sources by special screen. Surface of the specimen was polished in several stages by abrasive paper (final stage of polishing grit size does not exceed 3 µm); before start of the experiment, polished surface was covered by thin layer of amorphous carbon. Fig.2 Typical geometry of cylindrical specimens The second kind of experiments was carried out with cylindrical specimens (fig. 2) of pure titanium Grade 4 with different grain sizes (~25 µm and ~ 500 nm Fig. 3) to evaluate influence of grain size on fatigue strength and its dissipation properties. Structure was studied in optical microscope by chemical etching of prepared surface by sanding disc from 160 to 4000 grains per sq. cm. and
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