PSI - Issue 13

A. Vshivkov et al. / Procedia Structural Integrity 13 (2018) 1189–1194 Author name / Structural Integrity Procedia 00 (2018) 000–000

1191

3

by optic method. The strain field was measured by method of digital image correlation based on StrainMaster system and Lavision software. Before testing the surface of the sample near the crack tip was polished and covered with a black matte paint. Then white paint was sprayed over the black paint to obtain a high contrast image. A macro lens and an elevated Led lamp were used. To restore the deformation field in the crack tip area, each frame was subjected to additional processing: calibration to level distortions caused by distortion of the lens, compensate the movement of the subject as a hard whole, regulation the illumination with digital filters. The spatial resolution of the strain field near the crack tip is 3e-6 m. There was considered two-dimensional biaxial loading of a half of a sample. The applied load corresponds to the experimental. A shape of the crack was taken from the digital image correlation data. The system of equations for modeling of a strain field near the crack tip has the following form:    σ 0 (2)   : p   σ С ε ε (3)

1 2

T

  

  

(4)

   ε u u

F  

p

(5)



ε



σ

where F=σ m -σ ys , σ ys =σ ys0 + σ h (ε pe ). The isotropic hardening function σ h (ε pe ) was obtained from experimental data.

Figure. 1. Geometry of samples (all sizes in millimeters).

Figure. 2. Testing machine Biss BI-00-502, Biaxial test System.

3. Result of strain measurement The deformation field was measured at the fatigue crack tip. Figure 3 shows the characteristic result of measurements for the case of uniaxial loading. There is not symmetry of the field due to the influence of the direction of the crack. Figure 4 shows the shape of the plastic area boundary and shows the characteristic sizes which were used for the comparison of the experimental and numerical data. Table 1 gives a quantitative comparison of the obtained data.